METHODS OF FUEL INJECTION USED in C.I ENGINES ( DIESEL ENGINES)

There are two methods of fuel injection used in C.I Engines :

a) Air Injection System

b) Air-less or solid Injection

A) AIR INJECTION SYSTEM :

In this method, initially air is compressed to a very high pressure by means of compressor. The fuel was metered and pumped to the nozzle. which was also connected to a source of high pressure air. When the nozzle was opened, the air would sweep the fuel into the engine and deliver a well atomized spray. This method is not used now - a -days because of complicated and expensive system.

B) AIRLESS OR SOLID SYSTEM :

This method has greatly replaced the air injection method. The fuel under pressure is directly injected into the combustion chamber in atomized state. It requires a pump to deliver the fuel at high pressure ( as high as 300bar abs). It may be further classified into the following two commonly used systems.

i) Common Rail System

ii) Individual Pump System

i) COMMON RAIL SYSTEM :

Multi-cylinder high pressure pump is used to supply the fuel at a high pressure to a common rail on header. A metered quantity of fuel is supplied to each cylinder from the rail.

ii) INDIVIDUAL PUMP SYSTEM :

In this system, each cylinder of the engine is provided with an individual injection valve, a high -pressure pump and a metering device. It is quite compact but since at all operating loads and speeds each pump in this unit should very precisely match its companions, extremely close tolerances are required during manufacturing. Therefore, it involves higher costs.

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