Experimental Research On Combustion Features Of 4-stroke Aviation Kerosene Engine Under Low And Medium Load

Small piston aero-engine occupies the mainstream position of low power aircraft for its advantages including compact structure,low cost and high work-weight ratio.Due to the high flash point and high safety performance of aviation kerosene,it has attracted the attention of the field of civil aviation.However,aviation kerosene has the characteristics of high viscosity,difficult atomization and unstable combustion under low and medium load conditions.In addition,the poor antiknock property of aviation kerosene leads to detonation when ignited with spark plugs.Therefore,it is of great significance to study the combustion characteristic of piston aviation kerosene engine under low and medium load.Based on a single cylinder four-stroke aviation kerosene engine,the combustion characteristics of aviation kerosene under low and medium load including end of injection time,fuel preheating temperature,excess air coefficient and ignition energy were studied in this paper.The result shows that the end of injection time close to intake stroke can reduce the coefficient variation and increase the indicated mean pressure,and there exists an optimal end of injection time which can utilize the turbulent kinetic energy generated by the combustion-chamber shape to achieve the optimum stability and power performance.With the increase of fuel preheating temperature,the combustion delay period of aviation kerosene combustion is shortened gradually,and the fast combustion period is accelerated gradually,which improves the combustion stability and the work ability.Under current injection technology,aviation kerosene engine is more suitable for combustion in the dense mixture,and there is an optimal excess air coefficient λ=0.8,so that the combustion stability and power performance is optimal.Increasing the ignition energy can shorten the combustion delay period and fast combustion period,and improve the power performance of the engine,but ignition energy has the saturation value,and when it reaches saturation,the improvement of power performance becomes slow.Based on the method of waterfall diagram,the knock characteristics of aviation kerosene were analyzed by using dual-spark ignition strategy.The result shows that the knock characteristic frequency band of this engine is 8.0～14.8k Hz.Delaying synchronous phase ignition advance angle can reduce the heat release rate in the major frequency band and inhibit knock.There exists an optimal synchronous ignition advance angle,the engine has the strongest power performance and works in the knock boundary.With the increase of the asynchronous ignition phase difference of the dualspark ignition,the abnormal heat release phenomenon in the major frequency band disappeared gradually,and there exists an optimal phase difference makes the engine have the strongest power performance and it is superior to synchronous ignition strategy under the same working condition.Improving ignition energy can effectively improve the dynamic performance of the engine,but it cannot be used as the main means to suppress knock.The combination of high energy ignition and asynchronous phase ignition can effectively suppress knock and significantly improve the dynamic performance of the engine.