final design report - calvin college | grand rapids, michigan€¦ · · 2014-05-15final design...
TRANSCRIPT
NATURAFILL © 2013, TEAM 13, CALVIN COLLEGE LAST UPDATED: 5/15/2014
FINAL DESIGN REPORT
NATURAFILL: FUEL FOR THOUGHT
Team 13 Karl Bratt Jonathan Haines Brandon Koster
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
i
© 2014, Karl Bratt, Jonathan Haines, Brandon Koster, and Calvin College
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
ii
DEDICATION
For Our Friend and Former Teammate
Eric DeGroot
1992-2013
However great our labors, this project will be forever incomplete.
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
iii
Executive Summary
This report outlines the design, manufacture, and testing of a home refueling appliance capable of
compressing household natural gas to 3,600 psi, thereby producing compressed natural gas (CNG). The
team’s original goal was to design, build, and test a natural gas home refueling appliance that is lower
cost and more reliable than appliances currently on the market. In the course of nine months, team
NaturaFill developed a preliminary prototype of such system using a two-stage hydraulic cylinder
compression system. This design, composed of one double acting hydraulic cylinder, minimizes floor
space and overall cost. For reliability, the system’s manifolds and compression cylinders were
constructed from cold worked steel, guaranteeing strength and stability. For safety, the system is
controlled with input, output, and thermocouple modules affixed to monitoring software. All in all,
NaturaFill, has explored the many engineering and non-engineering aspects of this project and upon
completion of this report, NaturaFill believes that large-scale production of such a system would cost
approximately $3,500.
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
iv
Table of Contents
1 Project Overview ............................................................................................................................... 1
1.1 Calvin College Senior Design ......................................................................................................... 1
1.2 Mission Statement ........................................................................................................................ 1
1.3 Problem Statement ....................................................................................................................... 1
1.4 Industry Overview ......................................................................................................................... 1
1.4.1 Compressed Natural Gas....................................................................................................... 1
1.4.2 Benefits of CNG ..................................................................................................................... 2
1.4.3 Growth Rate Expectations .................................................................................................... 3
1.4.4 Barriers to Entry .................................................................................................................... 4
1.5 Project Proposal ............................................................................................................................ 5
1.5.1 Objective ............................................................................................................................... 5
1.5.2 Target Customers .................................................................................................................. 5
1.5.3 Existing Competitors ............................................................................................................. 5
1.5.4 Competitive Strategy ............................................................................................................ 7
1.6 Team Organization: ....................................................................................................................... 7
1.6.1 Team Members ..................................................................................................................... 7
1.6.2 Team Member Strengths ...................................................................................................... 8
1.6.3 Team Leadership and Management ..................................................................................... 9
1.7 Design Norms .............................................................................................................................. 10
1.7.1 Stewardship: ....................................................................................................................... 10
1.7.2 Trust .................................................................................................................................... 11
1.7.3 Integrity ............................................................................................................................... 11
2 Requirements .................................................................................................................................. 12
2.1 Safety .......................................................................................................................................... 12
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
v
2.2 Price ............................................................................................................................................ 12
2.3 Refueling Rate ............................................................................................................................. 12
2.4 Heat Loss ..................................................................................................................................... 12
2.5 Serviceability ............................................................................................................................... 12
2.6 Reliability ..................................................................................................................................... 12
2.7 Noise ........................................................................................................................................... 13
2.8 Size .............................................................................................................................................. 13
2.9 User Interface ............................................................................................................................. 13
3 Deliverables ..................................................................................................................................... 14
3.1 Project Proposal and Feasibility Study ........................................................................................ 14
3.2 Final Design Report ..................................................................................................................... 14
3.3 Working Prototype ...................................................................................................................... 14
3.4 Team Website ............................................................................................................................. 14
4 Design Considerations..................................................................................................................... 15
4.1 Compression System ................................................................................................................... 15
4.1.1 Motor Driven Reciprocating Compression .......................................................................... 15
4.1.2 Wobble Plate Compression ................................................................................................. 15
4.1.3 Pneumatic Cylinder Compression ....................................................................................... 16
4.1.4 Hydraulic Cylinder Compression ......................................................................................... 16
4.1.5 Decision ............................................................................................................................... 17
4.2 Lubricated vs. Oil-less ................................................................................................................. 17
4.3 Hydraulic System ......................................................................................................................... 18
4.3.1 Hydraulic Power Unit .......................................................................................................... 18
4.3.2 4-Way, 3 Position Solenoid Valve ....................................................................................... 19
4.4 Compression Cylinder System ..................................................................................................... 20
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
vi
4.4.1 Material ............................................................................................................................... 20
4.4.2 Surface Finish ...................................................................................................................... 21
4.4.3 Sizing ................................................................................................................................... 21
4.4.4 Manifolds ............................................................................................................................ 21
4.4.5 General Layout .................................................................................................................... 22
4.4.6 Fittings and Taps ................................................................................................................. 23
4.4.7 Bolts & Threaded Rod ......................................................................................................... 23
4.4.8 Gaskets ................................................................................................................................ 24
4.4.9 Pistons ................................................................................................................................. 24
4.5 Natural Gas System ..................................................................................................................... 26
4.5.1 Heat Removal ...................................................................................................................... 26
4.5.2 Pressure Sensors ................................................................................................................. 27
4.6 Control System ............................................................................................................................ 28
4.6.1 Raspberry Pi ........................................................................................................................ 28
4.6.2 National Instruments LabVIEW & FieldPoint ...................................................................... 30
4.6.3 Decision ............................................................................................................................... 30
5 Calculations ..................................................................................................................................... 32
5.1 Summary ..................................................................................................................................... 32
5.2 Autodesk CFD .............................................................................................................................. 32
5.2.1 Overview ............................................................................................................................. 32
5.2.2 Goals.................................................................................................................................... 32
5.2.3 Status .................................................................................................................................. 32
5.2.4 Results ................................................................................................................................. 32
5.2.5 Conclusion ........................................................................................................................... 33
5.3 Engineering Equation Solver ....................................................................................................... 34
5.3.1 Overview ............................................................................................................................. 34
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
vii
5.3.2 Procedure ............................................................................................................................ 34
5.3.3 Results ................................................................................................................................. 34
5.3.4 Conclusion ........................................................................................................................... 34
5.4 MathCAD ..................................................................................................................................... 34
5.4.1 Overview ............................................................................................................................. 34
5.4.2 Procedure ............................................................................................................................ 35
5.4.3 Results ................................................................................................................................. 35
5.4.4 Conclusion ........................................................................................................................... 35
6 Final Design ..................................................................................................................................... 36
6.1 Hydraulic System ......................................................................................................................... 36
6.1.1 Overview ............................................................................................................................. 36
6.2 Natural Gas System ..................................................................................................................... 37
6.2.1 Overview ............................................................................................................................. 37
6.2.2 Residential Natural Gas Supply ........................................................................................... 37
6.2.3 Piston Seals ......................................................................................................................... 37
6.2.4 Tubing.................................................................................................................................. 38
6.2.5 Check Valves ....................................................................................................................... 38
6.2.6 Relief Valve .......................................................................................................................... 38
6.2.7 Shut-off Valve ...................................................................................................................... 39
6.2.8 Manifolds ............................................................................................................................ 39
6.2.9 Pressure Gauges and Transducers ...................................................................................... 40
6.2.10 Heat Sinks ............................................................................................................................ 41
6.2.11 Blow-By Recovery System ................................................................................................... 42
6.2.12 Refueling Nozzle .................................................................................................................. 42
6.3 Control System ............................................................................................................................ 42
6.3.1 Enclosure Box ...................................................................................................................... 43
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
viii
6.3.2 FieldPoint Modules ............................................................................................................. 43
6.3.3 Solid State Relays ................................................................................................................ 44
6.3.4 Thermocouples ................................................................................................................... 45
7 Prototype Development ................................................................................................................. 46
7.1 Machining ................................................................................................................................... 46
7.2 Fabrication & Assembly .............................................................................................................. 46
7.3 Modifying .................................................................................................................................... 47
7.4 Mounting ..................................................................................................................................... 48
8 Testing ............................................................................................................................................. 50
8.1 Test Planning ............................................................................................................................... 50
8.2 System Testing ............................................................................................................................ 50
8.2.1 Air Testing ........................................................................................................................... 50
8.2.2 Natural Gas Testing ............................................................................................................. 50
8.3 Results ......................................................................................................................................... 50
8.3.1 Compression Ratios............................................................................................................. 50
8.3.2 Pressure and Temperature ................................................................................................. 52
8.3.3 Friction ................................................................................................................................ 52
9 Obstacles ......................................................................................................................................... 52
9.1 Controls ....................................................................................................................................... 52
9.2 Piston Seals ................................................................................................................................. 53
9.3 Storage Tanks .............................................................................................................................. 53
9.4 Gaskets ........................................................................................................................................ 54
9.5 Top Dead Center Volume ............................................................................................................ 55
9.6 Piston O-Ring Seal ....................................................................................................................... 55
10 Future Improvements ..................................................................................................................... 56
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
ix
10.1 Proper Component Sizing ........................................................................................................... 56
10.2 Noise Control .............................................................................................................................. 57
10.3 Imbedded Electronics ................................................................................................................. 57
10.4 Fabricating for Flexibility ............................................................................................................. 58
11 Financial Estimates .......................................................................................................................... 59
11.1 Cost of Development .................................................................................................................. 59
11.2 Cost of Production ...................................................................................................................... 60
12 Conclusion ....................................................................................................................................... 61
13 Acknowledgements ......................................................................................................................... 62
13.1 Professor Ned Nielsen ................................................................................................................. 62
13.2 Professor Steve VanderLeest ...................................................................................................... 62
13.3 Professor Matthew Heun ............................................................................................................ 62
13.4 Mr. Jimmy Moerdyk .................................................................................................................... 62
13.5 Mr. Lee Otto ................................................................................................................................ 62
13.6 Mr. Ross Pursifull ........................................................................................................................ 62
13.7 Mr. Phil Jasperse ......................................................................................................................... 62
13.8 Mr. Jerry LaBreck ........................................................................................................................ 62
13.9 Mr. Kevin Fern ............................................................................................................................. 63
13.10 Mr. Tim Wolfis ............................................................................................................................. 63
14 Appendix ......................................................................................................................................... 64
14.1 Appendix A. Work Breakdown Structure .................................................................................... 64
14.2 Appendix B. EES Calculations ...................................................................................................... 66
14.2.1 Two Stage Compression System Sizing Calculations ........................................................... 66
14.2.2 Heat Transfer Calculations .................................................................................................. 68
14.3 Appendix C. MathCAD Calculations ............................................................................................ 71
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
x
14.3.1 Pump/Reservoir Horsepower Requirement ....................................................................... 71
14.3.2 Stress in Spacer Plate Bolts (First Stage) ............................................................................. 71
14.3.3 Stress in Threaded Rod (First Stage) ................................................................................... 74
14.3.4 Friction Calculations ............................................................................................................ 76
14.4 Appendix D. As-Built Part Drawings ............................................................................................ 77
14.5 Appendix E. Raw Testing Data .................................................................................................... 92
14.6 Appendix F. Manufacturer Component Specifications ............................................................... 97
14.6.1 O-ring Groove Dimension Instructions ............................................................................... 97
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
xi
Table of Figures
Figure 1. Price Equivalent per Barrel of Oil and Natural Gas .................................................................... 2
Figure 2. Oil Price as a Multiple of Natural Gas Price ............................................................................... 3
Figure 3. Number of Natural Gas Vehicles by Region (1991-2001) .......................................................... 4
Figure 4. BRC FuelMaker Phill® ................................................................................................................. 6
Figure 5. CNG Pump II® ............................................................................................................................. 6
Figure 6. Ross Pursifill’s CNG Home Refueling Unit ................................................................................ 10
Figure 7. Motor Driven Reciprocating Compression System .................................................................. 15
Figure 8. Wobble Plate Compression System ......................................................................................... 16
Figure 9. Hydraulic Cylinder Compression System ................................................................................. 17
Figure 10: Custom Built Hydraulic Power Unit........................................................................................ 18
Figure 11: Off-The-Shelf Hydraulic Power Unit ....................................................................................... 19
Figure 12: Solenoid Valves ..................................................................................................................... 19
Figure 13: Tandem Centered 4-Way, 3-Position Solenoid Valve ............................................................ 20
Figure 14: Pre-honed Steel Tubing .......................................................................................................... 21
Figure 15: First & Second Stage FEA Stress Simulations ......................................................................... 22
Figure 16: Sandwich Stacking .................................................................................................................. 22
Figure 17: Pyramid Stacking .................................................................................................................... 23
Figure 18: O-Ring Seals on Manifold ....................................................................................................... 24
Figure 19: 5" Diameter Aluminum Piston ............................................................................................... 24
Figure 20: Layout of PTFE Seals & Rider Rings ........................................................................................ 25
Figure 21: Pressure Transmitter .............................................................................................................. 27
Figure 22: Pressure Gage ........................................................................................................................ 27
Figure 23: Raspberry Pi Computer .......................................................................................................... 29
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
xii
Figure 24: Raspberry Pi Control Schematic ............................................................................................. 29
Figure 26: NI FieldPoint Modules ............................................................................................................ 30
Figure 26: LabVIEW Interface .................................................................................................................. 30
Figure 27: LabVIEW Block Diagram ......................................................................................................... 31
Figure 28. Pressure Results from Simulation .......................................................................................... 33
Figure 29. Plane of Simulation Pressure Results ..................................................................................... 33
Figure 30: Hydraulic System Schematic .................................................................................................. 36
Figure 31. Natural Gas System Schematic .............................................................................................. 37
Figure 32. High Pressure Natural Gas Check Valves ............................................................................... 38
Figure 33. Adjustable High Pressure Natural Gas Relief Valves .............................................................. 39
Figure 34. Example of CNG Ball Valve ..................................................................................................... 39
Figure 35. Example of Manifold and Connections at End of CNG Compression Chamber ..................... 40
Figure 36. Pressure Transmitter Example ............................................................................................... 41
Figure 37. Pressure Gage Example .......................................................................................................... 41
Figure 38. Example of Tubing Loops ....................................................................................................... 41
Figure 39. General Purpose CNG Refueling Nozzle for Time-Fill ............................................................ 42
Figure 40: Compiled Control & Monitoring System ................................................................................ 43
Figure 41: Sealed Electrical Control Box ................................................................................................. 43
Figure 42: FieldPoint Module Communication with Windows XP .......................................................... 44
Figure 43: Solid State Relays ................................................................................................................... 44
Figure 44: Machining............................................................................................................................... 46
Figure 45: Fabrication & Assembly ......................................................................................................... 47
Figure 46: Piston Spacing Diagram .......................................................................................................... 48
Figure 47: Mounting of Final Prototype .................................................................................................. 49
Figure 48: Pressure Reaching 3,600 psi.................................................................................................. 51
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
xiii
Figure 49: Temperature Data from Testing ............................................................................................ 51
Figure 50: Blown Fuse in Ethernet Controller ......................................................................................... 53
Figure 51. Proposed Pressure Vessel ...................................................................................................... 54
Figure 52. Piston O-ring .......................................................................................................................... 55
Figure 53: Final NaturaFill Prototype ...................................................................................................... 61
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
xiv
Table of Tables
Table 1. NGV Reductions in Exhaust Emissions ........................................................................................ 2
Table 2. Compression Technology Decision Matrix ................................................................................ 17
Table 3. Steel Tubing Sizing Chart ........................................................................................................... 20
Table 4: Bolt & Threaded Rod Safety Factors ......................................................................................... 24
Table 5. Comparison of Development Boards ........................................................................................ 28
Table 6. Work and Heat Removal Calculation Results ............................................................................ 34
Table 7: Operational Budget ................................................................................................................... 59
Table 8: Costs of Production ................................................................................................................... 60
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
1
1 Project Overview
1.1 Calvin College Senior Design
Calvin College is a Christian liberal arts college located in Grand Rapids, Michigan. Calvin’s engineering
program is ABET accredited and has a reputation for producing well-rounded engineers by integrating
this liberal arts curriculum with engineering. Senior design is the capstone of the engineering program
in which students conceive, develop, and implement a project of their interest over the course of the
year, combining material learned both inside and outside the classroom.
