1
Environmental Benefits of Alternative Fuels and Advanced
Technology in Public Transit
Environmental Benefits of Alternative Fuels and Advanced
Technology in Public Transit
Jairo A. Sandoval and W. Scott Wayne, PhDCenter for Alternative Fuels, Engines & EmissionsDept. of Mechanical & Aerospace EngineeringWest Virginia University, Morgantown, WV
American Public Transportation Association2007 Bus Technical, Maintenanceand Procurement WorkshopNew Orleans, LAOctober 29, 2007
FTA REPORT No. 26-7003-07.2
2
This report evaluates potential environmental effects that could be affected through increased use of alternative fuels and advanced powertrain technologies in the U.S. transit bus industry.
Background
3
ObjectivesMethodologyEmissions From the Baseline U.S. Fleet Emissions Impacts of the “natural course” of Transit Bus ProcurementsImplications of Greater Use of Alternative Fuels and TechnologiesGreenhouse Gas EmissionsObservations and ConclusionsRecommendations for further study
Presentation Overview
4
Predict the emissions of the existing (2003) U.S. transit bus fleet as a baseline
Predict the emissions reductions from current bus procurements through 2009
Evaluate emissions reductions from implementation of alternative fuels and/or advanced technologies
Objectives
5
Technologies Considered
2007 and newer “clean-diesel” technology with ultra-low sulfur diesel fuel
Stoichiometric compressed natural gas (CNG)
Diesel-electric hybrid drive buses
Gasoline-electric hybrid drive buses
B20 biodiesel fuel (80% diesel, 20% biodiesel)
Objectives (cont.)
6
Carbon monoxide (CO),
Nitrogen oxides (NOx),
Non-methane hydrocarbons (NMHC),
Methane (CH4),
Total particulate matter (PM)
Carbon dioxide (CO2)
Fuel consumption
Emissions Evaluated
7
MethodologyAnalysis uses an atmospheric emissions inventory approach using existing chassis dynamometer test data.
Existing data uses a range of different test cycles which presents a difficulty in comparing test results
An approach was adopted to normalize data to the Orange County Bus Cycle.
Total MassEmissions
= ∑ *MilesTraveled
Test emissions[g/mile]
8
Methodology (cont.)
Not Considered in this AnalysisAnalysis does not include cutaways, and light-duty vans
Electrified Trolleybuses
Idle operation at bus garage and at waypoints
Deadheading between bus garage and start of route
Heating Ventilation and Air Conditioning Loads
Bus Lighting and Other Auxiliary (hotel) Loads
Life Cycle of Biodiesel fuel
9
Baseline (2003) Transit Bus Fleet
265
49,938
6,606
1,003 672 4890
10,000
20,000
30,000
40,000
50,000
60,000
Diesel Fuel/Jet A
Compressed Natural Gas
Liquefied Natural Gas
Trolleys (electric
catenary)
Diesel-Electric
Hybrid
Propane (liquefied petro
leum gas)
Fuel/Power System Technology
Nu
mb
er
of
Ac
tiv
e B
us
es
80
57
3928
5 3 3
0
20
40
60
80
100
Biodies
el
CNG-Dies
el Pilo
t Inje
...
