Numerical Simulation On Spray And Combustion Of Aviation Kerosene Air-assisted Direct Injection Spark Ignition Two-stroke Engine

In the field of small UAV power,spark ignition two-stroke engine has attracted extensive attention at home and abroad because of its high power-weight ratio and simple structure.The safety of aviation kerosene is better than gasoline,which is more suitable for small aviation engine.However,due to the physical and chemical properties of aviation kerosene,fuel atomization is difficult,combustion speed is slow,and knock is prone to occur,which has a great impact on the formation,distribution and combustion process of combustible mixture in cylinder.In order to solve the above problems,based on air-assisted direct injection technology,the air-assisted spray process of aviation kerosene and the combustion process of heavy-fuel direct injection ignition two-stroke engine were numerically simulated by computational fluid dynamics(CFD)software.The effects of ignition time,air-assisted injection time and equivalence ratio on the combustion characteristics and knock combustion of aviation kerosene direct injection ignition were analyzed.The main research contents and conclusions are as follows:(1)The effects of air-assisted injection and high-pressure injection of aviation kerosene on the formation and distribution of mixture were studied.It was found that air-assisted injection could form a double vortex ring structure to promote fuel fragmentation and spray diffusion,and the distribution of mixture was more uniform.The spray penetration distance of air-assisted injection was shorter than that of high-pressure injection.Hence,air-assisted injection was more suitable for the combustion chamber of small aviation piston engine.(2)The earlier injection time,the more uniform distribution of the mixture,contribute to the formation of combustible mixture;late injection time can reduce the sweep loss of fuel and form mixture stratification in combustion chamber;by increasing the injection pressure,it is also helpful to form a more uniform distribution of mixture,and improve the atomization ability of compressed air and reduce the particle size of heavy-fuel droplets.(3)The advance ignition time and injection time increase the cylinder pressure,combustion temperature and heat release rate;but too early ignition time will go up the tendency of knock;injection timing is too early,the combustible mixture can not be effectively stratified to increase the possibility of knock;the combustion pressure and temperature of aviation kerosene are the highest at equivalence ratio 1.1,and the heat release rate is faster,but the knock tendency is also the largest.The above research has important theoretical significance for the performance optimization of aviation kerosene two-stroke aviation engine.