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

v

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.

vi

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

ix

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

x

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

xi

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

xii

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

1

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.

2

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.

4

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

5

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.

10

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.

11

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

12

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.

13

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.

15

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.