重型天然气车实际道路排放特征与机理研究

为掌握重型天然气车在实际道路行驶过程中的排放特性，使用便携式车载排放测试系统(PEMS)对2辆国Ⅴ重型天然气车(简称“国Ⅴ车辆”)和2辆国Ⅵ重型天然气车(简称“国Ⅵ车辆”)进行实际道路排放测试，分析了CO和NO_x的排放特征和不同工况下的排放因子. 结果表明:①国Ⅴ车辆在3种代表性道路类型(市区路、市郊路、高速路)下CO和NO_x的高排放区主要分布在中低速区域的加速阶段，而国Ⅵ车辆CO和NO_x的高排放区在市区和市郊路上主要集中在速度大于30 km/h区间，在高速路两种污染物的高排放区分布较为零散. ②根据MOVES模型划分机动车比功率区间(VSP Bin)后发现，国Ⅵ车辆在Bin 11~Bin 18区间，CO和NO_x排放速率基本稳定且处于较低水平；在Bin 21~Bin 28区间，CO和NO_x排放速率均随VSP的增加而逐渐升高. ③国Ⅴ车辆综合工况下CO和NO_x排放因子分别为国Ⅵ车辆的1.1~3.9和3.3~8.2倍，其中，在市区路分别为3.0~25.0和11.3~30.2倍. ④国Ⅴ车辆的NO₂/NO_x(浓度比，下同)远高于国Ⅵ车辆，且在高速路国Ⅴ和国Ⅵ车辆的NO₂/NO_x均最低. 此外，对比不同研究的测试结果发现，本研究国Ⅵ车辆的CO和NO_x排放因子高于其他研究中国Ⅵ重型柴油车. 研究显示，国Ⅵ车辆的CO和NO_x排放因子均低于国Ⅴ车辆，且在市区路下与国Ⅴ车辆差距更明显，因此，推广使用国Ⅵ天然气车，逐步淘汰采用稀薄燃烧技术的天然气车，能有效减少NO_x的排放. 

Real World Driving Emission Characteristics and Mechanism of Heavy Duty Liquefied Natural Gas Vehicles

In order to investigate the emission characteristics of heavy-duty liquefied natural gas vehicle on real-world roads, real-world driving emission tests were performed on two China Ⅴ and two China Ⅵ heavy-duty vehicles using a portable emission measurement system (PEMS). The CO and NO_x emission characteristics were analyzed. The results show that the high emission areas of CO and NO_x for China Ⅴ vehicles on three types of roads (urban, rural, motorway) are mainly distributed under acceleration conditions of the low and medium speed. While high CO and NO_x emission areas under urban and rural conditions of China Ⅵ vehicles are mainly distributed in the range of speeds greater than 30 km/h, and high CO and NO_x emission areas under motorway conditions are discretely distributed. Notably, there are high NO_x emission areas under deceleration conditions with high speed. After dividing the vehicle specific power (VSP) bin according to the MOVES model, it is found that when driving condition bins in Bin11-18, CO and NO_x emission rates of China Ⅵ vehicles are stable and maintained at a low level. In Bin21-28, with the increase of VSP, CO and NO_x emission rates of China Ⅵ gradually increase. Comprehensive emission factors of CO and NO_x of China V vehicles are 1.1-3.9 and 3.3-8.2 times higher than those of China Ⅵ vehicles, respectively, and emission factors of CO and NO_x under urban conditions are 3.0-25.0 and 11.3-30.2 times higher than those of China Ⅵ vehicles. NO₂/NO_x ratios of China Ⅴ vehicles are much higher than those of China Ⅵ vehicles. But NO₂/NO_x ratios under motorway conditions are lower than those under other road type conditions. Compared with the results of other studies, it was found that the CO and NO_x emission factors of China Ⅵ heavy-duty vehicles were higher than those of China Ⅵ heavy-duty diesel vehicles. The study shows that CO and NO_x emission factors of China Ⅵ vehicles are lower than those of China Ⅴ vehicles, and the difference is more obvious in urban roads.