The Effect Of EGR On The Combustion And Emission Characteristics Of Premixed Compression Ignition Engine

With the rapid growth of car ownership around the world, the vehicle emissions ofpollutants have become the focus of attention. Reduce emissions by controlling thecombustion is one of the major clean-burning technologies of engines. In this paper, theEGR cooling main structural parameters were determined by setting compression-ignitionengine as the research object, establishing the high-pressure loop EGR system withsolenoid valve-driven, temperature controlled water-cooled tube-shell heat sink, and thenumerical simulation of EGR cooler was carried by using CFD software. In addition, the fuelinjection control system was established based on open ECU and INCA. The effects of EGRrate, EGR temperature and EGR coupled injection parameters on engine combustion andemissions were studied, and the role of EGR to the pre-mixed compression ignitioncombustion of engine was explored.The results showed that: with the EGR rate increased, the cylinder combustion pressuregradually decreased, the amount of premixed combustion increased, the emissions of NOxdecreased, whereas the emissions of soot, CO and HC gradually deteriorated. Cooled EGRcould reduce intake air temperature and prolong the combustion ignition delay, increase theproportion of premixed combustion, reduce the average temperature of combustion cylinder,and decrese the NOx and soot emissions. As oil pressure increased, the maximum cylinderpressure and the peak of heat release rate were increased, and pre-mixed combustion ofcombustion process also increased.When EGR rate is higher, the impact of changing theinjection pressure on premixed combustion was more obvious, and the improve of injectionpressure could significantly reduce the diffusion combustion ratio. As a result, by using alarge proportion of EGR to reduce NOx emissions while increasing injection pressure tosuppress soot emissions could realize. For two stages of jet, with the increase of EGR rate,pre-spray exothermic peak reduced, the main jet combustion exothermic peak increased, and the mixing ratio of the burning also increased; and as the main pre-injection interval becamelarger, the impact of EGR on the main jet burnning was more obvious. Under different EGRrates, the impact of main pre-spray interval on NOx and soot emissions was not the same:when the EGR rate was small, with the increase of main pre-injection interval, the NOxemissions and soot emissions both increased; when the EGR rate was large, the impact ofmain pre-injection interval on NOx emissions was significantly reduced, while sootemissions increased with the main pre-injection interval decreased. As the time of the mainjet ahead, the start of combustion heat was brought forward with the proportion of premixedcombustion increase and exothermic peak improvement significantly. At the same main jetangle, the pre-mixed combustion increased with EGR rate increased; the impact of EGRrate on the pre-mixed combustion was more obvious when the time of the main jet was moreadvanced. The use of EGR to reduce NOx emissions could cause the increase of sootemission, and ahead of main injection time could effectively reduce soot emissions. Whenthe main injection advance angle is large, large EGR could not only reduce NOx emissions,and also reduce soot emissions. But fuel injection advanced angle could bring burnningforward, increase peak heat release rates,and increase the pressure rise rates. Therefore, it isnecessary to choose the right EGR and injection pressure when utilize the EGR-coupledmain jet timeing to reduce engine emissions.