1.2 Mission Statement
NaturaFill, a design team comprised of three mechanical engineering
seniors, exists to decrease American dependence on foreign oil by
increasing the availability of abundant, clean burning natural gas
transportation to the average American.
1.3 Problem Statement
Today, there is scarcity in the infrastructure for compressed natural gas (CNG) in the United States
transportation landscape. Currently, only 605 public CNG refueling stations exist, compared to the
168,000 gasoline stations.1 In response, a few small companies, such as BRC Fuelmaker, have
developed home refueling units that run on electricity and connect to existing natural gas lines.2
Unfortunately, these models begin at $5,000 before installation.3
1.4 Industry Overview
1.4.1 Compressed Natural Gas
Natural gas is a colorless, odorless, non-corrosive, and extremely flammable mixture of hydrocarbon
gases. Natural gas, a fossil fuel, originates from the chemically breakdown of organic matter over time
to produce methane, or CH4.4 When compressed to 3600psi, natural gas is termed, “compressed
natural gas” or “CNG.”
1 http://www.afdc.energy.gov/fuels/natural_gas_locations.html 2 http://www.cngnow.com/vehicles/refueling/Pages/refueling-at-home.aspx 3 Jimmy Moerdyk, Moerdyk Energy Inc. (MEI), 9/27/13, 9:00AM 4 http://www.naturalgas.org/overview/background.asp
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
2
1.4.2 Benefits of CNG
CNG can easily be used as an alternative for gasoline in a dedicated vehicle engine or in conjunction
with gasoline in a “bi-fuel” application. In fact, the octane rating for CNG is higher than that of gasoline,
producing greater power, acceleration, and cruise speed for vehicles running on CNG. Though the
safety concerns are different, CNG’s narrow flammability range makes it inherently safer than gasoline.
In addition, emission comparisons of CNG and gasoline-fueled vehicles have revealed substantial
reductions in greenhouse gases (see Table 1. NGV Reductions in Exhaust Emissions).
Table 1. NGV Reductions in Exhaust Emissions
NGV Potential Reductions in Exhaust Emissions (%) Carbon
Monoxide (CO) Non-Methane Hydrocarbons
(NMHC) Nitrogen Oxides
(NOx) Carbon Dioxides
(CO2)
90% 75% 60% 25%
CNG not only provides a cleaner-burning fuel alternative to gasoline, it is also an economically feasible.
As a result of new shale gas discoveries and new drilling technology the supply of natural gas in the
United States has increased substantially. This increase in supply has forced the price of natural gas
down 70% over the last five years.5 The current pipeline natural gas of about $3.80 per million BTU6
has an energy equivalent price of $0.42 per gasoline gallon equivalent (GGE)7. Over the past twenty
years, this price drop has been reflected in a large price separation between gasoline and natural gas
(see Figure 1. Price Equivalent per Barrel of Oil and Natural Gas).
Figure 1. Price Equivalent per Barrel of Oil and Natural Gas8
5 http://www.infomine.com/investment/metal-prices/natural-gas/5-year/ 6 http://www.oil-price.net/ 7 http://www.energyalmanac.ca.gov/transportation/gge.html 8 http://pictorial-guide-to-energy.blogspot.com/2012/03/gaseous-emissions.html
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
3
In fact, the price of oil is over eight times higher than that of natural gas, as shown in Figure. 2. Oil
Price as a Multiple of Natural Gas Price.
Figure 2. Oil Price as a Multiple of Natural Gas Price9
1.4.3 Growth Rate Expectations
The economic and environmental incentives associated with CNG have already encouraged transit,
garbage, and transportation fleets to convert from diesel and gasoline fuel to CNG.10 Unfortunately,
this has been primarily restricted to vehicles such as taxicabs, transit and school buses, garbage trucks,
and public works vehicles. Because these vehicles are typically maintained and fueled at a central
location, it is has been economical for them to convert to natural gas. In total, the number of CNG
powered vehicles on the road is growing at a staggering rate of 30 percent a year.11 Currently, there
are 135,000 natural gas vehicles in the United States and 15.2 million worldwide12 (see Figure 3.
Number of Natural Gas Vehicles by Region).13
9 http://www.infomine.com/investment/metal-prices/natural-gas/5-year/ 10 http://www.cngnow.com/vehicles/fleets/Pages/government.aspx 11 http://www.ngvamerica.org/media_ctr/fact_ngv.html 12 http://www.ngvc.org/about_ngv/index.html 13 http://www.iangv.org/current-ngv-stats/
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
4
Figure 3. Number of Natural Gas Vehicles by Region (1991-2001)
In the coming years, it is also forecasted that the number of factory built bi-fuel vehicles will also be on
the rise. “Bi-fuel” indicates that a vehicle can run on both gasoline and natural gas fuel sources.
Presently, larger vehicles such as the 2013 Chevrolet Silverado and GMC Sierra 2500 HD are factory-
offered with bi-fuel capability. Ross Pursifull, a research specialist at Ford Motor Company, spoke with
the team14 and confirmed rumors that the 2015 Chevrolet Impala will also be built bi-fuel ready.15
Chevrolet’s decision results from increased market pressure for CNG vehicles in residential applications.
Increased demand for residential natural gas vehicles (NGVs) will correspondingly increase demand for
CNG fueling stations.
1.4.4 Barriers to Entry
The biggest hurdle to widespread consumer adoption of natural gas vehicles is availability to fueling
stations. There are over 270 publically accessible gasoline fuel stations for every one station supplying
CNG.16 The capability to fuel a CNG vehicle at home side-steps waiting for an adequate nationwide
network of fueling stations. Unfortunately, cost has been the major deterrent away from existing CNG
home refueling units.
14 Pursifull, Ross; Ford Motor Company; 11/9/13, 10:00AM 15 http://blog.caranddriver.com/antelope-in-the-gas-2015-chevrolet-impala-to-gain-bi-fuel-gasolinecng-capable-v-6-model/ 16 http://www.afdc.energy.gov/fuels/natural_gas_locations.html
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
5
1.5 Project Proposal
1.5.1 Objective
The objective of NaturaFill is to design, build, and test a natural gas home refueling appliance with a
production cost of less than $2,000 and refueling rate of 0.35 gasoline gallons equivalent (GGE) per
hour. The system must be capable of compressing natural gas to the standard pressure of 3,600 psi in
a safe and controlled environment.
1.5.2 Target Customers
This increased use of CNG in transportation vehicles has made it seemingly more affordable and feasible
in light-duty, consumer applications. In total, 56 percent of American households are currently using
natural gas for residential heating.17 As a result, NaturaFill’s natural gas home refueling appliance aims
to target customers with existing natural gas lines and fossil fuel dependent vehicles. A potential
secondary market for CNG vehicles and the system would include customers desiring reduced emission
large vehicle options, such as trucks or sports utility vehicles (SUVs). The majority of electric or hybrid
powered vehicles on the market today are small with little hauling capacity. In the realm of trucks and
SVUs, natural gas vehicles are a suitable option for improved environmental impact.
1.5.3 Existing Competitors
BRC FuelMaker
FuelMaker is currently the largest producer of CNG home refueling units. Their most popular unit, the
Phill®, costs $5,000 before installation. The Phill® (see Figure 4) refuels at an average rate between
0.4-0.5 GGEs per hour but is unreliable due to its reciprocating compression system.
17 http://www.naturalgas.org/overview/uses_residential.asp
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
6
Figure 4. BRC FuelMaker Phill®
CNGPump
CNGPump, maker of the CNG Pump®, uses hydraulic compression for conversion of natural gas into
CNG. Their cheapest model is the CNG Pump II®, which refuels at a rate of 2 GGEs per hour.
Unfortunately, their upfront cost is $7,000 before installation, an inhibitor for most customers.18
Figure 5. CNG Pump II®
18 http://www.cngpump.com/shoppingcart/products/CNGPUMP%252d2gge-%28Time-Fill%29-Hydraulic-Fueling-Station-for-cars%7B47%7Dtrucks-%282gge-per-hour%29.html
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
7
General Electric
The biggest potential competitor is General Electric (GE). They have announced a partnership with
Chesapeake Energy to develop a natural gas home refueling unit with an upfront cost of $500.19 If
proposition becomes a reality, it would undercut NaturalFill’s suggested retail price and therefore,
undermine its value proposition. From conversations with Ross Persifill, Research Specialist at the Ford
Motor Company, and other industry insiders, the general consensus suggests high unlikeliness of GE’s
proposition becoming a reality. For this reason, the team forecasts the elapse of a substantial amount
of time before GE enters this market.
1.5.4 Competitive Strategy
Existing in-home refueling units are currently in the price range or $5000-$7000+ and fill at a rate of
around 1-2 GGEs per hour. Today, most systems are currently made in Europe and the United States,
however, it is rumored that a less expensive Asian variety will soon be hitting the market will be released
soon. NaturaFill plans to compete by ensuring quality and safety and competing at a lower price point
by reducing the compression rate of approximately 0.35 GGEs. In actuality, this compression rate would
be comparable to charging a 100% electric vehicle overnight for average daily usage. The team’s
strategy to compete on price and differentiation will make residential use of natural gas vehicles more
economically feasible in the American transportation landscape.
1.6 Team Organization:
1.6.1 Team Members
Karl Bratt
Bratt is a Mechanical concentration engineering student also in pursuit of
a business minor. Originally from Racine, Wisconsin, Bratt has diverse
interests in business finance, operations, and supply chain. Bratt has had
two summer internships working for General Electric as a manufacturing
engineer and continuous improvement specialist. He is passionate about
the potential business opportunities involved with the NaturaFill project.
In his free time, he enjoys playing piano, golf, and tennis, and is an avid
runner. Last year, he ran the Chicago marathon.
19 http://oilprice.com/Finance/investing-and-trading-reports/Chesapeake-GE-Get-in-on-Home-Refueling-Game.html
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
8
Jonathan Haines
Haines is a Mechanical concentration engineering student also in pursuit
of a mathematics minor. Originally from East Brunswick, New Jersey,
Haines desires to work in the automotive industry in the design and
manufacture of fuel-efficient vehicles. His hands-on experience with
thermodynamics, CAD modeling, and manufacturing were valuable in the
design and construction of the final prototype. In his free time, Jon enjoys
playing guitar, traveling, and being outdoors during the summer months.
Brandon Koster
Koster is a Mechanical concentration engineering student and also
pursuing a business minor. Originally from Visalia, California, Koster has
been a natural gas transportation enthusiast for years, both from a
business and engineering perspective. Growing up as the son of a
contractor, Koster gained valuable fabricating, mechanical design, and
project execution skills at a young age. In his free time he enjoys rock
climbing, cheering the Los Angeles Dodgers, fixing his car, listening to
Texas Country music, and taking road trips.
1.6.2 Team Member Strengths
Karl Bratt
Bratt's background in project management was valuable in the organization and planning components
of the project. In addition, his experience in forecasting and cost analysis were helpful in evaluating
and marketing the value proposition of the product. Finally, Bratt’s willingness to learn was
instrumental in programing the electrical control and safety systems of NaturaFill.
Jonathan Haines
Haines’s experience with thermodynamics, Autodesk Inventor, and Autodesk CFD simulator were
valuable in the design and testing of various components. In addition, his experience in metal
fabrication was critical for the machining of metal manifolds, pistons, and spacer plates.
Brandon Koster
Koster’s industry knowledge served to connect the team to companies and individuals in the industry
that provided valuable guidance and support throughout the project. In addition, his background in
hydraulics has been instrumental in the design and modeling of the final prototype.
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
9
1.6.3 Team Leadership and Management
Project Manager
Bratt functioned as the Project Manager for NaturaFill. Bratt was primarily responsible for the
organizational components of the project. This included, but was not limited to, the planning and
scheduling of team meetings, review and on-time delivery of project deliverables, and work breakdown
of tasks among the team member using Microsoft Project.
Budget Manager
Koster acted as the Budget Manager for NaturaFill. Koster was primarily responsible for managing the
team’s operational budget. This included, but was not limited to, turning in all reimbursement forms,
requesting parts purchases, and communicating with team sponsors.
