Research On The Ignition Mechanism Of High-density And High-lean CNG Engine

In the face of the two major problems of energy crisis and environmental pollution and the increasingly stringent emission regulations,the study on the conventional combustion technology in the cylinder of the engine can not be enough to meet the needs of a large number of researchers.The international organization of the engine combustion is undergoing a revolutionary change that the engine combustion technology is moving towards extreme conditions such as high density,high dilution,and ultra-high pressure.In this article,a CNG engine simulation model,based on an in-cylinder direct injection gasoline engine,was established to study the influence of the various ignition parameters on the combustion and emission of natural gas under high density and high dilution gas conditions.In order to achieve efficient and stable combustion,the ignition system of the CNG engione was optimumed to achieve the goals of high power,high economy,low emissions and low exhaust temperature.Firstly,the validity of the combustion model is verified by the experimental data of the engine prototype.Secondly,we do some research on the effects of different ignition modes,double spark plug position,ignition timing and ignition energy on the combustion emissions of CNG engine underthe high-density and high-lean conditions.The results show that the ignition of double spark plug can shorten the propagation distance of flame,improve the propagation velocity of flame and improve the thermal efficiency of engine compared with the single spark ignition.However,it needs to cooperate with the ignition timing to achieve the best result.When studying the influence of the position of the double spark plugs,it was found that when A=2/3,the burning speed is the fastest,and the burning duration is the shortest.When double spark plug distance is too near or too far,it will reduce the engine's combustion speed,increase the duration of combustion.It will also lead to the economic deterioration and increase the emissions of pollutants..Under different operating conditions,the optimum ignition timing exists.When the equivalent ratio is 0.6,the optimum ignition timing is695°CA,and when the equivalent ratio is 0.55,the optimal ignition timing is 685°CA.By optimizing the ignition timing can compensate for the lack of power caused by the high-lean conditions.Finally,the research on the ignition energy shows that increasing the ignition energy can promote the development of the fire nuclear and shorten thedevelopment period of the flame.However,after the ignition energy increases to a certain value,if we continue to increase the ignition energy,there will be little improvement on the engine performance.When the equivalence ratio is 0.6,the minimum ignition energy is 45 mJ under high density and high lean gas conditions,and the minimum ignition energy is 35 mJ when the equivalent ratio is 0.55.Thus by optimizing the ignition system,it is possible to achieve a more efficient combustion with lower ignition energy at high lean gas conditions.