柴油和甲醇喷射相位对柴油微引燃甲醇直喷发动机的影响

Effects of diesel and methanol injection phases on the engine of diesel ignition and methanol direct injection

基于1台增压中冷柴油机,搭建了耦合化学反应动力学机理的柴油微引燃甲醇直喷发动机三维仿真模型。其中,柴油作为引燃物,在上止点前被喷入缸内,随后喷入主燃料甲醇。通过改变柴油和甲醇的喷射相位及喷射间隔角,研究了其对燃烧特性、燃油经济性、爆震强度及排放的影响,且通过观察温度云图来直观地分析缸内燃烧情况。数值模拟结果表明:太小的喷射间隔角会导致失火或粗暴燃烧,太大的喷射间隔角会降低燃油经济性。随着喷射间隔角的增大,缸内峰值压力降低,滞燃期先降低后保持不变,CA50呈近似线性增大。保持喷射间隔角不变,柴油喷射相位提前会导致更高的缸内峰值压力、声响强度(ringing intensity,RI)和NOx排放,以及更低的等效指示燃油消耗率(equivalent indicated specific fuel consumption,EISFC)和Soot排放。

A three-dimensional simulation model of an engine with directly injected methanol and pilot diesel,coupled with chemical kinetic mechanism,is built,based on a supercharged intercooled diesel engine.The diesel is injected into the cylinder before the top dead centre(TDC)to act as a pilot,and then methanol is also directly injected afterwards as the main fuel.The effects on combustion characteristics,fuel economy,knock intensity and emissions are investigated by changing the injection phase and interval angle of diesel and methanol,and the in-cylinder combustion is visually analysed by observing the temperature cloud map.Numerical simulation results show that too small interval angle leads to misfire or roar combustion,and too large interval angle reduces fuel economy.As the increase of interval angle,the in-cylinder pressure peak decreases,the ignition delay reduces first and then remains unchanged,and the CA50 increases in a nearly linear way.Earlier diesel injection contributes to higher in-cylinder pressure peak,ringing intensity(RI)and nitrogen oxides(NOx)emission,as well as lower equivalent indicated specific fuel consumption(EISFC)and soot emission with the same interval angle.