Senior Design Faculty Advisor
Ned Nielsen, a Mechanical Engineering professor at Calvin College, functioned as the faculty advisor for
mechanically concentrated Senior Design projects. He was responsibility for providing constructive
feedback on the project throughout the course of the year. Nielsen’s extensive engineering background
was be helpful for finalizing the team’s CNG refueling unit design and keeping the team on schedule.
Mechanical Faculty Consultant
Matthew Heun, a Mechanical Engineering professor at Calvin College, agreed to meet with NaturaFill
to address the transfer of heat released by the compression system. Heun has also gave the team
advice with the use of Autodesk CFD and National Instruments LabVIEW 8.5.
CNG Industry Consultant
Lee Otto, the Founder and CEO of CNGPump, Inc. in Appleton, WI, offered the team advice on seal
technology, heat dissipation, and control systems. Unfortunately, he was unable to provide any further
technical information due to confidentiality.
Automotive Industry Consultant
Ross Pursifull, a CNG enthusiast and Research Specialist at Ford Motor Company in Dearborn, MI,
agreed to meet with NaturaFill and discuss the CNG industry from an automotive industry standpoint.
In addition, he demonstrated the use of a home refueling unit to fuel his own NGVs (see Figure 6. Ross
Pursifull CNG Home Refueling Unit.
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
10
Figure 6. Ross Pursifill’s CNG Home Refueling Unit
Industry Mentor
Jimmy Moerdyk, the Vice President of Operations at Moerdyk Energy, Inc. in Grand Rapids, MI,
provided support and suggestions to the team based on his experience in CNG vehicle conversions and
installation of home refueling units. Moerdyk has been enthusiastic of NaturaFill’s $2,000 production
price target.
1.7 Design Norms
1.7.1 Stewardship:
As the concentration of CO2 in the atmosphere approaches the 400 ppm mark, the political, social, and
economic pressures for alternative energies has risen drastically.20 CNG, which burns cleaner than
coal or oil, could be a solution to this environmental and economic challenge.
Environmental Sustainability
It has been proven that natural gas vehicles produce less emissions than traditional gasoline powered
vehicles (see Table 1. NGV Reductions in Exhaust Emissions). As worries rise on the negative effects of
greenhouse gases on the environment, the team believes that transition from gasoline fueled
transportation to natural gas exemplifies good stewardship over the environment.
20 http://www.gasnaturally.eu/uploads/Modules/Publications/the-role-of-natural-gas-in-a-sustainable-energy-market-final.pdf
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
11
Economic and Political Sustainability
Natural gas is widely available in the United States. In fact, 98% of the natural gas consumed in the
United States is produced in either the US or Canada.21 In addition, the price of natural gas has declined
tremendously in the past five years, especially in comparison to oil (see Figure 1). The economic
feasibility of this project promotes the design norm of stewardship over limited financial resources.
Transitioning transportation fuels toward natural gas would also render the United States more energy
independent and therefore offer the world a chance for more political stability.
1.7.2 Trust
The team’s goal of creating a fully-functional natural gas home refueling unit will only be accomplished
if the prototype is proven safe. Since a prototype malfunction could be highly dangerous, the team
conducted all preliminary testing of the devise with a non-combustible gaseous materials. In addition,
emergency stops were integrated into the electronic controls to ensure system shutdown should
dangerous conditions arise. By designing the system with safety first, the team hoped to protect and
earn the trust of their end user.
1.7.3 Integrity
The design norm of integrity is closely associated with aesthetic beauty and ease-of-use. By integrating
easy-to-use controls and graphic interface, the team sought to incorporate beauty into the final design.
In addition, each component on the machine was carefully constructed to achieve both functionality
and aestheticism. Finally, the team’s logo was crafted to warrant professionalism and visual appeal.
21 http://anga.us/why-natural-gas/clean#.UmCKfPmsgyo
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
12
2 Requirements
2.1 Safety
Due to high pressures and the flammable nature of natural gas, the most important design requirement
for the home refueling appliance is safety. The system shall adhere to all safety standards and come
equipped with monitoring equipment and emergency stops (E-stops). The system will also have a
pressure relief valve to vent gas in the case of over-pressurization. In addition, a check valve and shut-
off valve will prevent backflow and pressurization of the household natural gas system.
2.2 Price
Since the majority of commercially available CNG home refueling units cost more than $5000, the unit
shall have a production cost under $2,500 and a 2014 selling price between $3,000 and $3,500.
2.3 Refueling Rate
Nearly all of the units on the market operate with a faster fueling rate, ranging from 1.2-2.0+ GGEs per
hour. The appliance team’s appliance shall be a slow filling unit with a refueling time comparable to
plugging in an electric car overnight. This design shall have a fueling rate of 0.35 GGEs per hour. At this
rate, 3.5 gallons of gasoline would be replace by 10 hours of CNG refueling. This will provide about 90
miles of range for an average sedan.
2.4 Heat Loss
During compression, the temperature of the natural gas increases due to work being done on the gas
and the conservation of energy. When compressing to 3,600 psi without external cooling, the
temperature of the gas will exceed 350°F. This will be too hot to safely pump into a natural gas vehicle.
The team’s appliance will deliver natural gas to the vehicle at below 100 °F.
2.5 Serviceability
The appliance shall have minimal complexity and promote ease-of-service by qualified technicians. The
appliance will also be designed in such a way that weight is minimized, making transportation to and
from a service center easier.
2.6 Reliability
To withstand daily use and cyclical fatigue, the unit shall be reliable for 5 years without repair. This shall
grant competitive advantage over less reliable motor driven reciprocating CNG compressors.
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
13
2.7 Noise
Designed for location in one’s garage, the refueling appliance shall operate with minimal noise
pollution. To achieve this, the noise level shall remain under 50 dB from a distance of ten feet away.
2.8 Size
As mentioned previously, this unit shall be stored in one’s garage. For this reason, the refueling
appliance shall take up less than 10 sq. ft. of floor space.
2.9 User Interface The unit shall incorporate an easy-to-use interface for simple operation and troubleshooting. This
aligns with the team’s design norm of integrity, making it easy for the user to understand the problem
with the appliance quickly.
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
14
3 Deliverables
3.1 Project Proposal and Feasibility Study
NaturaFill shall submit a complete project proposal and feasibility study detailing a background on the
project, a proposed solution, and the feasibility of this solution. This report will be submitted no later
than December 9, 2013 at 3:30pm E.S.T.
3.2 Final Design Report
NaturaFill shall submit a final report at the completion of the project to explain the project background,
research and data analysis, design alternatives and decisions, prototype design and testing, and final
design conclusions. This final design report will be submitted no later than May 14, 2014 at 3:30pm
E.S.T.
3.3 Working Prototype
The team will demonstrate a working prototype of the refueling unit at the Engineering Department
Senior Design Night on May 10, 2014. The team hopes to demonstrate, on-stage, the refueling of an
actual natural gas vehicle.
3.4 Team Website
The team shall maintain a website as a means of updating the college, sponsors, and the public on the
project status. These updates shall be executed by Andrew Hall and will occur at milestones throughout
the project lifespan. All final updates to the website, including published final versions of the PPFS and
Final Design Report, must be made by May 12, 2014 at 3:30pm E.S.T.
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
15
4 Design Considerations
4.1 Compression System
Early on in the project, a pivotal decision needed to be made as to what form of compression system
to use. Four types were analyzed: motor driven, wobble plate, pneumatic, and hydraulic.
4.1.1 Motor Driven Reciprocating Compression
A motor driven reciprocating compressor is the industry standard for compressing natural gas. Early
on in the process, the team ruled out this option due to lack of complexity and reliability issues on
similar refueling appliances constructed from these compressors. An example of this type of
compression system can be seen below in Figure 7.
Figure 7. Motor Driven Reciprocating Compression System
4.1.2 Wobble Plate Compression
The team talked to industry professionals and conducted extensive research to understand the function
and complexity of wobble plate compressors (see Figure 8. Wobble Plate Compression System). Lee
Otto, Founder of CNGPump, and Kurt Skov, Engineering Manager at Best Metal Products, both
expressed interest in this technology, which is typically used in automotive air conditioning units.
Research revealed high levels of complexity and potentials for unbalance in the linkages. Due to this
complexity and the perceived inability to prototype, the team determined that construction of a wobble
plate compression system was beyond the scope of the project.
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
16
Figure 8. Wobble Plate Compression System22
4.1.3 Pneumatic Cylinder Compression
A pneumatic, or air driven, compression system would require one or many double rod pneumatic
cylinders being used to compress the natural gas to the required pressure of 3,600psi. To the team’s
knowledge, this technology has never been used to compress natural gas. The team speculates that
this might be due to a low cycle rate, the energy lost to heat when gas is compressed, and the potential
safety risk of mixing oxygen with natural gas. One positive of this design would be that home users
would have the use of the air compressor for other applications as well, such as running pneumatic
tools.
4.1.4 Hydraulic Cylinder Compression
A hydraulic cylinder compression system (Figure 9. Hydraulic Cylinder Compression System) would
require one or many double rod hydraulic cylinders to compress gas at a low cycle rate, similar to the
operation of a pneumatic system. In commercial applications, this technology is slowly being
introduced as an alternative to the motor driven reciprocating compressors. Due to high reliability and
off-the-shelf componentry, many companies and individuals in the industry believe that hydraulic
compressors have the potential for becoming the industry standard in natural gas compression.
22 http://www.jaguar-swansea.co.uk/aircon/systems.htm
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
17
Figure 9. Hydraulic Cylinder Compression System23
4.1.5 Decision
To make the decision about what compression technology to utilize, a decision matrix (see Table 2) was
created by weighting a list of desired criteria and rating each design alternative on a scale of one to ten.
After totally the scores of each alternative, hydraulic compression was chosen due to its reliability, ease-
of-prototyping, and potential cost savings.
Table 2. Compression Technology Decision Matrix
Criteria Score Weight Motor Driven Wobble Plate Hydraulic Pneumatic
Cost to Manufacture 10 14% 5 5 5 6
Reliability 9 12% 5 8 9 7
Safety 9 12% 8 8 8 8
Ease of Use 7 12% 5 5 5 5
Serviceability 7 10% 4 3 10 10
Efficiency 6 10% 7 8 5 4
Prototype Cost 5 7% 5 8 8 9
Innovation 5 7% 1 10 6 8
Marketability 5 7% 5 8 7 5
Ability to Prototype 4 5% 7 5 8 7
Noise Pollution 3 4% 3 8 7 6
5.3 6.8 7.0 6.7
4.2 Lubricated vs. Oil-less
The team was faced with the problem of how to reduce friction in their system. There are two
common approaches to this problem: lubricated and oil-less. In natural gas compressors, lubricated
units require extra equipment to remove all the oil from the natural gas before it gets into the
vehicle’s fuel system. Oil-less compressors use low-friction polymer seals and cylinder linings to
23 http://www.hydropac.com/GRAPHICS/hydrogen3b.jpg
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
18
reduce friction. Most current large-scale natural gas compressors use lubrication, but there is an
increasing trend toward oil-less compressors for the sake of simplify, reduced maintenance costs, and
a lower risk of damaging the vehicle’s fuel system. The team choose to build an oil-less compressor
for the reasons listed above.
4.3 Hydraulic System
Having decided upon a hydraulic compression system, research was conducted to determine setup,
sizing, and structure of the compressor and necessary componentry. Initial calculations of pressure and
heat generation directed the team towards a four-stage compression system consisting of two double-
acting hydraulic cylinders. After further calculation (see Appendix B. EES Calculations), it was
discovered that a two-stage system consisting of one double acting cylinder was possible if each
compression stage had a 16:1 compression ratio. This would reduce cost and complexity, thereby
aligning with the team’s mission and design requirement of serviceability.
4.3.1 Hydraulic Power Unit
The team discussed their needs for a hydraulic power unit with Ryan Anderson, a hydraulic power unit
technician with Bond Fluidaire, during a visit. The team discuss many of their requirements with
Anderson and they discussed ballpark pricing for their budget. The low-noise and very high run time
(often >12 hours) makes the team’s hydraulic power unit specifications different than most units used
in the industry. This led the team to compare both custom and off-the-shelf options for the hydraulic
pump and reservoir.
Custom
These units (see Figure 10: Custom Built Hydraulic Power Unit)24 require each
component of the system to be purchased individually, thereby reducing overall
cost. Custom hydraulic pumps are generally designed with a specific application
of the unit in mind. Because they are customizable, the team would be able to
construct a unit to a size appropriate for the final appliance prototype. A
concern with customized systems is that they are not typically intended to
reliability run for long periods of time.
24 http://www.gshydraulics.com/images/products/large/HydraulicPowerUnit01_CustomCompact.jpg
Figure 10: Custom Built Hydraulic Power Unit
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
19
Off-The-Shelf
These units are all-in-one packages, designed for multiple applications. They are
comprised of a reservoir, hydraulic pump, electric motor, manifold, valves, and
piping and sold as one unit. These units are less customizable in size and can be
more expensive than their customized counterparts. On the flip side, off-the-
shelf hydraulic power unit units have increased reliability and require less labor
to assemble. Based on calculations (see Appendix C), the system would run at
full capacity with a pump rated for 4 gallons per minute. The team found a 1.25
gallon per minute hydraulic power unit in the parts closet in the Calvin College
Engineering Building, however, these calculations show that the team would
need to purchase a new pump in order to run the final prototype at full
capacity.
Decision
The team chose to use an off-the-shelf hydraulic power unit do to cost and accessibility. The optimal
off-the-shelf power unit would have the capacity of pumping 4 gallons of hydraulic fluid per minute.
The team decided to use the 1.25 gallon per minute power unit for their prototype. This system is not
optimum for meeting the team’s compression rate goals, but it will allow the team to prove the
mechanical concept of their design and still stay near their budget for the project.
4.3.2 4-Way, 3 Position Solenoid Valve
The team compared three methods of controlling the hydraulic fluid flow into the cylinder: open,
closed, and tandem centered solenoid valves (see Figure 12).
Open Centered
In neutral, all lines are open, placing the pump in open flow mode.2
Closed Centered
In neutral, all lines are blocked, also placing the pump in a state of stall.
