FUEL SUPPLY SYSTEM IN SI ENGINE

By. Amit S. Niwalkar

Fuel supply system in Spark Ignition Internal Combustion Engines plays an important role in the output power of an engine as well as its performance in terms of fuel consumption.

In a way to further improve the performance of the SI Engine and better control of pollutants, an improved fuel injection method called GDI (Gasoline Direct Injection) has been focused for the development of SI Engines. In the GDI method, fuel is been directly injected into the cylinder like in CI Engines.

Introduction :-

Float chamber (function) :-

Parts from fuel supply :-

Fuel tank :- The fuel tank made be made from pressed steel and coated inside to prevent corrosion, or a synthetic rubber compound or flame resistant plastic.

Fuel pipes :- These can be made from steel or plastic and are secured by clips at several points along the underside of the vehicle.

Fuel filters :- To prevent dirt and fluff entering the fuel pump a filter is fitted on the suction side of the pump.

Air filters :- Its most important function is to prevent dust and abrasive particles from entering the engine and causing rapid wear.Fuel pump :- This supplies fuel under high pressure to the fuel injection system, or under low pressure to a carburettor.

Carburettor :- This device which atomizes the fuel and mixes it which the correct amount of air.

(Ways)

Carburettor Fuel injection

Multi point fuel injection

Gasoline direct injection

Electronic fuel injection

Throttle body injection

Port injection

FUEL SUPPLY

Carburetor System is a proven technology for many years and is adopted is almost all SI Engines until 1990's.

In this method air and fuel are mixed in the required quantities in a device called carburettor before supplying to the engine cylinder. Many complex subsystems are required for the effective working of the engine as the engine is subjected to various operating conditions in practice.

Carburettor :-

fig. Carburettor

Air in

Air filter

Choke valveFuel in

Gas and Fuel mixture

VenturiFloat

Throttle valveFloat chamber

1. The carburettor has many wearing part. After wear it operates less efficiently.

2. Vapor lock in the fuel systems may result in hot weather.

3. Carburettors, with their choke tubes, jets, throttle valves, inlet pipe bends, etc., do not give a free flow passage for the mixture. Thus there is loss of volumetric efficiency on this account.

1. It is economical.2. Its air fuel mixture is easily set by mechanical.

Advantages of carburettor :-

Disadvantages of carburettor :-

fig. Port injection

Air in

Injector

Fuel spray

This MPFI system is to supply the proper ratio of gasoline and air to cylinders.

Multi Point Fuel Injection :-

In the port injection arrangement the injector is placed on the side of intake manifold near the intake port. The injector sprays gasoline into the air, inside intake manifold.

Port injection :-

fig. Throttle body injection

Injector

Air Air

Throttle body Fuel spray Intake manifold

Throttle body injection :-

In the throttle body injection system an injector is placed slightly above the throat of the throttle body. The injector sprays gasoline into the air in the intake manifold.

1. Increased volumetric efficiency and hence increased power and torque, due to the absence of any restriction such as ventures and other metering elements in the air passage.

2. Better distribution of mixture to each cylinder and hence lower specific fuel consumption.

3. Even in MPFI Engines there are limits to fuel supply response and the combustion control because the fuel mixes with air before entering the cylinder.

Advantages of MPFI :-

Gasoline engines work by inhaling a mixture of gasoline and air into a cylinder, compressing it with a piston, and igniting it with a spark; the resulting explosion drives the piston downwards, producing power. Traditional (indirect) fuel injection systems pre-mix the gasoline and air in a chamber just outside the cylinder called the intake manifold. In a direct-injection system, the air and gasoline are not pre-mixed; air comes in via the intake manifold, while the gasoline is injected directly into the cylinder.

Gasoline Direct Injection (GDI) :-

1. Upright straight intake ports for optimal airflow control in the cylinder.2. Curved-top pistons for better combustion.3. High-pressure fuel pump to feed pressurized fuel into the injector.

fig. Gasoline direct injection

The required technical features to incorporate GDI system are as follows :-

A fuel injector (may be 2) located in a throttle body assembly that sits on top of the inlet manifold. Fuel is sprayed into the inlet manifold from above the throttle valve, mixing with incoming air. Fuel quantity, how much fuel is injected is controlled by an ECU.

ECU

Fuel in

Inlet manifold

Air in

TB injector

fig. Electronic fuel injection

Electronic Fuel Injection (EFI) :-

An injector sprays fuel into the inlet manifold by use of a solenoid coil.

When the coil is switch on by the ECU, it pulls the armature/needle valve away from the nozzle, allowing pressurized fuel into the engine.

When the coil is not switched on, the spring pushes the armature/needle against the nozzle, no fuel is injected into the inlet manifold

Injectors are more precise and efficient than carburettors.

Electrical connector

Solenoid coilNeedle valve

Nozzle Armature Spring Fuel filter

Fuel in

Electronic Fuel Injector Operation :-