道路车用柴油机国六排放选择性催化还原系统的开发与验证

设计开发了一种配备新型周向变流式排气混合器的筒式后处理系统,以某型3.0L排量的国六柴油机后处理为例,首先设计了排气混合器结构,建立了该催化器的流动及尿素喷射、雾化和扩散模型,进行全尺寸排气流场模拟分析,研究了混合器后的速度均匀性、NH₃浓度分布和压降损失等,并对特征尺寸进行了优化。结果表明,优化的结构尺寸及设计使标定工况下NH₃均匀度可以达到0.996,混合器压降不超过4.17kPa。然后进行了发动机台架试验,验证了新开发设计优化的后处理系统阻力较小,标定工况下实测的NH₃均匀度高达0.98,不同空速和温度情况下,不带扰流板的混合器表现更优。最后进行了发动机排放试验,全球统一瞬态循环和全球统一稳态循环结果达到国六标准要求,确证了新开发的选择性催化还原系统及排气混合器能够用于道路车辆国六重型柴油机。

Design, Development and Validation of a SCR System for China 6 Emission Regulation of Road Diesel Engine

To meet the China 6 requirements of road diesel engine, the uniformity of fluid velocity and NH3 distribution before entering the SCR converter must be greatly improved, and the system pressure drop loss and geometrical size should be minimized as far as possible. A drum-type aftertreatment system equipped with a new type circumferential variable flow exhaust mixer is designed. Taking the aftertreat-ment of a 3.0L China 6 emission diesel engine as an example, firstly, the structure of exhaust mixer is designed, the flow and urea injec-tion ,atomization and diffusion models of the catalytic converter were established, the full-scale exhaust flow field simulation analysis was carried out, the velocity uniformity, NH3 concentration distribution and pressure drop loss of the mixer were studied, feature size is optimized, and the results show the uniformity of NH3 can reach 0.996 with the pressure drop of 4.17kPa in rated condition. The ex-periment showed that the new designed system has smaller resistance, 0.98 NH3 uniformity in rated condition measured, the mixer with-out spoiler performs better in different space velocity and temperature. Finally, the engine emission test was carried out, the WHTC and WHSC test cycle results reached the requirements of China 6 standard, confirming that the newly developed SCR system and mixer can be used in the China 6 heavy-duty diesel engine for road vehicles.