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WHY GASOLINE INJECTION?

• To have uniform distribution of fuel in a multicylinder engine.

• To improve volumetric efficiency.

• To reduce or eliminate detonation.

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Electronic Fuel Injection (EFI) system main components

Modern gasoline injection systems use:

1. Solenoid Operated Fuel Injectors

2. An Electronic Control Unit (ECU)

3. Sensors

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The fuel injector is a solenoid switch that’s either on (fuel flows) or off

(fuel doesn’t flow). (Courtesy Kawasaki Motor Corp., U.S.A.)

1. Fuel Injectors

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Typical sensors for an electronic fuel injection system

• Exhaust gas or oxygen sensor -

• Engine temperature sensor -

• Air flow sensor -

• Air-inlet temperature sensor -

• Throttle position sensor -

• Manifold pressure sensor -

• Camshaft position sensor -

• Knock sensor -

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Electronic fuel injection system

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Types of Injection Systems

• Gasoline direct injection into the cylinder (GDI)

• Port injection

• Manifold injection

Another Classification of Injection Systems

Multi-Point Injection (MPI)

(a) Gasoline direct injection into the cylinder (GDI).

(b) Port injection.

Single-Point Injection (SPI)

(c) Throttle body injection

Injection Systems can be classified into:

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a. Gasoline Direct Injection (GDI) Engine (Stratified-Charge Engines)

• Fuel is injected directly into the cylinder during the intake stroke or the

compression stroke

• High pressure injector required, 5-10 MPa

• Need bowl in piston design to direct the fuel spray towards the spark plug

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During intake stroke air enters the cylinder

Near the end of the compression stroke fuel is injected and directed

by the piston head bowl towards the spark plug

The mixture at the spark plug is “rich” in fuel thus easy to ignite but

the amount of fuel injected results in an overall “lean” fuel-air mixture

Lowers heat transfer to the walls but increases thermal cyclic load on

the spark plug, and standard catalytic converter doesn’t work

a. Gasoline Direct Injection (GDI) Engine (Stratified-Charge Engines)

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Engine that combines the best features of SI and CI engines:

• Operate at optimum compression ratio (12-15) for efficiency by injecting

fuel directly into engine during compression (avoiding knock associated

with SI engines with premixed charge)

• Control engine power by fuel added (no throttling no pumping work)

• Increasing the engine volumetric efficiency.

• Create easily ignitable fuel-air mixture at the spark plug and a leaner

fuel-air mixture in the rest of the cylinder.

• Lean burn results in lower emissions and higher energy efficiency

a. Gasoline Direct Injection (GDI) Engine (Stratified-Charge Engines)

Benefits of GDI system

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• Manifold wetting is eliminated due to the fuel being injected' into or

close to the cylinder and need not flow through the manifold.

• Formation of ice on the throttle plate is eliminated (Carburetor Icing).

a. Gasoline Direct Injection (GDI) Engine (Stratified-Charge Engines)

Benefits of GDI system

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Example:

Mitsubishi GDI engine achieves complete combustion with an air-fuel

ratio of 40:1 compared to 15:1 for conventional engines

This results in a 20% improvement in overall fuel efficiency and CO2

production, and reduces NOx emissions by 95% with special catalyst

a. Gasoline Direct Injection (GDI) Engine (Stratified-Charge Engines)

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b. Port Injection (Semi direct injection) Multi-point Fuel Injection (MPFI) system

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Multi point fuel injectors

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c. Single-Point Fuel Injection (SPFI) system Throttle Body Injection System

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Fuel Injection System

Throttle

Fuel tank

Air intake

manifold

During start-up the components are cold so fuel evaporation is very slow, as a result

additional fuel is added through a second injecting valve

200 KPa

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c. Throttle body for air flow control

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Problems associated with injection systems

• High maintenance cost,

• Difficulty in servicing,

• Possibility of malfunction of some sensors.

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Diesel Indirect-Injection (IDI) Process Diesel Direct-Injection (DI) Process

Injection in diesel engines