Research On Combustion Characteristics And Knock Control For Direct Injection Piston Aviation Kerosene Engine

The flash point of kerosene is very high so it's uneasy to ignite kerosene when the temperature is low,because kerosene is very convenient for transportation and storage,those piston aviation engines which use kerosene as fuel has been come tohigh attention of the area of military and unmanned aerial vehicle?There are obviously difference between kerosene and gasoline in the aspect of physicochemical property and these differences will lead to great changes in combustion characteristics.And kerosene are very prone to detonation under heavy load condition.So it's very meaningful to conduct research on the combustion characteristic of kerosene and try to find an appropriate way to constrain the knock?Based on the experiment implemented on a self-developed low pressure air-assistant direct injection piston aviation engine,the influence of different inject timing?advance ignition angle?excess air ratio on the combustion characteristics has been analyzed.The result shows that:The start of injection timing has an obviously impact on the oil evaporation and the formation of homogeneous mixture,the impact of the temperature of cool water on kerosene atomization is higher than gasoline atomization;kerosene's advance ignition angle is bigger than gasoline's due to its flame propagation velocity is lower than gasoline,and the impact of thermal efficiency on kerosene is more obvious than on gasoline when the advance ignition angle is deviated from the MBT;Compare with gasoline,kerosene is more suitable for burning in a rich mixture environment,when the excess air ratio of kerosene is in the range of 0.8 to 0.85,the ignition delay period will be the shortest and the COV will be the lowest.Several methods have been used to constrain the knock in a high load condition such as retard ignition timing?dual-spark ignition?stratified stoichiometric mixture?The result shows that:It doesn't work by using rich mixture because the auto-ignite temperature is too low;Retarding the ignition timing can eliminate knock effectively,but the thermal efficiency and output power will decrease;Using dual-spark plug can increase the velocity of flame propagation,but this method can't restrain knock effectively;Stratified stoichiometric mixture can decrease the knock intensity,As the second-injection timing retard and more fuel being injected in the second-injection process,the mixture will become more and more asymmetrical and lead to combustion deterioration,and decrease the speed of flame propagation.