柴油机后处理系统N2 O排放特性的试验研究

摘要

A bench test is conducted on the after-treatment system of a heavy-duty diesel engine to study its N2 O formation characteristics, including the N2 O formation rule in the processes of active regeneration in diesel par-ticulate filter ( DPF) , the reaction in selective catalytic reduction ( SCR) system and the oxidation in ammonia slip catalyst ( ASC) . The results show that in active regeneration of DPF, N2 O is formed in a by-action occurring on cat-alyst surface and between diesel fuel injected into exhaust pipe and nitrogen oxides in exhaust gas. With the increase in the temperature of diesel oxidation catalyst exit, the quantity of N2 O produced shows a tendency of rise first and then fall. In the reaction of SCR system, the most N2 O is formed with Cu-zeolite catalyst, the less with Cu/Fe com-pound catalyst and very few with other catalysts, and for former two catalysts, the quantity of N2 O produced shows a tendency of "rise then fall and rise again" when the temperature of SCR catalyst increases. The ammonia escaped from SCR also produces N2 O due to its oxidation in ASC with a rather large quantity of N2 O formed at a temperature range of 200~250℃.%对一台重型柴油机的后处理系统进行台架试验,研究其N2 O生成特性,包括在颗粒捕集器( DPF)主动再生、选择性催化还原( SCR)反应和泄漏氨气在氨气氧化催化器( ASC)的氧化过程中一氧化二氮( N2 O)的生成规律。结果表明,DPF主动再生时,喷入排气管的柴油与排气中的氮氧化物在催化剂表面发生副反应生成N2 O,其生成量随DOC出口温度的升高呈现先增后减的趋势。在SCR反应中,Cu沸石催化剂生成的N2 O最多,Cu/Fe复合催化剂次之,而其它催化剂生成的N2 O很少；对于前两种催化剂,随着温度的升高,N2 O生成量呈先增后减再增的趋势。从SCR催化器泄漏的氨气在ASC中被氧化生成N2 O,温度在200~250益时N2 O生成量较大。