Tandem Centered
In neutral, hydraulic fluid is cycled from the pump back into the reservoir. This
allows the pump to remain running, promoting longer life of the pump.
Decision
The team decided to use a tandem centered 4-way, 3-position solenoid valve for controlling the flow of
hydraulic fluid into the double acting hydraulic cylinder (see Figure 13). In doing so, the team hoped to
promote longer life of the pump, especially when operating in neutral, or centered, position.
Figure 11: Off-The-Shelf Hydraulic Power Unit
Figure 12: Solenoid Valves
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
20
Figure 13: Tandem Centered 4-Way, 3-Position Solenoid Valve
4.4 Compression Cylinder System
4.4.1 Material
Deciding upon material, thickness, and size of the compression cylinders were critical steps before
additional design of the system could be accomplished. Each compression cylinder, modeled as thick-
walled pressure vessels, required high strength materials to withstand the pressure and heat generated
by the pistons themselves. After calculations and conversations with Best Metal Products, a custom
hydraulic cylinder manufacturer, the team decided upon thick-walled steel tubing as the material of
choice. Thick-walled steel tubing is reliable, easy to purchase, and relatively inexpensive. However, it is
produced in a limited variety of diameters. Furthermore, some machining work might need to be done
to get the inside wall to the specified exact diameter and tolerance.
Table 3. Steel Tubing Sizing Chart25
25 http://www.swagelok.com/downloads/webcatalogs/EN/MS-01-107.PDF
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
21
4.4.2 Surface Finish
Having selected steel, the next challenge was reducing the amount of
friction between the piston and the compression chamber walls. The ideal
way of accomplishing this in industry is by using honed tubing. Honed
tubing can be purchased or machined in-house. Due to limitations of the
Calvin machine shop in maintaining honing tolerances, the team chose to
purchase the pre-honed steel (see Figure 14). The team also discussed the
possibility of coating the inside of the cylinders with PTFE, or Teflon, to
further reduce friction. This was deemed to be outside the scope of the
project because of the complexity and cost that would be required to
maintain extremely tight tolerances inside the cylinder with the PTFE
coated interior.
4.4.3 Sizing
The smallest and least expensive interior diameter available for honed steel tubing was 1.25”. Using
this sized tubing for the second compression chamber necessitated a 5” interior diameter of the first
stage compression cylinder, in order to maintain two 16:1 compression ratios while still using the same
stroke length for each stage (see Figure 14). Although this size cylinder diameter would reduce the
projected refueling rate for the final system, the team believed this design provided the most value for
the least cost.
4.4.4 Manifolds
The manifolds at each end of the compression chambers have many important functions within the
appliance. Needing to withstand the high pressures generated by the piston strokes, these manifolds
must have a high yield strength. In addition, they must be thick enough so that holes may be drilled
into the sides to release the compressed gas. Finally, there must be room for cylindrical milling on the
front faces of the manifolds themselves to secure the honed tubing in place.
Material & Thickness
After extensive modeling in AutoDesk Inventor and Solidworks, it was determined that 1” thick cold-
rolled steel would be strong enough to withstand impact force and pressures of 3,600psi, while
maintaining rigidity with the presence of internal cavities (see Figure 15: First & Second Stage FEA Stress
Simulations). One advantage is that steel is also relatively inexpensive compared to other high strength
materials. The downside is increased weight due to a density of 0.284 lb/in³ at STP.2
Figure 14: Pre-honed Steel Tubing
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
22
Sizing
Having decided upon a 6” outer
diameter of the first stage
compression cylinder, it was
calculated that the manifolds
would need to be at least 7”x7” in
size. All in all, at the most extreme
operating conditions, the
manifolds will still maintain a
safety factor of over 3, as
indicated in Figure 15: First &
Second Stage FEA Stress
Simulations.
4.4.5 General Layout
Using an iterative design approach, the team
transitioned from a sandwich to pyramidal stacking
system for the compression and hydraulic cylinders.
Sandwich Stacking
The team originally modeled the two-stage
compression system as a sandwich, with each
compression cylinder held together by tie rods (see
Figure 16). This model proved difficult to attach a
hydraulic cylinder to. In addition, this model
necessitated a large amount of unnecessary manifold
material on the second compression stage, thereby adding weight and cost.
Pyramid Stacking
To add reinforcement and reduce material waste, the team proposed a pyramidal stacking layout, in
which each compression cylinder would be sandwiched independent of one another (see Figure 17:
Pyramid Stacking). This necessitated the addition of spacer plates and bolts between the hydraulic and
compression cylinders. Although they added complexity to the overall design, these modifications
resulted in a lighter and more robust system.
Figure 15: First & Second Stage FEA Stress Simulations
Figure 16: Sandwich Stacking
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
23
4.4.6 Fittings and Taps
To reduce unnecessary complexity, the team sought to standardize the
threads and fittings used throughout the system. A key decision that
needed to be made involved whether to use NPT or SAE straight thread
fittings and taps. NPT, or National Pipe Thread, is normally tapered and
used primarily for gas and water pipe fittings. On the other hand, SAE
straight threading is more common in high pressure natural gas
applications. After conversations with two industry experts, both
recommended the use of SAE straight thread connections with O-ring seals
instead of Teflon tape seals on NPT threads. This, combined with the added
difficulty in machining tapered taps, led the team to decide on SAE-4
straight thread fittings and taps to pipe the natural gas out of each manifold
and into the next area of the system. In order to accommodate the
common fitting size of 1/4” NPT for monitoring equipment such as
thermocouples and pressure gages, the team also created 1/4” NPT taps in
their manifolds in addition to the SAE-4 taps.
4.4.7 Bolts & Threaded Rod
To insure the safety of the system, MathCAD was used to calculate the various safety factors for the
threaded rod and bolts in both compression system stages. Using an iterative design approach, the bolt
and rod specifications were modified until a minimum safety factor of 3 was found for each
compression stage. Modeled as a thick walled pressure vessel, the primary stress equations used in
these calculations were:
𝜎 = 𝑃𝑖𝑟𝑖
2−𝑃𝑜𝑟𝑜2
𝑟𝑜2−𝑟𝑖
2 ± 𝑟𝑖2𝑟𝑜
2 𝑃𝑜−𝑃𝑖
𝑟𝑖2(𝑟𝑜
2−𝑟𝑖2)
(1)
𝜏 = 𝐹
𝐴𝑒𝑓𝑓 (2)
𝑆𝑎𝑓𝑒𝑡𝑦 𝐹𝑎𝑐𝑡𝑜𝑟 = 𝜎𝑚𝑎𝑥
𝜎=
𝜏𝑚𝑎𝑥
𝜏 (3)
Using UNC bolts and threaded rod, a summary of the calculated safety factors has been tabulated (see
Table 4: Bolt & Threaded Rod Safety Factors).
Figure 17: Pyramid Stacking
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
24
Table 4: Bolt & Threaded Rod Safety Factors
1st Stage 2nd Stage
Safety Factor Spacer Plate Bolts Threaded Rod Spacer Plate Bolts Threaded Rod
Thread Shear 14.12 6.57 6.24 23.94
Tension 6.36 3.27 7.42 12.00
Tearout 482.75 84.48 241.38 307.75
Nut Stripping 16.18 6.73 7.61 24.51
4.4.8 Gaskets
The team originally intended to use a rubber-like material to seal the honed
cylinder to the manifolds. Having difficulty finding inexpensive gasket
materials, capable of withstanding the high temperature and pressures
generated by the compression chambers, the team consulted with Ross
Pursifull, a CNG research specialist from Ford Motor Co. Mr. Pursifull
recommended the use of O-rings instead of gasket materials. After further
conversations with Zatkoff Seals and Packings Inc., the team decided upon a
fluorocarbon rubber O-ring material for satisfactory sealing functionality (see
Figure 18: O-Ring Seals). The team decided to sill utilize gasket materials to seal between the manifolds
and the spacer plates and between the spacer plates and the hydraulic cylinders. These seals are part
of the low-pressure blow-by recovery system, which captures gas that slips past the pistons and carries
it back to the low pressure gas supply side of the system.
4.4.9 Pistons
Material
The team researched three materials for constructing the pistons:
steel, aluminum and PTFE (Teflon). Steel is relatively inexpensive
for its strength. The heaviest material of the three, raised concerns
over unnecessary unbalance issues. Aluminum pistons are most
common in both compressors and internal combustion engines,
due to their relatively light weight and high thermal conductivity.
There was some thought in possibly making the pistons out of PTFE
(Teflon). This would have eliminated the need for seal rings
Figure 18: O-Ring Seals on Manifold
Figure 19: 5" Diameter Aluminum Piston
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
25
because the entire piston would be made out of an extremely low-friction material. Disadvantages of
using PTFE include the very high cost of the raw material and fact that using PTFE as a piston material
is unproven. All this considered, the team eventually decided upon aluminum (see Figure 19).
Seals
The team researched three methods for sealing the pistons to the compression chamber walls: oil,
Teflon, and bronze sleeves. Oil sealing is the conventional method for sealing air and natural gas
compressors. Oil provides excellent wear protection and blow-by elimination. Disadvantages to oil
seals include the added complexity involved with preventing leaks and having to check oil levels on a
regular basis. Also, natural gas compressors equipped with oil seals require additional filters to ensure
that the oil does not contaminate the natural gas going into the vehicle.
Oil-less compressor technology uses low-friction cylinder wall coatings, such as PTFE (Teflon), and seal
rings made out of low friction polymers, such as PTFE or PEEK, to protect against wear and excessive
heat generation while still maintaining at tight seal. A disadvantage of this alternative is the high cost
of low-friction coatings and polymers.
In discussions with Lee Otto, founder of CNGPump, he recommended the use of a bronze sleeve inside
the cylinder wall and bronze bushing seals to provide a tight seal. This alternative would be simple and
inexpensive. A disadvantage of this alternative is the relatively high coefficient of friction of bronze
compared to oil seals and PTFE.
After weighting the pros and cons of each alternative, the team decided to use PTFE cylinder wall
coatings and PTFE rings. This decision was based on the team’s requirement for a very low friction seal,
as well as the need to avoid contaminating the natural gas with oil. In regards to layout, two PTFE
Figure 20: Layout of PTFE Seals & Rider Rings
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
26
(Teflon) rider rings will be used to stabilize the piston as it moves up and down inside the cylinder walls
(see Figure 20: Layout of PTFE Seals & Rider Rings)26. Located inside these rider rings will be two PTFE
(Teflon) seals, providing the majority of the main protection against blow-by inside the compression
chamber. This design is far more common in the industry and the team hypothesizes that the gas being
allowed to pass through the rider rings freely will lead to better stabilization for the piston. If the sealing
from this layout proves insufficient the team will modify it by adding additional seal rings.
4.5 Natural Gas System
The natural gas system will move the gas from a residential natural gas line, through each of the two
compression cylinders, and ultimately into the tank of a natural gas vehicle. It is designed to dissipate
heat, prevent backflow, and monitor the thermodynamic states of the natural gas using thermocouples,
pressure gages, and a pressure transducer.
4.5.1 Heat Removal
The team researched three ways for dissipating heat from the natural gas: fins, tubing loops, and fans.
Fins
Finned tubing is a very common way to dissipate heat from a working fluid. The fins provide increased
surface area for heat transfer to the air to occur and therefore increase heat transfer rates. A
disadvantage to this alternative is the fact that most finned tubing is designed for low pressure
applications. Should fins be installed on high pressure tubing, separation between the tube and fins
may occur due to thermal expansion and contractions in the metal. There is another type of finned
tubing in which the fins and tubing have been bonded together in a heat welding process. These custom
finned tubing systems, specifically designed for high pressure applications, are unfortunately very
expensive.
Tubing Loops
Another common means of heat dissipation within working fluids is tubing loops. Since natural
convection relies on surface area, adding loops to metal tubing increases surface area and thus, heat
transfer. In reference to the CNG refueling appliance, this method would increase the volume of gas in
the heat sink and allow more time for the compressed natural gas to cool. Disadvantages to tubing
loops include the additional cost of buying extra tubing and the additional labor cost involved in bending
the tubing to create the heat sinks.
26 http://www.ihi.co.jp/compressor/en/products/process-gas/gas-recipro/images/fea_photo_01.jpg
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
27
Fans
Fans are another very effective way to dissipate heat from a working fluid into the surrounding air.
Disadvantages to using fans include increased noise pollution and corrective maintenance due to the
additional moving parts. Fans also require routine maintenance and cleaning.
Decision
The team has decided to use tubing loops to cool the natural gas between each compression stage.
Due to this method’s added reliability and durability, the team sees this as the most ideal method for
heat removal. While it may cost more upfront, the team sees this as the better long-term option.
4.5.2 Pressure Sensors
Pressure Transmitter
Pressure transmitters (see Figure 21: Pressure Transmitter) measure pressure using
a strain gauge and output a low-voltage signal that corresponds to a certain
pressure. This low-voltage signal must be converted to a digital signal using a DC to
AC converter chip in conjunction with a computer-based control system. These
sensors would be used in combination with thermocouples to determine the
thermodynamic state of the compressed natural gas. This is critical for creating
accurate heat transfer and fluid flow models. In addition, these signals can be
interpreted by the computer control system to shut down the machine
should pressures get too high. The disadvantage of using pressure transmitters is their relatively high
cost compared to simple pressure gages.
Pressure Gages
Pressure gages (see Figure 22: Pressure Gage) provide a relatively inexpensive way of
measuring pressure. These gages are more robust and reliable than their digital
counterparts. In addition, their threaded mounts make them easily installable on
most tubes and fitting. The major disadvantage of pressure gages is that data
acquisition must be done manually by a human being. This not only reduces the
accuracy of the data, it greatly limits the number of pressure samples being
taken. Should corrective maintenance be necessary on the appliance, historic pressure data would be
unattainable. Furthermore, emergency safety stops cannot be computer programmed using pressure
gages.
Figure 22: Pressure Gage
Figure 21: Pressure Transmitter
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
28
Decision
The team has decided to use a pressure transmitter for the final compression stage and pressure gages
for all the other stages. At minimum, the team needs this one digital pressure transmitter to ensure a
final stage pressure of 3,600 psi and indicate to the computer when the natural gas vehicle tank is full.
