废气再循环瞬态修正控制策略对 重型柴油机排放性能的影响
Influence of EGR Transient Correction Strategy on Emission Performance of Heavy Duty Diesel Engine

针对重型柴油机瞬态工况(特指恒定转速、转矩瞬增工况)空气系统响应迟滞造成的排放恶化问题,设计了废气再循环(EGR)瞬态修正控制策略,从EGR阀预控制和瞬态需求空气量两方面进行EGR瞬态修正:当判定发动机处于瞬态工况时,将EGR阀预控制开度设定为0,加快EGR阀关闭速度;依据瞬态程度修正需求空气量,使实际进气量更早满足需求空气量,实现EGR阀适时开启。试验结果表明:经过EGR瞬态修正,改善了瞬态工况排放恶化、发动机动力性响应不及时等问题;在WHTC(world harmonized transient cycle)瞬态循环中加入EGR瞬态修正后,氮氧化物(NOx)排放降低了4.7％,碳烟排放降低了46.4％,碳氢化合物和一氧化碳排放分别降低了8.5％和30.3％,但二氧化碳排放增加了0.3％,油耗增大了0.6％。EGR瞬态修正控制策略虽然牺牲了0.6％的油耗,但是显著改善了NOx、碳烟、碳氢化合物和一氧化碳等有害气体的排放,因此可为重型柴油发动机排放性能的改善提供借鉴。
Aiming at solving the emission deterioration of diesel engine under transient working conditions caused by delayed response of air system, an exhaust gas recirculation (EGR) transient correction strategy is developed. EGR valve pre？？control and desired air mass are both corrected under the transient correction strategy. The EGR valve pre？？control value is set to zero when the engine is at a transient working condition to accelerate the closing of EGR valve. Meanwhile, the desired air mass is modified according to the transient level of engine by making the EGR valve open at reasonable time. With the EGR transient correction control, engine emissions and drivability under transient working condition are improved. Test results show that reductions of 4.7％ NOx, 46.4％ soot, 8.5％ HC and 30.3％ CO, but increase of 0.6％ fuel consumption, are obtained. Considering the obvious emissions improvement, the tiny fuel consumption increase can be ignored. It can be concluded that the proposed EGR transient correction strategy is effective for diesel engine performance improvement