Analysis And Optimization Of The Semi-Direct-Injection Mode Of Two-Stroke Hydraulic Free Piston Engine

The two-stroke engine has the advantages of high power density and simple structure.Hydraulic free piston engine takes hydraulic oil as the energy output medium,and it is difficult to use hydraulic energy to go down and back in the circulation process.Therefore,two-stroke working mode is a working mode suitable for hydraulic free piston engine.However,for two-stroke engines,the problem of fuel consumption is still the main factor restricting the development of two-stroke engines.By means of simulation and experiment,this paper studies the mixed gas generation and engine operation characteristics of two-stroke free piston engine from port injection to SemiDirect-Injection,and explores the means and methods to improve the fuel consumption of two-stroke engine.In this paper,using CONVERGE simulation modeling software built two stroke of the 3d simulation model of hydraulic free piston engine,in the first place of the original machine to simulate the process of using port injection,the results showed that in the process of port injection,the fuel spray are susceptible to airway in high-speed airflow by blow to the airway wall forming oil film,open valve when the jet fuel capture rate is only 53.3%.After the semi-direct injection,the fuel capture rate is increased to over 90%,which has a better fuel saving effect,but the gasification effect is decreased.In order to improve the mixture generation effect of Semi-Direct-Injection,this paper studies the influence of injector flow,injection phase and injection angle on the mixture preparation effect of two-stroke hydraulic free piston engine.The results show that the best injection window of the high flow injector is larger than that of the low flow injector,and the injection flexibility is better.The later the injection phase is,the higher the fuel capture rate will be,which can be optimized to 99%,39% higher than the fuel capture rate when using the airway injection(the fuel capture rate when using the closed valve injection is 60%),which greatly improves the fuel short-circuit problem of the two-stroke engine.There is an optimal fuel injection angle,with an angle of 43°～48° between the cylinder axis,at which time the gas rate can reach above 98.5%and the fuel capture rate can reach above 98.4%.If the fuel injection angle is too large,the escape of fuel will increase,but if it is too small,the fuel gas rate will decrease.Based on the optimization approach of the Semi-Direct-Injection mode obtained in the simulation process,the injection mode of the engine prototype was modified and the continuous test was carried out.The test results show that the applied Semi-DirectInjection way,the engine when the continuous and stable operation of low fuel consumption by 30.6%,combustion efficiency increased by 23.4%,effectively improve the two-stroke hydraulic free piston engine fuel economy and combustion efficiency,proves the Semi-Direct-Injection system to deal with the problem of two-stroke engine fuel consumption has great potential.