Simulation And Improvement Of The Flow Field In DI Engine's Combustion Chamber Burns DME

Dimethyl ether (DME) is one kind of newly and clean substitute for diesel engine, which is obviously different from diesel on property. As an alternative of diesel, DME improved the exhaust, moreover, which can alleviate the energy crisis. And the atomization of fuel spray, which is as the source of in-cylinder working process, has the most important influence on the subsequent combustion and exhaust of engines. So, after reading a great number of literature on relevant research field, and based on the theory, this paper take a thorough study on the spray characteristics of DME and the flow filed in the chamber by numerical simulation.The combustion process and emission characteristics in diesel engine are mainly depended on the mixture formation in cylinder. The gas flow and fuel spray status in combustion chamber affect the mixture formation mainly in diesel cylinder. So this dissertation utilizes the software FIRE provided by AVL Co. to simulate and analyze the flow field in combustion chambers for DI diesel engines ZS1100, also the property of DME has been considered. Because the original combustion chamber (type I ) and the spray hole are opposite in the cylinder middle line, for reference contrast, the combustion chamber and the spray hole all for the symmetry (type II) was established.Through the simulation, it can be concluded that the type I produces the turbulent flow early compared with type II ,and the turbulent flow is asymmetrical in compress stroke and expansion stroke. As a result of asymmetry, the oil injection should be asymmetry to form the uniform mixture. Before the TDC, the right region should inject more oil, and after the TDC, the left side region should inject more, this has brought the difficulty to the injection. Under original injection pressure, the oil spraying hit the wall phenomenon to be serious, which caused the fuel oil distribution to be uneven, and serious influence combustion process. Also oil spraying hit the wall exist in type II, but the turbulent flow assumes the symmetrical distribution, which consistent with the spray hole.Considered the good atomization ability of DME and hits wall's, when computation the injection pressure will be smaller than before. The result shows that, the different lug boss forms the different air movement, which has the difference slightly respectively to the air movement's conduction. And the pressure in chamber increased all in type III and IV, the air movement and the oil spraying situation coordination is good, which is advantageous to the oil gas uniform mixing in the cylinder. The results show that when organizes the air movement in the cylinder, the reasonable air movement distribution characteristic and the oil spraying the coordination, which can achieve forms the uniform mixture and is advantageous in the full combustion .