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STUDY OF EFFECTS OF FUEL INJECTION PRESSURE
ON PERFORMANCE FOR DIESEL ENGINE
AHMAD MUIZZ BIN ISHAK
Thesis submitted in fulfilment of the requirements for the award of the
Bachelor of Mechanical Engineering with Automotive Engineering
Faculty of Mechanical Engineering
UNIVERSITY MALAYSIA PAHANG
JUN 2012
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ABSTRACT
Diesel engines are used mainly in heavy duty machines and vehicles. Diesel engines
have many advantages such as high fuel efficiency, reliability and durability. The
performance of diesel engines depends on many parameters. One of the important
parameters which influence the performance of diesel engines is fuel injection pressure.
Fuel injection pressure plays an important aspect of power performance of the engine to
obtain combustion treatment. The objective of this project is to study the effects of fuel
injection pressure on the performance for diesel engine. Mathematical formulation for
fuel injection system developed to obtain the result to analyse the performance of diesel
engine based on fuel injection pressure. The results by using simulation are shown in
Chapter 4 from Figure 4.1 to Figure 4.6 and it can be concluded that the simulation
results can be used to predict and study the effect of fuel injection pressure on
performance for diesel engine.
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ABSTRAK
Enjin diesel digunakan secara meluas pada jentera dan kenderaan berat. Enjin diesel
mempunyai banyak kelebihan seperti kecekapan bahan api yang tinggi, ketahanan dan
kemampuan. Prestasi enjin diesel bergantung kepada beberapa aspek. Salah satu aspek
penting yang mempengaruhi prestasi enjin diesel ialah tekanan suntikan bahan api.
Tekanan suntikan bahan api memainkan peranan penting kepada prestasi kuasa enjin
untuk mencapai pembakaran terawat. Objektif projek ini ialah untuk mempelajari
kesan-kesan tekanan bahan api pada prestasi enjin diesel. Formulasi matematik untuk
system penyuntik bahan api telah dibangunkan untuk mendapatkan hasil untuk
menganalisis prestasi enjin diesel berdasarkan tekanan suntikan bahan api. Keputusan
simulasi ditunjukkan di Bab 4 dari Rajah 4.1 hingga Rajah 4.6 dan dengan ini dapat
disimpulkan bahawa keputusan simulasi dapat digunakan untuk menganggar dan
mengkaji kesan tekanan suntikan bahan api untuk prestasi enjin diesel.
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TABLE OF CONTENTS
CONTENTS PAGE
SUPERVISOR’S DECLARATION ii
STUDENT’S DECLARATION iii
ACKNOWLEDGMENT iv
ABSTRACT v
ABSTRAK vi
TABLE OF CONTENTS vii
LIST OF FIGURES ix
LIST OF SYMBOLS x
LIST OF GREEK SYMBOLS xi
LIST OF SUBSCRIPTS xii
LIST OF ABBREVIATIONS xii
CHAPTER 1 INTRODUCTION
1.1 Project Background 1
1.1.1 Fuel Injection System 2
1.2 Problem Statement 3
1.3 Project Objectives 3
1.4 Project Scopes 3
1.4.1 Flowchart Description 5
1.5 Thesis Organization 6
CHAPTER 2 LITERATURE REVIEW
2.1 Introduction 7
2.2 Diesel Engine and Fuel Injection System 7
2.3 Operation Cycle of Electronic Fuel Injection System 13
2.4 Advantages of Fuel Injection System 14
2.5 Types of Fuel Injections System 15
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CHAPTER 3 METHODOLOGY
3.1 Introduction 16
3.2 Overview of Methodology 16
3.3 Simulation Model 16
3.3.1 Simulation Model Flowchart 17
3.4 Mathematical Formulation 18
3.5 Hypotheses 20
3.6 Fluid 20
3.7 Container of Known Pressure 22
3.7.1 Pipe 22
3.8 Container of Unknown Pressure 28
3.8.1 Flow Passage 30
3.8.2 Valve 31
3.8.3 Laminar Flow 32
CHAPTER 4 RESULT AND DISCUSSION
4.1 Introduction 34
4.2 Results and Discussion 35
4.2.1 Pump Side Pressure 35
4.2.2 Nozzle Side Pressure 36
4.2.3 Effect of Pump Speed on Pressure of the Pump Side 37
4.2.4 Effect of Pump Speed on Pressure of the Nozzle Side 38
4.2.5 Effect of Pump Speed on the Injection Rate 39
4.2.6 Effect of Nozzle Opening Pressure on the Injection Rate 40
CHAPTER 5 CONCLUSION AND RECOMMENDATION
5.1 Conclusion 41
5.2 Recommendations 42
