柴油多次喷射对船舶DMCC发动机的影响

Effect of Diesel Multiple Injection on Marine DMCC Engines

为探究带预喷的柴油多次喷射对柴油/甲醇组合燃烧(diesel methanol compound combustion,DMCC)船舶发动机性能、燃烧和排放的影响,在一台船舶柴油机进行DMCC模式改造的基础上,选择该发动机推进特性常用的3个工况点开展了纯柴油模式和双燃料模式下有无预喷的试验研究.3个工况点分别为发动机25%、50%和75%额定功率点.研究结果表明,发动机采用带预喷的喷射策略可以使双燃料模式下的甲醇替代率大幅提升,并使当量比油耗降低,且负荷越大,当量比油耗降低越多.采用预喷策略后,发动机在两种燃料模式下的燃烧开始时刻都会提前,但在双燃料模式时提前更多,同时双燃料模式下的放热率峰值和压升率峰值大幅降低,燃烧定容度增加,热效率提高.此外,预喷策略可以使双燃料模式下的NOx排放大幅降低,3个工况点分别降低24.97%、37.98%和40.02%;PM(particulate matter)排放略有增加,但仍低于纯柴油无预喷模式.

To investigate the effect of pilot injection on the performance,combustion,and gas emissions of marine diesel/methanol compound combustion(DMCC)engines,a marine diesel engine was modified into the one featuring DMCC combustion mode.Further,bench tests for the marine DMCC engine were conducted in pure diesel mode and diesel/methanol dual fuel mode under three normally used operating cases,i.e.,25%,50%,and 75%of the full load with propeller characteristics.The testing results display that,in dual fuel mode,a pilot injection strategy can significantly increase methanol replacement rates and reduce brake specific fuel consumption(BSFC).Moreover,the higher the load,the larger the reduction in BSFC.When the pilot injection strategy was applied,ignition was initiated earlier;this change was more obvious in dual fuel mode than in pure diesel mode.When the pilot injection strategy was applied in the dual fuel mode,the peaks of the heat release and pressure rise rates remarkably declined;at the same time,the constant volume combustion ratio and the thermal efficiency increased.And NOx emissions remarkably decreased in dual fuel mode by 24.97%,37.98%,and 40.02%for 25%,50%,and 75%operating cases,respectively.Further,PM emissions increased slightly but remained lower than that in pure diesel mode without pilot injection.