CNG-Elec
tric H
ybrid
Gasoli
ne
CNG & G
asoli
ne
Propa
ne-E
lectri
c Hyb
rid
Hydro
gen
Diesel + CNG + LNG + Diesel-Electric Hybrid = 99.2%
Trolleybuses were excluded from the analysis
Distribution by fuel/powertrain type in 2003
10
4,31
7
5,34
5
10,6
85
20,0
66
6,00
1
4 8 217 1,48
3 4,91
4
983
0 0 0 0 32 457
3,52
4
0
5,000
10,000
15,000
20,000
25,000
Pre-1
988
1988
-199
0
1991
-199
3
1994
-199
7
1998
-200
2
2003
-200
5
Vehicle Model Year
Act
ive
Bu
ses
Diesel
CNG + LNG
Diesel-Electric Hybrid
Distribution by Model Year
Model year bins according to applicable EPA emissions regulation
11
Total annual VMT: 2,420.8 million miles
Number of Buses
COtons
NMHCtons
CH4
tons
NOx
tonsPMtons
CO2
tonsFuel Consumed (a)
thousands of gallons
Total Emissions
Diesel 49,938 15,886 2,611 65,669 1,494 6,497,649 589,135
CNG/LNG 7,609 1,194 308 5,879 6,318 7 796,630 100,393
Diesel Hybrid 489 5 0.6 220 0.5 35,865 3,361
Total 58,036 17,085 2,920 5,879 72,207 1,502 7,330,143 692,889
Average Emissions Levels per Bus
COg/mile
NMHCg/mile
CH4
g/mile
NOx
g/milePM
g/mileCO2
g/mileFuel Economy
mile/gal
Diesel 6.98 1.15 28.84 0.66 2,853 3.51
CNG/LNG 3.44 0.89 16.94 18.21 0.02 2,296 3.14
Diesel Hybrid 0.22 0.03 9.87 0.02 1,608 6.02
(a) Fuel consumed is expressed in Diesel-equivalent gallons
Emissions from Baseline Fleet (2003)
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In progress and planned procurements were determined from the 2005 APTA Transit Vehicle Database
The majority of new buses purchase will be used to replace aging buses
6.5% growth in the national bus fleet by year 2009
4% increase in vehicle miles traveled by 2009
2007-2009 emissions levels were estimated:
Diesel + Hybrids → 2004/2007 EPA certification limits ratio
CNG → European stoichiometric buses (VTT)
Impacts of “Natural” Procurements
13
0
4,5
39
10,6
85
20,0
66
10,7
31
3,9
82
4 8 217 1,4
83 4
,914
2,2
04
1,2
34
0 0 32 744
749
0
0
5,000
10,000
15,000
20,000
25,000
Vehicle Model Year
Acti
ve B
uses
Diesel
CNG + LNG
Diesel-Electric Hybrid4,
317
5,34
5
10,6
85
20,0
66
6,00
1
4 8 217 1,48
3 4,91
4
983
0 0 0 0 32 457
3,52
4
0
5,000
10,000
15,000
20,000
25,000
Pre-1
988
1988
-199
0
1991
-199
3
1994
-199
7
1998
-200
2
2003
-200
5
Vehicle Model Year
Act
ive
Bu
ses
Diesel
CNG + LNG
Diesel-Electric Hybrid
2009
2003
Distributions by vehicle model year:Replaced All Pre-1990 diesel buses
Power Source2004-2006
2007-2009
Total
Diesel 4,730 3,982 8,712
CNG 1,159 1,164 2,323
LNG 62 70 132
Diesel Hybrid 287 749 1,036
Gasoline-Electric Hybrid
85 46 131
Biodiesel 32 27 59
Hydrogen 25 4 29
Propane (LPG) 19 4 23
Gasoline 5 1 6
Total 6,404 6,047 12,451
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Number of Buses
COtons
NMHCtons
CH4
tons
NOx
tonsPMtons
CO2
tonsFuel Consumed
thousands of gallons
Total Annual Emissions
Diesel 50,003 9,577 1,667 53,981 843 6,289,918 573,989
CNG/LNG 10,064 1,331 364 6,902 7,229 9 1,003,149 125,818