REFERENCES 43
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LIST OF FIGURES
FIG. NO. TITLE PAGE
1.1 Fuel injection system 2
1.2 Flowchartب forب finalب yearبproject 4 2.1 Diesel fuel injection system 10
3.1 Simulation model flowchart 17
3.2 Elementary units of the mathematical model 18
3.3 Simplified model for the injection system 19
3.4 Characteristic grid 24 3.5 Concentrated vapour cavitation in a pipe node i 27
3.6 Laminar flow in the gap between the non-moving
piston and the sleeve 32
4.1 Pump side pressure 35
4.2 Nozzle side pressure 36
4.3 Effect of pump speed on pressure of the pump side 37
4.4 Effect of pump speed on pressure of the nozzle side 38
4.5 Effect of pump speed on the injection rate 39
4.6 Effect of nozzle opening pressure on the injection rate 40
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LIST OF SYMBOLS
SYMBOL DESCRIPTION
A pipe inside cross section area, cross-section area of a moving part,
controlling area
geometric cross-section area of a flow passage
… polynomial coefficients of speed of pressure pulse
… polynomial coefficients of diesel oil density
speed of pressure pulse in diesel oil, speed of pressure pulse in fluid,
d pipe inside diameter, piston diameter
f friction factor, viscous damping coefficient
spring initial force
acceleration due to gravity
K bulk modulus of elasticity of fluid, modulus of elasticity
k spring rate
l gap length
molar mass of vapour
m moving mass of valve
number of volumetric flows entering the container
number of moving parts
number of volumetric flow exiting the container
number of controlling pressures
P, pressure
total derivative of pressure in relation to time
initial pressure
pressure before the flow passage
pressure after the flow passage
density, fluid density, density of homogenous fluid
vapour density, density of fluid vapour
density of diesel oil at initial pressure
volume flow rate
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volume flow rate into a node, volumetric flow entering the container
volume flow rate out of a node, volumetric flow exiting the container
R molar gas constant
Re Reynolds number
T temperature
t time
v fluid velocity, velocity of the moving part, valve velocity
V volume
cavitation volume
velocity at the inlet point of the flow passage
x distance along pipe axis, lift of a moving part, valve lift
LIST OF GREEK SYMBOLS
SYMBOL DESCRIPTION
pipe angle to horizontal plane
clearance between piston and sleeve
⁄ relative roughness of the inside surface of the pipe
pressure difference between the sleeve ends
time step
flow coefficient
fictive flow coefficient
dynamic viscosity of the fluid
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LIST OF SUBSCRIPTS
SUBSCRIPT DESCRIPTION
c0…c2 polynomial coefficients of speed of pressure pulse
cav cavitation volume
g geometric cross-section area of a flow passage
in volumetric flows entering the container
m moving parts
out volumetric flow exiting the container
… polynomial coefficients of diesel oil density
v controlling pressures, vapour, fluid vapour, volume
vin volume flow rate into a node, volumetric flow entering the
container
vout volume flow rate out of a node, volumetric flow exiting the
container
LIST OF ABBREVIATIONS
ABBREVIATION DESCRIPTION
NO Nitrogen Monoxide
Nitrogen Oxides
HC Hydrocarbon
CO Carbon Monoxide
SO Sulphur Monoxide
HSDI High Speed Direct Injection
ECU Electronic Control Unit
EFI Electronic Fuel Injection
TBI Throttle Body Injection
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CHAPTER 1
INTRODUCTION
1.1 PROJECT BACKGROUND
Diesel engines are a compression ignition type of internal combustion engine. It
is well known technology in achieving major improvement in fuel economy and heavy
duty task presently. Diesel engines are commonly used in heavy duty application
vehicle such as constructional vehicles, trucks and lorries. But now it is widely
implemented in light vehicle such as cars and vans. Diesel engines can double the fuel
economy than spark ignition engines in light vehicles.
