低速货车的污染物排放特性

Emissions characteristics of low speed vehicles

为分析实际道路行驶时低速载货汽车的排放特征,该研究利用车载测试系统(portable emission measurement system,PEMS)在国道和乡村道上对6辆低速货车的污染物排放进行了测试,结果表明:不论在国道还是在乡村道上,污染物排放速率与车速的变化密切相关。乡村道上车辆的行驶速度变化较多,各污染物瞬时排放速率也呈现剧烈的波动。在国道和乡村道上,低速载货汽车匀速工况的比例最高,平均比例分别为68.33%和63.77%。在2种道路条件下,4种污染物平均排放因子均为加速行驶模式下最高,匀速次之,减速模式下最低。CO在加速模式下的平均排放因子分别是匀速和减速模式下的1.86和2.30倍;HC在加速模式下的平均排放因子分别是匀速和减速模式下的1.32和1.42倍。对于NOx,加速模式下的平均排放因子分别是匀速和减速模式下排放因子的1.57和3.09倍。而对于PM,加速模式下的平均排放因子分别是匀速和减速模式下排放因子的1.22和1.39倍。颗粒物粒径分布结果表明,2种道路颗粒物粒径分布规律类似。但在乡村道上颗粒物数量浓度高于国道上颗粒物数量浓度,平均高约32.0%。该研究成果为低速载货汽车的排放控制提供了技术参考。

Low-speed vehicles have a very high contribution to air pollution in China due to their considerable numbers, especially in the fringe area of city. In China, the low-speed vehicles emissions greatly exceed those of trucks and passenger cars because of their lower emission limits. Emissions of CO, HC, NOx and PM by low-speed vehicles accounted for 0.5%, 4.1%, 7.3%and 4.8%of the total vehicle emissions in 2012 in China. In 2005, the China Ministry of Environmental Protection issued the first-phase and second-phase emission standard （standards GB19756-2005 and GB19757-2005, respectively）. However, there were not many research-based data about the emission characteristics of low-speed vehicles. In this study, a Portable Emission Measurement System （PEMS）, which is comprised of a regulated gaseous emission analyzer （SEMTECH-DS） and an electrical, low-pressure impactor （ELPI）, was introduced to study the emission characteristics of low-speed vehicles in real road. Six low-speed vehicles were measured on national and rural roads using PEMS, which can measure CO, HC, NOx and PM emissions. The results indicated that vehicle speed had a very big impact on pollutant emissions on both national and rural roads. Emissions on rural roadways were much more variable than those on national roadways because of the variability in vehicle speed. The ratios of acceleration and deceleration modes were not very high both on national and rural roads （28.48% and 33.76%, respectively）. The emission factor of four pollutants was highest in acceleration mode on both national and rural roads. The CO, HC, NOx and PM emission factors in acceleration mode were 1.86, 1.32, 1.57, 1.22 times those in cruise mode, respectively. The CO, HC, NOx and PM emission factors in acceleration mode were 2.30, 1.42, 3.09, 1.39 times those in deceleration mode, respectively. The size distributions of particles emitted from low-speed vehicles were similar on national and rural roads. The ratio of coarse mode particles was very low （0.15 % and 0.16%, respectively） of the total particle number concentration on national and rural roads. Comparing the number concentration of particles emitted on national and rural roads, the particle-number concentration on rural roads was higher 32.0% than that on the national roads. Especially for particles of diameter 0.32μm, the number concentration was 62.2%higher than that on the national road, probably due to the poor combustion in the engine cylinders. This report could provide some reference for future emission control policies for low-speed vehicles.