Diesel Hybrid 1,525 12 2 489 1 107,814 9,805
Total 61,592 10,920 2,032 6,902 61,699 853 7,400,881 709,612
Relative Change 6% 36% 30% 17% 15% 43% 1% 2%
Average Emissions Levels per Bus
COg/mile
NMHCg/mile
CH4
g/mile
NOx
g/milePM
g/mileCO2
g/mileFuel Economy
mile/gal
Diesel 4.31 0.75 24.32 0.38 2,833 3.51
CNG/LNG 2.98 0.81 15.45 16.18 0.02 2,245 3.22
Diesel Hybrid 0.18 0.03 7.22 0.02 1,592 6.26
2003 - Average Emissions Levels per Bus
COg/mile
NMHCg/mile
CH4
g/mile
NOx
g/milePM
g/mileCO2
g/mileFuel Economy
mile/gal
Diesel 6.98 1.15 28.84 0.66 2,853 3.51
CNG/LNG 3.44 0.89 16.94 18.21 0.02 2,296 3.14
Diesel Hybrid 0.22 0.03 9.87 0.02 1,608 6.02
Estimated Emissions of 2009 Fleet
Reductions in CO and NMHC due largely to advent of diesel particulate filters. Lower CO emissions from stoichiometric CNG buses offset the increase in number of CNG buses
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Number of Buses
COtons
NMHCtons
CH4
tons
NOx
tonsPMtons
CO2
tonsFuel Consumed
thousands of gallons
Total Annual Emissions
Diesel 50,003 9,577 1,667 53,981 843 6,289,918 573,989
CNG/LNG 10,064 1,331 364 6,902 7,229 9 1,003,149 125,818
Diesel Hybrid 1,525 12 2 489 1 107,814 9,805
Total 61,592 10,920 2,032 6,902 61,699 853 7,400,881 709,612
Relative Change 6% 36% 30% 17% 15% 43% 1% 2%
Average Emissions Levels per Bus
COg/mile
NMHCg/mile
CH4
g/mile
NOx
g/milePM
g/mileCO2
g/mileFuel Economy
mile/gal
Diesel 4.31 0.75 24.32 0.38 2,833 3.51
CNG/LNG 2.98 0.81 15.45 16.18 0.02 2,245 3.22
Diesel Hybrid 0.18 0.03 7.22 0.02 1,592 6.26
2003 - Average Emissions Levels per Bus
COg/mile
NMHCg/mile
CH4
g/mile
NOx
g/milePM
g/mileCO2
g/mileFuel Economy
mile/gal
Diesel 6.98 1.15 28.84 0.66 2,853 3.51
CNG/LNG 3.44 0.89 16.94 18.21 0.02 2,296 3.14
Diesel Hybrid 0.22 0.03 9.87 0.02 1,608 6.02
Estimated Emissions of 2009 Fleet
Particulate Filters “mandated” on all 2007 and newer diesel buses + increase in inherently low PM emitting CNG buses
NOx reductions largely attributable to reduction in NOx limit from 2.5 g/bhpr to
1.2 g/bhphr in 2007
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Number of Buses
COtons
NMHCtons
CH4
tons
NOx
tonsPMtons
CO2
tonsFuel Consumed
thousands of gallons
Total Annual Emissions
Diesel 50,003 9,577 1,667 53,981 843 6,289,918 573,989
CNG/LNG 10,064 1,331 364 6,902 7,229 9 1,003,149 125,818
Diesel Hybrid 1,525 12 2 489 1 107,814 9,805
Total 61,592 10,920 2,032 6,902 61,699 853 7,400,881 709,612
Relative Change 6% 36% 30% 17% 15% 43% 1% 2%
Average Emissions Levels per Bus
COg/mile
NMHCg/mile
CH4
g/mile
NOx
g/milePM
g/mileCO2
g/mileFuel Economy
mile/gal
Diesel 4.31 0.75 24.32 0.38 2,833 3.51
CNG/LNG 2.98 0.81 15.45 16.18 0.02 2,245 3.22
Diesel Hybrid 0.18 0.03 7.22 0.02 1,592 6.26
2003 - Average Emissions Levels per Bus
COg/mile
NMHCg/mile
CH4
g/mile
NOx
g/milePM
g/mileCO2
g/mileFuel Economy
mile/gal
Diesel 6.98 1.15 28.84 0.66 2,853 3.51
