Research On Combustion System Matching Of Small Aviation Ignition Heavy Oil Engine Based On Knock Control

In the field of small aviation,gasoline is limited because of its low flash point and volatile nature according to the safety principle,especially gasoline is not allowed on ships.However,diesel engine does not meet the working requirements of UAVs because of its large volume and complex structure.An important strategy to solve the problem is to develop the heavy oil ignition piston engine.The fuel of heavy oil aviation piston engine is heavy oi,which has high viscosity and high density characteristics.At the same time,heavy oil is liable to detonation due to its low octane value and ignition condition.It will damage the engine and seriously affect the life of the engine,which make the suppression of deflagration being particularly important.It is inevitable to optimize and match the parameters of the engine combustion system to restrain deflagration and meet the working requirements of the engine,the influence on the power and economy of the engine must be as light as possible.In this paper,the intake-fuel-combustion coupled model of the ROTAX914 engine is established to simulate the intake,fuel injection and combustion process of the engine.First,the deflagration of combustion process in cylinder under different mixing conditions is simulated,and the influence of mixture distribution on deflagration is analyzed.When the mixture concentration area tends to the spark plug side,the mixture will be easy to Ignite and spread the flame,and the deflagration trend is larger.Secondly,this paper analysis the influence factors of the mixture distribution,and obtained the impact significance of various factors on deflagration based on this.The air intake has little influence on the mixture gas distribution,which will cause the lower deflagration trend.When the injection time is earlier,the injection pressure is higher,orthe injection angle increases or decreases from 15 degrees,the distribution of the mixture in the cylinder is more favorable for the combustion process in the cylinder,which will cause the higher deflagration trend.The distribution of the mixture in the combustion chamber of the concave piston is more favorable for the combustion process in the cylinder than the flat top.The combustion chamber with flat top and concave piston is more conducive to the formation of a mixture distribution with smaller deflagration trend.Then,this paper analysised the influence of ignition and EGR on deflagration.The ignition time and EGR have obvious influence on deflagration,while ignition time has little effect on deflagration.Based on the above research and analysis,this paper selected some more influential factors of deflagration in the combustion system parameters of the engine and used the orthogonal designto match these factors,analyzes the importance of these factors of deflagration effects,and give the best combination of parameters.After matching,the deflagration trend of the combustion process in the cylinder is significantly reduced compared with that before matching,and the power and burning consumption rate of the combustion engine decreases by11% or so,which satisfies the working needs of the engine.