Analysis Of The Heat-work Conversion Process In Cylinder And General Trends For Natural Gas Engines Under Steady And Transient Conditions

The study was carried out in a turbocharged, natural gas fuelled, spark ignited engine. Based on electric engine test bench and combustion analyzer and other supporting equipments, both steady state and transient tests are conducted. Through the analysis of experimental data, it will analyze the heat-work conversion process in cylinder of natural gas engine under steady and transient conditions, and summarize the general trends.The steady-state condition test is first to be carried out to obtain a large number of test data, including the cylinder pressure traces of the entire operating cycle, the performance parameters and operating parameters. By the analyses of the main combustion characteristics, performance parameters that affect the heat-work conversion process in cylinder, it could be concluded that XMEP and the intake parameter(ρ0/λ) have a good linear relationship; The inlet pressure has a linear relation with the maximum explosion pressure in cylinder in different speed conditions; the position of the peak cylinder pressure is decided by the 50% burning location; Keeping in heavy load conditions can reduce much pumping losses and mechanical friction losses and improve engine thermal efficiency; Excess air coefficient is the main factor in combustion process, speed and load are secondary factors, the leaner the mixture is the longer the combustion duration will be; Engine load have little influence on 50% burning location; 50% burning location has a significant impact on the heat-work process and need be optimized; FMEP and BMEP are positively correlated to the engine speed.And then, transient condition tests are conducted. Through adding compressed air into the intake system on different locations under different operating conditions, the intake boost pressure would undergo an abrupt increase and then level off. This study take that process as transient condition. Engine operating and performance parameters are cycle-to-cycle continuous recorded during the load step transient process, together with the in-cylinder pressure traces. Illustrate and analyze the influence of key parameters to the heat-work conversion process and find out the general trends that some conclusions could be drawn. Speed and the other parameters have no obvious interdependent relationship, while engine speed fluctuation is very small, the other operating parameters and performance parameters could change dramatically. The influence of excess air coefficient on the combustion process in engine cylinder is greater than changes in load, speed, etc. The in-cylinder process during a transient load step could be better understood by the cycle-to-cycle monitoring of cylinder pressure traces and ROHR curves.