Research On The Characteristics Of Real Driving Emissions (RDE) For Light-duty Vehicles

Motor vehicles provide a great convenience to people's production and life,but also bry great pollution to the environment.Against the dangers of motor vehicles emissions,countries have developed strict regulations to strengthen the supervision and control of motor vehicles emissions.Among them,the light-duty vehicles emissions test is mainly based on laboratory chassis dynamometer or engine bench dynamometer.However,there are a lot of factors that affect the emissions of vehicles running on the road,which is difficult to reproduce in the laboratory,and the real driving emissions(RDE)of urban vehicles are usually much higher than the emissions measured by the laboratory.Therefore,it is necessary to develop RDE test method for light-duty vehicles as soon as possible,so as to strengthen the monitoring and effectively control the real driving emissions of light-duty vehicles.In this paper,the RDE test methods and data evaluation methods of European lightduty vehicles are studied in detail,and the Portable Emission Measurement System(PEMS)is used to measure the the real driving emissions of the light-duty vehicles under various factors.In this paper,the AVL M.O.V.E series of PEMS and the Silver Scan-Tool software designed by RA Consulting Gmb H are used to carry out RDE tests on a number of light-duty vehicles which meet China's fifth phase emission standard in Qinghai,Yunnan,Tianjin,Beijing and other places,and the moving average window method is used to evaluate the real driving emissions of the vehicles,and the moving average window method is modified according to the characteristics of the actual running conditions of the light-duty vehicles in China.The effects of driving habits,engine cold start and hot start and altitude on the real driving emissions of light-duty vehicles are analyzed.The study of the data evaluation method shows that the European moving average window method is not suitable for direct evaluating the real driving emissions of lightduty vehicles in China.In this paper,the primary tolerance is corrected to increase the upper limit from 30% to 50%,so as to improve the passing rate of window normal check,so that the moving average window method can effectively evaluate the real driving emissions of light-duty vehicles in China.The assessment of the real driving emissions of light-duty vehicles found that: most of the light-duty petrol vehicles that meet China's 5th stage emission standards can meet the requirements of the RDE test in the China's 6th stage emission standards.GPF can effectively reduce the 85.5% PN emissions for petrol vehicles using direct injection and turbocharging technology.For light-duty diesel vehicles,the lack of SCR brings extremely high NO_x emission.The compliance factor is between 7.11 to 8.52 relative to the 5th stage emission standard limit,and the compliance coefficient is between 36.57 to 43.83 relative to the 6th stage emission standard limit.Only using EGR technology may not be able to make the actual NO_x emissions from light-duty diesel vehicles to meet the 6th stage of emission requirements.The analysis of the impact of influencing factors on the real driving emissions of light-duty vehicles shows that: the emissions of CO,NO_x and PN of radical driving are 9.2 times,3 times and 2.8 times of moderate driving respectively.Moderate driving will reduce vehicles CO2 emissions,resulting in the test can not meet the normal requirements of the window.For the test of cold start of the engine,the proportion of CO,NO_x and PN emissions in the cold start phase to total emissions was 69.9%,23.1% and 68.8%,respectively.But since the moving average window method eliminates the cold start phase emission data,the engine cold start or hot start have little effect on the moving average window method.When the altitude is between 0m and 3000 m,the environmental pressure will be reduced with the increase of altitude,the CO and PN emissions will increase first and then decrease,and reach the maximum at 2400m;the NO_x emission will decrease first and then increase,and reach the minimum at 2400 m.This paper shows that the Portable Emission Measurement System is an effective method to obtain the real driving emissions of light-duty vehicles.The research in this paper provides data support for the development of China's 6th stage light-duty vehicles emissions standard,which makes up for the method of measuring vehicles emissions in laboratory that the method can not fully reflect the real driving emissions of vehicles,and at the same time,this research also provides experience for the future more standardized RDE test,and it has great significance for effectively controlling the emission of light-duty vehicles.