Simulation Research On Stratified Charge Combustion Of GDI Engine Based On Various Injection Strategies

Under the pressure from both energy crisis and environmental pollution, it has been thekey issue for motor company world-wide to realize clean and efficient combustion. For theimportant role GDI plays in power and torque performance, and it’s huge advantage inreducing fuel consumption and emissions, it has become a major project in the research ofgasoline engine. The technology of Stratified Charge Combustion, therefore, will be moremeaningful and widely used in the future within the area of engine in low and mid rotationand load, thus, the further of it, under the current state of development, will be essential tomotivate the potential of thermal efficiency improvement and pollutant emissions reduction.In this paper, by establishing the GDI model, the author studies the influences of single anddouble injection strategy in Stratified Charge Combustion through numerical simulation andanalysis. The contents and achievements of this paper are as follows:First, under the strategy of single injection, how the injection timing and ignition timingaffects the Stratified Charge Combustion in GDI engine is analysed. The result shows that asthe injection timing is delayed, the in-cylinder average pressure and temperature are loweredand the pressure peak is pushed back; the peak of rate of heat release is lowered; the NOemission mass fraction is also gradually reduced with the soot emission mass frationincreased. In consideration of overall in-cylinder pressure， rate of heat release，combustiontemperature， fuel stratificatio，etc.，and the balance between NO and Soot emission, theperfect injection timing is70°CA BTDC. In the situation of ignition timing delayed, thein-cylinder average pressure and temperature are lowered and the pressure peak is pushedback; the peak of rate of heat release is reduced with its position pushed back; NO emissionmass fraction and the peak of soot emission mass fraction are reduced with its peak positionpushed back. After the peak of soot emission mass fraction, part of soot is oxidized and ittends to be stable during the remaining combustion process. Consideration of in-cylinder pressure, rate of heat release, combustion temperature and fuel stratification,etc.,the perfectignition timing is17°CABTDC.Second of all, under the strategy of double injection, how the fuel distributionproportion,injection timing and Ignition timing affect the Stratified Charge Combustion inGDI engine is analysed. The result shows that if the fuel distribution proportion is different,the in-cylinder pressure and its peak position will be almost the same as in-cylindertemperature，but as the proportion enlarges, the peak of rate of heat release will be graduallyincareased with its position pushed back and then forward; as the injection proportionenlarges, the NO emission mass fraction will be reduced with the soot emission mass frationarriving at its lowest point when the injection proportion is1:3; as the injection timing isdelayed, compared with single injection strategy, the in-cylinder average pressure will begradually lowered with its maximum added to3%-7%, though the pressure peak position isalmost the same as in single injection strategy’s, the peak of rate of heat release will belowered as the injection delayed, and compared with single injection strategy, it hasincreased about5%with its position also pushed forward about0.5°CA.At the same time,the NO emission mass fraction will be reduced to30%-80%with soot emission massfraction almost to one order of magnitude; as the injection timing is delayed, compared withsingle injection, the in-cylinder maximum pressure will be reduced and the highest pressureincreased to3%-5%with its peak position almost unchanged. Moreover, the peak of rate ofheat release will be gradually lowered but increased to10%-15%with its position pushedforward0.5°CA in comparison with in single injection’s; as the injection timing delayed,the NO emission mass fraction will be gradually reduced to40%-60%with the soot emissionmass fraction reduced to10%-30%compared with single injection strategy.