CNG/LNG 3.44 0.89 16.94 18.21 0.02 2,296 3.14
Diesel Hybrid 0.22 0.03 9.87 0.02 1,608 6.02
Estimated Emissions of 2009 Fleet
Very modest increase in CO2 and fuel consumption despite increase in number of buses and miles traveled … largely offset by increase in hybrid buses
Methane emissions increase due to higher number of CNG buses
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Number of Buses
COtons
NMHCtons
CH4
tons
NOx
tonsPMtons
CO2
tonsFuel Consumed
thousands of gallons
Total Annual Emissions
Diesel 50,003 9,577 1,667 53,981 843 6,289,918 573,989
CNG/LNG 10,064 1,331 364 6,902 7,229 9 1,003,149 125,818
Diesel Hybrid 1,525 12 2 489 1 107,814 9,805
Total 61,592 10,920 2,032 6,902 61,699 853 7,400,881 709,612
Relative Change 6% 36% 30% 17% 15% 43% 1% 2%
Average Emissions Levels per Bus
COg/mile
NMHCg/mile
CH4
g/mile
NOx
g/milePM
g/mileCO2
g/mileFuel Economy
mile/gal
Diesel 4.31 0.75 24.32 0.38 2,833 3.51
CNG/LNG 2.98 0.81 15.45 16.18 0.02 2,245 3.22
Diesel Hybrid 0.18 0.03 7.22 0.02 1,592 6.26
2003 - Average Emissions Levels per Bus
COg/mile
NMHCg/mile
CH4
g/mile
NOx
g/milePM
g/mileCO2
g/mileFuel Economy
mile/gal
Diesel 6.98 1.15 28.84 0.66 2,853 3.51
CNG/LNG 3.44 0.89 16.94 18.21 0.02 2,296 3.14
Diesel Hybrid 0.22 0.03 9.87 0.02 1,608 6.02
Estimated Emissions of 2009 Fleet
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Greater Use of Alternative Fuels & Technology
Consider the national emissions impact of replacement of 15% of the existing fleet with each of the following new technologies:
Clean-diesel,
CNG,
Diesel-electric hybrid,
Gasoline-electric hybrid and
Biodiesel powered buses
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COtons
NMHCtons
CH4
tons
NOx
tonsPMtons
CO2
tonsFuel Consumed (a)
thousands of gallons
Clean Diesel 1,723 377 - 3,291 201 35,251 2,664
CNG 689 341 422 4,239 205 220,758 2,154
Diesel Hybrid 1,776 366 - 4,418 202 491,352 50,658
Gasoline Hybrid 6,178 211 - 5,963 199 74,114 2,833
Biodiesel (B20) (a) 384 166 - 369 38 25,087 3,876
Percent Incremental Change
Clean Diesel 16% 19% - 5% 24% 0% 0%
CNG 6% 17% 6% 7% 24% 3% 0%
Diesel Hybrid 16% 18% - 7% 24% 7% 7%
Gasoline Hybrid 57% 10% - 10% 23% 1% 0%
Biodiesel (B20) (b) 4% 8% - 1% 4% 0% 1%
(a) Fuel consumed is expressed in Diesel-equivalent gallons(b) Implemented in the older diesel buses of the fleet
Greater Use of Alternative Fuels & TechnologyReductions are in addition to those shown in the previous table
Conventional & hybrid diesel buses have similar reductions in CO, NMHC and PM emissions because they benefit from the same engine advancements. Diesel hybrid buses gain an advantage in NOx emissions over conventional diesels.
Conventional & hybrid diesel buses have similar reductions in CO, NMHC and PM emissions because they benefit from the same engine advancements. Diesel hybrid buses gain an advantage in NOx emissions over conventional diesels.
