Study on ignition control strategy of spark plug-assisted methanol engine
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甲醇缸内直喷点燃技术在提高燃油经济性和降低排放方面有着显著优势,但存在中低负荷工况下燃烧不稳定及容易失火等问题,为此以MAN公司L23/30H型柴油机作为目标机型构建三维仿真模型,通过Converge软件建立原柴油机的缸内燃烧仿真模型,并结合甲醇的理化性质和甲醇燃烧反应机理建立甲醇缸内直喷发动机燃烧仿真模型,分析火花塞位置、火花塞数量以及甲醇喷射时刻和点火时刻对缸内燃烧特性的影响.研究发现:当火花塞安装在位置1(距燃烧室壁面40 mm)时,缸内压力峰值和燃烧放热率峰值较大;根据对燃烧效率、指示热效率和燃烧相位的分析,喷射时刻对应的上止点前曲轴转角(crank angle before top dead center,CA BTDC)为30°、点火时刻对应的CA BTDC为15°的喷射策略最有利于甲醇的缸内燃烧;使用多点点火策略会促进其余(未通过火花塞引燃)雾束的着火,但同时需要喷射时刻与点火时刻的优化匹配,不然会导致燃烧速率加快,燃烧相位提前,使热能转化成指示功的有效程度降低,指示热效率下降,不利于发动机高效工作.
Methanol in-cylinder direct injection ignition technology has significant advantages in improving fuel economy and reducing emissions,but there are problems such as unstable combustion and easy to misfire under low and medium load conditions.Therefore,this paper takes the L23/30H diesel engine of MAN company as the target model to build a three-dimensional simulation model,and establishes the in-cylinder combustion simulation model of the original diesel engine by Converge software.Combined with the physicochemical properties of methanol and the reaction mechanism of methanol combustion,the combustion simulation model of the methanol in-cylinder direct injection engine is established,and the effects of the spark plug position,the number of spark plugs,and the timing of methanol injection and ignition on the in-cylinder combustion characteristics is analyzed.It is found that the peak in-cylinder pressure and the peak combustion exothermic rate are larger when the spark plug is installed at position 1(40 mm from the wall of the combustion chamber).According to the analysis on the combustion efficiency,the indicated thermal efficiency,and the combustion phases,the injection strategy with a crank angle before top dead center(CA BTDC)of 30° for the injection timing and 15° for the ignition timing is the most favorable for the in-cylinder combustion of methanol.The use of the multi-point ignition strategy can promote the ignition of the remaining(not ignited by the spark plug)mist bundles,but at the same time,it requires an optimal matching of the injection timing and the ignition timing.Otherwise,it can lead to accelerated combustion speed and advanced combustion phases,so that the effective degree of heat energy converted into indicator work is reduced,and the indicated thermal efficiency is reduced,which is not conducive to the efficient work of the engine.
low/zero carbon fuelmethanol fuelin-cylinder direct injectionmulti-point ignitionindicated thermal efficiency
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