| The trade-off relationship between combustion and emissions of internal enginehas been become one of the most challenging problem. In order to improve theemission of diesel engine, a lot of new combustion mode is put forward whichgeneral use of higher EGR combined with flexible injection characteristics. But thehigher EGR rate will increase cooling burden and decrease of thermal efficiency andother issues. The concept of EGR stratification, which can improve componentdistribution and combustion conditions in cylinder, reduce the introduction of EGRamount, control emissions generation environment, reduce the negative effect ofEGR on the performance of diesel engine. In this work the combustion based onCA6DL2-35E3heavy duty diesel engine with common rail fuel injection system,numerical simulation platform is built by using STAR-CD software, with the help ofthe intake process time division of different gas components, the formation of EGRin cylinder stratified. By adjust the fuel injection parameters analysis theperformance on combustion and emissions of diesel engine with EGR stratified,which can further reveal the fundamental reason why the timing sequential intakecan improve better than the uniform intake on the performance of engine.The original machine operating point under the condition1650r/min, injectionpressure is120MPa, nozzle hole diameter is0.186mm, injection time is-8oCAATDC; a simulation analysis is carried out by adjust the inject pressure, nozzlediameter, injection time, the main conclusion as follows: As the injection pressureincrease and the Nozzle hole diameter reduced with timing sequential intake,causethe fuel atomization quality become better, the combustion can improved. Theindicated thermal efficiency an emissions with the monotonic change trend. Inparticular, the high fuel injection pressure and little orifice not only can bothimprove engine performance and reduce Soot emission but also brings the increaseof NO. The injection timing advanced, the formation of more mixed gas during theignition delay period, combustion occurred more close to the TDC, the increasing proportion of premixed combustion, can improve the thermal efficiency, NO andSoot emissions with the injection timing advanced monotonically increases anddecreases respectively. Keep the injection parameters of single factor unchanged,timing sequential intake both reduced NO and Soot compared with the uniformintake. The original machine operating point NO and Soot respectively decrease33%,13%.It also brings the deterioration of fuel economy. Keep the same CO2ratein cylinder, the timing sequential intake make the CO2at the upper zone in thecombustion chamber, the O2at the lower region. The main spray combustion regionhas a relative higher CO2rate, the ignition delay period is prolonged, the combustiontemperature is reduced, the first peak heat release rate increase, but the cylinderpressure is lower.Simulation comparison and analysis of multiple injection and single injectionon engine performance, make it clearly with multiple injection under the timingsequential intake condition can further reduce the emissions, the research resultsshow that: Under the timing sequential intake, the multiple injection can reduce bothNO and Soot emissions with the multiple injection. And it also brings negativeinfluence such as the fuel economy deteriorated and thermal efficiency decreased.The post injection quantity and main post injection interval angle respectively hasits minimum inflection point corresponding to Soot emission trend, considering thethermal efficiency, the post quantity of10%and the main post injection intervalangle as the optimization of operating condition of engine performance. Keep thecycle fuel injection quantity is unchanged, under the timing sequential intake withmultiple injection, combustion gas flow in the cylinder to drive the thick O2at theend of the combustion chamber to the anoxic zone that the main injectioncombustion caused. It will promote the oxidation of Soot. |
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