过量空气系数对甲醇/柴油反应活性控制压燃发动机性能的影响

Effects of Excess Air Coefficients on Performances of Methanol/Diesel Reactivity Controlled Compression Ignition Engines

对某高压共轨柴油机进气歧管进行改造,搭建了甲醇/柴油二元燃料反应活性控制压燃(reactivity controlled compression ignition,RCCI)发动机专用试验台架,系统地研究了最大转矩转速(1 600 r/min)、不同负荷下甲醇替代率和过量空气系数对发动机经济性与排放性能的影响规律。结果表明:中、低负荷下,随着甲醇替代率增大,有效当量燃油消耗率先降低后略微升高,有效热效率先增加后略微降低,排气温度降低;中高、高负荷时,随甲醇替代率增大,有效当量燃油消耗率和排气温度降低,有效热效率升高;负荷率75%下,甲醇替代率为30%时,有效当量燃油消耗率较纯柴油模式平均降低3.8%,有效热效率则平均升高6.7%。不同负荷工况下,随甲醇替代率增大,NO;排放和烟度大幅降低,CO;排放量减少,CO、甲醇和甲醛排放量增加。中、低负荷下,烯烃排放量随甲醇替代率升高而增加,中高、高负荷下则随替代率升高而降低。不同负荷、不同甲醇替代率下,随着过量空气系数减小,CO;排放量和烟度增加,NO;和CO排放变化不明显,甲醇排放量减少;高负荷下,随过量空气系数的减小,烯烃排放升高,甲醛排放降低;低负荷下,随过量空气系数减小,烯烃排放降低,甲醛排放变化不明显。采用甲醇/柴油RCCI燃烧策略有助于降低CO;、NO;排放和烟度,双燃料模式下适当关小节气门开度,减小过量空气系数,对降低甲醇、甲醛非常规污染物排放有利。

The intake manifold of the diesel engine was modified to run the engine in dual fuel reactivity controlled compression ignition combustion. The effects of different methanol substition rates and excess air coefficients on the economic performance and emission characteristics of diesel engines operated in reactivity controlled compression ignition(RCCI)mode at different load conditions with a constant speed of 1 600 r/min were studied. Results revealed that with the increase of methanol substitution rate,the brake specific fuel consumption(BSFC) first decreased and then slightly increased,and the effective thermal efficiency increased first and then slightly decreased at low and middle loads. At high load, with the increase of methanol substitution rate,the BSFC and exhaust temperature decreased,and the effective thermal efficiency increased.The BSFC dropped by 3. 8%,and the effective thermal efficiency rose by 6. 7% with 30% methanol substition rate when the throttle valve was fully opened at 75% load. With the increase of methanol proportion,the NO;and smoke emissions dropped dramatically,and the CO;emissions reduced,while the CO,methanol and formaldehyde emissions increased sharply. With the decrease of excess air coefficient,the CO;and smoke emissions rose,and the NO;and CO emissions did not change significantly,while the methanol emission decreased. With the decrease of excess air coefficient, the olefin emission increased, and formaldehyde emission decreased at high load,while the olefin emission decreased,and formaldehyde emission changed little at low load. Methanol/diesel RCCI combustion strategy can reduce CO;, NO;and smoke emissions significantly. Under RCCI mode,it is beneficial to reduce the non-regulated emissions by properly reducing the valve opening and the excess air coefficient.