Research Of The Injection Law And Response Characteristics Of Injector For High-pressure Common-Rail Diesel Engine

Diesel engine power performance and fuel economy is better than gasoline engine's, therefore, it has been widely used in commercial vehicle, construction machinery and agricultural vehicle. But relatively high NOX and PM emissions limits the futher promotion of diesel engine. In order to control diesel engine emissions, all countries around the world have adopted stringent emissions regulations, which has become the driving force of diesel engine technological progress rather than an obstacle.The main pollutants in diesel engine emissions are NOX and PM. Because the in-engine emission control messures to reduce NOX or PM are conflicting, the technologies of reducing NOX and PM at the same time are a popular research field in the study of Diesel emissions control. In order to achieve the increasingly stringent emission regulations, it should maximize the effect of in-engine purification before using after-treatment technologies.Diesel engine performance is determined by the heat release rate. Designing the heat release rate according to diesel engine performance objectives is the development direction of the study on the heat release rate. When the combustion system and injection system are constant, the heat release rate is determined by the injection law.The high pressure common rail injection system can control the injection law flexibly, therefore, it is the best injection system to achieve the ideal injection rate. Multiple-injection is a advanced injection law, which is achieved by the high pressure common rail injection system. This dissertation has investigated different injection law on the impact of heat release rate, injection parameters on the impact of heat release rate and heat release rate on the impact of diesel engine performance based on diesel engine model built up using GT-POWER, with the methods of injecting the quantitative fuel into cylinder in different injection rates, under the same boundary conditions. The results as following: 1) Pilot injection strategy reduces the peak of the heat release of main injection. Two main injections strategy reduces the peak of the heat release of main injection to a lower lever, but it increases the heat release duration and delay the center of gravity of the heat release rate. 2) Changing injection timing changes the delay time of heat release of main injection, the heat release duration and the center of gravity of the heat release rate for single injection strategy. Increasing the amount of pilot injection reduces the delay time of heat release of main injection, the heat release duration, and advances the center of gravity of the heat release rate. Increasing the time gap between pilot and main injections increases the delay time of heat release of main injection and delays the center of gravity of the heat release rate, but has no effect on the heat release duration. After the main injection is divided into two injections, advancing the first main injection timing increases the delay time of heat release of main injection, the heat release peak of second main injection, and delay the center of gravity of the heat release rate, but has no effect on the heat release duration. Increasing the time gap between first and second main injections increases the heat release peak of second main injection and the heat release duration and delays the center of gravity of the heat release rate.High pressure common rail injection system is better than other injeciton systems in the injection law control, because of its good response characteristics. In order to improve the response charateristics in futher, this dissertation analyzed the internal structure of the injector of the second generetion Bosch high pressure common rail injection system and investigated the factors affecting the response characteristics of the injection system based on the injection system model built up using GT-FUEL. The results as following: Increasing the needle cone area reduces the valve opening time and increases the valve closing time. The maximum lift of the armature core has no effect on the response characteristics. Increasing the electromagnetic force has no effect on the response characteristics except the needle rising delay time. Increasing armature core spring preload has great effect on the needle declining delay time and a little effect on the the needle rising delay. Increasing control volume makes the response characteristics poorer. Increasing the inlet orifice of control volume increases the the valve opening time and reduces the valve closing time. Increasing the outlet orifice of control volume reduces the the valve opening time and increases the valve closing time. The response characteristics become better when common rail pressure is higher.