Experimental Research On Cold Start Of Four-stroke Piston Aviation Kerosene Engine

In this paper,a low-pressure air-assisted direct-injection single-cylinder testing machine with a displacement of 650 m L was used as a test platform to conduct a coldstart test study.The engine cold start dynamic process includes two phases.The first is the ignition phase,that is,the process from the start of injection and ignition to the formation of the first cycle of combustion.The cold start performance test research is conducted around the problem of low temperature and poor atomization,which makes it difficult to form a fire core.,To improve the ability to form a fire nucleus;then the warm-up phase,around the problem of abnormal combustion due to low cylinder temperature and unstable intake air,the combustion characteristics after the first cycle were studied to improve the work ability.These two phases are improved to fully optimize the cold start dynamic process of the engine.The ignition stage is aimed at the problem of poor cold start performance of aviation kerosene engines.From the perspectives of improving the preparation of the mixture and increasing the ignition energy,the effects of the firing speed,fuel temperature,and ignition energy on the ability to form a fire nucleus were studied.The research shows that with the increase of the injecting speed,the starting time tends to be shorter and then longer.When the injecting speed is compromised,the fire core formation ability is the strongest and the starting time is the shortest.The increase of fuel temperature not only strengthens the mixture The atomization quality can also accelerate the temperature rise in the combustion chamber,thereby reducing the activation energy required for the combustion reaction,accelerating the formation of fire nuclei,and greatly reducing the start-up time;increasing the ignition energy can ionize more free radicals and help ignite The mixed gas reduces the difficulty of forming a fire nucleus,thereby shortening the startup time.In the warm-up phase,experimental research was conducted on the problems of incomplete combustion,misfire,and flameout after the engine was successfully started.The combustion characteristics were optimized from the perspective of improving the engine’s functional capabilities.The oil-gas interval,jet cut-off time,air-fuel ratio,and Effect of ignition timing on combustion characteristics.The results show that too large or too small oil and gas interval will adversely affect the formation of the mixture.When the oil and gas interval is 3 ms,the cyclic fluctuation of the maximum combustion pressure is small and the misfire phenomenon disappears.At the beginning of the compression stroke at the beginning of the compression stroke,at 120 ° ～ 180 °,it is easy to form a thicker layered mixture near the spark plug,and the average engine IMEP is higher.The strategy of accurately controlling the air-fuel ratio based on the intake air volume is used to avoid the phenomenon of flameout caused by the excessively rich mixture.When the excess air coefficient transitions from 0.65 to about 0.75,the average IMEP of the engine is the largest and the function is enhanced.When the ignition advance angle is gradually reduced from the initial value of 30 ° to 15 ° at the start,the engine has the shortest flash period during the combustion process,the highest combustion pressure is high,and the average IMEP is the largest.