With the advancement of science and technology, the problem of pollution has gradually attracted people’s attention, especially the issue of energy saving and emission reduction. How to reduce nitrogen compounds and tiny particles is one of the important tasks to reduce pollution emissions. At present, diesel engines commonly used in my country are the main source of nitrogen compounds and particulate matter, so how to improve the combustion mode of diesel engines is the key to reducing emissions. The application of super multi-nozzle nozzles can make the fuel burn more fully and greatly reduce the emission of pollutants. It is of great significance to study the spraying rules of super-multi-nozzle nozzles.
About Super Multi-Nozzle
The super multi-nozzle nozzle is composed of a needle valve and a needle valve body, and its characteristics are shown in the following two aspects: the upper part of the needle valve body is provided with a double-layer nozzle hole; the spray angle of the upper nozzle is smaller than that of the lower nozzle.
Because the super-multi-nozzle nozzle adopts double-layer nozzle technology, the comprehensive flow area of the nozzle hole is greatly increased, so that all fuel enters the cylinder at the start, which is a prerequisite for premixed combustion of the diesel engine.
Also, because the upper injection angle of the super-multi-nozzle nozzle is smaller than the injection angle of the lower injection hole, the oil in the opposite direction meets in the cylinder, which can prevent the injection of oil from directly hitting the inner wall of the cylinder, and can also improve the deflection of the injection of fuel and promote diesel and oil mist. Mix evenly to form an oil and gas mixture of appropriate density, so that the diesel engine can achieve the purpose of homogeneous premixed combustion.
It is possible to compare the fuel nozzles currently in common use with the fuel nozzles with super-multi-holes. At present, the commonly used fuel nozzle has only one layer of injection holes, so the possibility that fuel injection directly collides with the inner wall of the cylinder is very high, which increases the emissions of hydrocarbons and carbon monoxide. The super multi-nozzle nozzle adopts a nozzle with double nozzle holes to avoid direct impact between the oil beam and the inner wall and promote the mixing of oil and gas, which is a prerequisite for premixed combustion.
Research on the fuel injection law of the super-multi-nozzle injector
By comparing the ordinary nozzle with the super multi-nozzle nozzle, the difference between the two nozzles under the influence of pressure, fuel injection control pulse width and injection amount is studied, and the injection rule of the super multi-nozzle nozzle is obtained, which provides a premixed combustion for diesel engines. data.
1 Overview of nozzle spray rule test
Over time, the fuel injection rate will also change. There is a certain rule between the time and the injection rate, which is the injection rule of the nozzle. By studying the injection rule curve of the nozzle, we can see: the start time and end time of the injection, the angle and the injection speed maintained during the injection process; whether there are secondary injection, intermittent injection, or needle valve jump. Whether the injection law meets the theoretical combustion process and heat dissipation law. When starting a diesel engine, it is impossible to directly measure the injection pattern of the fuel injector, but it can be measured indirectly. It can be achieved through a variety of indirect measurement methods, such as pressure generation method, stroboscopic collection method, honeycomb plate method, long tube method, etc. This article uses constant volume method for measurement. The test mechanism of the constant volume method is: inject v1 diesel into a constant volume container, the pressure change of diesel is p formula: P=K*v1/V
K-diesel volume change coefficient.
Given the diesel density and time, the fuel injection rate can be calculated by the following formula:
? Turbidity = V/K (dp/dt)
? Turbidity-fuel injection rate;-diesel density
In fact, there is a difference in the pressure change P of diesel, namely the injection rate. The advantage of the constant volume method is that the measurement process is simple and easy to understand, with good accuracy and stability.
2 Fuel system used in routine tests
The injection mode test of the injection hole uses a high-pressure common rail system. The pressure pump increases the pressure of the diesel, then enters the common rail system, and is controlled by the solenoid valve to inject fuel to the cylinder at the appropriate time. The pressure sensor in the common rail system measures the pressure of the diesel in the system, and transmits the information to the controlled equipment in time. The controlled equipment then issues commands to the pressure pump to ensure that the common rail system can be maintained within the appropriate pressure range. Because it is a pressure system controlled by electronic technology, fuel injection time, fuel injection pressure, fuel injection cycle, etc. Can be adjusted quickly and in a timely manner. It can be said that the high-pressure common rail system controlled by electronic technology is very suitable for the fuel injection rule test of the super multi-nozzle nozzle, and can easily adjust various factors affecting the fuel injection.
Analysis of fuel injection rules of super multi-nozzle injector
1 The pulse width of the injection control remains unchanged, changing the injection pressure of the injection pattern of the nozzle
In the experiment of fuel injection law, the rotation speed is controlled at 600 rpm, the pulse width of the fuel injection control is kept at 1 millisecond, and the fuel injection pressure is divided into 60 MPa and 110 MPa.
