The steady and transient test of diesel engine were carried out under the conditions of pre-DOC and non-DOC and the effect of pre-DOC on NOx emission was studied .The results show that the pre-DOC can obviously increase the V (NO2 ):V (NOx ) volume fraction ratio st SCR entrance ,accelerate the SCR reaction ,raise the conversion efficiency of NOx and improve NOx emission .Effect of DOC on V (NO2 ):V (NOx ) volume fraction ratio decreases with the increase of oxygen content ,ex-haust temperature and air speed in ESC except idle .When the exhaust temperature exceeds a certain range ,the effect of V (NO2 ):V (NOx ) volume fraction ratio on NOx conversion rate decreases due to the sharp increase in the selectivity of NH3 to O2 .The limited heat of DOC reaction is not enough to increase the entrance temperature of SCR ,but the accumulated heat of ceramic substrate can increase the entrance temperature in ETC ,however it is not the main method to improve NOx emission .%对装配前置DOC和无DOC的SCR系统柴油机进行稳态和瞬态试验 ,研究了前置DOC在不同循环状态下对NOx 排放的影响.结果表明 :前置 DOC 能显著提高 SCR入口处 NO2 与 NOx 的体积比 V (NO2 ):V (NOx ) ,加速SCR反应 ,提高NOx 转化效率 ,改善NOx 排放 ;在ESC非怠速工况下 ,DOC对V (NO2 ):V (NOx )的影响会随着排气中氧含量和排气温度、空速的提高逐渐降低 ;温度超过一定范围时 ,N H3 对O2 的选择性突然提高 ,V (NO2 ):V (NOx )对NOx 转化效率的影响将减小 ;DOC内氧化反应产生的热量有限 ,不足以提高SCR入口处排气温度 ,而DOC陶瓷载体的储热特性在瞬态循环下会对SCR入口温度产生一定影响 ,但这并不是改善NOx 排放的主要原因.
展开▼
