Indirect fuel delivery system is one where traditional method of fuel injection system is used. This type of system is used mostly in gasoline engines. In indirect fuel injection system, the air/fuel mixture is mixed outside the combustion chamber.

In an indirect injection diesel engine, fuel is delivered into a prechamber off the combustion chamber and then, air/fuel mixture is spreads into the main combustion chamber. The prechamber is carefully designed to supply adequate amount of mixing of fuel with the compression-heated air. Whereas in a gasoline engine, air/fuel mixture is mixed in the carburetor and is sent to the combustion chamber. In this article, we are going to discuss the working and benefits of indirect fuel injection system.

Working of an Indirect fuel delivery system

  • In an indirect injection diesel engine, fuel is delivered into a prechamber off the combustion chamber, where combustion begins and the mixture enters the main combustion chamber due to turbulence created.
  • In the main combustion chamber power stoke happens at the end of the compression stroke which is used to run the vehicle. This system allows smoother, quieter running, and injector pressures can also be lowered.
  • The prechamber has the disadvantage of higher heat loss due to the engine’s cooling system and restricts the combustion resulting in fall in efficiency by 5-10% in comparison with a direct injection engine.
  • The indirect fuel delivery system requires some form of cold-start device like glow plugs.

Indirect injection systems were used widely in small-capacity high-speed diesel engines. Indirect injection engines are inexpensive to build.

Advantages of direct fuel delivery system

  • Direct fuel delivery system has a high rate of swirl over a wide range of engine speeds.
  • It does not require any expensive ultra high pressure injection system.
  • The construction of indirect fuel injection system is cheaper than the direct injection system.
  • Higher engine speeds can be reached, since burning continues in the prechamber.
  • Less chances of fuel injector blockage due to self cleaning pintle injectors.

Indirect injection engines vs direct injection engines

  • Indirect injection engines are simple and are easy for maintenance since the injection systems are mechanical and there are no computer controls or sensors to malfunction.
  • Indirect injection engines produce less noise than direct injection engines.
  • Many newer direct injection engines are equipped with intake baffles and advanced injection controls to reduce noise.
  • Direct injection is more efficient than indirect injection due to the higher level of atomization of the fuel.
  • Indirect injection engines have much higher compression ratio than direct injection engines.
  • Indirect injection engines are operated at much lower fuel injection pressure than the direct injection engines.
  • The injectors for indirect injection engines are much cheaper than those for direct injection engines.