Experimental Study for Effect of Multi-Site Spark Ignition on Dedicated Hybrid Engine Performance under High Dilution Condition

In this study,a triple spark ignition scheme was first designed on a three-cylinder 1.5-L dedicated hybrid engine（DHE）.On this basis,the effect of different ignition modes on engine combustion and emission characteristics was studied,especially under high dilution condition.The results tested at 2000 r/min and 0.8 MPa BMEP（brake mean effective pressure） show that with highly increased in-cylinder flow intensity,using only passive prechamber（PPC） has a lower lean limit than that with single central spark plug（CSP）,thereby leading to slightly higher minimum fuel consumption and nitrogen oxides（NOx） emissions.Adding side spark plugs（SSP）based on PPC can result in improved capability of lean limit extension and engine performance than CSP.However,the improvement level is lower than that with triple spark plugs（TSP）.As the excess air ratio λincreases,the advantage of PPC and PPC with SSP in improving the combustion phasing compared with CSP gradually weakens.Correspondingly,the increasing tendency of their ignition delay and combustion duration is more obvious.The added SSP based on PPC can effectively shorten the ignition delay of leaner mixture,but the combustion duration can be only slightly improved.As a result,under extremely lean condition,the advantage of PPC and PPC with SSP in terms of combustion characteristics over CSP becomes much smaller.In contrast,the TSP ignition can achieve much shorter ignition delay and combustion duration simultaneously under this condition.Due to the highest available dilution level,the TSP ignition achieves the lowest raw NOx emissions.Moreover,it can also reduce the raw carbon monoxide（CO） and hydrocarbons（HC） emissions compared to CSP due to a more thorough combustion of the end gas mixture.Based on the excellent performance of TSP,the highest engine brake thermal efficiency（BTE） was further explored.The results show that with normal RON 92 fuel,the engine finally achieved 43.69% and 45.02% BTE under stochiometric mode with exhaust gas recirculation（EGR） and lean-burn mode respectively.When using RON 100 fuel,the highest BTE was further increased to 45.63% under lean-burn mode.