应用推迟点火、废气再循环及过稀混合气降低稀燃甲醇发动机NO_x排放

NO_x emission reduction of a lean-burn methanol engine by retarding ignition timing,exhaust gas recirculation and leaner air/fuel mixture

为降低稀燃时NO_x排放及改善燃油消耗率-NO_x排放"(be-NO_x)"折中关系,以一台基于柴油机改制的进气道喷射点燃式甲醇发动机为试验对象,在1400r/min、4.52kg/h甲醇消耗量工况条件,以及1.5过量空气系数和21°CA BTDC点火提前角的基础上,研究了推迟点火、废气再循环(EGR)及过稀混合气3种策略对稀燃甲醇发动机燃烧和NO_x排放的影响。结果表明:3种策略均能在机内有效净化NO_x排放,实现接近零排放的效果。在相同NO_x排放水平下,与过稀混合气策略相比,EGR策略的燃烧滞后和延长程度有所减弱,循环变动降低,而推迟点火策略的燃烧更为滞后,但燃烧持续期和循环变动减小。对比而言,EGR策略能获得更佳的"be-NO_x"折中关系;推迟点火策略的"be-NO_x"折中性能虽较EGR策略有所降低,但排气温度有所升高,有利于提高样机在低负荷时后处理器的转化效率,从减小排放角度具有一定应用潜力。

To reduce NO_x emission and improve the trade-off relationship between fuel consumption ratio（be）and NO_x under lean-burn operation,the influences of three strategies：retarding ignition timing,Exhaust Gas Recirculation（EGR）and leaner air/fuel mixture on the engine combustion performance and NO_x emission were experimentally investigated at light load on a port-injection and spark ignition methanol engine,which was modified from a diesel engine.In the experiments the engine speed,fuel consumption,air excess coefficient and ignition advance angle were fixed at 1400r/min,4.53kg/h,1.5mand 210°CA BTDC respectively.Results show that all three strategies can achieve the effect of NO_x purification inside the cylinder,and the NO_x emission approach zero.At the same level of NO_x emission,compared with the air/fuel mixture strategy,the combustion delayingand extension of the EGR strategy are weakened,and the coefficient of cyclic variation is decreased.The combustion of the retarding ignition timing strategy is more delayed than the leaner air/fuel mixture strategy,but the duration of combustion and the coefficient of cyclic variation are decreased.In contrast,the EGR strategy can get better be-NO_x trade-off than retarding ignition timing;however,the rise of the exhaust temperature by retarding ignition timing is helpful to improve the conversion efficiency of the catalytic converter at light load.Therefore,retarding ignition timing has the application potential to reduce emissions.