Diesel engines use fuel injection system. The fuel injection system is a system
used to supply fuel into internal combustion engine which replaced carburetor function
to supply the fuel into the engine. Fuel injector atomizes the fuel by forcibly pumping it
through a small injection nozzle under high pressure. It is because diesel engine ignites
the fuel by the high temperature created by the compression of air and fuel mixture.
Diesel engines have many advantages such as high fuel efficiency, reliability
and durability. The performance of diesel engines depends on many parameters. One of
the important parameters which influence the performance of diesel engines is fuel
injection pressure. Fuel injection pressure plays an important aspect of power
performance of the engine to obtain combustion treatment.
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1.1.1 Fuel Injection System
Fuel injection is a technology that is being used in most of cars and other
automotive transportation these days. The technology is used to eliminate the need for
carburetors. The technology helps the engine to supply fuel directly to the cylinder in
the intake manifold, eliminating the use if carburetor to much extent. Overall, the fuel
injection is required to supply fuel directly to the engine.
The system works by the fuel is directly supplied to the cylinder in the intake
chamber. Sensors located in such engines will regulate the flow of fuel injected and
maintains it to appropriate levels. As long as the sensors which are usually electronic
are working properly, the possibilities of breakdown and choke are immensely reduced.
Figure 1.1 : Fuel injection system
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1.2 PROBLEM STATEMENT
Engine performance depends on many factors. There are fuel injection pressure,
engine speed, air fuel ratio, air flow rate, boost pressure, turbocharger speed,
combustion efficiency, exhaust temperature and other factors. The fuel injection
pressure need to be experimented to know how the varied injection pressure will affect
the engine performance. In this study, the effects of fuel injection pressure on
performance of diesel engines are investigated.
1.3 PROJECT OBJECTIVES
This project objective is to study the effects of fuel injection pressure on
performance for diesel engine with simulation.
1.4 PROJECT SCOPES
In order to achieve the objective stated for this project successfully, this work is
guided by several scopes. A flowchart for this project was made to show the clear of the
progress of this project and make sure the project running under its scopes. The
flowchart of the project is as shown in Figure 1.1.
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Figure 1.2 : Flowchart for final year project
Start
Collecting data and literature review
Design the program coding for FORTRAN
Input the coding of the program in FORTRAN
Running the simulation
Conclusion
Data
acquired
End
Unsatisfied
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1.4.1 Flowchart Description
The flowchart above describes what the progress is now and what is going to
happen in this study. In starting this study, the objectives and scopes of the study
developed to know what the main focus of the study is. Tools and equipment for this
study were also listed to follow the objective and the scopes.
For collecting data and literature review, all related data on this study will be
collected and reviewed to find more information and deeper understanding of this study.
There are already some literature review pertaining this study but it need to be improved
later in case new source for literature of this study was found later.
In designing program coding in FORTRAN, the basic of FORTRAN need to be
studied and at least know some intermediate knowledge and skills in using FORTRAN.
The coding to achieve the project’s objectives will be studied thoroughly and how it
will fulfill the objectives and the scopes required. More simple coding and side program
need to be known and done in strengthening the basic and to follow the progress of
coding the program.
For input the coding of the program, the designed coding of the program will be
coded in into the program. Along this progress, the program will be run in each step and
lines to troubleshoot and make amendments on the coding to achieve the objectives.
In running the simulation, after the coding was fully input, the program will be
run to acquire the desired output. If the output resulted in error or the data collected
result were unsatisfactory, the program coding will be repaired and the program will be
run again until the desired data obtained.
The collected data will be processed and checked with the objective of the
project. If all the data merge well with the objectives, the project will summarized and
concluded and the full report of the project will be done. End of project.
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1.5 THESIS ORGANISATION
This thesis consists of five chapters ranging from Chapter 1 to Chapter 5.
Chapter 1 gives an overview of the study conducted. It also included with objective,
scopes of the project and problem statement. Chapter 2 reviews the previous research
works that was conducted by other people. All the relevant material including technical
paper, journals and books taken from those researchers will be discussed in this chapter.
Chapter 3 is the methodology. It is about the method used and the progress of
the project. It will discuss about the programming coded and flow in details of this
research. Result from the coding program will be discussed in Chapter 4. Chapter 5
which is the last chapter concludes the entire thesis.
