Study On The Emission Characteristics Of Single Vehicle Of Light-duty Vehicles With On-board Measurement

The number of the motor mobile in the Xi'an city is increasing with the high speed of 12.7% in these years. The emission from automobiles is becoming gradually one of the major pollution sources influencing the air quality of Xi'an. There have been 211258 single vehicles in the urban until the end of the year 2004. Compared with the number of 2000 the increasing range is 110.34%. The light-duty vehicles have been the major increase in Xi'an. It was found that the vehicle flow of the west road surround the city was the largest among all the main-roads. The vehicle flow of the light-duty vehicles in the second-round road was becoming increase year after year. The vehicle flow was 2～3 times of those in other main-roads in the same year. The rush hours of the second-round road were around 10:00 am and 18:00 pm.By the investigation of the speed distribution of the tested vehicles it was found that the proportion of the tested vehicles which were running in low speed and medium speed was 90.46% and the high-speed vehicles were less. But in the arterial roads of the city zone the proportion of the high-speed and medium-speed vehicles was more than 90% and the low-speed vehicles were less. With the study of the relationship between speed and the emission rate it was found that the NO_X emission rate was not susceptible to low-speed and at mode of high speed the average emission rate of NO_X was larger with the speed increasing. We also found that the HC and CO emission rate were more susceptible to the acceleration stage at mode of low speed and the decelerating period at mode of high speed. Under different traffic flow models, according to the emission factors of the tested single vehicle, we found that in rush hours the NO_X emission factors were 6.34% higher than that in normal condition, the HC emission factors were 5.39% higher and the CO emission factors were 12.26% higher. In the tested vehicles which the natural gas is used as fuel, the peak of the NO_X emission rate was not more than 40mg/s. In the course of testing the peaks of the NO_X emission rate were more with great fluctuation. And the peak of the NO_X emission rate was not more than 60mg/s. According to the emission factors of the tested single vehicles, compared with the vehicles which use 93# gasoline as fuel, the single vehicle emission factors of HC, NO_X, CO were respectively reduced 67.21%, 65.86% and 45.41%. So it was known that the use of clean fuels has obvious effect on the improvement of the urban air condition.Through the study of the vehicle operating and the contaminant emission of the light-duty vehicles in Xi'an and from the point of the bus development strategy and traffic management the author gives some advices on how to control the pollution of the light-duty vehicles in Xi'an in order to offer reference for the government to control motor vehicle.