Numerical Analysis Of Combustion Process For A Spray-Wall Complex Guided Of Two-stroke LPG Direct Injection Engine

With the rapid development of automobile industry,the research of high performance and low pollution vehicle has become the trend of automobile development.Liquefied petroleum gas(LPG),as a kind of clean automobile fuel,has the advantages of low boiling point,high vapor pressure,good storage and so on.Two stroke engine has the advantages of high speed,simple structure,large specific power and so on,but the formation time of the mixture in the cylinder is short when the exhaust port is closed.Thus it is necessary to study the formation quality of the mixture in the cylinder.The formation and combustion process of two stroke LPG direct injection engine is studied in this paper.The spray-wall guided combustion system has been put forward in this paper.The working principle and the position of nozzle and spark plug,the dia meter of nozzle and the number of holes is explained.The method of experiment and simulation is used to verify the formation of free spray and mixture and the results show that both are consistent.The three-dimensional solid model and the grid model were established to study the formation process of the stratified mixture and the formation process of the homogeneous mixture.The results show that the formation of the mixed gas is similar at 4800 rpm under different loads(50% and 60%),which can form a stable mixture near the spark plug,but the concentration is slightly different.To determine the different conditions(2000rpm,20% load;4800rpm,80% load;6000rpm,80% load)of homogeneous gas injection time and through the image display at different speeds and loads at BTDC20°CA,the mixture can be evenly distributed among the cylinder.Chemkin software is used to simplify the detailed chemical kinetics mechanism of LPG.The detailed mechanism consists of 155 components and 689 chemical reaction equations.The simplified mechanism consists of 32 components and 69 chemical reaction equations.The simplified mechanism and the detailed mechanism are simulated under the same conditions,and the results are compared,thus the validity of the simplified mechanism is verified.In the spray-wall guided mode,the air-fuel ratio is 40:1,the mixture of cylinder combustion and emission process were analyzed.It shows that at an earlier ignition time BTDC29°CA,there are more residual gas in the left combustion chamber when the piston is 740°CA.In the late ignition time BTDC20°CA,the maximum temperature and heat release rate are lower than the rest time.However,when the ignition time is BTDC23°C A and BTDC26°CA,the residual gas in the cylinder is less,the heat release rate and the cylinder temperature are higher,and the combustion performance is better.It can be seen that the content of CO and NO emission curved decreases with the delay of ignition time.