Furthermore, readings from this transmitter are necessary for the system’s programmable safety stops.
Multiple pressure transmitters throughout the system were deemed too costly and not value added.
4.6 Control System The team looked into two options for the electronic controls and display of the overall system: a
Raspberry Pi development board and LabVIEW/FieldPoint module assembly.
4.6.1 Raspberry Pi
In comparison to similar development boards (see Table 5), the Raspberry Pi (see Figure 23)
accomplishes all necessary mechanical, safety, and relay functionalities at approximately half the cost.
Table 5. Comparison of Development Boards27
Dev Board Raspberry Pi BeagleBone Black CubieBoard
Price $25-$30 $45-$55 $50-$60
CPU 700 MHz Low Power ARM1176JZ-F
AM335x 1GHz ARM Cortex-A8
Arm Cortex A8 1GHz
GPIO 8 GPIO pin I²C, SPI, UART
Two 46 Pin Configurable Bus
Two 48 Pin Configurable Bus
Power 5V, 1A 5V, 700mA 5V, 2A
Memory 512MB SDRAM (Model B)
2GB embedded MMC
NAND (max 64GB) SATA II, SD
Card 3.0
Dimensions 8.6x5.4x1.7(cm) 10×6 (cm) 90x40x13(mm)
Application Learning Embedded apps Robotics
Basic Learning Embedded apps Robotics
Advanced Learning Embedded apps Video Robotics
Ease of Use Easy Easy (but closed) I/O and peripherals are not so easy to manage
27 http://www.open-electronics.org/a-comprehensive-comparison-of-linux-development-boards/
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
29
The only downside to the Raspberry Pi is the limited onboard input and
output (I/O) ports. In addition, the onboard I/O is limited in connection
pins and zero tolerance to anything above 0.0 or 3.3V. Furthermore, the
onboard general-purpose input/output (GPIO) pins are connected directly
to the connection pins of the processor, causing potential for the entire
board to fry. The Slice of PI/O is just one available option for protecting
the Raspberry Pi’s unguarded input and output pins. This Slice of PI/O ad-
on is inexpensive and provides the Raspberry Pi a buffer, conversion levels,
analog I/O, and protection devices to avoid the risk of damage. Overall,
there are many breakout boards that have been developed and can be
easily plugged into the Raspberry Pi’s GPIO pins. This development
board, an all-in-one package, would function well to control the final appliance and relay data to an
ascetically appealing user interface (see Figure 24: Raspberry Pi Control Schematic).
Figure 24: Raspberry Pi Control Schematic
Figure 23: Raspberry Pi Computer
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
30
4.6.2 National Instruments LabVIEW & FieldPoint
The second option analyzed involved using lab monitoring equipment from National Instruments (NI).
Using NI FieldPoint input, output, thermocouple, power supply, and Ethernet modules (see Figure 26),
the team would record and display temperature and pressure data. In addition, feedback loops could
be created to shut the system down should the system reach an unsafe operating environment. All
data and programming would be managed using National Instruments LabVIEW 8.5 (see Figure 26).
4.6.3 Decision
Originally, the team decided on the Raspberry Pi because of its compact size, ease of use, and vast
online community presence for additional support. At the beginning of February 2014, the team was
notified that the only electrical engineer in the group, was dropping out of engineering. Having already
chosen and purchased a Raspberry Pi development board, the team of three mechanical engineers
began researching how to program it. It was soon realized that this was beyond their technical
knowledge. Therefore, the team has chosen to use NI LabVIEW & FieldPont to demonstrate the
mechanical feasibility of the final prototype (see Figure 27: LabVIEW Block Diagram). Should this
appliance go into production, a Raspberry Pi would be used instead.
Figure 26: NI FieldPoint Modules Figure 26: LabVIEW Interface
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
31
Figure 27: LabVIEW Block Diagram
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
32
5 Calculations
5.1 Summary
In order to determine the size requirements for the natural gas compression cylinders, the stressed
experienced by the system, and the heat transfer required in the tubing connecting the cylinders, the
team has decided to use a combination of Engineering Equation Solver (EES), MathCAD, and Autodesk
CFD simulator. EES was chosen for its ease of use, integration of thermodynamic properties, and
potential for optimization. Autodesk CFD simulator was chosen for its ability to simulate fluid flow,
compression, and heat transfer simultaneously. MathCAD was used in order to calculate the stresses
incurred by compression.
5.2 Autodesk CFD
5.2.1 Overview
Due to the complexity of this project and the difficulty and expense in implementing design changes
after production begins, the team will use Autodesk CFD to test initial designs. A variety of design
changes such as length of the cylinders, diameters of the cylinders, and wall thickness of the cylinders
will be altered and simulated in order to optimize our design.
5.2.2 Goals
The end goal of using Autodesk CFD is to have a full working model of the system that simulates and
shows the changes in pressure and temperature as the natural gas goes through it.
5.2.3 Status
Currently a simple model of compression has been successfully simulated. The purpose of creating this
model was to
5.2.4 Results
Figure 28. Pressure Results from Simulation shows the trend of the data obtained from the simulation
modified to account for calibration error.
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
33
Figure 28. Pressure Results from Simulation
Figure 29. Plane of Simulation Pressure Results shows a plane from the simulation pressure results
showing the higher pressure after compression.
Figure 29. Plane of Simulation Pressure Results
5.2.5 Conclusion
After obtaining these results from Autodesk CFG, it was decided that additional testing would be time
consuming and would be a poor use of the limited time.
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
34
5.3 Engineering Equation Solver
5.3.1 Overview
In conjunction with simulating the compressor, calculations are being done in EES in order to ensure
that the results obtained from the simulation are accurate as well as create the frame work for the
initial design.
5.3.2 Procedure
A model of compression was used to determine the bore of the two compression cylinders along with
the stroke. Once those values were obtained, a mass flow rate could be calculated to perform a heat
transfer analysis
5.3.3 Results
Table 5 shows the results for work required from the pistons and heat removal requirements assuming
that the temperature will be brought down to about room temperature in between compression
stages. Full results and calculations can be found in Appendix B. EES Calculations.
Table 6. Work and Heat Removal Calculation Results
First Stage Work Required 1,167 (BTU/hr)
First Stage Heat Removal Require 1,121 (BTU/hr)
Second Stage Work Required 1,137 (BTU/hr)
Second Heat Removal Require 1,137 (BTU/hr)
5.3.4 Conclusion
From these calculations it was determined that a two stage compression with two 16 to 1 compression
ratios would compress the gas to the required pressure. From there it was determined that at the
desired flow rate, with a low value of convective heat transfer rate, that 10 feet of tube would be
enough to cool the gas off to the required temperature.
5.4 MathCAD
5.4.1 Overview
In order to insure safety, stress calculations needed to be done on each mode of failure in the bolts that
will hold the compressor together. To perform these calculations MathCAD was used for its user
interface and capability to format equations neatly.
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
35
5.4.2 Procedure
Stress calculations we performed on each mode of failure for each bolt. The axial stress that would pull
the manifolds apart were calculated using a thick walled pressure vessel calculation. The stresses in
shear for both the threads on the rod and the nut, along with axial tension, and tear-out stress were
calculated using the appropriate effective area. Once the stresses were found, the safety factors were
calculated using the minimum proof stress of the bolts in consideration.
5.4.3 Results
The results of the safety factor calculations have been tabulated in Table 4: Bolt & Threaded Rod Safety
Factors.
5.4.4 Conclusion
Given that the minimum safety factor calculated was 3.27, it was decided that the bolts specified would
adequately hold the compressor together even in the case of a malfunction causing an unexpected
pressure increase.
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
36
6 Final Design
6.1 Hydraulic System
6.1.1 Overview A hydraulic system will be used to convert electrical energy into mechanical work that will drive the
pistons a therefore compress the gas. An overview schematic of the proposed hydraulic system is
shown below in Figure 30: Hydraulic System Schematic.
Parker 3L Series Double Rod
Hydraulic Cylinder
Ashcroft 5000 psi
Pressure Gauge(s)
Figure 30: Hydraulic System Schematic
D03 Solenoid-Operated
Hydraulic Control Valve
5000 psi Tubing
with SAE 6 Straight
Thread Fittings
1.25 Gallon Hydraulic Pump &
Reservoir Monarch Hydraulics Inc.
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
37
6.2 Natural Gas System
6.2.1 Overview The natural gas system will move the gas from a residential natural gas line, through each of the four
compression cylinders, and ultimately into the tank of a natural gas vehicle. It also is designed to
prevent backflow at every possible point and monitor the thermodynamic state of the natural gas using
thermocouples, pressure gages, and a pressure transmitter. A schematic of the natural gas system is
shown below in Figure 31.
Figure 31. Natural Gas System Schematic
6.2.2 Residential Natural Gas Supply The team’s unit will be optimized to operate on a residential natural gas system with a pressure of 2
psi. This is the industry standard for larger homes, while 0.3 psi is standard for average homes. Natural
gas utility companies will usually install a 2 psi meter/regulator on a house if the customer has a special
reason to have one. Since the team’s system is an “intensifier” type of compressor, the initial pressure
into the first stage of the compressor is very important. To protect older appliances not design to used
2 psi natural gas, the team will recommend that customers who have to upgrade to a 2 psi
meter/regulator add an additional step down regulator to their residential natural gas system so that
their other appliances can continue to operate on 0.3 psi.
6.2.3 Piston Seals
After completing some initial research, the team realized that getting the piston seal to hold high
pressure gas and prevent it from blowing by the piston would be the most difficult part of the project.
The team had a conference call with Lee Otto of CNGPump, who makes hydraulic natural gas
compressors, and discussed the issue of piston seals. Mr. Otto stressed the importance of a “mirror-
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
38
like” finish on inside of the chamber. The team achieved this by using honed tube. He also mentioned
starting with bronze bushings as seals for a crude prototype. He mentioned that PTFE (or Teflon) seals
would be a good next step. He mentioned that his compressors use a proprietary material that he
claims has ten times less friction than PTFE.
The team decided that they wanted to start with PTFE to increase their chances of having a successful
prototype. This led them to contact Zatkoff Seals and Packings, were they meet Mr. Jerry LaBreck. Mr.
LaBreck assisted the team in finding the seals that would best suit their needs. Mr. LaBreck contacted
engineers inside the seals division of the Parker Hannifin Corporation and they prescribed the FBS-C
Flexiseal product to best meet the team’s requirements. The seals are made of carbon reinforced PTFE
and contain a spring that “energizes” the seal to constantly maintain contact with the inside of the
cylinder wall.
6.2.4 Tubing The team will be using stainless steel tubing to pipe the natural gas between compressor stages. The
team has selected ¼ in. OD tubing, with a wall thickness of 0.049 in. According to Table 3, this will give
the team the capability to handle 3600 psi with a safety factor of 2.
6.2.5 Check Valves As displayed in Figure 32, the team’s design uses check valves at every point where backflow could
possibly occur.
Figure 32. High Pressure Natural Gas Check Valves28
6.2.6 Relief Valve The design utilizes an adjustable pressure relief valve after the final stage. Gas is always free to flow in
the forward direction, therefore if over-pressurization occurred anywhere in the system it will be
relieved through this relief valve. An examples of adjustable relief values made for high pressure
natural gas applications are shown below in Figure 33. As a cost saving measure, a relief valve was not
28 http://www.hylokusa.com/products/valves/check-relief-valves.aspx
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
39
used in the prototype. The system was still adequate because it was to be attended by a team member
during testing to ensure over-pressurization did not occur.
Figure 33. Adjustable High Pressure Natural Gas Relief Valves29
6.2.7 Shut-off Valve A manual shut-off valve will be utilized between the residential natural gas system and the first stage
of the compressor. The will allow the compressor to be shut of manually during servicing. An example
of a ball valve made for compressed natural gas applications is shown below in Figure 34. This was not
implemented into the prototype because the team was only compressing atmospheric air during
testing.
Figure 34. Example of CNG Ball Valve30
6.2.8 Manifolds Manifolds will be used to distribute the compressed natural gas at the end of each compression
chamber. The piping system will be attached to the manifolds using SAE Straight Thread O-Ring and
NPT treaded adapters and Teflon tape to seal the connection. These manifolds will be constructed out
29 http://www.hylokusa.com/products/valves/check-relief-valves.aspx 30 http://www.hylokusa.com/compressed-natural-gas/cng-parts.aspx
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
40
of steel. An example of a manifold used to distribute gas at the end of a hydraulic natural gas
compression system is shown below in Figure 35.
Figure 35. Example of Manifold and Connections at End of CNG Compression Chamber31
6.2.9 Pressure Gauges and Transducers The team knew that they would have to monitor pressure and temperature inside each stage to test
and optimize their design. Temperature and pressure will be known so that the thermodynamic state
can be determined. This will allow the team to perform accurate heat transfer and fluid flow analyses
on the system.
Pressure transducers are very costly, however the team needed at least one to monitor the pressure
after the final stage. An example of a pressure transmitter is shown below in Figure 36. This is
necessary in order to tell the control system when the vehicle tank is full (pressure has reached 3600
psi). Regular pressure gages will be used to monitor the pressure of all other stages, these an example
of one of these gages is shown below in Figure 37.
31 http://www.gonaturalcng.com/wp-content/uploads/2012/11/cng_compressors.png
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
41
Figure 36. Pressure Transmitter Example
Figure 37. Pressure Gage Example
6.2.10 Heat Sinks The compressor design will utilize tubing loop heat sinks and a fan to being the compressed gas back to
room temperature following each compression stage. An example of utilizing tubing links as a heat sink
in conjunction with a fan is shown below in Figure 38. This will improve the overall isentropic efficiency
of the system and result in safer operation that is less prone to overheating.
Figure 38. Example of Tubing Loops32
32 http://www.lmcompressor.com/images/Web%20Page%20CNG_3021%20_.jpg
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
42
6.2.11 Blow-By Recovery System
After discussions with consultant Leo Otto and Professor Nielsen, it became apparent that the team
would have to devise a system to recover the natural gas that slips past the piston during compression.
The team decided to feed this gas back into the low-pressure supply of the system. This will allow the
volume behind each piston to remain at supply pressure. Check values were used to prevent backflow.
