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ABSTRACT

DIGITAL FUEL INJECTION SYSTEM

The fuel injection system supplies the engine with a combustible air-fuel mixture.

Modern cars have a digital engine control system. It controls the ignition and the fuel

injection systems. Technological developments in the automobile field resulted in the

digital fuel injection system. The digital Fuel injection system is a solution to all the

problems of carburetor. The controller in a Digital Fuel injection system is an electronic

control module or the ignition and Fuel Injection System. Various components of the

engine and fuel system send electrical signals to the ECM and ECM continuously

calculates how much fuel to inject. It then opens thee fuel injectors so proper amount of

fuel sprays out to produce the desired air- fuel ratio.

The seminar aimed at discussing the various parts of the digital fuel injection system.

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ACKNOWLEDGEMENT

I take this opportunity to express my profound sense of gratitude to all those who

have contributed to the successful completion of my seminar.

I wish to express my sincere gratitude to Mr. JITIN YADAV, Head of Department.(AE).

I also thank all other Lectures of Automobile Department for there all hearted Co-

Operation and Guidants in completing my seminar successfully.

I also have to appreciate the encouragement and constructive Criticism I received from

my Friends which went a long way to make this seminar as satisfying experience for me.

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INTRODUCTION

All the combustion engines are design on the principle that they use some fuel as the

intake and convert this into energy, to produce work. A mixture of fuel and air is a must

for any combusting engine to function. Over a period Technologies have changed and

evolved methods to Feed this mixture to the engine.

The fuel injection system supplies the engine with a combustible air-fuel mixture. Old

petrol Engine cars used to the conventional carburetors for supplying air-fuel mixture to

the combustion Chamber. The Carburetor technology was found insufficient to cater to

the needs of the challenging environment and has many this advantages like low fuel

economy, High pollution rate, delayed starting, etc.

Technological development in the automobile field resulted in the digital fuel injection

system. The digital fuel injection system is a solution to all the problems of carburetor.

The controller in a Digital Fuel Injection System is an electronic control module (ECM)

or electronic control unit (ECU) the ECM controls the ignitions and fuel injection

systems. Various Components of the engine and fuel system send electrical signals to the

ECM and ECM continuously calculates how much to eject. It then opens the fuel

injectors so the Proper amount of fuel sprays out to produce the desired air-fuel ratio.

The Digital fuel Injection System lacks a carburetor. It incorporates an injector similar to

that in a diesel system, through which petrol is sprayed into the intake manifold. The

ECM acts as the command centre and the decision is made based on the data supplied by

seven sensors provided at deferent locations on the chassis.

In the Digital Fuel Injection System the mixture of fuel and air reaches the piston head in

predetermined ratio. This mixture is then fed in to the combustion chamber. Once inside

the combusting chamber it ignites with the help of a spark from the spark plug. As the

ignition is turned on, The sensors are activated and the fuel is sent through injectors

directly to the combustion chamber where it is sprayed on top of the piston heads. The air

is taken separately through a set of valves. The fuel and air are mixed just before entering

the combustion chamber. In the Digital Fuel Injection System the injectors are controlled

by an Electronic sensor which is turned to the throttle.

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SCHEMATIC DIAGRAM OF DIGITAL FUEL INJECTION

SYSTEM

Figure: 1-2

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DIGITAL FUEL INJECTION SYSTEM

The main important components of the Digital Fuel Injection System are:-

1) Electronic Control Module (ECM)

2) Electronic Engine Controls (EEC)

3) Sensors

ELECTRONIC CONTROL MODULE (ECM)

The nerve centre of the Digital Fuel Injection System is the Electronic Control Module

(ESM) and all the data collected from the various sensors are directed towards ECM. It

serves as the processor or decision maker in an Electronic Control System.

The mane parts of an ECM are the IC Chips that contain the microprocessor and the

memory. The microprocessor is the Central Processing Unit (CPU). It is the solid-state

devise that control information flow in a computer. By following a set of instructions

called program, The micro processor does the calculation and make the decisions solve.

The microprocessor chip is sealed in a protective package or career. The signals from the

sensors are received and sent through connections or terminals in the ECM. The

information needed by the microprocessor is stored in an electronic storage device called

a memory.

The Random Access Memory may be volatile or non-volatile. A volatile memory stores

informations temporarily, as long as battery power is available. The information stored

in a non-volatile memory is not lost by disconnecting the battery. The Look up Tables of

ECM is an non-volatile type memory.

ELECTRONIC ENGINE CONTROL (EEC)

The Electronic Engine Control (EEC) usually controls the fuel and injection systems. The

input devices are sensors and the output devices are actuators. The EEC allows the engine

to operate as fuel efficient as possible.

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SENSOR

A sensor is a device that receives and reacts to a signal. This may be a change in pressure,

Temperature or voltage. The ECM then calculate for how long to open the injectors.

The various sensors that report to the ECM includes

1) Engine speed sensor

2) Oxygen sensor

3) Manifold absolute pressure (MAP) sensor

4) Engine coolant temperature sensor

5) Intake air temperature (IAT) sensor

6) Camshaft position (CP) sensor

7) Throttle position sensor (TPS)

The ECM continuously receives all this data and checks this data with other data stored

in look-up tables in the memory then the ECM decides to open the injectors and for how

long.

