Fuel injection pump
The pump produces high pressure necessary for fuel injection, in the order of 100-400 bar. The function of the fuel injection pump is to measure and deliver the correct quantity of fuel required for different loads and speeds. The Figure shows the working principle of a fuel injection pump. This is most commonly used in diesel engines.
1) Plunger The plunger reciprocates inside a pipe called barrel. The plunger can also be rotated by rack and pinion arrangements. The linear movement of the rack causes the pinion to rotate. At the same time the plunger can reciprocate (move up and down) inside the barrel by means of a cam.
The plunger has a vertical rectangular slot. The plunger also has a deep helical (spiral) groove on its outer surface.
2) Barrel The barrel has two parts, the supply port and spill port. These ports are opened and closed the moving plunger. It is through the supply port that the diesel enters, and any fuel that is not delivered through the delivery valve is rejected through the spill port and is circulated back in to the system.
3) Delivery valve The fuel delivery valve is seated by the force of the springs through this valve that the diesel is sent out through the fuel passage and finality in the fuel injector
Simplified sketch of a fuel pump is shown in Figure. It consists of a plunger which moves up and down in the barrel by the cam and spring arrangement provided for pushing and lowering the plunger respectively. The fuel oil is highly filtered by means of oil filter before the barrel entering the pump. The amount of fuel delivered and injected into the engine cylinder depends upon the rotary position of the plunger in the barrel. The plunger is designed so that the correct amount of fuel is delivered to the injector.
When the plunger is at the bottom of its stroke, fuel enters the barrel through the inlet port. As the plunger rises it comes opposite the spill port. Then the fuel escapes down the groove and out through the spill port so that injection ceases. The plunger can be made to rotate in the barrel and therefore more fuel is injected. When the plunger is rotated so that the groove is opposite to the spill port, no fuel at all is injected and thus the engine stops.
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