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COtons
NMHCtons
CH4
tons
NOx
tonsPMtons
CO2
tonsFuel Consumed (a)
thousands of gallons
Clean Diesel 1,723 377 - 3,291 201 35,251 2,664
CNG 689 341 422 4,239 205 220,758 2,154
Diesel Hybrid 1,776 366 - 4,418 202 491,352 50,658
Gasoline Hybrid 6,178 211 - 5,963 199 74,114 2,833
Biodiesel (B20) (a) 384 166 - 369 38 25,087 3,876
Percent Incremental Change
Clean Diesel 16% 19% - 5% 24% 0% 0%
CNG 6% 17% 6% 7% 24% 3% 0%
Diesel Hybrid 16% 18% - 7% 24% 7% 7%
Gasoline Hybrid 57% 10% - 10% 23% 1% 0%
Biodiesel (B20) (b) 4% 8% - 1% 4% 0% 1%
(a) Fuel consumed is expressed in Diesel-equivalent gallons(b) Implemented in the older diesel buses of the fleet
Greater Use of Alternative Fuels & TechnologyReductions are in addition to those shown in the previous table
Conventional diesel, stoichiometric CNG, diesel hybrid and gasoline hybrid offer near identical reductions in particulate emissions.
Conventional diesel, stoichiometric CNG, diesel hybrid and gasoline hybrid offer near identical reductions in particulate emissions.
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COtons
NMHCtons
CH4
tons
NOx
tonsPMtons
CO2
tonsFuel Consumed (a)
thousands of gallons
Clean Diesel 1,723 377 - 3,291 201 35,251 2,664
CNG 689 341 422 4,239 205 220,758 2,154
Diesel Hybrid 1,776 366 - 4,418 202 491,352 50,658
Gasoline Hybrid 6,178 211 - 5,963 199 74,114 2,833
Biodiesel (B20) (a) 384 166 - 369 38 25,087 3,876
Percent Incremental Change
Clean Diesel 16% 19% - 5% 24% 0% 0%
CNG 6% 17% 6% 7% 24% 3% 0%
Diesel Hybrid 16% 18% - 7% 24% 7% 7%
Gasoline Hybrid 57% 10% - 10% 23% 1% 0%
Biodiesel (B20) (b) 4% 8% - 1% 4% 0% 1%
(a) Fuel consumed is expressed in Diesel-equivalent gallons(b) Implemented in the older diesel buses of the fleet
Greater Use of Alternative Fuels & TechnologyReductions are in addition to those shown in the previous table
Gasoline hybrids offer the largest overall NOx reductionsGasoline hybrids offer the largest overall NOx reductions
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COtons
NMHCtons
CH4
tons
NOx
tonsPMtons
CO2
tonsFuel Consumed (a)
thousands of gallons
Clean Diesel 1,723 377 - 3,291 201 35,251 2,664
CNG 689 341 422 4,239 205 220,758 2,154
Diesel Hybrid 1,776 366 - 4,418 202 491,352 50,658
Gasoline Hybrid 6,178 211 - 5,963 199 74,114 2,833
Biodiesel (B20) (a) 384 166 - 369 38 25,087 3,876
Percent Incremental Change
Clean Diesel 16% 19% - 5% 24% 0% 0%
CNG 6% 17% 6% 7% 24% 3% 0%
Diesel Hybrid 16% 18% - 7% 24% 7% 7%
Gasoline Hybrid 57% 10% - 10% 23% 1% 0%
Biodiesel (B20) (b) 4% 8% - 1% 4% 0% 1%
(a) Fuel consumed is expressed in Diesel-equivalent gallons(b) Implemented in the older diesel buses of the fleet
Greater Use of Alternative Fuels & TechnologyReductions are in addition to those shown in the previous table
B20 used in older model buses without DPFs results in slight increase in NOx emissions and modest decrease in PM emissions. B20 also results in a modest increase in gallons of fuel consumed due to lower energy content; however biodiesel displaces use of imported petroleum.
B20 used in older model buses without DPFs results in slight increase in NOx emissions and modest decrease in PM emissions. B20 also results in a modest increase in gallons of fuel consumed due to lower energy content; however biodiesel displaces use of imported petroleum.
