Study On Start Of High Pressure Common Rail Diesel Engine

The tendency of automotive power is moving towards the diesel engine in these years. Currently, in the United States, Europe and Japan, the rate of diesel engine used on heavy-duty vehicle and commercial vehicle is near 100%. The development of diesel cars is also in an extraordinary speed, but there are some inherent disadvantages in diesel engine. Therefore, high pressure common rail fuel injection technology is introduced in order to solve these problems. The emission during start process greatly influences the realization of emission goal. Especially in EuroⅢand EuroⅣemission regulations, besides lower emissions requirement, test procedures are also updated. The first 40 seconds without taking emissions measurement originally must be taken into consideration now. It is important to control the emissions during start process for the diesel engine consequently. Otherwise, instability of diesel engine during start process must be improved as a serious problem that all diesel vehicle manufacturers are facing. High pressure common rail diesel engines also have these problems during starting process,so it is necessary to study on start of the high pressure common rail diesel engine.In this thesis, with the engine 4dc produced by DaLian diesel engine works, which is matched with Bosch high pressure common rail system, and INCA calibration software produced by ETAS company, a lot of experiments were done to improve the start performance of the high pressure common rail engine.The main work in this thesis includes:1. Bosch high pressure common rail system was studied, and the high pressure common rail system in the experiment was assembled.2. The test-bench of start was designed and made.3. The influence of end symbol rotate speed of start to start time and HCemission was analysed and researched through experiments.4. The influence of high pressure common rail system's control parameters (such as starting fuel quantity, main injection advanced angle, rail pressure, pilot injection quantity and pilot injection timing) to start time and HC emission is analysed and researched through experiments.5. The influence of surroundings (such as intake temperature, coolant temperature, battery voltage) to start time and HC emission was analysed and researched through experiments.6. The optimization of the injection control parameters was found out through orthogonal experiments.Experiment results show that:1. There is an optimum value along with the increase of end symbol rotate speed of start, which can make start time shortest and HC emission lowest. Higher or lower than this value will lower start performance.2. On the condition of invariable end symbol rotate speed of start, along with the increase of the starting fuel quantity, the start time firstly decreases and then increases while HC emission increases all the times. When starting fuel quantity is too little, the engine cannot be started because the mixture in the cylinder is too lean to self-ignite.3. There is an optimum value along with the increase of the main injection advanced angle, which can make start time shortest and HC emission lowest. Higher or lower than this value will lower start performance. When the main injection advanced angle equals to 0oCA, the engine cannot be started because the mixture in the cylinder is too lean to self-ignite.4. In start process, rail pressure is changing. The higher the rail pressure is set, the higher peak it can firstly get to. In the dragging process, the undulation of rail pressure is larger. There is an optimum value along with the increase of the rail pressure, which can make start time shortest and HC emission lowest. Higher or lower than this value will lower start performance. Especially when rail pressure is too high, it needs a longer time to make engine start because too much fuel is injected on the surface of the combustion chamber.5. Because of the cold flame produced by pilot injection, the temperature in the cylinder increases and activating atmosphere is produced. So it can effectively improve the start performance of diesel engine. There is an optimum value along with the increase of the pilot injection quality, which can make start time shortest and HC emission lowest. Higher or lower than this value will lower start performance. The pilot injection timing has the same tendency as the pilot injection quality.6. Intake preheating is contributed to the improvement of the temperature in the combustion chamber, so it can effectively improve the start performance of diesel engine. And intake preheating can decrease the optimum main injection advanced angle. The essential of intake air heater works is: it increases the temperature in compress terminal; and it also increases the evaporation ratio of fuel and the mixing of fuel and air.7. There is a same point on the both curves of start time–coolant temperature and HC emission–coolant temperature. Start time and HC emission decrease while coolant temperature increases by the left side of the point and change a little when coolant temperature increases by the right side of the point.8. Battery voltage influences the start performance through influencing the drag rotate speed of starter. Along with the increase of the voltage the drag rotate speed of starter increases gradually. And the higher the voltage is, the shorter the start time is and the lower HC emission is.9. According to the orthogonal experiment, on the condition that the temperature is 11oC and the atmospheric pressure is 100kPa, the optimization combination of injection control parameters is that starting fuel quantity is 20mg/cyc, main injection advanced angle is 10oCA, rail pressure is 30MPa, pilot injection quantity is 2mg/cyc and pilot injection timing is 2000μs. And it is found that in the start process, the starting fuel quantity has the furthest influence on start time, but for the parameters as main injection angle, rail pressure and pilot injection quantity and pilot timing, the influence on start time is descending. And the parameters which influence HC emission are mainly the starting fuel quantity and the main injection advanced angle. Rail pressure, pilot injection quantity and pilot injection timinghave the same influence on HC emission. The conclusion that the experiment of the influence of the injection control parameters to start performance can be carried out through orthogonal experiment is also drawn.