Reduction of automotive nitrous oxide emissions during cold start comprises supplementary injection of ammonia from holding reservoir

摘要

In the reduction of automotive nitrous oxide exhaust emissions by selective catalytic reduction, a dosed amount of a first agent (urea) is injected to the exhaust gases. The first agent is especially first subject to partial chemical conversion into a second type of agent (ammonia) and intermediate ammonia storage (4). The second agent is introduced to the exhaust gases in parallel, or as an alternative to, the first agent. In normal operation only the first agent is introduced to the exhaust emissions. The second agent is introduced during and immediately after a cold start. Chemical conversion takes place during normal operation and continues only until the ammonia storage unit (4) is full. The amount of ammonia stored is adequate to cover the cold-start phase. The storage unit is a zeolite body or a salt which forms an ammonium complex. The storage unit may be externally heated by exhaust gases as required to maximize ammonium discharge. An Independent claim is included for an exhaust gas treatment assembly for use in the above process.