It can be seen from the experiment that at a lower injection pressure, that is, at a pressure level of 60 MPa, the injection rate of the ordinary nozzle and the super multi-orifice nozzle is basically the same during the experiment, but the maximum injection rate is slightly different. If the injection control pulse width is constant, the actual injection holding time is quite different, so the total injection amount is maximized in each cycle.
At relatively high injection pressures, ie 110 MPa, ordinary nozzles show many defects at this time. The spraying speed and comprehensive spraying volume of ordinary nozzles are much lower than those of super-multi-hole nozzles. The maximum comprehensive injection volume of the super multi-nozzle nozzle is about 70% more than that of the ordinary nozzle. In the case where the injection control pulse width is unchanged, the actual injection period is reduced by one cam angle compared to the ordinary nozzle. Therefore, it can be seen that the ultra-multi-nozzle nozzle is beneficial to the premixed combustion mode of the fuel engine.
After the above comparison, one cannot help asking why the super-multi-orifice nozzle shows these characteristics. When the injection pressure is low, why the difference between the ordinary nozzle and the super multi-orifice nozzle is not large, and when the injection control pulse width is fixed, the actual injection period measured is also different. Therefore, it is necessary to analyze the change between the actual passing area of the super-multi-nozzle nozzle and the ordinary nozzle and the lift of the needle valve. Tests show that when the lift of the needle valve is less than 0.08 mm, the minimum passage area of the surface of the needle valve and the seat of the needle valve controls the actual injection passage area of the nozzle. The actual fuel injection area is independent of the number of fuel injection holes and the diameter of the fuel injection holes. Therefore, in the initial stage of needle valve start-up, it can also be said that when the needle valve lift is less than 0.08 mm, the super-multi-orifice nozzle and the ordinary orifice nozzle have roughly the same spray pattern. However, if the needle valve lift exceeds 0.08 mm and gradually increases, in this case, because the super-multi-orifice nozzle has a larger passage area, there will be a higher injection speed, which can be achieved in a very short time The required diesel is quickly injected into the cylinder.
Due to the large flow area of the super multi-nozzle nozzle, when the needle valve is lowered, the pressure in the cylinder changes rapidly, and the needle valve seat also changes and accelerates. Therefore, during the decrease in the injection speed, the ultra-multi-hole nozzle decreases faster and the pressure continues to increase, so the injection speed is faster.
2 Fuel injection law under certain fuel injection quantity and fuel injection pressure change
In this experiment, a fixed diesel engine was used to compare the ultra-multi-orifice nozzle with the ordinary nozzle. Therefore, 16 nozzles, a super multi-orifice nozzle with a nozzle diameter of 0.16 mm, and 8 nozzles, a common nozzle with a nozzle diameter of 0.17 mm, have a constant injection volume and a rotation speed of 700 rpm in each cycle .
Experiment 1: First, set a lower injection volume in each cycle. Injection pressure is divided into 80 MPa, 96 MPa and 112 MPa.
It can be seen from the comparative experiment that in the case of relatively low fuel injection volume per cycle, no matter how high the fuel injection pressure is adjusted, the fuel injection rules of the super multi-orifice nozzle and the ordinary nozzle are basically the same. Data such as speed, maximum fuel injection speed, and fuel injection maintenance period are basically the same, except at the maximum pressure, the maximum fuel injection speed of the super multi-nozzle nozzle is slightly larger.
Experiment 2: When the injection volume per cycle was relatively high, the injection pressure was set to 80 MPa, 96 MPa, and 112 MPa.
When the injection quantity per cycle is relatively high, as the injection pressure continues to increase, the injection speed of the ultra-multi-hole nozzle will be greatly increased. At this time, the spray speed of the super multi-nozzle nozzle is much higher than that of the ordinary nozzle, and the spray maintenance time is also greatly shortened. This provides very favorable conditions for realizing premixed combustion and is of great significance for reducing pollutant emissions.
In summary, it can be concluded that since the needle valve remains closed for a long time in a complete fuel injection cycle, and the passage area between the needle valve and the needle valve seat controls the cross-sectional area of the actual fuel injection nozzle, so when When the amount of diesel fuel injected is in a relatively low range, there is no significant difference in the injection speed between the super multi-hole fuel injection nozzle and the ordinary fuel injection nozzle; when the injection pressure continues to increase, the super multi-hole nozzle nozzle is at the injection speed And the injection holding time is more advantageous, which is very beneficial to the actual premixed combustion of the engine. During the descent, compared with the ordinary fuel injection nozzle, the ultra-multi-hole injection nozzle drops faster, which can reduce the discharge of pollutants.