24 February 2016

Fuel injection system in diesel engine

The fuel injection system is the most important component of CI engine operation. The system of injection must fulfil the important task of initiating and controlling the process of combustion.

Injection system main purpose is to the preparation of the combustible charge and is same as carburetion.

  • Fuel injection pump such as elevated pressure to high pressure
  • A high-pressure pipe which sends fuel to the injection nozzle
  • Injection nozzle that injects the fuel into the cylinder
  • Feed pump that sucks fuel from the fuel tank
  • Fuel filter which filtrates the fuel
The diesel fuel injection system consists of following below. 

Requirements of an injection system :

  • Accurate metering of the fuel injected per cycle
  • Timing the injection of the fuel  correctly
  • To obtain maximum power, fuel efficiency 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. 

By varying air pressure, the rate of fuel admitted into the combustion chamber can be controlled.

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

The fuel valve is opened through a mechanical connection operated by the camshaft that controls the injection timing. 

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

Solid injection system : 

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

It is also termed as a mechanical injection. 

Solid injection system can be classified into four types listed below. 
  • Individual pump & injector
  • Unit injector system
  • Common rail system
  • Distributor system