Numerical Simulation Of The Working Process Of A Gasoline Engine And Performance Optimization

As the crystallization product of modern industrial technology,the design process of engine is highly integrated with a large number of intelligent achievements of industrial society.For a complete engine,in order to continuously improve the performance of the engine,it is necessary to optimize the engine performance as much as possible from the design,development,optimization to the test stage.In the process of engine calibration,it is a huge work to comprehensively analyze all the adjustable parameters except the design parameters and find the operation scheme with better comprehensive performance,which requires high theoretical and practical requirements of designers and calibration engineers.In this paper,we hope to use the numerical simulation method to cooperate with the calibration test of the model under development,and give play to the advantages of computer numerical simulation to improve the engine performance.In this paper,a two-cylinder gasoline engine for carrying unmanned aerial vehicle developed by our team is taken as the research object.Through experiments and numerical simulation,the formation of the engine mixture and the combustion in the cylinder are analyzed.Then,based on the actual engineering requirements,the engine ignition system is improved to optimize the performance of the whole machine.This paper uses professional engine simulation software CONVERGE to carry out 3D simulation of the target model.Through the research findings:(1)Under the same injection volume,the air mixture concentration in the cylinder is higher in the valve-open injection mode,and the air mixture in the cylinder is more evenly distributed in the cylinder in the valve-close injection mode,but due to the higher quality of the Coanda oil film,the concentration of the mixture is higher.relatively low.When using secondary injection,the proportion of combustible mixture in the cylinder will be higher than that in single injection;(2)The in-cylinder combustion simulation model was built on the basis of the study of the mixture formation and its rationality was verified.The influence of some adjustable parameters including equivalence ratio and ignition timing on the thermochemical performance of the engine cylinder combustion was further studied.As well as the impact on emissions,the study found that when the cylinder mixture equivalent ratio is close to 1.0under high-speed operating conditions,the maximum explosion pressure and combustion temperature in the cylinder will be the highest.As the mixture concentration becomes richer or leaner,it will cause the cylinder The decrease in internal pressure and temperature,and the increase in the concentration of the mixture,the increase in the amount of carbon monoxide produced in the cylinder,and the incomplete combustion due to the excessive concentration of the mixture,which leads to an increase in the production of hydrocarbons.The study found that with the advance of the ignition advance angle,the ignition delay period of the combustion in the cylinder is prolonged,the explosion pressure in the cylinder,the rate of pressure rise,and the heat release rate of combustion all increase,and the production of hydrocarbons and carbon monoxide decreases,and the amount of nitrogen is reduced.The production of oxygen compounds increases.(3)In order to improve the combustion performance in the cylinder and the ignition rate under actual operating conditions,it is decided to improve the ignition system of the engine in combination with the research of the previous mixture and the combustion performance in the cylinder.Improve the ignition system under the condition of ensuring the interchangeability of the engine as much as possible.On the basis of the original spark plug ignition,a secondary spark plug is added to improve the combustion performance in the cylinder and the ignition rate of ignition.In the comparison between the single-spark plug ignition system and the dual-spark plug ignition system,it is found that the maximum explosion pressure in the lower cylinder of the dual-spark plug ignition system is increased by 9.2%,which corresponds to the advancement of the crankshaft angle.At the same time,due to the optimization of the combustion situation,the amount of carbon monoxide produced has been reduced,and the amount of nitrogen oxide produced by the dual-spark plug ignition system has increased due to the increase in the temperature in the cylinder.The effect of ignition timing on the combustion and emissions in the cylinder is further studied under the dual spark ignition system.The results show that the maximum explosion pressure in the cylinder of asynchronous ignition has a slight drop compared with synchronous ignition.At the same time,due to the difference in the combustion situation in the cylinder,The amount of carbon monoxide and nitrogen oxides produced in the asynchronous ignition cylinder will be lower than that of the synchronous ignition.