EGR对点燃式大功率甲醇发动机的影响研究

Experimental Study into the Effect of EGR on a Spark Ignition High-power Methanol Engine

以一台进气道喷射点燃式大功率甲醇发动机为试验对象,研究高、中、低三转速低负荷工况下不同EGR率对M100甲醇发动机燃烧和排放特性的影响。试验过程中保持发动机转速、喷醇量、过量空气系数和点火提前角不变。研究结果表明:在燃烧特性方面,甲醇发动机应用高压EGR系统,能够使峰值缸压和放热率下降,燃烧重心推迟,滞燃期延长,循环变动率增大,压升率降低;虽然燃烧持续期有所缩短,但随着EGR率的增大,主体放热过程(约占累计放热量70%)的燃烧化学反应速度减缓。在排放特性方面,随着EGR率的增加,CO和NO_(x)排放显著降低,较EGR率为0%时最大降低幅度分别高达39.13%和97.17%;HC排放最大增长幅度为341%;未燃甲醇和甲醛的排放呈现上升的趋势,最大增长幅度分别高达376.3%和163.1%。

Taking a port injection spark ignition type high-power methanol engine as the test object,the effects of different EGR rates on the combustion and emission characteristics of M100 methanol engine under high,medium and low speed and low load conditions are studied.During the test,keep the engine speed,the amount of methanol injection,the excess air coefficient and the ignition advance angle unchanged.The research results show that:in terms of combustion characteristics,the application of high-pressure EGR system to methanol engines can reduce peak cylinder pressure and heat release rate,delay the combustion center,prolong the ignition delay period,increase the coefficient of variation,and reduce the pressure rise rate;although the burn duration has been shortened,but as the EGR rate increases,the combustion chemical reaction speed of the main heat release process(approximately accounting for 70% of the cumulative heat release)slows down.In terms of emission characteristics,as the EGR rate increases,CO and NO_(x)emissions are significantly reduced,and the maximum reductions are as high as 39.13% and 97.17% compared with no EGR;l the largest increase in HC emissions was 341%;unburned methanol and formaldehyde emissions show a rising trend,and the maximum reductions are as high as 376.3% and 163.1%.