Technical Paper
Understanding catalyst overheating protection (COP) as a source of post-TWC ammonia emissions from petrol vehicle
2022-08-13
2022-01-1032
In this research, the formation of post-catalyst ammonia emission from a China-6a certified light-duty vehicle was examined at the chassis level, with the presence of catalyst overheating protection (COP). Given the well-aligned changes in catalyst temperature and ammonia concentration, a COP event has been confirmed as a source of extra ammonia emission because it required the use of richened air-fuel mixtures which resulted in high CO and THC emissions. The results also inferred that post-catalyst ammonia from a gasoline vehicle could be formed at any temperature once the catalyst got warm enough, unlike it was reported in some prior reactor-based studies that there was a so-called “celling temperature”, and above which, the production rate of post-catalyst ammonia would be restricted. Moreover, ammonia storage phenomenon in the constant volume sampling (CVS) system at a time scale of a few hundred seconds was observed, which in general agreed with previous publications.