Simulation Studies On The Effect Of The Distribution Of DME And Spark Assistant On Micro-flame Ignition Hybrid Combustion Of A Gasoline Engine

Spark ignition-controlled auto-ignition(SI-CAI)hybrid combustion confronts problems in combustion phasing control and cyclic variation under high dilution conditions.In order to solve these problems,the concept of dimethyl ether(DME)micro flame ignition(MFI)was proposed.In this paper,the influence of DME spatial distribution and spark assisted ignition on the initial flame core and development of MFI mixed combustion and later spontaneous combustion process is studied by means of simulationFirstly,the DME distribution at different DME injection time and the effect to the micro flame ignition and combustion heat release has been studied on a threedimensional numerical calculation platform of a thermodynamic single cylinder gasoline engine by CFD method,which shows the mechanism of different DME injection time to the initial spontaneous combustion.The result shows that early injection of DME shows a discrete distribution,the heat release shows a multi-point spontaneous combustion in order and single peak on the heat release curve.The discrete distribution of DME improve the activity of the mixture gas in cylinder,and the initial spontaneous combustion point is positively correlated with the regional temperature with a single condition.Highly congregate DME whose temperature is lower and the molar ratio is higher is used as a high-energy ignition source and the PRF lead the late spontaneous combustion,which make the boundary condition of spontaneous combustion is wider.Secondly,the effect of spark on MFI hybrid combustion process and the effect of different distribution of DME on early flame ignited by spark has been studied.Finally,this paper focused on the influences of spark timings on MFI hybrid combustion.The results show that the auxiliary role of spark ignition is to control whether the combustion can be carried out in the early injection stage and control the spontaneous combustion time at the later injection stage under the condition of high dilution.The later DME injection timing is,the easier of DME rich zones to reach autoignition condition after spark ignition,and the earlier of micro-flame initial ignition timing,the shorter the duration is,the greater the exothermic ratio is,and the starting point of the flame propagation stage is earlier.In the early injection cases,more DME participated in the early flame propagation stage,which can maintained and promoted the development of the initial igniter and showed the induction effect on the initial flame development.The DME injected into the cylinder could be used to accelerate the flame propagation and induce the auto-ignition in hybrid combustion at high dilution conditions.DME plays a role as an active ignitor and combustion accelerant at diluted conditions.In the MFI hybrid combustion with locally rich DME mixture mode,spark ignition will not form normal flame propagation,but the forming of micro flame can be enhanced by raising the temperature of the mixture near the spark plug,which and regulation of flame propagation and end gas mixture autoignition.The earlier of spark timing,the larger of micro flame's volume,whose ignition capability is stronger.The research results show that the combination of DME distribution characteristics and spark assisted ignition can enhance the control ability of MFI strategy for mixed combustion,thereby improving the stability of combustion.