Fuel air mixing analysis in a multiport fuel injection

(MPFI) spark ignition (S.I.) engine

INTERN REPORT ON COMPUTATIONAL FLUID

DYNAMICS

Submitted in partial fulfillment of requirements for

the degree of

BACHELOR OF TECHNOLOGY in

MECHANICAL ENGINEERING.

SUBMITTED BY

Md Shahid(11M177)

Subham k Burnwal(11M257)

DEPARTMENT OF MECHANICAL ENGINEERING

National Institute of Technology Karnataka,

Surathkal, Mangalore- 575025.

September 2013

ACKNOWLEDGEMENT

Before everything I heartily acknowledge Professor G. N. Kumar

for believing in us, and giving this project which proved to be

really challenging and equally enlightening, besides it required

our intense involvement. It compelled us for real brainstorming

and continuous effort.

Secondly I thank our friend Mr. Ravi Teja for making us do it all,

and really helping us in time of need. For being an awesome

instructor, to help us to clear any kind of problem we used to

face during the work progress without the slightest of difficulty

and hesitation.

Last but not the least I thank god the supreme power the

omnipotent and omniscient who has been there watching us do

our job, for being the supreme guide; the incessant source of

everything.

Md Shahid

Subham k Burnwal

ABSTRACT

Flow of the fuel and air into the cylinder of an engine requires pre mixing of the fuel-air mixture into the inlet manifold of the engine. The performance of an engine depends largely on the proportion and efficiency by which the mixing takes place.

Conventionally carburetors were used to meter the flow, but they were not very accurate. Hence, a more effective way for fuel injection called the multiport fuel injection was introduced. MPI system is accurate and leads to effective mixing of the fuel and air. The present study is aimed at Modeling and simulation of inlet manifold of an MPI engine. With the use of Computational Fluid Dynamics (CFD) the total work of the multi-dimensional modeling and analysis of flow simulation of the mixture in an inlet manifold, that otherwise takes some weeks to months of work may be made possible in some days. The tools used in making this attempt possible were – solidworks 2012 for the geometry and fluid flow analysis using FLUENT solver in workbench in ANSYS 14.0.

KEYWORDS

Inlet manifold, Fuel Injector, Carburetor, ANSYS, CFD, I.C.

Engines.

TABLE OF CONTENTS

pages

Acknowledgement I

Abstract ii

Keywords ii

Table of contents iii

1. Introduction iv

1.a - carburetor

Disadvantages of carburetors

vii

1.b - fuel injector vii

Benefits of fuel injectors ix

1.c - CFD (general)

1.d- Ansys

2. Objectives

3. Methodology

4. Results and dissensions

5. Conclusion

6. References

1.INTRODUCTION

Ecological and economical issues have always challenged us to try and

innovate, to bring newer and efficient technologies. Traditional internal

combustion engines used carburetor to fire fuel into their cylinder.

1. (A) - Carburetor

A carburetor is a device that blends air and fuel in an internal combustion

engine. It works on the Bernoulli’s principle; the faster air moves, the lower

its static pressure and the higher it’s dynamic pressure. Carburetor is

essentially just a tube through which filtered air flows from the automobile’s

air intake. Within this tube, there is a narrowing, or a venturi, where a

vacuum is created. There is a small hole in the narrowing called a jet which

is fed fuel via the float chamber. The float chamber is a container filled with

an amount of fuel that is set by a float. The vacuum created in the venturi

draws in fuel from the float chamber, which is at ambient pressure. The

faster the filtered air comes in through the carburetor throat, the lower the

pressure in the venturi. This leads to a higher pressure difference between

the venturi and the float chamber, and thus more fuel flows out of the jet

and mixes with the airstream.

Older engines used updraft carburetors, where the air enters from below

the carburetor and exits through the top. This had the advantage of

never “flooding" the engine, as any liquid fuel droplets would fall out of the

carburetor instead of into the intake manifold. It also lent itself to use of

an oil bath air cleaner, where a pool of oil below a mesh element below the

carburetor is sucked up into the mesh and the air is drawn through the oil-

covered mesh; this was an effective system in a time when paper air

filters did not exist.

In the late 1930s, downdraft carburetors were the most popular types used.

Then the sidedraft carburetors replaced downdraft as free space in the

engine bay decreased.

Downstream of the jet, there is a throttle valve that opens when the

accelerator pedal is engaged. This throttle valve restricts how much air

enters the carburetor. If you push the gas pedal all the way down, the

throttle valve opens fully, allowing air to flow more quickly through the

carburetor, creating a bigger vacuum in the venturi, sending more fuel into

the engine, creating more power. At idle, the throttle valve is fully shut, but

there is an idling jet that bypasses the throttle valve and sends a set

amount of fuel and air into the engine. Without an idling jet, the engine

would shut off if the throttle were not activated by the driver during idle.

Disadvantages

The main disadvantages of a carburetor's operation are as:

• With carburetors’ complexity, the car owner is subject for more

expenses because it needs to be cleaned and opened up regularly to

obtain outstanding fuel economy;

• It cannot meter the correct AFR (air fuel ratio) needed to obtain

maximum power;

• More fuels are consumed since carburetors are heavier;

• More air emissions;

• Not-so-good use of fuel since normally each car has one carburetor

for all of its cylinders;

• Maintenance cost of carburetor is higher.

