1 February 2017

What is fuel injection system

Fuel injection system in a diesel engine : 

Fuel-injection system is most vital the component in the working of CI engines.

The injection system has to perform the important duty of initiating and controlling the combustion process.

Injection system main purpose is to the preparation of the combustible charge and is same as carburetion.
The diesel fuel injection system consists of :
  • Fuel injection pump - pressurises fuel to high pressure
  • High-pressure pipe - sends fuel to the injection nozzle
  • Injection nozzle - injects the fuel into the cylinder
  • Feed pump – sucks fuel from the fuel tank
  • Fuel filter - filtrates the fuel

Requirements of and injection system :
  • Accurate metering of the fuel injected per cycle
  • Timing the injection of the fuel  correctly
  • To obtain maximum power, fuel economy and clean-burning
  • Proper control of the rate of injection
  • Proper atomization of fuel
  • A rapid mixture of fuel and air
  • Uniform distribution of fuel droplets 
  • To supply equal quantities of fuel
  • No lag during the beginning and end of injection

Classification of Injection system :
  •  Air injection system 
  • Solid injection system

Air injection system:

Fuel is forced into the cylinder by means of compressed air to very high pressure. 

The rate of fuel admit into the combustion chamber can be controlled by varying the pressure of air. 

The fuel is metered & pumped to the fuel valve by a camshaft is driven fuel pump. 

The fuel valve is opened by means of a mechanical linkage operated by the camshaft which controls the timing of injection. 

The fuel valve is also connected to a high-pressure airline fed by a multi-stage compressor which supplies air at a pressure of about 60 to 70 bar.

Solid injection system:

Fuel is injected directly into the combustion chamber without primary atomization and is termed as solid injection. 

It is also termed a mechanical injection. 

Solid injection systems can be classified into four types: 

Fuel injection system in a petrol engine : 

Fuel-injection system is commonly used in CI engine.

In present gasoline injection system is also coming in SI engines because following the drawbacks of the carburetion.
  • Non-uniform distribution of mixture in multi-cylinder engines.
  • Loss of volumetric efficiency.
A gasoline injection system eliminates all these drawbacks.  

The injection of fuel into SI engine can be done by the following methods :
  • Direct injection of fuel into the cylinder
  • Injection of fuel close to the inlet valve
  • Injection of fuel into the inlet manifold
There are two types of the injection system of gasoline systems :
  1. Continuous Injection: In continuous injection, fuel is continuously injected. 
  2. Timed Injection: In timed injection, fuel is injected only during induction stroke. Injection timing is not a critical factor in SI engines.

Advantages of fuel-injection in an SI engines :
  • Increased volumetric efficiency
  • Increase thermal efficiency
  • Low exhaust emissions
  • High-quality fuel distribution