6.2.12 Refueling Nozzle Fuel will be dispensed using a purchased compressed natural gas fueling nozzle. There is an accepted
industry standard for these nozzles. Any nozzle purchased will fuel any compressed natural gas vehicle.
More complex and expensive nozzles are available, but because they are design for fast-fill units.
Because the team’s compressor is a time-fill unit, the simplest nozzles will be sufficient. An example of
a general purpose compressed natural gas refueling nozzle is shown below in Figure 39. This was not
integrated into the team’s prototype because the team made a direct connection into the CNG tank
using stainless steel SAE straight thread O-ring tube fittings instead. This was done to save cost and
was feasible because the demonstration tank was permanently mounted to the top of the appliance.
Figure 39. General Purpose CNG Refueling Nozzle for Time-Fill33
6.3 Control System The final prototype combined the functionality of National Instruments FieldPoint modules and a
computer loaded with LabVIEW 8.5 to demonstrate the mechanical functionality of the overall system
(see Figure 27: LabVIEW Block Diagram). This system had many components, including, but not limited
to, a sealed enclosure box, input and output FieldPoint modules, three solid state relays, a power
distribution bus bar, two high temperature thermocouples, a pressure transducer, a power supply, and
multiple strain release gaskets to preserve the functionality of the wires (see Figure 40).
33 http://www.opwglobal.com/Product.aspx?pid=138
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
43
6.3.1 Enclosure Box
A sealed enclosure box was used to ensure that any potential natural gas leaks would not ignite with
sparks generated by the electrical componentry (see Figure 41). Nylon glands were used to seal around
the cords entering the box and silicone sealant was used to seal around holes in the boxes that were
left over from previous users.
Figure 41: Sealed Electrical Control Box
6.3.2 FieldPoint Modules
Din rail mounted FieldPoint modules were used for all data collection and feedback. These
components, valued at over $2,000, were lent to the team by the college for testing purposes. Using
an FP-2000 Ethernet controller, data was channeled from the modules, through a router, and then into
a Windows XP computer capable of supporting legacy FieldPoint software (see Figure 42).
Figure 40: Compiled Control & Monitoring System
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
44
Figure 42: FieldPoint Module Communication with Windows XP
6.3.3 Solid State Relays
Solid State relays used the extremely small current DC output of the FieldPoint IO device to switch 120V,
12A AC current for powering of the hydraulic pump and solenoid valve. These relays were used because
they could be switched with .005mA of input DC current, thus aligning with the FieldPoint unit’s output
capabilities (see Figure 43).
Figure 43: Solid State Relays
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
45
6.3.4 Thermocouples As stated above, the team needed to monitor the pressure and temperature of the gas at each stage
for accurate heat transfer and fluid flow modeling. Monitoring the temperature at every stage was
more important than monitoring the pressure at each stage because it is impossible for over-
pressurization to occur during the first three stages because gas is always free to flow in the forward
direction. Over-heating, however, can theoretically occur at any stage in the system. Therefore, a
thermocouple was installed after each compression stage to monitor the temperature of the gas leaving
that stage. Using this temperature data, LabVIEW was programmed to shut down the pump and
solenoid valve should temperature exceed 250 degrees Fahrenheit. These thermocouples were pipe-
plug type that threaded into the manifolds using 1/4” NPT threads and provided a high pressure seal to
prevent gas from escaping through the thermocouple port.
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
46
7 Prototype Development
7.1 Machining
In order to build a compressor, a variety of parts needed to be machined with some requiring tight
tolerances. The parts machined by the team include, four end-plate manifolds, two spacer plates, four
spacing collars, a coupling nut, honed tube for cylinder wall, and six total pieces required to form two
pistons. The technical drawings of these parts can be found in the appendix. A steel frame was also
constructed in order to hold all the components together.
Figure 44: Machining
7.2 Fabrication & Assembly
Once all the components of the compressor where machined, their dimensions were verified and
assembled to insure proper fit. The compressor was then assembled using the bolts and threaded rod
specified earlier.
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
47
Figure 45: Fabrication & Assembly
7.3 Modifying
Once initial assembly was completed, the team tested the compression ratios of the first and second
stage compressors. Due to some uncertainty in calculating the top-dead-center volume, the team
planned to adjust the position of the piston on the extended tie-rod of the hydraulic cylinder, thereby
reducing the volume at the end of compression. An example of this is shown below (see Figure 46:
Piston Spacing Diagram). The team made a number of changes until the desired compression ratios
were achieved.
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
48
Figure 46: Piston Spacing Diagram
7.4 Mounting
Once the system was tested, it was mounted in a steel case with the hydraulic pump. Once mounted,
steel tubing was used to connect all aspects of the hydraulic system and the natural gas system (see
Figure 47: Mounting of Final Prototype).
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
49
Figure 47: Mounting of Final Prototype
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
50
8 Testing
8.1 Test Planning
As previously mentioned, LabVIEW was chosen to test the feasibility of the system. Multiple
thermocouples and a pressure transducer were set to take data during testing. In addition to the
collection of data, the LabVIEW software was used to set up safe guards which would shut down the
system if an unsafe pressure or temperature was reached. Finally LabVIEW was used to control the
solenoid valve of the hydraulic cylinder, thereby controlling the system.
8.2 System Testing
8.2.1 Air Testing
To insure safety while still testing the feasibility of the system, initial testing of the system will be testing
using air. The goal of this test is to insure that the system can withstand the pressures associated with
compression.
8.2.2 Natural Gas Testing
Once testing with air proved that there is no potential for leaks in the system, the team was planning
on testing the system with natural gas. The results from this test were to show if the system meet the
required goals. The team was unable to test their prototype with natural gas due to safety concerns
and a lack of adequate time. However, the team is confident their system is capable of safely
compressing natural gas.
8.3 Results
8.3.1 Compression Ratios
The team started testing each cylinder individually using atmospheric air. The goal of these tests were
to verify that each stage was indeed result in a 16:1 compression of the air. This meant that the team
had to achieve a maximum pressure of about 225 psi from an input of atmospheric are. The team
adjusted the spacing between the piston and the rear of the threaded portion of the hydraulic rod in
order to adjust the total volume in the cylinder. After the team was confident that both stages were
near a 16:1 ratio, they plumbed the two stages together with a heat sink and check valves in between
the two chambers.
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
51
The team then plugged the output of the second stage manifold in order to determine the maximum
pressure that the compressor could achieve. These tests went very well, and the team was able to
achieve their goal of the compressor generating the target pressure of 3600 psi, as seen in Figure 48.
Figure 48: Pressure Reaching 3,600 psi
Figure 49: Temperature Data from Testing
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
52
8.3.2 Pressure and Temperature
The team set out to monitor pressure and temperature during these tests, however the team was
unable to gain good data from the pressure transducer. In the Figure 49, the pressure has been
approximated by manual observation due to the malfunction of the team’s pressure transducer. This
approximation was conducted by applying a linear fit to the beginning and final pressures achieved
through the test run.
8.3.3 Friction
The team saw a pressure in the hydraulic lines of approximately 400 psi when the piston was moving
without pressure. Calculations were done to find the force required to overcome the friction force in
the system, these calculations are shown in Appendix C. The results of these calculations showed a
force of 8.73 kN needed to overcome the friction in the system. This high number is to be expected
because of the extremely tight, interface fits between the seals and rider rings and the inside of the
cylinder.
9 Obstacles
9.1 Controls
As mentioned previously, the team unfortunately lost its only electrical engineering during the month
of February. This led to the decision of using National Instruments equipment to control the system.
Since all the remaining team members were mechanical engineers, there was a lack of experience in
wiring the control panel. This inexperience prompted the wiring of AC current to the DC input $1,500
Ethernet control module. The module failed to operate after several attempts of rewiring. Finally, it
was discovered that a fuse had been blown during the accident (see Figure 50).
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
53
Figure 50: Blown Fuse in Ethernet Controller
By soldering a wire between the connectors of the fuse holder (see Figure 50), the module came back
to life and was able to operate flawlessly for the remainder of the project. The team member who
made this mistake has learned his lesson and will not make such mistake again.
9.2 Piston Seals
After the team had selected a carbon-reinforced PTFE Parker FBS-C Flexiseal with the help of Mr. Jerry
LaBreck from Zatkoff Seals and Packings and engineers from the Parker Hannifin Corporation, the team
was told that these seals were a custom product and that they would have a 6 – 8 week lead time. This
was discouraging to the team, because they had initially planned on building a small, single stage model
of their design before beginning to construct their final prototype. The long lead time associated with
the seals forced the team to reconsider this plan and eventually opted to move on to building their final
prototype without building a small scale model. Mr. LaBreck and the Parker engineers also assisted the
team by supplying basic build parameters for the pistons that the seals would mount to. The team was
satisfied with the performance of the seals and their decision to move directly to building their final
prototype.
9.3 Storage Tanks
For the sake of simplicity, cost savings, and reduced testing time, the team initially proposed using part
of the honed tube that was donated to create a miniature pressure vessel to hold the compressed gas.
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
54
The team was informed by the company that donated the honed tube that it was against ASME
regulations to use the honed tube for this purpose. This led to the team needing to acquire a tank to
compress air and eventually natural gas into. The proposed design of the pressure vessel is shown below
in Figure 51.
Figure 51. Proposed Pressure Vessel
Because of this, the team was forced to find natural gas tanks which are costly. Luckily the team was
able to borrow the tanks from Crazy Diamond which helped the team substantially.
9.4 Gaskets
The team initially thought that they would use gaskets to seal between the honed tube and the
manifolds. The team contacted a few local gasket distributors, but found it difficult to find a gasket
material that would withstand the high temperatures and pressures that the design required. This lead
the team to address this issue in a conversation with their mentor, Ross Pursifull of Ford Motor
Company. Mr. Pursifull suggested that the team use O-rings instead of gaskets to achieve the seal
between the honed tube and the manifolds. We contacted Jerry LaBreck at Zatkoff Seals and Packings
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
55
and he supplied us with the O-rings we needed as well as the specifications for the grooves that were
to be cut in the manifolds to hold the O-rings in place.
9.5 Top Dead Center Volume
The team calculated a top dead center volume knowing that there may be some inaccuracy with the
calculation due to the complexity of determining exactly where top dead center is due to the check
valves. Upon initial tests however the team found that the on the second stage, the volume in the veins
of the top manifold to too large, meaning that a 16:1 compression ratio could not be achieved. To solve
this problem the team had to redesign and remake the manifold with smaller holes for the gas to flow
through. This redesign eliminated the problem and allowed the team to achieve a 16:1 ratio in the
second stage and therefore achieve their target pressure of 3600 psi.
9.6 Piston O-Ring Seal
In order to seal the piston so that no gas could get through the center hole of the piston, O-rings were
placed on both the top side and bottom side of the piston with the bottom O-ring held in place by a
washer. The bottom of the piston with the O-ring is shown below in Figure 52.
Figure 52. Piston O-ring
The problem that the team faced with this O-ring was first of all that the inner diameter was too large.
This caused the washer to cut through the O-ring when used. The washer was replaced with a second
O-Ring
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
56
washer, however after testing it was found that the O-ring has squeezed around the washer. A final
washer was used with a small enough inner diameter and a large enough outer diameter. After testing
with the third washer it appears that the O-ring is not sealing the way the team had hoped. To solve
this problem, the team recommends cutting a groove into the bottom of the piston for the O-ring to sit
in.
10 Future Improvements
10.1 Proper Component Sizing
As shown in the hydraulic power unit calculations in
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
57
Appendix C. MathCAD Calculations, the hydraulic power unit used for the final prototype does not
provide enough power to move the system at a frequency of 4 cycles per second. The team was
achieving about 10 seconds per cycle with their 1.25 gallon per minute hydraulic pump.
In order to correct this disparity, the team thinks it would be best to reduce the size of the compressor
as opposed to increasing the size of the hydraulic power unit. This decision was made in light of the
fact that 1.25 gallon per minute hydraulic power units are readily available at a very economic cost
because they are used for common applications such as log splitters and pipe benders. The team think
that they would be able to create a unit that averages a compression rate of around 0.2 GGE per hour
with this change. This is under the goal that the team initially set out to achieve, but it is the only way
the team forces being able to build a compressor that is economical for home residential applications.
A large CNG tank could be added to a low-rate system like this in order to provide a buffer should the
customer need fuel quickly.
10.2 Noise Control
The team initially planned to implement a noise control system with their final prototype. When the
team was forced to prioritize with features were most important to include in their final prototype, the
noise control system was ruled out because it was non-essential to proving the mechanical viability of
the system and would have made accessing the system for modifications, testing, and demonstration
difficult.
If the team were to take their prototype to production, a noise control system would be an essential
part of the final product. The team believes that covering the outside of the frame with sheet metal
and spraying the inside of the sheet metal with a polyurethane foam would be the best initial design
for implementing noise control. One difficulty with this approach would be that heat would be trapped
inside the enclosure, along with the noise. Initial testing shows that heat generation for the prototype
is low due to its low compression rate. The team feels that the heat generation would be small enough
to not cause a problem with the noise control system, but there is no way to test this hypothesis at this
time.
10.3 Imbedded Electronics
As mentioned, a production model of this system will incorporate all the electronic functionality of the
current system using an imbedded development board. This board will communicate to an LED display
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
58
and allow for ease-of-use and aesthetic appeal. In addition, this onboard computer will have all the
necessary safety systems and emergency stops.
10.4 Fabricating for Flexibility
When the team fabricated the frame for the equipment to mount in, they welded all of the cross-
member mounts that the equipment would sit on. This meant that the equipment could not be
removed from the bottom of the unit. This often meant that the team had to spend many hours
unbolting the entire compressor to adjust some the volume of the chambers. If the team would have
had the foresight to bolt the mounts to the frame, modifying and tuning the compressor would have
been much easier.
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
59
11 Financial Estimates
11.1 Cost of Development
The estimated and actual budget for the development of the team’s home refueling unit prototype is
listed in Table 7: Operational Budget. Initial research into the component costs for the preliminary Bill
of Materials resulted in a total operational budget of $3,000.
