WLTC循环下汽油车氨排放影响因素分析

In order to study the effects of the conventional pollutants and driving conditions on the ammonia emission of gasoline vehicles under the WLTC cycle, the molar emissions of CO₂, CO, NO_x and ammonia were measured on the selected vehicles which met the China-5 emission standard and were equipped with three-way catalyst (TWC). The results showed that the linear correlation coefficients of CO, NO_x and ammonia emissions were 0.626 and 0.321, respectively. The high emission of ammonia was accompanied not only by high CO emission, but also by high speed and continuous positive acceleration. The differences of the NO_x emission concentrations between pre-catalyst and post catalyst were used to express the conversion amount of NO_x. It was found that the high conversion of NO_x didn't necessarily correspond to the high emission of ammonia. In the later stage of the cycle, the large amount of NO_x generation would restrain ammonia emissions. As the vehicle specific power (VSP) can reflect the driving condition synthetically, the relationship between VSP and ammonia was analyzed when studying the influence of driving cycles on ammonia emissions. It could be concluded that when VSP Bin was greater than 0, the ammonia emissions based on CO₂ increased with the increasing of VSP Bin by using the VSP clustering method. And the VSP range corresponding to the maximum ammonia emissions based on CO₂ had a continuous positive acceleration. In conclusion, CO and NO_x had different effects on ammonia emissions, and the acceleration, as one of the characterization parameters of driving conditions, would directly or indirectly affect the formation of ammonia by affecting CO and NO_x emissions.