Abstract: Cold and hot start emissions play a more and more important role in light-duty vehicles in China. Three gasoline taxi cabs were chosen, which comply with China Ⅳ emission standards, for emission testing on the real road using a portable emission measurement system (PEMS). The results show that cold start almost ended its impact on vehicle emissions after 300 s, and hot start almost ended after 120 s according to the emission data. There are significant differences in HC and CO emissions under different kinds of vehicle starts conditions. The shorter the interval between engine stop and start, the less HC and CO emissions right after the starts. During the cold start, HC and CO emissions were 3.3 g and 21.9 g, which are 10 and 6 times of those in the first hot start, and 31 and 12 times of those in the sencond hot start, respectively. The influence of start conditions is not so significant on NOx emission, which is affected more by driving behavior.
 

Key words: light-duty vehicles, China Ⅳ emission standards, cold and hot start, portable emissions measurement system (PEMS)