Table 7: Operational Budget
Originally, the college granted the team $2,000 of this $3,000 proposed budget, assuming the rest
would be supplemented by donations. Although Wolverine Oil & Gas did grant the team an additional
$500, there remained a $500 budget gap.
Thanks to part donations by Harbor Steel, Best Metal Products, and Crazy Diamond Performance, the
team was able to complete the project only $177.14 over budget. After conversations with the team’s
faculty advisor midway through the year, it was promised that exceeding the budget by a few hundred
dollars would be covered by emergency funds provided by the college. NaturaFill is very grateful to the
Date Vendor DescriptionBudgeted
Amount
Actual
Cost Difference
12/6/2013 Amazon SainSmart 4-Channel Relay Module 20.00$ 13.50$ 6.50$
12/6/2013 Speedway Gas for 11/2/2013 Ross Pursifull Visit -$ 42.65$ (42.65)$
12/6/2013 Office Depot Paper for Sponsorship Letters 20.00$ 18.54$ 1.46$
12/6/2013 Printing Services Brochures and Envelopes 60.00$ 62.45$ (2.45)$
12/6/2013 Printing Services Postage for Sponsorship Letters 10.00$ 11.50$ (1.50)$
12/9/2013 NovaTech High Pressure Pipe-Plug Thermocouple 40.00$ 37.59$ 2.41$
2/6/2014 McMaster Carr Multipurpase Pressure Gauges (2) 30.00$ 19.68$ 10.32$
2/27/2014 Harbor Steel Supply 5' x 7" x 1" CR Steel Plate 150.00$ -$ 150.00$
3/1/2014 Bond Fluidaire Hydraulic Power Unit 550.00$ -$ 550.00$
3/1/2014 McMaster Carr Hydraulic Solenoid Valve 300.00$ 192.69$ 107.31$
3/1/2014 Best Metal Products Steel pipe for compression cylinders 150.00$ -$ 150.00$
3/1/2014 Bond Fluidaire Hydraulic Fittings and Teflon Tape -$ 10.49$ (10.49)$
3/1/2014 eBay Small Hydaulic Test Cylinder -$ 70.64$ (70.64)$
3/4/2014 Zatkoff Seals Seals 200.00$ 481.32$ (281.32)$
3/12/2014 Bond Fluidaire Hydraulic Fittings and Tubing 50.00$ 44.00$ 6.00$
3/13/2014 Great Lakes Fluid Power Hydraulic Fittings 10.00$ 9.34$ 0.66$
3/15/2014 Speedway Gas for 3/15/2014 Ross Pursifull Visit -$ 38.91$ (38.91)$
3/15/2014 Crazy Diamond Performance 2 CNG Tanks & Pressure Regulator -$ -$ -$
3/19/2014 Bond Fluidaire Hydraulic Cylinder 650.00$ 527.80$ 122.20$
4/6/2014 Northern Tool + Equipment Hydraulic Solenoid Valve 120.00$ 119.99$ 0.01$
4/6/2014 McMaster Carr Hardware and Piston Aluminum Stock 200.00$ 212.40$ (12.40)$
4/6/2014 NovaTech High Pressure Pipe-Plug Thermocouple 40.00$ 37.59$ 2.41$
4/17/2014 McMaster Carr Coupling Nuts, O-Rings -$ 25.11$ (25.11)$
4/22/2014 Omega Presure Transducer -$ 175.00$ (175.00)$
4/28/2014 Swagelok Check valves, Fittings, Tubing 400.00$ 396.00$ 4.00$
5/2/2014 Home Depot / Lowe's Paint & Primer -$ 24.47$ (24.47)$
5/3/2014 McMaster Carr Misc. Bolts -$ 20.00$ (20.00)$
5/5/2014 McMaster Carr Misc. Power Supply Components -$ 63.60$ (63.60)$
5/6/2014 Swagelok Pressure Regulator, Fittings, Adapters -$ 410.11$ (410.11)$
5/7/2014 McMaster Carr Washers, Hexnuts, and Cord Grip -$ 89.86$ (89.86)$
5/8/2014 McMaster Carr Additional Cord Grip -$ 21.91$ (21.91)$
Total 3,000.00$ 3,177.14$ (177.14)$
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
60
college for providing these emergency funds, which enabled the completion of the team’s home
refueling unit prototype.
11.2 Cost of Production
Should a revised version of the prototype enter production, a detailed statement of cash flows has been
listed in Table 8: Costs of Production. Using component costs listed in the operational budget (see Table
7: Operational Budget), a preliminary production budget was calculated by assuming industry standards
in economics of scale. Based on these industry standards as well as suggested future changes to the
prototype, the cost to manufacture was estimated at $2,080 per unit. At an initial selling price of $3,500
and moderate annual growth in sales and price, the team believes that NaturaFill would be profitable
in its third year of existence as a Limited Liability Corporation (LLC).
Table 8: Costs of Production
Year 1 Year 2 Year 3
Estimated Sales 50 200 500
Selling Price ($/Unit) 3,500$ 3,750$ 4,000$
Fixed Variable
Employees ($/Unit) -$ 40$
Parts ($/Unit) -$ 2,000$
Distribution ($/Unit) -$ 40$
Building Rent & Utilities 120,000$ -$
Administrative Costs 300,000$ -$
Prototype Materials 3,000$ -$
Marketing 30,000$ -$
Machines & Tooling 100,000$ -$
Total Revenue 175,000$ 750,000$ 2,000,000$
Total Cost (657,000)$ (969,000)$ (1,593,000)$
Net Income (482,000)$ (219,000)$ 407,000$
Gross Profit Margin -275% -29% 20%
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
61
12 Conclusion
The goal of the NaturaFill project was to design, build, and test a natural gas home refueling appliance
that is lower cost and more reliable than appliances currently on the market. While the current
prototype would have cost close to $7,000 without donations and educational pricing, the team still
believes that a production model could be sold for as low as $3,500, taking into account the changes
proposed in section 10 Future Improvements.
Lessons learned from doing this project included:
Creating a more accurate plan where tasks are accomplished in an orderly manner, without unnecessary rework.
The difficulty and value in being able to troubleshoot problems and come up with effective solutions.
The benefit for fabricating components with ease-of-disassembly in case of needed repair or cleaning.
The value in budgeting more conservatively, to account for additional shipping costs and requirements for ordering in bulk.
Overall, the team continues to believe that transitioning domestic energy consumption away from
imported oil, in favor of cleaner, American natural gas, is vital for long term economic, environmental,
and political stability. With an estimated market price of $3,500, the team desires that, in some small
way, NaturaFill has helped in carrying out that mission.
Figure 53: Final NaturaFill Prototype
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
62
13 Acknowledgements
13.1 Professor Ned Nielsen
Professor Ned Nielsen is the faculty advisor for NaturaFill. The team is grateful to Professor Nielsen for
his insights and constructive criticism throughout the design process.
13.2 Professor Steve VanderLeest
Professor Steve VanderLeest is an adjunct advisor for NaturaFill. The team is grateful to Professor
Nielsen for his presentation feedback and advice on the project’s electronic control systems.
13.3 Professor Matthew Heun
Professor Matthew Heun is a Mechanical Engineering professor with a wide range of knowledge in
thermodynamics. The team is grateful to Professor Heun for providing feedback on the AutoCAD CFD
simulation and supporting the team’s efforts to model heat generation by the compression system.
13.4 Mr. Jimmy Moerdyk
Mr. Jimmy Moerdyk is the VP of Operations of Moerdyk Energy, Inc. The team is grateful to Mr.
Moerdyk for his mentorship and industry insights.
13.5 Mr. Lee Otto
Mr. Lee Otto is the CEO and founder of CNGPump, Inc. The team is grateful to Mr. Lee for his advice to
the team regarding hydraulic cylinder seal technology and safety controls.
13.6 Mr. Ross Pursifull
Mr. Ross Pursifull Otto is a Research Specialist at the Ford Motor Company. The team is grateful to Mr.
Lee for his industry insight on the future of CNG and willingness to demonstrate the use of his CNG
home refueling unit.
13.7 Mr. Phil Jasperse
Mr. Phil Jasperse is the Calvin College metal and wood shop supervisor. The team is grateful to Mr.
Jaspers for his training in metal cutting and fabrication. The team is also grateful to Mr. Jaspers for his
advice on the fabrication of components.
13.8 Mr. Jerry LaBreck
Mr. LaBreck is a sales manager at Zaktkoff Seals and Packing. He provided the team with valuable advice
and discounted or sample sealing products to help ensure that the sealing was done properly and within
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
63
budget. He also was instrumental in communicating with Parker Hannifin engineers on behalf of team
to obtain the necessary integration instructions for the seals throughout the system.
13.9 Mr. Kevin Fern
Mr. Fern is the president of Crazy Diamond Performance, a CNG technology company in Shelby
Township, MI. He graciously allowed the team to borrow two small CNG tanks and provided the team
with much helpful advice on safely handling high pressure natural gas.
13.10 Mr. Tim Wolfis
Mr. Wolfis is a sales representative for Grand Rapids Valve and Fitting, a Swaglok distributor. He was
able to provide the team with valuable advice regarding high pressure system plumbing and was able
to arrange an agreement for the team to receive high pressure fittings and tubing at a discounted rate.
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
64
14 Appendix
14.1 Appendix A. Work Breakdown Structure
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
65
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
66
14.2 Appendix B. EES Calculations
14.2.1 Two Stage Compression System Sizing Calculations
"Constants" MM_CH4 = MolarMass(CH4) T_cr = 190.7 [K] P_cr = 4640 [kPa] GGE = 2.567 [kg] P_atm = 100 [kPa] T[1] = 300 [K] "Inputs" P_g_service_psia = 0.5 [psi] "!High Pressure Residential Gas Meter" "Design Variables" CyclePeriod = 4 [s] "!Design Variable" "Capacity" "GGE_dot = 0.5" "!Specified Result" "Compression Ratios" r = 16 "Input Variable" "Hyrdaulic Cylinder" Bore_H = (2.5 [in]) * convert(in,m) "Input Variable" "Isentropic Efficiency"
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
67
eta = 0.8 "!Stream 1" m_dot = m_cycle / CyclePeriod GGE_dot = (m_dot / GGE) * convert('hr', 's') P_g_service = P_g_service_psia * convert('psi', 'kPa') P[1] = P_atm + P_g_service s[1] = entropy(CH4, T = T[1], P = P[1]) v[1] = volume(CH4, T = T[1], P = P[1]) m_cycle = Vol[1] / v[1] h[1] = enthalpy(CH4, T=T[1]) Bore_1 = (5 [in]) * convert(in,m) "Input Variable" Bore_1_in = Bore_1*convert(m,in) Stroke_1_2 = (6 [in]) * convert(in,m) Stroke_1_2 = Vol[1] / ((Bore_1^2)*(1/4)*pi) Stroke_1_2_in = Stroke_1_2 * convert(m,in) HydroAdv_1 = (Bore_H^2) / (Bore_1^2) "!Stream 2" v[2] = v[1] / r Vol[2] = v[2] * m_cycle s_s[2] = s[1] h_s[2] = enthalpy(CH4, v = v[2], s = s_s[2]) eta = (h_s[2] - h[1]) / (h[2] - h[1]) T[2] = temperature(CH4, h = h[2]) T_F[2] = ConvertTemp(K,F,T[2]) P[2] = pressure(CH4, v = v[2] , h = h[2]) P_psia[2] = P[2] * convert(kPa, psia) s[2] = entropy(CH4, v = v[2] , h = h[2]) "Stage 1" W_avg_cycle[1] = (h[2] - h[1]) * m_dot "Stream 2 Cooling" T_cool[2] = 300 [K] h_cool[2] = enthalpy(CH4, T = T_cool[2]) s_cool[2] = entropy(CH4, T = T_cool[2], v = v[2]) Q_cool[2] = m_dot*(h[2]-h_cool[2]) P_cool_psia[2] = pressure(CH4, v = v[2] , h = h_cool[2]) * convert(kPa, psia) "!Stream 3"
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
68
v[3] = v[2] / r Vol[3] = v[3] * m_cycle s_s[3] = s_cool[2] h_s[3] = enthalpy(CH4, v = v[3], s = s_s[3]) eta = (h_s[3] - h_cool[2]) / (h[3] - h_cool[2]) T[3] = temperature(CH4, h = h[3]) T_F[3] = ConvertTemp(K,F,T[3]) P[3] = pressure(CH4, v = v[3] , h = h[3]) P_psia[3] = P[3] * convert(kPa, psia) s[3] = entropy(CH4, v = v[3] , h = h[3]) ((Bore_2^2)*(1/4)*pi) = Vol[2] / Stroke_1_2 Bore_2_in = Bore_2*convert(m,in) HydroAdv_2 = (Bore_H^2) / (Bore_2^2) "Stage 2" W_avg_cycle[2] = (h[3] - h_cool[2]) * m_dot "Stream 3 Cooling" T_cool[3] = 300 [K] h_cool[3] = enthalpy(CH4, T = T_cool[3]) s_cool[3] = entropy(CH4, T = T_cool[3], v = v[3]) Q_cool[3] = m_dot*(h[3]-h_cool[3]) P_cool_psia[3] = pressure(CH4, v = v[3] , h = h_cool[3]) * convert(kPa, psia)
