Mechanical fuel injection systems

In the year of 1927 Bosch brought the first mechanical fuel injection system for truck diesel engines. This made diesel engines familiar among people. In 1932 the complete fuel system consisting of nozzle holder assembly, nozzle, and filter system was introduced.

Jerk pump injection system

The jerk pump controlled system has a single reciprocating type pump for each fuel injection. The pump is separately mounted on the engine block. The pump is driven by an accessory shaft. The pump plunger has a constant stroke with a variable effective stroke. The injector is connected to the pump by suitable tubing.

The injector is opened by lifting the needle valve automatically by fuel pressure. When the fuel pressure in the system falls below a certain value, the spring loaded injector needle valve terminates fuel injection.

Multi cylinder in line pump unit is produced by a number of manufacturers under license from ROBERT BOSCH Company of Germany. It is characterised by having one pump with a delivery valve and a injector for each cylinder in the engine.

Distributor fuel injection system

There are several types of distributors fuel injection system. One type provides a high pressure metering pump with a distributor which delivers fuel to the various cylinders. Another design provides a low pressure metering and distributor. High pressure needed for injection is provided by the injection nozzles which are cam operated.

In these systems, the metered fuel is directed to the proper cylinder by the rotating distributor with drilled passage ways. The distributor is driven by the camshaft of the engine.

Distributor pump system is used by General motors, Volkswagen, Cummins and others. It is characterised by having one pump to supply fuel to outlets leading to each engine cylinder.

Constant pressure common rail system

The constant pressure common rail system was developed by M/s.Vickers company. This system consists of a high pressure pump which distributes fuel to a common rail or header to which each injector is connected. A spring loaded bypass valve on the header maintains a constant pressure of 330 to 530 kscm in the system and returns all excess fuel to the supply tank.

The fuel injectors are operated mechanically. The metering and timing of fuel injection are accomplished by the spray valve. The amount of fuel injected into the cylinders is controlled by the lift of the needle valve in the injector. The duration of injection depends on the length of time the valve is off its seat.

The quantity of fuel injected depends on the duration, size and number of holes in the nozzle tip and fuel pressure and air pressure in the cylinder.

The nozzles must therefore be closely matched to ensure equal distribution among the cylinders. The common rail system tends to be self-governing. That is if the speed falls, an increased quantity of fuel is injected. Remember, supply pressure is independent of engine speed.