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CHAPTER 2
LITERATURE REVIEW
2.1 INTRODUCTION
This chapter covers the recent review or related articles to this research. All the
studies focused on the articles related to diesel engine and fuel injection system are
included.
2.2 DIESEL ENGINE AND FUEL INJECTION SYSTEM
Diesel engine is a type of internal combustion engine and also known as
compression ignition engine, where the fuel ignited solely by the high temperature
created by the compression process of air and fuel mixture. It works by injecting the air
into the cylinder and the piston compresses the air. Then the fuel is injected directly into
the cylinder for combustion process.
There are a great variety of diesel engine designs for wide range of applications,
such as car, truck, locomotive, marine vessel and power generation. The diesel engine is
more efficient than the petrol engine because it is fuel efficient.
From Karki et al. (2010), in present diesel engines, fuel injection system
designed to obtain higher injection pressure. It is aimed to decrease the exhaust
emissions by increasing efficiency of diesel engine. It is because when the fuel injection
pressure is low, fuel particle diameters will enlarge and ignition delay period during the
combustion will increase.
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There are several functions of fuel injection such as to filter the fuel, to meter or
measure the correct quantity of fuel to be injected, control timing of fuel injection, to
control the rate of fuel injection, to atomize or break up the fuel to fine particles and to
properly distribute the fuel in the combustion chamber.
Though the functional objectives for different types of fuel injections vary, the
main task is to supply fuel to the combustion process. The objectives of a fuel injection
are fuel efficiency, reliability, emission performance, output power, to accommodate
alternative fuels, smooth operation, basic cost, maintenance cost, diagnostic capability
and environmental operation. It is practically impossible for a single system to have all
these objectives as certain combinations are conflicting. But all the systems try to
supply most of these objectives.
There are many benefits of fuel injection including, smoother and dependable
engine response during quick transitions, easier and faster engine starting, better
operation at a high or low ambient temperature, increased fuel efficiency and increased
maintenance intervals. Modern electronic fuel injections help in maintaining accurate
fuel metering and help in producing less air pollutants.
The fuel injection system in a direct injection diesel engine is to achieve a high
degree of atomization in order to enable sufficient evaporation in a very short time and
to achieve sufficient spray penetration in order to utilize the full air charge. The fuel
injection system must be able to meter the desired amount of fuel, depending on engine
speed and load, and to inject that fuel at the correct time and with the desired rate.
Further on, depending on the particular combustion chamber, the appropriate
spray shape and structure must be produced. Usually, a supply pump draws the fuel
from the fuel tank and carries it through a filter to the high-pressure injection pump. The
fuel injection pressure in a standard diesel is in the range of 200 to 1700 atm.
According to Shimada et al. (1989), low pollution and low fuel consumption are
the most important demands imposed on engines and these requirements are becoming
ever more stringent, year after year. To satisfactorily reduce smoke and exhaust
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emissions and also reduce fuel consumption, which generally is adversely affected
when lowering pollutant levels, an increase in the fuel injection pressure of direct
injection type diesel engines has been conventionally adopted as an overall solution.
The effect of high pressure fuel injection was investigated with in-cylinder fuel
spray observation and single cylinder engine to reduce exhaust emission and fuel
consumption. It is based on spray impingement on the cavity wall which promotes
mixing with air and reduction on the nozzle area thus extends the wall impingement as
result of increasing both fuel injection and injection period.
Modifying injection rate of fuel pump and nozzle area will increase injection
pressure, and also improves smoke and fuel consumption at low and medium speeds in
particular. To extend these effects of high pressure injection, more optimized
combustion system and minimized injection equipment drive torque required. To
resolve the problem of high pressure injection such as higher combustion noise and
increase in emissions, the combination with pilot injection can be an effective
method.
However, the relationship between fuel injection characteristics and exhaust
emissions or fuel consumption performance, such as how the optimum injection
pressure or injection duration should be, can hardly be said to have been sufficiently
clarified. Therefore, the authors proceeded by first observing fuel spray, which is the
basis of diesel combustion, and examining the relationship between fuel injection
pressure and engine performance using high pressure fuel injection equipment and a
single cylinder engine
Marcic and Kovacic (1985) said that the diesel engine has for many years been
used with great success in heavy duty field haulage. Its high thermal efficiency, long
service life and great reliability it has also gained ground in medium heavy goods
transport, and more recently advanced into the passenger cars, particularly in Europe.
