Experimental Study And Simulation Of Diesel Engine Starting Process

The diesel engines have high fuel efficiency and reliability. Compared with gasoline engines, diesel engines have higher thermal efficiency, because they have larger compress ratio and air fuel ratio, and have not throttle loss. The technology of high pressure common rail increases the performance of diesel engines, therefore,diesel engines are used widely.Startability is one of the most important capabilities of diesel engine .But when the engines in cold state, especially in low temperature environment, they have lots of problems, such as long motoring time, fluctuant speed, bad combustion and emission. etc.For the research of start process of diesel engines, a transient measurement and control system was established based on a 135 single DI diesel engine. This system could change the injection time and pulse width, implement variable EGR rate via controlling the EGR valve and exhaust back-pressure valve. Depended on the test system, experiments of start process of engines with different EGR valve opening were finished, tests of controlling EGR rate to improve the startability were also carried out. The results indicated that, EGR hastened the appearance of the first firing cycle. The bigger the EGR rate was, the earlier the first firing cycle appeared. At the same time, too much EGR deteriorated the combustion quality, made the misfiring cycles increase. As a result, the whole combustion performance became bad. Controlling valves to carry out different EGR rate before and after the first firing cycle improved the combustion quality and emission performance during start process of diesel engines.The method of experimental research could not be the only way to investigate the start process of diesel engines, meanwhile, the simulation research could reflect detailed process of the fuel injection and combustion. STAR-CD software was used to simulate the first firing cycle of the engine. A one dimensional GT-POWER model and a three dimensional STAR-CD model were established to verify the structure parameter. Other important operating parameters like speed were also identified. Besides, fuel injection rate was necessary for simulating the atomization and combustion in cylinder chamber, so the injector calibration tests were carried out. ES-ICE was used to form the moving meshes and to examine the grids at every crank angle. Set various parameters of every sub-model in the STAR-CD pre-processing software and calibrated the stimulant model on the basis of experimental data. After that, the working process in the cylinder was analyzed particularly. Additional calculations were simulated to research that how the injection angle and EGR affect combustion. As a result, rational injection angle and EGR rate both improved the combustion performance in the cylinder. It was also discovered via simulations that both the fuel composition and radical composition could improve the combustion performance in the CI cylinder.