The Study Of Diesel Engine Parameters Coordination Control Based On Low-temperature Combustion Theory

Diesel engines have been intensively used in all kinds of fields including vehicleand ship as a high efficiency and low-energy tool. In order to control diesel engine’semission, Low temperature combustion (LTC) as a new combustion process comesforth in recent years, arousing the attention of international and domestic scholars.NOXand soot emissions can be simultaneously reduced to extremely low levelsbecause of the low temperature combustion and good quality of gas mixture in thediesel engine cylinder.This paper scientifically studied combustion control parameters of diesel enginebased on low temperature combustion theory by using the AVL-Fire numericalsimulation software. It is mainly to consider the change of EGR rate、injection timeand combustion chamber shape adding bump to analyze the influence to dieselcombustion and emission. Firstly, the combustion chamber was designed byAuto-CAD software along with grid divide in AVL-Fire software. Then establish thecombustion model of diesel engine to simulate working condition of diesel engine,and the model would confirm by comparing with experimental value. And then,multiple operating modes of low temperature combustion in diesel combustion wereimitated and analyzed, the main results are as follows:1) With the increasing of EGR rate, ignition delay period will extend so that thecombustion pressure and temperature will decrease. NOXproduction is graduallydecreased, but the soot emission will rise. NOXwill get an obviously decrease with alarge EGR rate because of the increasing ignition delay period and mixtureconcentration decrease.2) Injection timing has a large influence on diesel combustion. Later injectiontiming could make the combustion temperature decrease and ignition delay periodlonger if injection timing is after TDC. Soot emission increase heavily because of therice mixture. At the same time, the heat quantity of premixed combustion phase canhave a loss. Temperature rising in the diffuse combustion phase results in NOXemission decrease.3) A secondary jet would be formed when the fuel impinges on the wall with aBUMP which can control the secondary spray and mixture formation. Thecombustion temperature and NOXproduction can decrease when BUMP height isincreased, but CH and Soot emission will increase at the same time. 4) When the BUMP location on the wall is in the direction of fuel injection angle155degree, the combustion temperature and NOXemission can be reduced. Some fuelcan access to clearance because of the secondary jet which will increase the Sootemission.In conclusion, it is proved that a high EGR rate will efficiently reducecombustion temperature and lower NOXemission; But Soot emission of diesel enginewill increase with the increase of EGR rate. When injection is after TDC, laterinjection can increase NOXemission and Soot emission at the same time. However,the Soot emission and NOXemission will rebound if fuel injection is too late. BUMPis a good way to realize diesel’s low temperature combustion process, soot and NOXemission would decrease under the condition of having a good control to the locationand height of bump.