Fuel pump and metering devices
The fuel injection system is extremely important for the efficient operation of the engine.
4 functions are to be satisfied :-
1.Deliver an accurately measured quantity of fuel to each cylinder regardless of load.
2.Deliver the fuel at the correct time at all loads with rapid opening and closing of fuel injection valve.
3.Inject the. Fuel at the controlled rate.
4.Atomise and distribute the fuel in the cylinder
Broadly there are three types of fuel injection modes :-
A)Jerk injection (Bosch Type/ Valve control system )
B)Common rail (Smokeless Injection )
C)Timed injection ( P & T )
Jerk Injection :- This is the most common process employed in modern marine Engines.The pump consists of cam operated plunger in a barrel with very fine tolerances.
The hydraulically compressed fuel pressurize the needle valve in the injectors lift and allow fuel into the cylinder.
The second type of pumps are valve controlled type.
Common rail injection system :-
Here, a single pump deliver fuel into a common pressure manifold.
Fuel lines separately delivers fuel into individual units 1500 – 2000 bar pressure through control fuel injectors.Control may be with electronic ,hydraulic or piezo electric devices.
Here ,the fuel pump delivers to the timing valve and thence to the spring loaded injector.No lost motion clutch is required as the cam does not drive the pump plunger but operates a valve.
The cam is symmetrical w.r.t engine dead centre.