高低压EGR对重型柴油机性能影响的试验研究

Effects of High and Low Pressure EGR on Heavy-Duty Diesel Engine Performance

针对一台两级增压的高压共轨重型柴油机,围绕高压废气再循环(HPEGR)和低压废气再循环(LPEGR)在不同工况下对重型柴油机的两级增压系统、进排气参数和排放特性的影响机理展开试验研究。研究结果表明:不同工况下,仅开低压EGR对柴油机的两级增压系统、进排气参数基本无影响,而仅开高压EGR对以上参数影响较大;中速中高负荷在开低压EGR时,可明显改善NOx与燃油消耗率(BSFC)和NOx与烟度的Trade-off关系;而高速开高压EGR时,也可明显改善NOx与BSFC的Trade-off关系,但烟度会出现小幅度恶化趋势;在高速高负荷点开高压EGR时,存在由于泵气损失降低带来油耗下降和燃烧恶化带来油耗升高的平衡点,但在高速低负荷点并未出现类似平衡点;在高低压EGR分配策略方面,中速中高负荷时以低压EGR为主,高速低负荷时以高压EGR为主,高速高负荷时以高压EGR为主,低压EGR为辅,从而实现较低原排的同时拥有较好燃油经济性和烟度。

An experimental study was performed on a common-rail heavy-duty diesel engine with two-stage supercharging,which was about the effect mechanism of two-stage supercharging system,intake and exhaust manifold parameters and emission characteristics under different conditions.The results show that only low pressure EGR has little effect on the two-stage supercharging and intake and exhaust manifold parameters,but only high pressure EGR has an apparent effect.The low pressure EGR can improve the Trade-off relationship of NOx with BSFC and soot respectively in medium and high loads at medium speed and the high pressure EGR can also improve the Trade-off relationship of NOx with BSFC at high speed,but with the deterioration of soot emission.There is a contradiction at high speed and high load that the fuel consumption drops due to the reduced pump loss and increases due to the deteriorated combustion,which will not occur at high speed and low load.Accordingly,it should be adopted to mainly use low pressure EGR in medium and high loads at medium speed,mainly use high pressure EGR at high speed and low load,and use high pressure EGR assisted with low pressure EGR at high speed and high load,and hence both the low emission and the good fuel economy and soot can be achieved.