electronic injection system

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1. ELECTRONIC INJECTION SYSTEMS

In carburettor engine, uniformity of mixture strength is

difficult to realize in each cylinder of a multicylinder engine

Fig 10.1 maldistribution

Injection system instead of carburetion

To have uniform distribution of fuel in multi cylinder

engine

To improve breathing capacity ie Volumetric efficiency

To reduce or eliminate detonation

To prevent fuel loss during scavenging in case of two

stroke engine


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Types of Injection Systems - Classification

Gasoline direct injection into the cylinder GDI

i. Manifold injection

ii. Port Injection

a. Continuous and b. Timed

The above fuel injection systems can be grouped under

Single - point or Throttle body injection system and

Multi point or Port injection

Single - point or Throttle body injection system

One or two injectors mounted inside throttle body

assembly

Fuel spray directed at one point or at the center of the

intake manifold

Multi point or Port injection

One injector for each cylinder


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Fuel is injected in more than one location commonly

used

a. Continuous fuel injection system

Rotary pump injects fuel through a nozzle located in

the manifold immediately down stream of the

throttle plate at a gauge pressure of 0.75 to 1.5 bar

In a super charged engine, fuel is injected at the

entrance of the supercharger

The timing and duration of the injection is

determined by the Electronic Control Unit (ECU)

depending on the load and speed

b. Timed fuel injection system

Fuel pump injects fuel through nozzle in the

manifold or the cylinder head port at about 6.5 bar

or into combustion chamber at about 16 to 35 bar

Injects fuel usually during early part of suction stroke

Direct in cylinder injection is superior always

desirable and better compared to the manifold

injection but causes oil dilution

Both low and high volatile fuels can be used with high

volumetric efficiency


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Components of Injection system

Objectives

Meter Atomize Uniformly distribute the fuel throughout

the air mass in the cylider Must maintain the required A/F

ratio as per the load speed requirement of the engine

Pumping element from fuel tank to injector through

pipes and filter

Metering Element Measures and supplies fuel at the

rate determined by load and speed conditions of engine

Mixing Element Atomize the fuel and mixes it with air

to form a homogenous mixture

Metering Control Adjust the metering in accordance

with load and speed conditions of the engine

Mixing Control adjusts the fuel air ratio as demanded

by the load and speed conditions of the engine


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Distributing Element Divides the metered fuel equally

among the cylinders

Timing Control - Fixes the start and stop of the fuel air

mixing process

Ambient control Compenstas for changes in T and P

of either air or fuel that may affect the various elements

of the system

2. ELECTRONIC FUEL INJECTION SYSTEM

Modern gasoline injection sytem use engine sensors, a

computer and solinoid operated fuel injectors to meter

and inject the right amount of fuel

These systems called electronic fuel injection (EFI) use

elctrical and electronic devices to monitor and control

engine operation

An electronic control unit (ECU) receives elctrical signals

in the form of current or voltage from various sensors

It then uses the stored data to give necessary commands

to the injectors, ignition system and other engine related

devices

As a result the vehicle gives better milage

Typical Sensors for an EFI system


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o Exhaust Gas or Oxygen Sensor calculates the air fuel

ratio changes in proportion

o Engine Temperature Sensor senses the engine coolent

temperature adjust the mixture strength to rich side for

cold starting

o Air flow sensor Monitors mass or volume of air flowing

into the intake manifold for adjusting the quantity of fuel

o Air Inlet Temperature Sensor Cheks the temperature of

the ambient air entering the engine for fine tuning the

mixture strength

o Throttle Position Sensor Senses the movement of the

throttle plate so that the mixture flow can be adjusted for

engine speed and acceleration

o Manifold Pressure Sensor Monitors vacuum in the

engine intake manifold so that the mixture strength can

be adjusted with changes in engine load

o Camshaft Possition Sensor Senses the rotation of the

camshaft / crank shaft for speed and timing of injection

o Knock Sensor Microphone type sensor that detects ping

or preignition noise so that the engine timing can be

retarded

Merits of EFI System

Improvement in volumetric efficiency due to less

resistance in intake manifold eliminates pressure loss in

carburettor and manifold heating

Manifold wetting is eleminated fuel being injected into

or close to the cylinder


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Atomization is independent of cranking speed and hence