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Figure 2.1 : Diesel fuel injection system
Source : Marcic and Kovacic (1985)
To meet the increasing demands for even greater thermic efficiency, minimized
gaseous emissions, lower black smoke in the exhaust gases as well as diminished noise,
an improved combustion process is called for. One of the key elements that have an
impact upon the combustion process in diesel engines is the injection system, the
optimization of which requires both analytical and experimental research.
In the past the optimization of the injection system used to be exclusively
experimental. Introducing computer simulation of the injection system can substantially
reduce the period of time required for experimentation, and, besides being more cost-
effective than the conventional. Method of experimenting, computer simulation also
facilitates a more explicit evaluation of the influence individual elements of the
injection system exert upon the parameters of the injection procedure.
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Computer simulation itself, however, requires a more thorough theoretical
knowledge of both hydraulic and dynamic phenomena occurring during the fuel
injection procedure. It goes without saying that a great many experimental data on the
injection system like the shape of the pump camshaft, hydraulic losses during the flow
through the nozzle etc. Which have an influence upon both hydraulic and dynamic
phenomena during the fuel injection process must be ready at hand in order to work out
a suitable mathematical model.
To check the accuracy of the computer simulation, exact measurements of the
fuel injection parameters like injection pressure, injection rate, injection timing etc. of
the conventional injection systems as well as comparison of the data obtained by
computing and gauging have to be carried out. As soon as a sufficient accuracy of the
computed data compared with those measured has been achieved, computer simulation
may be applied in dimensioning new injection systems.
Campbell et al. (1981) said that the diesel engines have better fuel economy and
emit lower quantities of gaseous hydrocarbon (HC) and carbon monoxide (CO) than
comparable spark ignition engines. This has made the diesel more attractive to vehicle
manufacturers. Also, with the recent increase in fuel costs, diesel engines are a viable
alternative to gasoline engines. Due to these and other reasons, the diesel engine has
recently experienced a large increase in use in cars and trucks
According to Greeves (1979), future needs for efficient and low emissions
power units have stimulated efforts to develop the full potential of the diesel engine.
The aim is to minimise the emissions of smoke, HC, CO, odour, particulates and noise,
while maximising fuel economy and the smoke limited power output. In order to meet
these various requirements there is need to develop a fundamental understanding of the
many complex combustion processes so that the system may be fully optimised.
Some of the principal factors involved have been established in previously
published work. Computer modelling of the combustion and supporting experimental
work have established that fuel-air mixing has a first order importance in diesel
combustion. Experiments show that fuel economy improves with shorter burn-times and
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this is to be expected since the thermodynamic ideal for best fuel economy is to release
all the heat at top dead centre crank angle.
In addition to improvements in fuel economy, both calculation and experiment
show that faster fuel-air mixing reduces soot formation. This is because the residence
time for soot formation reactions is reduced since the fuel-rich regions which produce
soot are ‘leaned-out' more rapidly.
Crua (2002) said that, within the last decade, the High-Speed Direct Injection
(HSDI) diesel engine has become a realistic alternative to the gasoline engine for
modern passenger car applications. Good drivability and durability together with high
economy hassled to its increasing popularity in the market place. The modern
turbocharged aftercooled diesel offers an efficient, low emissions automotive power
plant.
The fuel injection equipment is one such sub-system that has been found to lend
itself to developments leading to improvement in engine performance and emission
quality, and will continue to play a vital role in the development of improved diesel
engines for the foreseeable future.
Ultimately the nature of the combustion process is determined by the quality of
the fuel spray and its distribution and mixing within the combustion chamber. Breakup
and distribution of the spray is largely determined by the in-cylinder conditions (air
motion, density and temperature), the injection pressure, nozzle design and geometry
From Celikten (2003), he said that the diesel engine produces lower amounts of
HC, CO, and NO than the comparable gasoline engine. HC and CO is lower because of
more complete combustion of the fuel and air. is lower because the peak
temperature is not maintained for very long. Smoke, or particulate emissions, occurs
when there is insufficient air to completely burn the fuel.