1. (B)- Fuel Injector

Fuel injection systems are becoming more popular nowadays. There are

two different kinds of fuel injection techniques; Modern internal combustion

engines use:

Single point injection

Continuous injection

Central port injection

Multi port fuel injection (MPFI)

Gasoline direct injection (GDI)

swirl injection.

Multi port fuel injection system is the most popular of all it atomizes the fuel

by forcibly pumping it through a small nozzle under high pressure. The

electronics used in the system will calculate this information and constantly

adjust accordingly.

Present I.C. Engines equipped with multi port fuel injector sprays fuel

directly through the intake valve or valves into the combustion chamber.

Here each injector is activated separately by wire. One can measure how

much gas an engine needs by how much air it is sucking in. Once the

engine starts, the measuring of air begins.

Early fuel injection systems used a vane system, which was basically a flap

inside a tube, to measure how much air was being sucked. There are lots

and lots of variations to fuel injection systems. Such as electronic fuel

injection, mechanical fuel injection, systems with one oxygen sensor

systems with four oxygen sensors , etc. with injector right into the intake

port just above each cylinder's intake valve, instead of at a central point.

Benefits of fuel injectors

The main benefits to using direct injection is that the amount of fuel and air

can be perfectly released and then injected into the cylinder according to

the engine load conditions. This type of controlled fuel injection results in a

higher power output, Greater fuel efficiency and much lower emissions. Not

only can fuel injection make more power, it can be manipulated to run

smoother, run better cold and hot, easier starts, and better fuel mileage.

1. (C)- CFD (general)

Computational fluid dynamics, usually abbreviated as CFD, is a branch

of fluid mechanics that uses numerical methods and algorithms to solve

and analyze problems that involve fluid flows. It provides qualitative

sometimes quantitative prediction of fluid flow by means of

Mathematical modeling (Partial differential equations)

Numerical methods (discretization and solution techniques)

Software toos (Solver, pre- and postprocessing utilities)

Computers are used to perform the calculations required to simulate the

interaction of liquids and gases with surfaces defined by boundary

conditions. With high-speed supercomputers, better solutions can be

achieved. Ongoing research yields software that improves the accuracy

and speed of complex simulation scenarios such as transonic or

turbulent flows.

The fundamental basis of almost all CFD problems are the Navier–Stokes

equations, which define any single-phase (gas or liquid, but not both) fluid

flow. These equations can be simplified by removing terms describing

viscous actions to yield the Euler equations. Further simplification, by

removing terms describing vorticity yields the full potential equations.

Finally, for small perturbations in subsonic and supersonic flows

(not transonic or hypersonic) these equations can be linearized to yield the

linearized potential equations.

Uses of CFD

• architects to design comfortable and safe living environments

• Designers of vehicles to improve the aerodynamic characteristics

• Chemical engineers to maximize the yield from their equipment

• Petroleum engineers to devise optimal oil recovery strategies

• Surgeons to cure arterial diseases (computational hemodynamics)

• Meteorologists to forecast the weather and warn of natural disasters

• Safety experts to reduce health risks from radiation and other

hazards

• Military organizations to develop weapons and estimate the damage

• CFD practitioners to make big bucks by selling colorful pictures

Experiments vs. Simulations

CFD gives an insight into flow patterns that are difficult, expensive or

impossible to study using traditional (experimental) techniques.

Fluid characteristics

Macroscopic properties:

Density(rho), viscosity(mu), pressure(p), temperature(T),

velocity(v).

Classification of fluid flow:

Viscous, inviscid, compressible, incompressible, steady,

unsteady, laminar, turbulent, single-phase, multi-phase.

The reliability of CFD simulations is greater

For laminar/slow flows than for turbulent or fast ones

For single-phase flows than for multi phase flows

For chemically inert system than for reactive flows.

CFD analysis process

1. Problem statement- information about the flow

2. Mathematical model- IBVP = PDE + IC + BC

3. Mesh generation- nodes/cells, time instants

4. Space discretization- coupled ODE/DAE systems

5. Time discretization- algebraic system Ax = b

6. Iterative solver- discrete function values

7. CFD software- implementation, debugging

8. Simulation run- parameters, stopping criteria

9. Post processing- visualization, analysis of data

10. Verification- model validation / adjustment

1. (D)- Ansys

ANSYS is a general purpose software, used to simulate interactions of all

disciplines of physics, structural, vibration, fluid dynamics, heat transfer and

electromagnetic for engineers.

So ANSYS, which enables to simulate tests or working conditions, enables

to test in virtual environment before manufacturing prototypes of products.

Furthermore, determining and improving weak points, computing life and

foreseeing probable problems are possible by 3D simulations in virtual

environment.

ANSYS software with its modular structure as seen in the table below gives

an opportunity for taking only needed features. ANSYS can work integrated

with other used engineering software on desktop by adding CAD and FEA

connection modules.

