柴油引燃式天然气发动机最佳引燃柴油量及过量空气系数浓限、稀限的研究

A Study on Determination of Amount of Pilot Injection and Richand Lean Boundaries of Premixed CNG/Air Mixture for aCNG/Diesel Dual Fuel Engine

以气口顺序喷射、全电控、柴油引燃天然气发动机为实验发动机,对柴油引燃天然气发动机的最佳引燃柴油量及过量空气系数的浓限、稀限进行了研究。研究发现:对于柴油引燃天燃气发动机的不同运行工况,存在相应的最佳引燃柴油量;最佳引燃柴油量并非越小(或天然气替代率越高)越好,在较小的引燃柴油量下,存在一个对碳烟排放不敏感的引燃柴油量;在这个不敏感的引燃柴油量范围内,适当增加引燃柴油量可以使天然气/空气混合气工作在较稀的过量空气系数下,降低NOx排放。通过实验得到了天然气/空气混合气过量空气系数的浓限、稀限,指出过量空气系数浓限是由NOx的排放标准所决定的,稀限则是由碳烟、HC、CO排放标准所决定的。

A sequential port injection,lean burn, fully electrocontrolled CNG/Diesel dual fuel engine was developed based on a turbocharged and intercooled D.I.diesel engine.During the optimization of engine overall performance,the effects of pilot diesel and premixed CNG/air mixture equivalence ratio on emissions (CO,HC,NOx,soot),knocking,misfire and fuel economy are studied by summarizing and analysis of experimental data.The rich and lean boundaries of premixed CNG/air mixture versus engine load are also given,considering acceptable value of NOx and THC emissions respectively.It is interesting to find that there is a critical amount of pilot diesel for each load and speed point,which proved to be the optimun amount of pilot fuel.Decrease in amount of pilot diesel from this optimum amount results in increase of NOx emissions,because the premixed CNG/air mixture must get richer,otherwise THC emission would increase.However,the soot emission almost keeps unchanged at a very low level.