Characteristics of Plunger Type Fuel Injection Pump for Diesel Engine 1

In order to gain a deeper understanding of the working principle and characteristics of plunger fuel injection pumps, Dingbo Electric will explain one by one how this type of fuel injection pump meets the working requirements of diesel engines.

(1) The timing of fuel supply ensures that the injection advance angle is an important parameter affecting the performance of diesel engines, and different types of diesel engines have different requirements for the size of the injection advance angle. The fuel injection pump must strictly ensure that it starts supplying fuel at the specified time.

Fuel injectors are generally compressed Inject fuel into the combustion chamber in front of the top dead center. Due to the fact that the fuel injector extends into the combustion chamber, the injection timing is difficult to observe and measure under normal conditions. Therefore, only the fuel supply advance angle is specified for each type of diesel generator set diesel engine. The so-called fuel supply advance angle refers to the period from the time when the fuel injection pump starts supplying fuel to the high-pressure fuel pipe to the compression top dead center, expressed as crankshaft angle 0 (CA). When rotating the crankshaft, observe the oil level at the outlet of the oil valve at the same time. The moment when the oil level begins to fluctuate is the start of oil supply.

From the working process, it can be seen that the oil supply starts when the upper end face of the plunger completely covers the oil inlet hole, and the corresponding crankshaft angle at this time is the oil supply advance angle. In fact, this angle mainly depends on the relative position of the gears on the camshaft of the fuel injection pump and the crankshaft drive gear. Usually, there are markings on these two gears, and when installing the fuel injection pump onto the body, the markings must be aligned.

For multi cylinder fuel injection pumps, if the camshaft position of the fuel injection pump is fixed and there are differences in the fuel supply timing of some cylinders, it is necessary to adjust the adjustment mechanism of each sub pump. The methods of adjustment vary depending on the structure.

(2) The adjustment of fuel supply quantity: The amount of diesel fuel supplied by the fuel injection pump to the injector mainly depends on the effective stroke of the plunger and the diameter of the plunger, which is equal to the distance from the lower edge of the inclined groove at the return hole to the lower edge of the return hole when the plunger starts to press the oil (ha in Figure 5-6). The longer the distance and the longer the effective stroke, the greater the fuel supply, and the length of this distance can be changed by rotating the plunger. The fuel control mechanism adjusts the fuel supply by rotating the plunger according to the load of the diesel engine, making it suitable for the load.

There are two forms of fuel control mechanisms: gear bar type and fork type.

The gear rod oil control mechanism is currently widely used, with a strip-shaped protrusion at the lower end of the plunger extending into the gap of sleeve 2, while sleeve 2 is loosely fitted outside of plunger sleeve 5. The upper part of sleeve 2 is locked with a fixing screw 6 to an adjustable gear ring 3, which meshes with the gear rod 4. Move the gear rod 4 to change the fuel supply. When adjusting the fuel supply of a certain cylinder, first loosen the fastening screw 6 of the adjustable ring gear 3, then rotate the sleeve 2 to drive the plunger to rotate a certain angle relative to the ring gear, and then fix the ring gear. This type of oil control mechanism has smooth transmission and reliable operation, but its structure is relatively complex.

The fork type oil control mechanism mainly consists of an oil supply rod 5, an adjusting fork 10, and an adjusting arm 1. When the fuel supply rod 5 moves, the adjustment fork 10 fixed on the rod immediately moves the adjustment arm l, causing the plunger 2 to rotate together, thereby changing the fuel supply amount. The plunger 2 can greatly change the fuel supply by only rotating a small angle, so the fork type fuel control mechanism is very sensitive to adjusting the fuel supply. Its structure is simple, easy to manufacture, and suitable for small and medium-sized diesel engines.

When the plunger diameter is constant, the longer the effective stroke, the greater the fuel supply, and the longer the fuel injection duration. If the fuel injection duration is too long, the performance of the diesel engine will deteriorate due to insufficient combustion of the fuel injected later on. Therefore, diesel engines with large fuel supply must choose larger plunger diameters.

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