Types of fuel injection system

In a constant-pressure cycle or diesel engine, the air is compressed in the cylinder and then fuel is injected into the cylinder by means of a fuel injection system. For proper running and good performance from the engine, fuel injection is needed. There are different types of fuel injection system are used. Let we discuss that different kind of fuel injection system which is used.

Mainly fuel injection system classified in two categories:

  • Air injection system 
  • Solid injection system 
The solid injection system is again classified below :
  • Individual pump and nozzle system 
  • Unit injector system 
  • Common rail system 
  • Distributor system 
Now let we discuss the above all types in detail :
  • Air injection system :
Air injection is a method of reducing exhaust emissions by injecting air into each of the exhaust ports of an engine so that air mixes with the hot exhaust and oxidizes HC and CO.

In this system, fuel is forced into the cylinder by means of compressed air. It is little used nowadays because it requires a bulky multi-stage air compressor. This causes an increase in engine weight and reduces the brake power output further.

Manufacturers use this system by a different name :

Here are a list of the different companies and their respective name for using this system :
American Motors call it Air Guard 
Chrysler names it Air Injection System
Ford calls it Thermactor Air Injection System and 
General Motor names it Air Injector Reactor (AIR) 

How it works?

The air injection smog pump pushes air into the exhaust system right after the exhaust manifold, to help intercept and burn those unburnt fuels. It is critical to help cars achieve government emissions standards. 
  • Solid injection system :
It is the injection of atomized fuel oil into the combustion chamber of a diesel engine under the pressure of the liquid fuel itself.
The solid injection system is also called the airless mechanical injection system.

In this system, the liquid fuel is injected directly into the combustion chamber without the aid of compressed air. Hence, it is called airless mechanical injection system.

Now we can see the different types of injection in solid injection system in details :
  • Individual pump and nozzle system :
In this system, each cylinder is provided with one pump and one injector.

Individual pump and nozzle system
As per we can see in above figure this arrangement a separate metering and compression pump is provided for each cylinder. The pump may be close to the cylinder or they may be arranged in a cluster. The high-pressure pump plunger is actuated by a cam, and produce the fuel pressure necessary to open the injector valve at the correct time.
The amount of fuel injected is depends on the effective stroke of the plunger.

  • Unit injector system :
In this system the pump and the injector nozzle are combined in one housing. Each cylinder is provided with one unit injectors. Fuel is brought up to the injector by a low pressure pump where at the proper time a rocker arm actuates the plunger so it injects the fuel into the cylinder.
By the use of effective stroke of the plunger the amount of fuel injected is regulated.

  • Common rail system :
In this system HP pumps supplies fuel, under high pressure, to a header. High pressure in the header forces the fuel to each nozzles located in the cylinders of this system. At that time, a mechanically operated valve allows the fuel to enter the proper cylinder through the nozzle. By varying the length of the push rod stroke the amount of fuel entering the cylinder is regulated.

  • Distributor system :
In this system the pump which pressurizes the fuel also meters and times it. The fuel pump after metering the required amount of fuel supplies it to a rotating distributor at the correct time for supply to each cylinder. The number of injection strokes per cycle for the pump is equal to the number of cylinders used in this system.

All of the above solid injection system comprise mainly of the following components :
  • Fuel tank.
  • Fuel feed pump to supply fuel from the main fuel tank to the injection system.
  • Injection pump to meter and make pressurize fuel for injection.
  • Governor to ensure that the amount of fuel injected is in accordance with variation in load.
  • Injector to take the fuel from the pump and distribute it in the combustion chamber by atomizing it into fine droplets.
  • Fuel filters to prevent dust and abrasive particles from entering the pump and injectors so that minimizing the wear and tear of the components.
You can also check it out the requirements of an fuel injection system.