This is another important part of fuel injection pump system in diesel engine.It is used in the individual system of a solid injection and consist of a plunger driven by a cam and tappet mechanism at the bottom.The plunger reciprocates in the barrel.The quantity of plunger varies with the number of cylinder in the engine.The plunger has a rectangular vertical groove which extends from the top to another helical groove.The delivery valve can be lifted off its seat under the pressure of liquid fuel and against the force of the spring.The passage is connected to the fuel atomiser.
When the plunger is at the bottom of its stroke and supply as well as spill ports are uncovered,oil from fuel feed pump,after filtration is forced into the barrel.The supply and the spill port are sealed at certain stage when the plunger is pushed away with the help of cam and tappet mechanism which is provided at bottom.
During the further movement of plunger the fuel above it gets compressed and the high pressure developed,lifts the delivery valve off its seat and fuel starts flowing through the passage to the atomiser.As the plunger rises up still further,at a particular moment the helical groove connects the spill port through the rectangular vertical groove,to the fuel in the upper part of the plunger.
Consequently there is a sudden pressure drop due to which the delivery valve falls back on its seat under the force of spring.This increases the volumetric capacity of the delivery system resulting in sudden pressure drop in the delivery pipe.Thus the discharge from nozzle of the injector is cut off suddenly and the fuel is prevented from dribbling into the cylinder even after the injection ceases.The cycle is repeated frequently.
During each stroke of plunger,the duration of the delivery is more or less,according to the spill port is made to communicate,earlier or later,with the high pressure fuel in the upper part of the barrel.This depends up on the position of the helical groove which can be changed by rotating the plunger with help of rack.
When engine at full load,the position of the helical groove on the plunger is kept below the passage.At partial load or normal delivery,the plunger is rotate to a position near by passage,in which the delivery takes place for shorter period.When the engine is stopped,the plunger is rotate to the position where helical groove is opposite to the passage,in which rectangular slot is in line with the spill port.There is no pressure built up above the top of the plunger,the delivery valve is not at all lifted and hence no delivery of fuel to the atomiser takes place.
The bore of the pump ranges in eight sizes from 5 mm to 10 mm but the stroke of the plunger is standardised at 9 mm.
I hope,with this details you can open and see the actual fuel injection pump without any doubt.
You may also interested in following........
Important Components Of Fuel Injection System For Diesel Engine.
Various Parts And Its Function In Internal Combustion Engine.
How Fuel Is Supplied In Diesel Engine?