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COtons
NMHCtons
CH4
tons
NOx
tonsPMtons
CO2
tonsFuel Consumed (a)
thousands of gallons
Clean Diesel 1,723 377 - 3,291 201 35,251 2,664
CNG 689 341 422 4,239 205 220,758 2,154
Diesel Hybrid 1,776 366 - 4,418 202 491,352 50,658
Gasoline Hybrid 6,178 211 - 5,963 199 74,114 2,833
Biodiesel (B20) (a) 384 166 - 369 38 25,087 3,876
Percent Incremental Change
Clean Diesel 16% 19% - 5% 24% 0% 0%
CNG 6% 17% 6% 7% 24% 3% 0%
Diesel Hybrid 16% 18% - 7% 24% 7% 7%
Gasoline Hybrid 57% 10% - 10% 23% 1% 0%
Biodiesel (B20) (b) 4% 8% - 1% 4% 0% 1%
(a) Fuel consumed is expressed in Diesel-equivalent gallons(b) Implemented in the older diesel buses of the fleet
Greater Use of Alternative Fuels & TechnologyReductions are in addition to those shown in the previous table
Diesel-hybrid buses appear to offer the greatest overall environmental advantage.Diesel-hybrid buses appear to offer the greatest overall environmental advantage.
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6.876.78
6.40
6.656.886.856.76
0
1
2
3
4
5
6
7
8
2003 Bus Fleet
2009 Bus Fleet
Clean DieselCNG
Diesel Hybrid
Gasoline Hybrid
Biodiesel
Te
rag
ram
s (
Tg
) C
O2 E
qu
iva
len
t G
WP
CH4
CO2
(a) B20 Implemented in the older diesel buses of the fleet Tailpipe only
Global Warming Potential
If B100 in all the fleet:Life cycle Life cycle emissionsemissions↓ ~ 40%
25
Observations & ConclusionsReplacement of older model diesel buses with lower emitting buses equipped with advanced NOx control technologies and catalyzed diesel particulate filters brings about substantial emissions reductions
NOx reductions from CNG are slightly better than predicted for clean-diesel buses
Compared to clean-diesel buses, CNG buses offer superior reductions in CO2 emissions, less advantage in terms of CO emissions and produce methane emissions
Diesel hybrid buses yield the largest reductions in CO2 emissions and are the only technology to show a reduction in fuel consumption
Gasoline-electric hybrid buses offer the highest NOx emissions reductions due to the vanishingly low NOx levels of gasoline engines with 3-way catalysts
26
Comments of Biodiesel ImplementationThe results indicate that the maximum benefit of B20 biodiesel usage would be achieved by converting the oldest buses in the fleet to biodiesel rather than newer buses
There is a broad consensus that biodiesel and biodiesel blends produce significant reductions in PM emissions and increase in NOx emissions for engines up to about 1997 model year
For newer engines there are very little data available but ongoing research exists
Data indicate that biodiesel increases the reactivity of PM in a diesel particulate filter thereby improving regeneration of DOCs and diesel particulate filters (DPFs)
Production and use of soybean based biodiesel (B100) releases 59% of the net greenhouse gas emissions of an energetically equivalent amount of petroleum diesel
27
Update the analysis with latest APTA data
Repeat and extend the analysis to include actual 2007 compliant bus emissions data + Estimated 2010 compliant buses
Further emissions testing needs to be conducted to better quantify and understand the impact of biodiesel fuels on emissions of both legacy and new technology diesel engines and vehicles
The emissions and fuel economy of hybrid transit buses is highly affected by driving conditions (i.e. route duty cycles) and power train configuration. Further study is needed to better understand and quantify these effects in order to enable that hybrid buses are utilized in applications which maximize their benefits
Recommendations
28
Include transit operation information (e.g. duty-cycles)
Account for idle and auxiliary loads
Consider Variability and Uncertainty (Monte Carlo Simulations)
Future work – Bus inventory modeling
29
U.S. Department of Transportation, Federal Transit Administration, “Environmental Benefits of Alternative Fuels and Advanced Technology in Transit.” FTA-WV-26-7003-07.2, Washington, DC, 2007.
Wayne, W.S., Sandoval, J.A., and N.N. Clark, “Emissions benefits from alternative fuels and advanced technology in U.S. transit bus fleet.” Energy & Environment, 2009, 20(4), 497-515.
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