空气辅助和无空气辅助SCR系统尿素喷雾特性的对比试验研究

摘要

利用高速摄影技术,对空气辅助和无空气辅助两种典型的柴油机氮氧化物(NOx)选择催化还原(SCR)尿素喷射系统,在常温常压下的尿素喷雾特性和在定容燃烧弹内对空气辅助喷射系统在不同温度下的尿素喷雾特性进行了可视化试验研究.结果表明,随着尿素溶液喷射速率的提高,空气辅助喷射系统的喷雾贯穿距增大,喷雾锥角变小,且随着环境温度的上升贯穿距明显减小,发生碰壁现象的可能性减小；而无空气辅助喷射系统的喷雾形态则基本不受喷射速率的影响.应用粒子动态分析仪(PDA)对两种喷射系统的喷雾粒径分布进行的测试结果表明,空气辅助喷射系统的喷雾液滴粒径明显小于无空气辅助喷射系统,因而具有良好的喷雾特性.%By using high-speed photography, a visualized experimental study is conducted on the urea spray characteristics of two typical selective catalytic reduction (SCR) injection systems (with and without air assistance) at normal temperature and pressure, as well as that of SCR injection system with air assistance in constant-volume combustion bomb at different temperatures. The results show that for the SCR injection system with air assistance, the penetration distance of urea spray gets longer and the spray angle gets smaller with the increase of urea injection rate, and the spray penetration distance gets shorter, hence the possibility of wall impingement reduces with the rise in ambient temperature. Whereas for the SCR injection system without air assistance, the injection rate has basically no effects on urea spray pattern. In addition, the measurements of spray droplet size indicate that the droplet size in SCR injection system with air assistance is much smaller compared with that in SCR injection system without air assistance, hence leading to better spray characteristics.