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ELECTRONIC ENGINE CONTROL SYSTEMS (EEC)

Figure: 1-4

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ELECTRONIC ENGINE CONTROL CHART

Figure: 1-3

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ENGINE SPEED SENSOR

The engine speed sensor is actually a crank shaft position sensor that tells the ECM how

fast the engine crank shaft is turning. The ECM uses this data to control fuel metering,

ignition spark advance, and the shifting of electronic automatic transmissions and

transaxles.

Crankshaft position sensors are either Hall-effect sensors or magnetic sensors. In the case

of Hall-effect switch the ECM count the number of crankshaft rotations per second. The

crankshaft harmonic balance carries three vanes which pass between a permanent magnet

and a transducer and the magnetic field transistor on and off, switching the signal voltage

to the ECM. The ECM counts this voltage pulses to determine the crankshaft speed.

OXYGEN SENSOR

The oxygen sensor is installed in the exhaust manifold or exhaust pipe. It measures the

amount of oxygen in the exhausted gas. It is used primarily as a means of controlling

exhaust a emissions by keeping the air-fuel ratio close to 14.7:1.

The oxygen sensor is about the size of as spark of plug and produces a small voltage

when exposed to oxygen. This varying voltage is sent to the ECM, the voltage varies with

the amount of oxygen in the exhaust. Oxygen sensor voltage is between 1.3V and 1.5V

and when the voltage is close to 0.45V, the air-fuel ratio is close to ideal 14.7:1. If the

voltage is higher then 0.45V, the oxygen content is low i.e. the air-fuel ratio is rich and if

the voltage is less then 0.45V the oxygen content is high and the air fuel ratio is lean.

The varying voltages tell the ECM whether the air-fuel mixture is rich or lean. The ECM

then adjusts the duty cycle of the fuel injectors. It then turns them on for a longer or

shorter time, each time they open. This enriches or leans out the air fuel mixture. The

oxygen sensor will not work unless it is hot. It must be between 200 o and 800o. While the

engine is warming up, the electronic engine- control system is in open loop mode.

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As soon as the engine and the oxygen sensor reach operating temperature, the oxygen

sensor voltage signal is sent to the ECM. The ECM switches to closed loop mode and

begins using oxygen sensor to compute injector duty cycle.

MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR

MAP sensor is a semi conductor that senses change of pressure in the intake manifold

and relays it to the ECM as digital signal. The ECM gets an accurate value as to the

volume of air in the intake manifold and pressures.

Intake manifold is measured in two ways:-

1) With a vacuum gauge

2) With a manifold absolute pressure gauge.

The two gauges are basically the same. Both have a flexible diaphragm that separates the

two champers in the gauge. The difference is that one chamber of the vacuum gauge is

open to the atmosphere. One chamber of absolute pressure gauge contains a vacuum.

The vacuum gauge compares atmospheric pressure with intake manifold pressure. The

manifold absolute pressure gauges Computer the actual pressure in the intake manifold

with the vacuum. This is more accurate.

ENGINE COOLANT TEMPERATURE SENSOR

The coolant temperature sensor is a thermistor that continuously reports engine

coolant temperature to the ECM. This is a varying voltage signal that the ECM

uses in deferent ways. If the coolant temperature is low, the ECM signals the fuel

metering system to supply additional fuel for cold engine operation. The ECM

also alters the ignition time to suit the engine temperature.

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Most transverse engine uses an engine cooling fan. When the engine is cold, no

cooling is added. The fan does not run when the engine gets hot. The signal from

the coolant temperature sensor may cause the ECM to turn on the fan.

INTAKE TEMPERATURE SENSOR

Changing air temperature, changes the density of air. Hot air at low atmospheric pressure

is less dense and contains less oxygen than as equal volume of cooler air under high

atmospheric pressure.

The intake air temperature sensor is a thermistor. Its electrical signal decreases as its

temperature increases. The IAT sensor is located after the air filter and helps to compute

actual density of air at the intake manifold. The IAT sensor sends varying voltage signals

to the ECM and so it knows the air temperature.

INTAKE AIR TEMPERATURE (IAT) SENSOR

Figure: 2-6

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The air temperature sensor uses a thermistor that loses resistance as it is heated

THROTTLE POSITION SENSOR (TPS)

Figure: 2-8

Rotary throttle position sensor

As the throttle position changes, the wiper blade moves which changes the voltage signal

to the ECM.

This varies from about 5 volts at wide-open throttle to a fraction of a volt at closed

throttle.

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CAMSHAFT POSITION (CP) SENSOR

The Camshaft position sensor informs the ECM of the position of the cylinders and the

engine speed. This information is often crucial in deciding the direction and the amount

of the fuel injected as well as the ignition advance and the control of the knock through

ECM in the absence of a knock sensor.

THROTTLE POSITION SENSOR (TPS)

The throttle body contains the throttle valve. The assembly usually mounts on the intake

manifold. The throttle valve connects by linkage to the accelerator pedal. Depressing the

accelerator pedal opens the throttle valve.