14.2.2 Heat Transfer Calculations
"Heat Transfer Calculations Senior Design Team 13: Naturafill" "!Givens" GGE = 2.567 [kg]*convert(kg,lbm) Cycle_Period = 6 [sec] GGE_dot = 0.5 [1/hr]"GGE" GGE_dot = m_dot/GGE *convert(1/sec,1/hr) eta =0.80 T_atm = 100[F] d_tube = 0.25[in]*convert(in,ft) h_conv_nat = 20 [W/m^2*K]*convert(W/m^2*K,BTU/hr*ft^2*F)
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
69
"!Stage 1: inlet" P[1] = 16[psi] T[1] = 70[F] h[1] = enthalpy(CH4,T=T[1]) s[1] = entropy(CH4,T=T[1],P=P[1]) "!Stage2: First stage Compression" h_s[2] = enthalpy(CH4,s=s[1],v=v[2]) v[1] =volume(CH4,T=T[1],P=P[1]) eta = (h_s[2]-h[1])/(h[2]-h[1]) P[2] =Pressure(CH4,v=v[2],T=T[2]) T[2] = temperature(CH4, h=h[2]) v[2] = v[1]/16 W_first = m_dot*(h[2]-h[1])*convert(1/sec,1/hr) "!Stage3: First Stage Cooling" s[3] = entropy(ch4,T=T[3],P=P[3]) T[3] = 100 [F] "cooling temperature" h[3] = enthalpy(CH4,T=T[3]) P[3] = Pressure(CH4,T=T[3], v=v[2]) Q_conv_23 =m_dot*(h[2]-h[3])*convert(1/sec,1/hr) Q_conv_23 = pi*d_tube*Length_tube_1*h_conv_nat*(T[2]-T_atm) w_second = m_dot*(h[4]-h[3])*convert(1/sec,1/hr) "!Stage4: Second Stage Compression" v[4] = v[2]/14 h_s[4] = enthalpy(ch4,s=s[3], v=v[4]) eta = (h_s[4] - h[3])/(h[4]-h[3]) T[4] = temperature(ch4, h=h[4]) P[4] = Pressure(ch4,T=T[4], v=v[4]) "!Stage5: Second Stage Cooling" T[5] = 100 [F] "cooling final" P[5] = pressure(ch4,T=T[5],v=v[4]) h[5] = enthalpy(ch4,T=T[5]) Q_conv_45 =m_dot*(h[4]-h[5])*convert(1/sec,1/hr) Q_conv_45 = pi*d_tube*Length_tube_2*h_conv_nat*(T[4]-T_atm)
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
70
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
71
14.3 Appendix C. MathCAD Calculations
14.3.1 Pump/Reservoir Horsepower Requirement
14.3.2 Stress in Spacer Plate Bolts (First Stage)
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
72
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
73
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
74
14.3.3 Stress in Threaded Rod (First Stage)
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
75
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
76
14.3.4 Friction Calculations
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
77
14.4 Appendix D. As-Built Part Drawings
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
78
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
79
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
80
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
81
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
82
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
83
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
84
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
85
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
86
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
87
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
88
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
89
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
90
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
91
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
92
14.5 Appendix E. Raw Testing Data
Testing w/ Air Compression - 5/14/14 Thermocouples (deg F)
Time (s)
*Time (min)
First Stage
Second Stage
**Pressure Approx. (psi)
0.00 0.0000 67.8739 67.8739 260.000
0.10 0.0017 67.8739 67.8179 260.003
0.20 0.0033 67.8739 67.8179 260.006
0.30 0.0050 67.8739 67.8179 260.009
0.40 0.0067 67.8739 67.8179 260.012
0.50 0.0083 67.8739 67.8179 260.015
0.60 0.0100 67.8739 67.8179 260.018
0.70 0.0117 67.8739 67.8179 260.021
0.80 0.0133 67.8739 67.8179 260.024
0.90 0.0150 67.8739 67.8179 260.027
1.00 0.0167 67.8739 67.8179 260.030
1.10 0.0183 67.8739 67.8179 260.033
1.20 0.0200 67.8739 67.8179 260.036
1.30 0.0217 67.8739 67.8179 260.039
1.40 0.0233 67.8739 67.8179 260.042
1.50 0.0250 67.8739 67.8179 260.045
1.60 0.0267 67.8739 67.8179 260.048
1.70 0.0283 67.8739 67.8179 260.051
1.80 0.0300 67.8739 67.8179 260.054
1.90 0.0317 67.8739 67.8179 260.057
2.00 0.0333 67.8739 67.8179 260.060
2.10 0.0350 67.8739 67.8179 260.063
2.20 0.0367 67.8739 67.8179 260.066
2.30 0.0383 67.8739 67.8179 260.069
2.40 0.0400 67.8739 67.8179 260.072
2.50 0.0417 67.8739 67.8179 260.075
2.60 0.0433 67.8739 67.8179 260.078
2.70 0.0450 67.8739 67.8179 260.081
2.80 0.0467 67.8739 67.8179 260.084
2.90 0.0483 67.8739 67.8179 260.087
3.00 0.0500 67.8739 67.8179 260.090
3.10 0.0517 67.8739 67.8179 260.093
3.20 0.0533 67.8739 67.8179 260.096
3.30 0.0550 67.8739 67.8179 260.099
3.40 0.0567 67.8739 67.8179 260.102
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
93
3.50 0.0583 67.8739 67.8179 260.105
3.60 0.0600 67.8739 67.8179 260.108
3.70 0.0617 67.8739 67.8179 260.111
3.80 0.0633 67.8739 67.8179 260.114
3.90 0.0650 67.8739 67.8179 260.117
4.00 0.0667 67.8739 67.8179 260.120
4.10 0.0683 67.8739 67.8179 260.123
4.20 0.0700 67.8739 67.8179 260.126
4.30 0.0717 67.8739 67.8179 260.129
4.40 0.0733 67.8739 67.8179 260.132
4.50 0.0750 67.8739 67.8179 260.135
4.60 0.0767 67.8739 67.8179 260.138
4.70 0.0783 67.8739 67.8179 260.141
4.80 0.0800 67.8739 67.8179 260.144
4.90 0.0817 67.8739 67.8179 260.147
5.00 0.0833 67.8739 67.8179 260.150
5.10 0.0850 67.8739 67.8179 260.153
5.20 0.0867 67.8739 67.8179 260.156
5.30 0.0883 67.8739 67.8179 260.159
5.40 0.0900 67.8739 67.8179 260.162
5.50 0.0917 67.8739 67.8179 260.165
5.60 0.0933 67.8739 67.8179 260.168
5.70 0.0950 67.8739 67.8179 260.171
5.80 0.0967 67.8739 67.8179 260.174
5.90 0.0983 67.8739 67.8179 260.177
6.00 0.1000 67.8739 67.8179 260.180
6.10 0.1017 67.8739 67.8179 260.183
6.20 0.1033 67.8739 67.8179 260.186
6.30 0.1050 67.8739 67.8179 260.189
6.40 0.1067 67.8739 67.8179 260.192
6.50 0.1083 67.8739 67.8179 260.195
6.60 0.1100 67.8739 67.8179 260.198
6.70 0.1117 67.8739 67.8179 260.201
6.80 0.1133 67.8739 67.8179 260.204
6.90 0.1150 67.8739 67.8179 260.207
7.00 0.1167 67.8739 67.8179 260.210
7.10 0.1183 67.8739 67.8179 260.213
7.20 0.1200 67.8739 67.8179 260.216
7.30 0.1217 67.8739 67.8179 260.219
7.40 0.1233 67.8739 67.8179 260.222
7.50 0.1250 67.8739 67.8179 260.225
7.60 0.1267 67.8739 67.8179 260.228
7.70 0.1283 67.8739 67.8179 260.231
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
94
7.80 0.1300 67.8739 67.8179 260.234
7.90 0.1317 67.8739 67.8179 260.237
8.00 0.1333 67.8739 67.8179 260.240
8.10 0.1350 67.8739 67.8179 260.243
8.20 0.1367 67.8179 67.8179 260.246
8.30 0.1383 67.8179 67.8179 260.249
8.40 0.1400 67.8179 67.8179 260.252
8.50 0.1417 67.8179 67.8179 260.255
8.60 0.1433 67.8179 67.8179 260.258
8.70 0.1450 67.8179 67.8179 260.261
8.80 0.1467 67.8179 67.8179 260.264
8.90 0.1483 67.8179 67.8179 260.267
9.00 0.1500 67.8179 67.8179 260.270
9.10 0.1517 67.8179 67.8179 260.273
9.20 0.1533 67.8179 67.8179 260.276
9.30 0.1550 67.8739 67.8179 260.279
9.40 0.1567 67.8739 67.8179 260.282
9.50 0.1583 67.8739 67.8179 260.285
9.60 0.1600 67.8739 67.8179 260.288
9.70 0.1617 67.8739 67.8179 260.291
9.80 0.1633 67.8739 67.8179 260.294
9.90 0.1650 67.8739 67.8179 260.297
10.00 0.1667 67.8739 67.8179 260.300
10.10 0.1683 67.8739 67.8179 260.303
10.20 0.1700 67.8739 67.8179 260.306
10.30 0.1717 67.8739 67.8179 260.309
10.40 0.1733 67.8739 67.8179 260.312
10.50 0.1750 67.8739 67.8179 260.315
10.60 0.1767 67.8739 67.8179 260.318
10.70 0.1783 67.8739 67.8179 260.321
10.80 0.1800 67.8739 67.8179 260.324
10.90 0.1817 67.8739 67.8179 260.327
11.00 0.1833 67.8739 67.8179 260.330
11.10 0.1850 67.8739 67.8179 260.333
11.20 0.1867 67.8739 67.8179 260.336
11.30 0.1883 67.8739 67.8179 260.339
11.40 0.1900 67.8739 67.8179 260.342
11.50 0.1917 67.8739 67.8179 260.345
11.60 0.1933 67.8739 67.8179 260.348
11.70 0.1950 67.8739 67.8739 260.351
11.80 0.1967 67.8739 67.8739 260.354
11.90 0.1983 67.8739 67.8739 260.357
12.00 0.2000 67.8739 67.8739 260.360
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
95
12.10 0.2017 67.8739 67.8739 260.363
12.20 0.2033 67.8739 67.8739 260.366
12.30 0.2050 67.8739 67.8739 260.369
12.40 0.2067 67.8739 67.8739 260.372
12.50 0.2083 67.8739 67.8739 260.375
12.60 0.2100 67.8739 67.8739 260.378
12.70 0.2117 67.8739 67.8739 260.381
12.80 0.2133 67.8739 67.8179 260.384
12.90 0.2150 67.8739 67.8179 260.387
13.00 0.2167 67.8739 67.8179 260.390
13.10 0.2183 67.8739 67.8179 260.393
13.20 0.2200 67.8739 67.8179 260.396
13.30 0.2217 67.8739 67.8179 260.399
13.40 0.2233 67.8739 67.8179 260.402
13.50 0.2250 67.8739 67.8179 260.405
13.60 0.2267 67.8739 67.8179 260.408
13.70 0.2283 67.8739 67.8179 260.411
13.80 0.2300 67.8739 67.8179 260.414
13.90 0.2317 67.8739 67.8739 260.417
14.00 0.2333 67.8739 67.8739 260.420
14.10 0.2350 67.8739 67.8739 260.423
14.20 0.2367 67.8739 67.8739 260.426
14.30 0.2383 67.8739 67.8739 260.429
14.40 0.2400 67.8739 67.8739 260.432
14.50 0.2417 67.8739 67.8739 260.435
14.60 0.2433 67.8739 67.8739 260.438
14.70 0.2450 67.8739 67.8739 260.441
14.80 0.2467 67.8739 67.8739 260.444
14.90 0.2483 67.8739 67.8739 260.447
15.00 0.2500 67.8739 67.8739 260.450
15.10 0.2517 67.8739 67.8739 260.453
15.20 0.2533 67.8739 67.8739 260.456
15.30 0.2550 67.8739 67.8739 260.459
15.40 0.2567 67.8739 67.8739 260.462
15.50 0.2583 67.8739 67.8739 260.465
15.60 0.2600 67.8739 67.8739 260.468
15.70 0.2617 67.8739 67.8739 260.471
15.80 0.2633 67.8739 67.8739 260.474
15.90 0.2650 67.8739 67.8739 260.477
16.00 0.2667 67.8739 67.8739 260.480
16.10 0.2683 67.8739 67.8739 260.483
16.20 0.2700 67.8739 67.8739 260.486
16.30 0.2717 67.8739 67.8739 260.489
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
96
16.40 0.2733 67.8739 67.8739 260.492
16.50 0.2750 67.8739 67.8739 260.495
16.60 0.2767 67.8739 67.8739 260.498
16.70 0.2783 67.8739 67.8739 260.501
16.80 0.2800 67.8739 67.8739 260.504
16.90 0.2817 67.8739 67.8739 260.507
17.00 0.2833 67.8739 67.8739 260.510
17.10 0.2850 67.8739 67.8739 260.513
17.20 0.2867 67.8739 67.8739 260.516
17.30 0.2883 67.8739 67.8739 260.519
17.40 0.2900 67.8739 67.8739 260.522
17.50 0.2917 67.8739 67.8739 260.525
17.60 0.2933 67.8739 67.8739 260.528
17.70 0.2950 67.8739 68.0981 260.531
17.80 0.2967 67.8739 68.0981 260.534
17.90 0.2983 67.8739 68.0981 260.537
18.00 0.3000 67.8739 68.0981 260.540
18.10 0.3017 67.8739 68.0981 260.543
18.20 0.3033 67.8739 68.0981 260.546
18.30 0.3050 67.8739 68.0981 260.549
18.40 0.3067 67.8739 68.0981 260.552
18.50 0.3083 67.8739 68.0981 260.555
18.60 0.3100 67.8739 68.2101 260.558
18.70 0.3117 67.8739 68.2101 260.561
18.80 0.3133 67.8739 68.2101 260.564
18.90 0.3150 67.8739 68.2101 260.567
19.00 0.3167 67.8739 68.2101 260.570
19.10 0.3183 67.8739 68.2101 260.573
19.20 0.3200 67.8739 68.2101 260.576
19.30 0.3217 67.8739 68.2101 260.579
19.40 0.3233 67.8739 68.2101 260.582
19.50 0.3250 67.8739 68.2101 260.585
19.60 0.3267 67.8739 68.2101 260.588
19.70 0.3283 67.8739 68.1541 260.591
19.80 0.3300 67.8739 68.1541 260.594
19.90 0.3317 67.8739 68.1541 260.597
20.00 0.3333 67.8739 68.1541 260.600
20.10 0.3350 67.8739 68.1541 260.603
20.20 0.3367 67.8739 68.1541 260.606
20.30 0.3383 67.8739 68.1541 260.609
*Data continues to Time = 22.8 minutes
**Pressure approximated due to malfunctioning pressure transducer.
FINAL DESIGN REPORT LAST UPDATED: 5/15/2014
97
14.6 Appendix F. Manufacturer Component Specifications
14.6.1 O-ring Groove Dimension Instructions