Effect Of Diesel Split Injection On Low Load Performance Of Marine Diesel/Natural Gas Dual Fuel Engine

With the shortage of petroleum resources and the increasingly serious environmental pollution,marine diesel/natural gas dual fuel engine with clean and efficient natural gas as the main fuel has gradually become one of the main development trends of marine power in China,and has been widely concerned.At present,the problem of high CH₄ and CO emissions of marine diesel/natural gas dual fuel engine under low load conditions is quite prominent,which is difficult to meet the requirements of the second stage of marine engine exhaust pollutant limits.It limits the application and promotion of diesel/natural gas dual fuel engine in ship field.In order to solve this problem,the influence of diesel split injection on low load performance of marine diesel/natural gas dual fuel engine was experimentally studied on an electronically controlled high pressure common rail 6-cylinder marine diesel/natural gas dual fuel engine platform,and the coupling effect of diesel split injection parameters was further analyzed.The test was conducted at 1134r/min and 25%load.The diesel pre injection timing range was 40～60°CA BTDC,the pre injection diesel flow rate was 0.389kg/h to 1.213kg/h,the main injection timing range was-2～10°CA BTDC,the main injection diesel flow rate was 0.920kg/h to 2.756kg/h,the natural gas replacement rate was 85%to 93%,and the excess air coefficient was 1.53 to 1.65.In this range,100 test points are designed.The test results show that:under low load conditions,the delay of diesel pre injection timing,the increase of diesel pre injection mass ratio,the advance of diesel main injection timing and the decrease of diesel main injection mass ratio will lead to the improvement of power performance and economic efficiency,reduction of CH₄ and CO emissions and increase of NO_X emission of marine diesel/natural gas dual fuel engine.The coupling effect analysis of diesel split injection parameters shows that:compared with diesel pre injection timing,diesel main injection timing and diesel pre injection mass ratio have more obvious effects on power performance,economy,CH₄ and CO emissions of marine diesel/natural gas dual fuel engine under low load;compared with diesel pre injection timing and diesel pre injection mass ratio,diesel main injection timing has more obvious influence on NO_X emission of marine diesel/natural gas dual fuel engine under low loadThe diesel split injection mode to reduce CH₄ and CO emissions of marine diesel/natural gas dual fuel engine under low load is as follows:firstly,increase the proportion of diesel pre injection mass ratio,which improves the power and economy of marine diesel/natural gas dual fuel engine,and reduces CH₄ and CO emissions.After that,the main diesel injection timing is delayed and the diesel pre injection timing is advanced to reduce the NO_X emission to meet the emission limit requirements.In this process,the interval angle between diesel pre injection and diesel main injection should be less than 50°CA.