The ECM must always know the position of the throttle valve. A TPS on the throttle body

continuously reports throttle position to the ECM. The position of throttle valve is important in

the control of the idle speed and in the sharp patterns of automatic transmission and transaxles.

When the throttle valve closes during the deceleration, The ECM shuts of fuel flow. This prevents

and over-rich mixture during deceleration.

A rotary throttle position sensor is a variable resistor or potentiometer. It has a coil of resistance

in the form of a half circle. One end connect to the ground and other end connect to a 5V source

from the ECM. As the throttle valve position changes, the wiper blade moves along the coil. As

the wiper slides, the voltage through the coil increases and correspondingly a voltage are sent to

the ECM. The voltage tells the ECM the position of the throttle valve.

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FUEL INJECTORS

There are two types of fuel injectors to deliver fuel in to the air entering the engine. They

are:-

1) Solenoid operated fuel injector

2) Mechanical fuel injector

SOLENOID OPERATED FUEL INJECTOR

The solenoid operated fuel injector is tuned on and off by the ECM. When the ignition

key is on, voltage is present at the injector. The solenoid is energized when the ECM

provides a ground. Then the injector opens and fuels sprays out. When the solenoid is de-

energized, fuel spray stops.

In many engines, the injector delivers fuel in to an intake port that as only one intake

valve. A single spray injector delivers a wide spray pattern through a single hole. A duel

spray injector has two holes in the tip. The holes are positioned so the spray from each

hole delivers fuel to one of the intake valve.

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SOLENOID OPERATED FUEL INJECTOR

Figure: 3-2

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MECHANICAL FUEL INJECTOR

The mechanical fuel injector is used in continuous injection systems. The injector

is basically a fixed orifice with a mechanical needle valve operated by fuel pressure. The

amount of the fuel injector dependence on the pressure applied to the fuel.

MECHANICAL FUEL INJECTOR

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COLD START VALVE

Engines with electronic fuel injection have a cold start valve. It supplies extra fuel

to satisfy a cold engine. The valve is similar to a solenoid operated fuel injector.

A thermo time switch limits the time the cold start valve can inject. This prevents the

engine from receiving too much fuel or flooding. The thermo-time switch has a

thermostatic blade, a pair of contacts and a heating element. When the engine cold, the

blade is straight and the contacts are closed. The cold start valve sprays fuel when the

engine cranks. As the engine warms up, the thermostatic blade bends and the contacts

separate. This opens the cold start value.

COLD START VALVE

Figure: 3-4 The cold start valve is used to supply extra fuel for starting a cold engine.

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THERMO-TIME SWITCH

Figure: 3-5

Thermo-Time switch limits how long the cold start valve can inject fuel

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ACTUATORS

Sensors feed information into the ECM. The ECM then makes decisions and sends

commands to various actuators. These are the device that operates automotive and enginecomponents

Actuators are transducers that usually connect electrical signals from the ECM in to

mechanical motion. Inputs are usually from sensors and switches. Outputs are usually

sent to actuator, which then operates switches, valves and other devices.

ELECTRONICPORT-INJECTION TIMINGThe timing of the injection in an electronic port injection system varies for

different engines.

In some four and six cylinder engines, all fuel injectors open at the same time - once each

crankshaft revolution. This arrangement is the simultaneous injection system. Each

injector opens twice for each time its intake valve opens. The intervals between injection

and intake valve opening are short that there are short that there is little loss in efficiency.

Some systems open half of the injections at the same time. This is group injection. Other

systems open each injector separately in firing order sequence. This is sequential

electronic fuel injection. It provides the most accurate fuel delivery and best engine

performance while minimizing exhaust emissions.

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ELECTRONICPORT-INJECTION TIMING

Figure: 3-6

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ADVANTAGES OF DIGITAL FUEL INJECTON SYSTEM

The major advantages of Digital Fuel Injection Systems are:-

1) The ECM can control all aspects of the combustion of the air-fuel ratio under all

conditions

2) With the Digital Fuel Injection System the engine will be reliable, run smoothly,

be more economical and have a longer lifespan.

3) The altitude and ambient temperature compensation ensure optimum performance

at all altitudes, temperatures and seasons

4) The extremely accurate and optimal fuel delivery at any rpm and every load

translates in to more horse power, better economy and less emission.

5) It dont need constant tuning or adjustments.

6) The ECM can actually help prevent engine damage by not allowing full power

and torque to be generated until or fluids are up to their normal operating

temperature.

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DISADVANTAGES OF DIGITAL FUEL INJECTON SYSTEM

1) It is very experience and has pushed the prices of the vehicle.

2) It takes time to perform an effective conversion.

3) The local fuel quality is the biggest enemy of fuel injection. Adulteration

and excessive gum content can play havoc, causing blockage of the pin hole

small injectors.

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CONCLUSIONS

Researches are going on and developments are made each day in the field

of fuel injection systems. The digital fuel injection system has changed the

complete concept of fuel injection and resulted in better efficient and powerful

vehicles.

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