米勒循环结合可变涡轮增压优化柴油机性能的仿真与试验

Simulation and Experiment on Miller Cycle Combined with VGT Optimization of Diesel Engine Performance

在开发一款机车柴油机过程中,采用仿真和试验相结合的方法,研究在最高爆发压力不超过设计限值的前提下,如何优化设计参数,使柴油机在排放达标时能获得理想的油耗指标。仿真结果显示,相比推迟喷油提前角,强米勒可以更有效降低NO_X排放,缺点是涡轮前排温升高和油耗增加。进一步的试验研究表明,在同为5℃A喷油提前角时,标定工况点强米勒方案比中米勒方案的NO_X排放降低58%,但是油耗增加1.1%,PM排放增加30.2%,涡轮前排温增加7.4%。增大强米勒方案的喷油提前角,相比中米勒5℃A提前角方案,PM排放仍然增加18.3%,涡轮前排温增加5.3%。考虑到中米勒方案NO_X比排放量6.68g/(kW·h),通过部分负荷工况点的优化,按标准计算的加权排放值可以满足EPATier3法规要求,PM排放和涡轮前排温远低于强米勒方案。因此,综合各方面性能参数的比较结果,在满足排放要求的前提下,中米勒为优选方案。

In the process of developing locomotive diesel engine,a combining method of simulation and experiment is used to study how to optimize the design parameters under the premise that the maximum firing pressure does not exceed the design limit so that the diesel engine can obtain the ideal fuel consumption value when the emissions meet the standards.The simulation results show that,compared to postponing the advance injection angle,strong Miller can reduce NO_X emissions more effectively.The disadvantage is that the exhaust temperature before the turbine increases and the fuel consumption increases.Further experimental research shows that at the same 5℃A advance injection angle,at the rated operating point,the strong Miller solution has a 58%reduction in NO_X emissions compared to the middle Miller,but the fuel consumption has increased by 1.1%,the PM emissions have increased by 30.2%,and the exhaust temperature before the turbine has increased by 7.4%.Increasing the advance injection angle of the strong Miller,compared with the 5℃A advance injection angle of the middle Miller,PM emissions still increased by 18.3%,and the exhaust temperature before the turbine increased by 5.3%.Considering the NO_X specific emission of 6.68 g/(kW·h)in the middle Miller,through the optimization of the partial load operating point,the weighted emission value calculated according to the standard can meet the requirements of the EPA Tier3 regulations,and the PM emissions and the exhaust temperature before the turbine are much lower than those of the strong Miller.Therefore,based on the comparison of the performance parameters of all aspects,under the premise of meeting the emission requirements,middle Miller is the preferred solution.