Study On Spark-assisted Ignition Controlled Auto-ignition Combustion Characteristics Of Methanol Engine

Methanol fuel has the advantages of good explosion resistance,high lean burn tolerance,and low cost and easy availability.It is worth studying the SI-CAI combustion of methanol from both the combustion performance and energy safety perspectives.In this study,Changchai ZR180 single-cylinder diesel was converted into an electronically controlled engine with spark ignition and port injection.The external heater was used to heat the intake air to achieve methanol SI-CAI combustion.The combustion boundary conditions and The effect of compression ratio on the SI-CAI combustion process of methanol,and a cam-driven hydraulic variable valve mechanism suitable for Changchai ZR180 is designed.This mechanism can get rid of intake air heating to achieve SI-CAI combustion.The research results show that the ignition timing can adjust the heat release ratio of the two stages of SI-CAI combustion,so that SI combustion transitions to SI-CAI combustion.Boundary conditions affect the ignition timing required for SI-CAI combustion.The excess air coefficient increases.The boundary below SI-CAI combustion ignition timing advances.The larger the excess air coefficient,the larger the boundary advance below the ignition advance angle;the higher the speed.The lower boundary of the ignition timing is further advanced;the intake air temperature is increased,and the lower boundary of the SI-CAI combustion ignition timing is pushed back,the operating range of the SI-CAI combustion mode is increased.Increasing the intake air temperature and the ignition timing will advance the SI-CAI combustion phase,accelerate the combustion speed,increase the maximum burst pressure,pressure increase rate,heat release rate and compression ignition ratio,shorten the combustion duration,and burn.The cyclic variation is reduced,and there is an optimal ignition timing to maximize IMEP.The increase of the excess air coefficient reduces the maximum burst pressure,pressure increase rate,and heat release rate of SI-CAI combustion,increases the duration of combustion,decreases IMEP,and increases the cycle variation coefficient.As the EGR rate increases,the maximum burst pressure,pressure increase rate,heat release rate,and temperature in the cylinder decrease,the combustion phase is delayed,and at the same time,the combustion stability is reduced.The HC and CO emissions increase,the NOx emissions decrease,and the combustion The cyclic variation coefficient is increased.Increasing the compression ratio can effectively expand the operating range and lean burn limit of SI-CAI combustion,make the lower boundaries of the ignition timing of SI-CAI combustion significantly shifted back,and reduce the requirements for intake air temperature.After increasing the compression ratio,the load range of SI-CAI is expanded,and the expansion effect is more obvious under high-speed and large-load conditions.After increasing the compression ratio,the maximum burst pressure,maximum heat release rate,maximum pressure increase rate,and temperature of SI-CAI combustion increase,and the combustion rate is accelerated,the combustion duration is shortened,the combustion cycle fluctuation is reduced.Finally,to improve the practicality of the SI-CAI combustion mode in the test prototype,this paper recalculates,simulates and arranges the cam-driven hydraulic variable valve mechanism developed by the research group based on the specific parameters of the test prototype.The cam driven hydraulic variable valve mechanism of this research prototype and preliminary processing trial production have laid the foundation for further research.