starting will be easier

Better atomization and vaporisation will make the engine

less knock prone

Ice formation of on throttle plate is completely eliminated

Less volatile fuel can be used since distribution of fuel is

independent of vaporisation

Variation of air fuel ratio almost negligible during

turing travelling in grades and in uneven roads etc

Position of the injection unit is not so critical and thereby

the height of the engine may be less

Demerits of EFI System

High maintenance cost

Difficulty in servicing

Possibility of malfunction of some sensors


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Multi Point Fuel Injection (MPFI) System

a. Port injection

b. Throttle body injection

a. Port injection

Injector placed on the side of the intake manifold fig

10.3 - sprays fuel into the air inside the intake manifold

Fig 10.4 MPFI system each cylinder will have an

injector

b. Throttle body injection


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Fig 10.5 - Injector placed slightly above the throat of the

throttle body

Injector spray the fuel into the air near the throat of the

throttle body

Timed / Continuous Injection System (for both a & b)

In the timed injection system fuel is sprayed from injector

in pulses

In continuous injection system fuel is sprayed

continuously from the injectors

MPFI System : Classified as D-MPFI and L-MPFI

D-MPFI System

Fig 10.6 manifold fuel injection system

First vacuum is sensed followed by volume of air by its

density


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As air enters into the intake manifold, the manifold

pressure sensor detects the intake manifold vacuum and

sends the information to ECU

The speed sensor also sends information about the rpm of

the engine to the ECU

The ECU in turn sends commands to the injector to

regulate the amount of fuel supply for injection

When the injector sprays fuel in the intake manifold the

fuel mixes with air and the mixture enters the cylinder

L-MPFI System

Fig 10.7 port fuel injection system also called air mass

metering or air flow metering

In this type the fuel metering is regulated by the engine

speed and the amount of Air that actually enters the

engine

Functional Divisions of MPFI System

a. Electronic Control system


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b. Fuel System

c. Air Induction System

a. MPFI - Electronic Control System

Fig 10.8 Sensors that monitor : intake air temperature,

air flow, oxygen, water temperature, the starter signals,

throttle position, engine speed sensors sends information

signals to ECU

The ECU in turn sends commands to the injector to

regulate the amount of fuel supply for injection

b. MPFI Fuel System

Fig 10.9 At the time of starting the cold start injector is

operated by the cold start injector time switch

The cold start injector injects fuel into the air intake

chamber, thus enriching the air-fuel mixture


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The pressure regulator regulates the pressure of the fuel

The injectors receive signals from the ECU and inject

the fuel into the intake manifold

c. MPFI Air Induction System

Fig 10.10 Air cleaner, air flow meter, throttle body and

air valve supply a proper amount of air to the air intake

chamber / intake manifold

The quantity of air supplied is just what is necessary for

complete combustion


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Electronic Control System

It mainly consists a. ECU which determines the duration

of operation of the injectors

b. Cold start injector - to control its operation c. Starter

timing switch

Circuit opening relay to control fuel pump operation

Resistor to stabilize the injector operation

a. Electronic Control Unit (ECU)

ECU in the electric control system receives signals from

the sensors and determines the opening time for the

injectors which also controls the injection volume


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b. Cold Start Injector

Fig 10.11 Cold start injector serves the purpose of

supplying more fuel at the time of starting a type of

solenoid valve

c. Timing switch

Duration of injection time is controlled by a timing switch

The main injector also supplies fuel at the same time


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When the engine is hot, the cold start injector will stop

injection

Air Valve

The position of air valve - Fig 10.11 for cold engine

When T is low the air valve opens completely

As the temperature rises, the air valve closes gradually

During normal operating T, air valve closes completely

Injection Timing

According to the firing order, the injection of fuel takes

place inside the inlet manifold at various timings

The ECU calculates the approximate injection timing for

each cylinder and the air fuel mixture is made available

at each suction stroke

To meet the operating conditions, the injection valve is

kept open for a longer time by ECU

3. GROUP GASOLINE INJECTION SYSTEM

Fig 10.12 shows a block diagram with sensors & ECU

for a group injection system


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In an engine having group injection system, the injectors

are not activated individually, but are activated in groups

In six cylinder engine there are two groups each group

having 3 injector

The timing of injectors is decided by engine speed sensor

Based on the signals from the speed sensor, the ECUactivates one group of injectors