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There are several factors that the engine designer varies to provide low emission
levels with high performance and good fuel economy. Some of these factors are the
shape of the combustion chamber, the location and angle of the nozzle, the injection rate
and nozzle spray pattern, injection timing, and camshaft timing.
Generally, with the diesel engine, emission levels have been lowered through
engine refinements. This has also had a positive effect on economy and performance. In
present diesel engines, fuel injection systems are designed to obtain higher injection
pressure. So it is aimed to decrease the exhaust emissions by increasing efficiency of
diesel engines. When fuel injection pressure is low, fuel particle diameters will enlarge
and ignition delay period during the combustion will increase.
This situation leads to increase pressure. SO, NO and CO emissions will increase
since combustion process goes to a bad condition. When injection pressure is increased
fuel particle diameters will become small. Since formation of mixing of fuel to air
becomes better during ignition period, smoke level and CO emission will be less. But, if
injection pressure is too higher ignition delay period becomes shorter. So, possibilities
of homogeneous mixing decrease and combustion efficiency falls down.
2.3 OPERATION CYCLE OF ELECTRONIC FUEL INJECTION SYSTEM
The operation cycle of electronic fuel injection system is as follows:
i. Air enters the engine through the air induction system where it is measured by
the air flow meter. As the air flows into the cylinder, fuel is mixed into the air by
the fuel injector.
ii. Fuel injectors are arranged in the intake manifold behind each intake valve. The
injectors are electrical solenoids which are operated by the Electronic Control
Unit or known as ECU.
iii. The ECU pulses the injector by switching the injector ground circuit on and off.
When the injector is turned on, it opens, spraying atomized fuel at the back side
of the intake valve.
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iv. As fuel is sprayed into the intake airstream, it mixes with the incoming air and
vaporizes due to the low pressures in the intake manifold. The ECU signals the
injector to deliver just enough fuel to achieve an ideal air/fuel ratio of 14.7:1,
often referred to as stoichiometric.
v. The precise amount of fuel delivered to the engine is a function of ECU control.
The ECU determines the basic injection quantity based upon measured intake air
volume and engine rpm.
vi. Depending on engine operating conditions, injection quantity will vary. The
ECU monitors variables such as coolant temperature, engine speed, throttle
angle, and exhaust oxygen content and makes injection corrections which
determine final injection quantity.
2.4 ADVANTAGES OF FUEL INJECTION SYSTEM
There are many advantages of fuel injection system. First is uniform air/fuel
mixture distribution; each cylinder has its own injector which delivers fuel directly to
the intake valve. This eliminates the need for fuel to travel through the intake manifold,
improving cylinder to cylinder distribution.
Second is high accurate air/fuel ratio control; throughout all engine operating
conditions Electronic Fuel Injection or EFI supplies a continuously accurate air/fuel
ratio to the engine no matter what operating conditions are encountered. This provides
better drive ability, fuel economy, and emissions control.
Third is superior throttle response and power; by delivering fuel directly at the
back of the intake valve, the intake manifold design can be optimized to improve air
velocity at the intake valve. This improves torque and throttle response.
Fourth is excellent fuel economy with improved emissions control; cold engine
and wide open throttle enrichment can be reduced with an EFI engine because fuel
puddling in the intake manifold is not a problem. This results in better overall fuel
economy and improved emissions control.
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Fifth is improved cold engine startability and operation; the combination of
better fuel atomization and injection directly at the intake valve improves ability to start
and run a cold engine. And the last is simpler mechanics, reduced adjustment
sensitivity; the EFI system does not rely on any major adjustments for cold enrichment
or fuel metering. Because the system is mechanically simple, maintenance requirements
are reduced.
2.5 TYPES OF FUEL INJECTIONS SYSTEM
First is throttle-body injection, commonly known as TBI, this system injects fuel
at the throttle body. Second is continuous injection, in this system, the fuel sprays
continuously from injector rather than getting pulsed every time a stroke is given to the
engine. Third is multi-point fuel injection, in this system, the fuel is injected into the
intake port along the side of cylinder’s intake valve rather than a central point.
Fourth is central port injection, in this system, tubes along with valves used to
spray fuel at each intake rather than full throttle body. And the last is direct injection, it
is the most used fuel injection. In this system, the nozzle used for injection is placed in
the combustion chamber and the piston causes a depression when an initial combustion
takes place.