ANSYS can import CAD data and also enables to build a geometry with

its "preprocessing" abilities. Similarly in the same preprocessor, finite

element model (a.k.a. mesh) which is required for computation is

generated. After defining loadings and carrying out analyses, results can

be viewed as numerical and graphical.

ANSYS can carry out advanced engineering analyses quickly, safely

and practically by its variety of contact algorithms, time based loading

features and nonlinear material models.

ANSYS Workbench is a platform which integrates simulation

technologies and parametric CAD systems with unique automation and

performance. The power of ANSYS Workbench comes from ANSYS

solver algorithms with years of experience. Furthermore, the object of

ANSYS Workbench is verification and improving of the product in virtual

environment.

ANSYS Workbench, which is written for high level compatibility with

especially PC, is more than an interface and anybody who has an

ANSYS license can work with ANSYS Workbench. As same as ANSYS

interface, capacities of ANSYS Workbench are limited due to possessed

license.

2.OBJECTIVES

This project is an attempt to study the behavior of the mixing of fuel into the

inlet manifold taking into consideration the design of the manifold. Using

numerous experimental and Reynolds-averaged Navier–Stokes (RANS)

based numerical investigations concentrated on gaining insight into the

mean behavior of the spray in IC-engines.

3.METHODOLOGY

At present most inlet manifolds are designed by trial and error, method or

study through prototypes that takes much time and effort to reach an

optimal design and that there is a lack of a systematic process. To help

design an inlet manifold of a higher efficiency, which would require a

reduction in cost in the experimental setup and study, is the need of the

hour. Through the advancement of the computer system performance it is

made possible to run softwares that can analyze to give results of even the

most complicated real life situations which are impossible to fabricate.

In this study, to develop a new framework for the design of inlet manifolds,

characteristics of flow patterns inside it are investigated by using

computational fluid dynamics (CFD). In addition to analysis of flow patterns,

a CFD-based optimal design procedure is proposed.

The design methodology can be depicted in the form of this flowchart

RESULT AND DISSENSIONS

1. Import the solid model into ansys 14.0 fluent

workbench

The model of the inlet manifold is made with the help of solidworks. The

model is then saved in the igs format. This model then can be imported

in ansys workbench environment. The model is then imported in the

ansys workbench and then it is genereated to provide us the model in

design modeler. Then the model can be used to be meshed by the

Ansys mesher.

Design modeler (Ansys workbench)

2. Generate mesh

once the design modeler has generated the solid body it is then

meshed using the mesher in Ansys workbench. The mesher provides

us with various parameters to mesh the model. After setting the

various parameters like sizing of mesh, type of analysis to be made,

solver to be used for calculation, etc we go fo meshing the material.

The 3d model is taken as fluid

Model after getting meshed

3. Set up the boundary conditions

After the model is been meshed into the Ansys mesher, the various

conditions are implied to the model into the fluent environment. The

various conditions include; materials, phases, cell zone conditions,

boundary conditions, etc.

Fluent environment window

4. Solve using Fluent solver

Once all the conditions have been implied onto the model then it is

ready to be solved to give results. The fluent solver generates the

solution after the number of iterations is mentioned, solution method

is specified and initialization of the various variables is made.

Graph showing calculation done by fluent

5. Obtain result using fluid flow CFD Post

After the solution is been done by the fluid flow fluent solver next we

proceed to obtaining the various forms of results that can be obtained

in the CFD post. The variation of various parameters like pressure,

phase velocity, stream lines of inlet air, animation of fluid molecoles

flow, etc.

Variation of pressure

Contour of velocity

ccc m

Total pressure contour

3D streamline of inlet air

Particle animation of fluid mixture

Velocity vector plot of the fluid

CONCLUSION

The investigation and analysis of the in-cylinder flow motion characteristics, during the intake stroke, is numerically carried out by using a CFD code This project aims at providing a virtual prototype for the analysis of a real world component (i.e. the inlet manifold) of a four stroke I.C. Engine, the analysis of which on the other hand is a real challenge otherwise. This method is not only a very efficient way to a really difficult problem but is also very effective, economical, efficient and precise approach to such a problem.

REFERENCES CFD-based optimal design of manifold in plate-fin

microdevices - Department of Chemical Engineering, Kyoto University, Katsura Campus, Nishikyo-ku, Kyoto 615-8510, Japan Received 31 July 2003; accepted - 28 October 2003.

Influence of intake manifold design on in-cylinder flow and engine performances in a bus diesel engine converted to LPG gas fuelled, using CFD analyses and experimental investigations- 2011.- (Aug. 03, 2013)

Rapid CFD Simulation of Internal Combustion Engines – 1999- Citeseer. - (Aug. 23, 2013)

Computational Fluid Dynamics- The Basics with Applications – John D Anderson, Jr – (Aug. 28, 2013)

The Wikipedia- carburetor

http://en.wikipedia.org/wiki/Carburetor - (Aug. 21, 2013)

The Wikipedia – Fuel injector

http://en.wikipedia.org/wiki/Fuel_injection – (Sept. 11, 2013)

The Wikipedia- Computational fluid dynamics

http://en.wikipedia.org/wiki/Computational_fluid_dynamics - (Sept. 20, 2013)