Construction of Plunger Type Fuel Injection Pump for Diesel Generator Set

The fuel injection pump (also known as the high-pressure fuel pump) is one of the most important components in the fuel supply system of a diesel engine. Its function is to deliver a certain amount of diesel at a certain high pressure to the injector at a specified time according to the working requirements of the diesel engine. The basic requirements for fuel injection pumps mainly include the following aspects.

(1) Strictly follow the prescribed fuel supply time to start fuel supply and have a certain duration of fuel supply.

(2) Supply the corresponding amount of fuel according to the load of the diesel engine. When the load is high, the fuel supply increases; When the load is low, the fuel supply should be correspondingly reduced.

(3) According to the form of diesel engine combustion chamber and the way of mixture formation, the fuel injection pump must supply a certain pressure of diesel fuel to the injector to obtain good spray quality.

(4) The start and end of fuel supply require quick and decisive measures to prevent fuel injector dripping or abnormal injection after fuel supply stops, which may affect the service life of the injector.

For the fuel injection pump of multi cylinder diesel engines, it is also required that the fuel supply sequence of each cylinder should comply with the selected engine firing sequence, and the parameters such as fuel supply timing, fuel supply quantity, and fuel supply pressure of each cylinder should be as similar as possible to ensure the uniformity of each cylinder's operation. There are many structural forms of fuel injection pumps, which can be roughly divided into four categories according to their different operating principles: plunger fuel injection pumps, distributed fuel injection pumps, pump nozzle and PT pumps. At present, the most widely used in diesel generator sets is the plunger fuel injection pump. This fuel injection pump has a simple and compact structure, is easy to maintain, is reliable to use, and has precise fuel supply adjustment.

The basic structure of a plunger fuel injection pump is to use the reciprocating motion of the plunger in the plunger sleeve to suction and pressure oil. The plunger and plunger sleeve are collectively referred to as a plunger pair (or plunger pair), and each plunger pair only supplies oil to one cylinder. According to their different constructions, plunger fuel injection pumps are divided into two types: single unit and integral. All parts of the single unit fuel injection pump are installed in the pump body, and the fuel injection pump cam is usually made on the same shaft as the valve cam. The governor is installed inside the body. This type of fuel injection pump is mainly used for single cylinder or two cylinder diesel engines. The integral fuel injection pump is a master cylinder composed of several sets of pump components (sub pumps) installed together in a pump body, driven by a camshaft of the fuel injection pump. A plunger type fuel injection pump is usually composed of a pump body, a pump oil mechanism, an oil quantity control mechanism, and a transmission mechanism.

The pump oil mechanism is the main body of the fuel injection pump, also known as the sub pump in multi cylinder pumps. The diagram shows the structure of a sub pump. The pump oil mechanism is mainly composed of plunger fittings (plunger and plunger sleeve) and outlet valve fittings (outlet valve and outlet valve seat). The plunger is a smooth cylinder with a slanted groove milled at the upper part, in which radial holes are drilled and connected to the central axial hole. The lower part of the plunger is fixed with an adjusting arm, which can be used to rotate the plunger. There are two small holes drilled at different heights on the plunger sleeve, the upper one is the fuel supply and speed control system inlet hole, and the lower one is the return hole. Both holes are connected to the low-pressure oil chamber in the pump body. There is an oil outlet valve 3 on the upper part of the plunger, which is pressed against the oil outlet valve seat by the oil outlet valve spring. The lower end of the plunger is in contact with the pad installed in the roller body. The plunger spring 8 pushes the plunger downwards through the spring seat and keeps the roller 12 in contact with the cam on the camshaft. The camshaft of the fuel injection pump is driven by the crankshaft. For a four stroke diesel engine, the crankshaft rotates twice and the camshaft of the fuel injection pump rotates once.

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