Subsequently the ECU activates other group of injectors

Fig 10.13 Injector grouping for six cylinder engine


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Injectors for cylinders 1, 3 and 5 open at the same time

and inject the fuel into the intake manifold

After these injectors close, the injectors for the cylinders

2, 4 and 6 open and inject fuel

Fig 10.14 shows port injection using electronic group fuel

injection system for an eight cylinder engine Eight injectors are divided into two groups having four each


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4. ELECTRONIC DIESEL INJECTION SYSTEM

For an engine to operate at high efficiency and low emission

levels the parameters to be precisely controlled with injection

pump are

Timing

Rate of injection

End of injection

Quantity of injected fuel

Precise control can be achieved by means of EFI system

Injection timing

Fuel injection quantity

Injection rate during various stages of Injection

Injection pressure during Injection

Nozzle operating speed and

Pilot Injection timing and its quantity

The following are easy to obtain with EFI systems

Very high Injection pressure

Sharp start and stop of Injection

Cylinder cut off

Diagnostic capability

Turbocharger control and

Two stage injection


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Electronic Diesel Injection Control

There are various versions of electronically controlled

diesel fuel injection systems

a. Electronically controlled Injection pumps (Inline and

Distributor type)

b. Electronically controlled unit Injectors

c. Common rail fuel injection system

a. Electronically controlled diesel fuel injection systems may use

the following as inputs

o Engine Speed

o Crank shaft position

o Accelerator pedal position

o Intake air temperature

o Lubricating oil Temperature

o Ambient air Temperature

o Turbocharger boost Temperature

o Intake air mass flow rate


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Electronically Controlled Unit Injectors

Fig 10.15 shows schematic layout of entire system


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Unit injectors can be combination of high pressure pumps and

injectors in one unit do not have high pressure pipe lines and

hence the injection lag is low


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The main high pressure pump is situated above injector

A simplified cross section of the unit injector and phases of

injection are shown in Fig 10.16

The fuel pushed down by the injector just by passes the

injection nozzle till the solenoid controlled spill valve closes the

spill port

The closure of the spill port iniates the injection process

The injection stops when the solenoid valve opens the spill port

The ECU generates the pulses to operate the solenoidcontrolled spill valve

Electronically Controlled Injection Pumps (Inline and

Distributor Type)


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In the case of the electronically controlled there will be a

control sleeve which can be moved up and down by an

actuator which is controlled by the ECU

The ECU determines the amount of fuel based different

parameters

Fig 10.17 shows schematic block diagram of an

electronically controlled inline fuel injection system

ECU determines correct quantity of the fuel to be injected

based on the inputs and the data in the look up table


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ECU can also regulate the fuel quantity depending on

other conditions like braking

ECU also protects the engine against over heating by

regulating the maximum quantity of fuel delivered

Common Rail Fuel Injection System

The common rail fuel injection system is finding

increasing use in diesel engines as it has the potential to

drastically cut emissions and fuel consumption

This system provides control of many important

parameters linked to the injected system

It has a wide range of applications: some important

features are:

Very high injection pressures of the order of 1500

bar

Complete control over start, and end of injection

Injection pressure is independent of engine speed

Ability to have pilot, main and post injection

Variable injection pressure

Fig 10.18 shows a typical layout of the common rail fuel

injection system


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Fig 10.18. Sensors of a Common Rail Injection System, together

with Various System Components

1. ELECTRONIC INJECTION SYSTEMS


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Injection system instead of carburetion

Types of Injection Systems - Classification

Components of Injection system

2. ELECTRONIC FUEL INJECTION SYSTEM

Typical Sensors for an EFI system

Merits of EFI System

Demerits of EFI System

Multi Point Fuel Injection (MPFI) System

Timed / Continuous Injection System (for both a & b)

MPFI System : Classified as D-MPFI and L-MPFI

Functional Divisions of MPFI System

Electronic Control System

Electronic Control Unit (ECU)

3. GROUP GASOLINE INJECTION SYSTEM

4. ELECTRONIC DIESEL INJECTION SYSTEM

Electronic Diesel Injection Control

Electronically Controlled Unit Injectors

Electronically Controlled Injection Pumps (Inline and

Common Rail Fuel Injection System

electronic injection system

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