WLTC循环下汽油车氨排放影响因素分析

为研究WLTC（worldwide light-duty test cycle，全球轻型汽车驾驶循环）循环下常规污染物和行驶工况对汽油车NH₃排放的影响，选定一辆满足国Ⅴ排放标准、配备TWC（three way catalyst，三元催化器）尾气后处理装置的轻型汽油车，测定其在WLTC循环下CO₂、CO、NO_x和NH₃的摩尔排放量.结果表明:CO、NO_x与NH₃排放的线性相关系数分别为0.626和0.321.NH₃高排放的出现除了伴有CO的高排放外，还需车辆具有高速和持续的正向加速度.用配备TWC尾气后处理装置前、后NO_x排放量的差值表示NO_x的转化量发现，NO_x的高转化量并不一定对应NH₃的高排放量，在循环后期大量产生的NO_x会抑制NH₃的排放.由于VSP（vehicle specific power，比功率）能综合反映行驶工况，研究行驶工况对NH₃排放的影响时主要分析VSP与NH₃之间的关系，通过VSP聚类方法将VSP划分为不同区间，得出当VSP Bin（vehicle specific power bin，比功率区间）大于0时，基于CO₂的NH₃排放基本呈随VSP Bin增大而增加的规律，并且基于CO₂的NH₃排放量最大值对应的VSP Bin为持续正向加速工况.研究显示，常规污染物中CO和NO_x对NH₃的排放会产生不同程度的影响，加速度作为行驶工况的表征参数之一会直接或通过影响CO和NO_x的排放间接影响NH₃的生成. 

Analysis of Factors Affecting Ammonia Emission from Gasoline Vehicles under WLTC Cycle

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.