Study On Key Issues And Characteristics Of PEMS-based Emission Factor Development For Light-duty Gasoline And Hybrid Electric Vehicles

The rapid growth of vehicle ownership has made vehicles an important contributor to the air pollution in China.However,as the data base for scientific control of air pollution from motor vehicle emissions,the high emission inventory uncertainty still existed,in which the emission factor is one of the most important uncertainty sources.Therefore,the research on the development of PEMS-based emission factors for vehicle source is of great significance to the establishment of high spatial-temporal resolution vehicle emission inventory and scientific control of vehicle emissions.However,there are still many deficiencies in the research on vehicle emission factors.In this paper,PEMS were used to build test platform for light-duty gasoline vehicles and a process framework of vehicle emission factors development under real-world operating conditions was constructed.The key issues of establishing vehicle emission factors based on steady-state and real-world driving operating conditions were identified,respectively.Fifteen light-duty gasoline vehicles and four plug-in hybrid electric vehicles in Guangzhou were taken as examples,their real-world driving condition emission factors were tested and emission characteristics were obtained.The main conclusions of this paper were showing as follows:?1?The emission factors of different types of motor vehicles under idle,acceleration and constant speed with 25km/h can be quickly developed based on PEMS,though the steady-state operating conditions can not completely simulate the real-world driving characteristics of motor vehicles.The testing time was about 120 second for one testing vehicle.However,due to the great difference between these two driving conditions,it is necessary to further carry out the on-road test.?2?the vehicle emission factors with good parallelism can be obtained under the framework of emission factors development after identifying the key issues.The important factors that need special consideration were identified as:driving route,testing time,air conditioning working mode and road type.?3?the PEMS-based emission factors of fifteen typical light-duty gasoline vehicles in Guangzhou were studied and the results showed that:the emission factors of CO₂,CO,NO_x and THC decreased significantly with the tightening of vehicle emission standards;the correlation coefficient between CO₂ emission and vehicle speed was greater than 0.9 while the correlation between CO,NO_x,THC,PN and vehicle speed is not significant;acceleration has an important impact on their emission;different pollutants,especially for THC,have different emission characteristics during idle cold start and driving cold start,which cannot be ignored in the calculation of vehicle emissions.?4?the results of the VSP-based emission factors showed that:the emission rate of CO,NO_x,and THC in each VSP mode decreased with the tightening of the emission standard,but the CO₂ emission rate of the China?vehicles is lower than that of China?vehicles;the CO₂ emission factor and fuel consumption rate of the turbocharged gasoline vehicle was the highest and the emission factors of NO_x and THC of the direct injection vehicle were the smallest;the displacement of vehicles also had an important impact on the emission of pollutants and fuel consumption which had an important relationship with the operating conditions.?5?the on-road test with different driving modes was carried out for BYD-Qin hybrid electric vehicle under the framework of life cycle assessment method and the results showed that:the fuel consumption under ECO mode is lower than that of traditional gasoline vehicle while there was no significant difference in the fuel consumption between PHEV under SPORT mode and traditional gasoline vehicles;in terms of emissions,the life-cycle emissions of CO₂,NO_x and THC of PHEV had obvious reduction compared with traditional gasoline vehicles while the CO emissions were higher than that of China?gasoline vehicles.The light-duty gasoline vehicles and hybrid electric vehicles were taken as examples and their PEMS-based emission factors were systematically studied in this study.Establishment of the process framework for PEMS-based emission factors development and the assessment method of life-cycle emissions for PHEV can not only effectively obtain vehicle emission factors with good parallelism and provide guidance for other cities to test and establish local vehicle emission factors,but also provide reference sources for the establishment of technical specifications for PEMS-based emission factors development in China.It is expected to promote the establishment of vehicle emission factor database based on PEMS method in China.