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Working Principle Of Pump Nozzle Diesel Engine

Jun 16, 2023 | Technical Literature | 0 comments

The electronically controlled pump nozzle injection system for diesel generators is a new type of fuel injection system that directly integrates the plunger coupling (high pressure pump) and the fuel injector coupling in one housing. It is equivalent to canceling the high-pressure oil pipe in the pump-pipe (common rail)-injector system, avoiding the problems of high pressure resistance and high pressure sealing of the high pressure common rail injection system. Because the pump nozzle type injection system has no high-pressure oil pipe, the high-pressure fuel generated by the high-pressure pump pumps oil directly into the pressure-bearing ring groove of the injector through a short path to realize the fuel injection process of the diesel generator.

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Features of electronic control technology

Diesel engine electronic control technology has many similarities with gasoline engine electronic control technology. The whole system is composed of three parts: sensors, electronic control units and actuators. Among the sensors used in electronically controlled diesel engines, such as speed, pressure, temperature, etc. The sensor and accelerator pedal sensor are the same as the gasoline engine electronic control system. The electronic control unit is also very similar in terms of hardware, and there are also similarities in the software of the vehicle management system. Gasoline engine electronic control technology has matured abroad and has a high degree of commercialization, so most sensors and electronic control units are not difficult points, nor are diesel engine electronic control technology difficult points. Diesel engine electronic control technology has two obvious features: one is that its key technology and technical difficulties lie in the diesel engine injection electronic control actuator; the other is the diversification of diesel engine electronic control injection systems.

Diesel engine is a power machine with relatively high thermal efficiency. It uses a high-pressure fuel injection pump (including an advancer) and a fuel injector to inject an appropriate amount of fuel into the combustion chamber of the diesel engine at an appropriate time and in an appropriate space, so as to create the best mixture of fuel and air and the most favorable combustion conditions to meet the requirements of diesel engines in terms of power, torque, speed, fuel consumption rate, idle speed, noise, emissions, etc. The fuel injection of diesel engines has the characteristics of high pressure, high frequency, and pulsation, and its injection pressure is as high as 60-150MPa, or even 200MPa. It is hundreds of times, thousands of times that of gasoline injection. It is much more difficult to implement electronic control of fuel injection quantity for high-pressure fuel injection system. Moreover, diesel injection has high requirements on the accuracy of injection timing, and the angular position relative to the top dead center of the piston of a diesel engine is far more accurate than that of a gasoline engine, which leads to a much more complicated electronically controlled actuator for diesel injection. Therefore, the key and difficult point of the diesel engine electronic control technology is the diesel injection electronic control actuator, that is, the electronic control diesel injection system. The main control quantity is the fuel injection quantity and fuel injection timing.

Today’s gasoline engine electronic control technology has matured internationally, and tends to a relatively single mode, that is, multi-point injection. Electronically controlled carburetors have been eliminated, and the application of single-point injection has been greatly reduced. Some companies are researching multi-point in-cylinder injection. In the era of mechanical control of diesel engines, there have already been systems with completely different structures such as in-line pumps, distribution pumps, pump nozzles, and single-cylinder pumps. Each system has its own characteristics and scope of application, and each system has many different structures. The executive mechanism implementing the electronic control technology is relatively complicated, so the diversification of the diesel injection system has been formed.

Pump nozzle type injection system structure

As the name suggests, the pump nozzle is the combination of the fuel injection pump and the fuel injector to save the high-pressure fuel pipe and obtain a fuel system with high injection pressure. Since there is no high-pressure fuel pipe, the influence of pressure wave and fuel compression in the long high-pressure fuel pipe can be eliminated, and the high-pressure volume is greatly reduced, so that the required high injection pressure can be generated. The control of fuel injection quantity and fuel injection time is controlled by solenoid valve, and the control accuracy is greatly improved.

The structure of the electronically controlled pump nozzle is mainly composed of a pump nozzle body, a driving mechanism, a control valve and a solenoid valve. The pump nozzle body integrates the fuel injection pump and the fuel injector, and cancels the spiral groove on the plunger of the mechanical fuel injection pump for controlling the fuel supply. The injection timing and injection quantity are controlled by the high-speed solenoid valve to control the opening moment and opening duration of the pump nozzle inlet valve. Because this electronically controlled pump nozzle injection system installs the fuel injection pump plunger, fuel injector and electromagnetic control valve (composed of plunger valve, baffle, etc.) It is very small, so it allows higher injection pressure (currently it has reached more than 200MPa), and at the same time reduces the sealing surface and sealing joint, so the reliability is good. However, a special driving mechanism is needed to drive, and the driving mechanism is composed of a camshaft, a rocker arm and a tappet, etc., so the structure is complicated. The driving camshaft is driven by the timing gear of the crankshaft, and the oil supply timing must be ensured during installation.

Pump nozzle type injection system working principle

In the pump nozzle system of the diesel generator, the closing moment of the detected solenoid valve is used as the feedback signal to realize the feedback control of the injection process. The closing time of the solenoid valve can be determined by detecting the voltage or current waveform of the solenoid valve coil, without additional sensors. When the voltage waveform is used as the detection signal, the current flowing through the solenoid valve coil needs to be adjusted with a regulator so that the current in the solenoid valve coil remains unchanged after reaching a certain set value. In this way, when the solenoid valve power supply is turned on, the spool starts to move, and the voltage at both ends of the solenoid valve coil increases accordingly; when the spool moves to the limit position and stops moving, the coil voltage suddenly drops to a level that can only maintain the current constant level. This voltage drop can be easily measured. In order to improve the response speed of the solenoid valve, in addition to adopting short-stroke, small-mass, pressure-balanced valves and flat disc-shaped valve core structures, it is also necessary to reduce the inductance of the coil to ensure that the current can flow quickly enough under very low power supply voltage. speed reaches saturation. With this method, the accuracy of detecting the closing moment of the solenoid valve can reach ±0.25° (CA). At the same time, this method can eliminate the fluctuation of fuel supply and fuel injection timing caused by the change of power supply voltage.

Features of the pump nozzle

Compared with the high-pressure common rail injection system, the pump nozzle of the diesel generator cancels the high-pressure oil pipe, and integrates the plunger pump and the fuel injector, which simplifies the system and avoids the problem of high-pressure sealing. However, due to the setting of a special drive mechanism, the structure is complicated, and the injection pressure changes during the injection process. The injection law is controlled by the pump oil law, and this pump oil law depends on the cam line and its working section.

Generally, the fuel injection pressure of the nozzle of the electric control pump is as high as 2050bar, and because of the use of the electric control system, the system control is flexible, and the controllable pre-injection can be realized through the two actions of the solenoid valve, which greatly reduces the noise and vibration, and improves the emission. In addition, because the electronic control pump nozzle and the driving device are installed on the cylinder head, the engine structure is compact and the shape is reduced, and the low-pressure oil inlet and return passages can be set on the cylinder head and other new-generation diesel fuel injection systems. Compared with the common rail system, the biggest feature of the electronically controlled pump nozzle is that it is easy to realize high-pressure fuel injection. However, due to its structural characteristics, especially the many high-pressure parts that need to be sealed, the high pressure that the common rail system can achieve is limited. Secondary injection and other aspects are not as free as the common rail system.

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