Working Principle of the Fuel System
The most widely used type of diesel generator is the inline piston type fuel injection pump.
1. Working principle of the fuel system
The straight-acting plunger type fuel injection pump is generally driven by the timing gear of the diesel engine's crankshaft. The piston-type fuel pump fixed on the fuel injection pump body is driven by the camshaft of the fuel injection pump. When the diesel engine is operating, the fuel pump sucks diesel from the diesel tank, removes water from the diesel through the oil-water separator, filters out impurities from the diesel through the diesel filter, and then delivers it to the fuel injection pump. After the diesel is pressurized and metered in the fuel injection pump, it is sent to the fuel injector through the high-pressure fuel pipe and finally sprayed into the combustion chamber through the fuel injector. At the front end of the fuel injection pump, there is an injection advance device, and at the rear end, it is integrated with the governor. The excess diesel supplied by the fuel pump and the return oil from the top of the fuel injector both return to the diesel tank through the return oil pipe. In some small diesel engines, the fuel pump is often not installed, and gravity supply is relied on (the position of the diesel tank is higher than that of the fuel injection pump).
2. Working Principle of Plunger-Type Fuel Injection Pump
When the plunger moves upward, the oil distributor sucks fuel into the plunger. When the plunger moves downward, the fuel is compressed and at the same time the fuel injector opens, spraying the fuel into the engine combustion chamber. The speed and stroke of the plunger are controlled by the governor, which can be adjusted according to the engine's load and speed to ensure the accuracy of the fuel injection volume and injection time.
3. Working Principle of Injector
The fuel injector is located at the top of the cylinder and is connected to the combustion chamber of the cylinder. When the fuel pump delivers high-pressure fuel to the fuel injector, the fuel injector will open the spray holes and the fuel will be sprayed into the cylinder through the spray holes. The structural design of the fuel injector is very crucial. It needs to be able to atomize the fuel into fine particles and spray them uniformly into the cylinder. The design of parameters such as the shape and size of the spray holes, and the fuel injection angle of the fuel injector will all affect the fuel injection effect and combustion efficiency. In summary, the working principle of diesel engine fuel injectors mainly includes the high-pressure output of the fuel pump, the spraying of the fuel injector, and the regulation of the fuel injection control device. These three components cooperate with each other to ensure that the fuel is sprayed into the cylinder at the appropriate pressure and time, thereby achieving the normal combustion process of the diesel engine. Only when the fuel injector works normally can the diesel engine operate efficiently and stably.
The working principle of diesel engine injectors is an important component in modern diesel engine technology. Its performance and stability directly affect the working efficiency and emission performance of diesel engines. With the development of science and technology, the structure and control methods of injectors are constantly being improved to meet the demands for more efficient and cleaner diesel engines. By continuously optimizing the working principle and structural design of injectors, the combustion process of diesel engines can be more precisely controlled, improving the combustion efficiency and economy of diesel engines, and also reducing environmental pollution.
4. Principle of Fuel Injection Control
The fuel injection control device regulates the fuel injection volume and duration by controlling the movement of the fuel injection pump. The fuel injection control device is usually driven by the cam or camshaft on the fuel injection pump and is achieved through mechanical or electronic control methods. The fuel injection control device can adjust the size of the fuel injection volume and the duration of fuel injection according to the working conditions of the engine, such as speed and load parameters, thereby achieving the best combustion effect and fuel economy.
(1) Oil circuit supply
The injector obtains fuel from the fuel tank or fuel pump through the fuel system. After filtration and pressure regulation, the fuel is sent into the oil circuit of the injector.
(2) Atomization of fuel injection
The injector sprays fuel at high speed through the nozzle and, through special design and shape, forms fine mist-like particles of fuel in the air, which is the fuel atomization process. This can increase the contact area between the fuel and air, thereby improving the combustion efficiency.
The plunger fuel injection pump is an efficient, precise and reliable fuel injection device. Its principle is to utilize the up-and-down movement of the plunger within the pump body to compress the fuel and then spray it out. It can meet the demands of engines with different loads and speeds, and is an indispensable and important component in modern engines.
The type of injector
The fuel for diesel generators is injected into the cylinder near the end of the compression process. The function of the injector is to atomize the fuel into fine particles and distribute them appropriately in the combustion chamber to form a good combustible mixture. Therefore, the basic requirements for the injector are to have a certain injection pressure, a certain spray range, a certain spray cone angle, good spray quality, and to stop the fuel injection quickly at the end of injection without dripping. Currently, closed-type injectors are commonly used in small and medium power diesel generators. When the injector is not injecting fuel, the spray hole is closed by a needle valve pressed by a strong spring, separating the combustion chamber from the high-pressure oil chamber. Before the fuel is injected into the combustion chamber, the spring force must be overcome to open the needle valve. That is to say, the fuel must have a certain pressure to start injection. This can ensure the quality of fuel atomization, quickly cut off the fuel supply, and avoid fuel dripping and leakage. This is particularly important during low-speed and low-load operation. There are mainly two types: hole-type and needle-type.
1.Orifice type fuel injector
The hole-type fuel injector is mainly used in direct injection diesel generators. Due to the fact that the number of injection holes can be several and the hole diameters are small, it can spray several jets with small cone angles and long ranges. Generally, the number of fuel injection holes is 2 to 8, and the hole diameters are 0.15 to 0.50 mm. The number and direction of the injection holes depend on the requirements for atomization quality of various combustion chambers and the arrangement of the fuel injector in the combustion chamber. For example, the combustion chamber of the G-type diesel generator for 6-cylinder engines is of the ω shape. The formation of the mixture is mainly achieved by directly spraying fuel into the combustion chamber space. Therefore, a 4-hole closed fuel injector is adopted. The hole diameter is 0.35 mm, the injection angle is 150°, and the needle valve opening pressure is 17.5 MPa. The injection shape is adapted to the ω-shaped combustion chamber.
2. Needle-type fuel injector
The needle-type fuel injectors are mostly used in swirl chamber type and pre-combustion chamber type diesel generators. The working principle of this type of injector is similar to that of the orifice type injector. Its structural feature is that the needle valve protrudes from the sealing cone surface at the lower end of the needle valve body in the form of a reverse conical shape. The needle protrudes outside the fuel injection hole, making the fuel injection hole a circular ring-shaped slit. Thus, during fuel injection, the injection will be in the form of a hollow conical or cylindrical shape. The size of the cross-section of the fuel injection hole and the shape of the injection angle depend on the shape and stroke of the needle valve. Therefore, the shape of the needle valve must be precisely machined.
Most of the common needle-type fuel injectors have only one or two injection holes. The diameter of the injection holes is generally 1 to 3 mm. Due to the large diameter of the injection holes, the fuel injection pressure is relatively low, usually ranging from 10 to 13 MPa. This facilitates manufacturing and processing. Meanwhile, during operation, the needle moves reciprocally in the injection holes, which can remove the carbon deposits in the holes and improve the reliability of the operation.