Study And Development On The Test Methods For China 5?6 Emissions From Heavy Duty Vehicles With Gasoline Engines Based On Chassis Dynamometer

With the increasing of air pollution,the vehicle exhaust enission requirements are more and more strict in China and the corresponding regulations were carried out.At present,the emission regulations in China are basically equivalent to those in Europe and United State,even some parts arestricter.Among them,the sixth-stage standard of light vehicles and diesel fuelled heavy-duty vehicles were released in December 2016 and June 2018 respectively.The standard for gasoline fuelled heavy-duty vehicles is still in the fourth stage.The emission measurement method based on engine bench is difficult to reflect the emission level of gasoline fuelled heavy-duty vehicles in actual use.In addition,the pollutant emissions of gasoline fuelled heavy-duty vehicle are mainly concentrated in the cold start phase which current emission test methods are not included.The temperature below zero has a signficant impact on vehicle emissions,while current standards do not address below-zero temperature cold-start emissions testing.This paper studies the emission test methods of gasoline fuelled heavy-duty vehicles,including the development of chassis dynamometer emission test system for gasoline fuelled heavy-duty vehicle,the study of gasoline fuelled heavy-duty vehicle emission test method based on chassis dynamometer,and the influence of ambient temperature on pollutant emissions of gasoline fuelled heavy-duty vehicles.The research on pollutant emission of gasoline fuelled heavy-duty vehicles based on CHTC(chinese driving cycle)is also carried out.This study provides the basis for the revision of the new stage emission standards for gasoline fuelled heavy-duty vehicles.Emission test based on vehicle can better reflect the real driving emissions of gasoline fuelled heavy-duty vehicles.This study develops and builds a chassis dynamometer emission test system.The technical requirements of the chassis dynamometer,and the sampling and analysis methods of the exhaust pollutants are specified.The emission calculation method based on vehicle test is also proposed.The emission calculation method based on engine cycle power is converted into the calculation method based on the mileage of the whole vehicle.It is verified that the emission test on chassis dynamometer can truly reflect the actual road emissions,through the comparison of the chassis dynamometer with real road emission test at constant speed,and the repeatability comparison analysis of the chassis dynamometer with actual road emission test.The differences between chassis dynamometer emission test and real drive emission test are compared.Then,the emissions under different test cycles(NEDC cycle,FTP75 cycle and C-WTVC cycle)are compared and analyzed for the vehicle test method.The test is verified according to the actual road driving situation.Finally,it is concluded that the C-WTVC cycle is the most proper gasoline fuelled heavy-duty vehicle emission test cycle.Further research on the emission test under the cold start condition of the vehicle is carried out,and the proportion of the reasonable hot and cold start test cycle is adopted to establish an emission test evaluation system based on the chassis dynamometer.Ambient temperature has a significant impact on the cold start emissions of gasoline fuelled heavy-duty vehicles.Based on the above methods and evaluation system,the effects of ambient temperature on the cold start emissions of gasoline fuelled heavy-duty vehicles were studied.The effect of ambient teperature(normal,-7 ? and-10 ?)on CO,THC and NOx emissions of the vehicle were compared.It is concluded that the pollutant emissions of gasoline fuelled heavy-duty vehicles are mainly concentrated in the cold start stage.CO and THC emissions have increased significantly with the decrease of the ambient temperature by analyzing transient pollutant emissions.After the cold start is completed,the pollutant emissions are reduced,and the emissions are little effected by ambient temperature.By analyzing pollutant emissions of the entire test procedure,we could conclude that the ambient temperature has the greatest impact on CO emissions of gasoline fuelled heavy-duty vehicles,followed by THC emissions,and have a little impact on NOx emissions.Based on the extend-range gasoline fuelled heavy-duty truck,the adaptability study of the Chinese car driving conditions on this test method was carried out.The effects of three drving cycles(included CHTC-HT,C-WTVC and actual road PEMS cycle(1800s))on the combined emissions and transient emissions of CO,THC and NOx were compared and analyzed.As for the comprehensive emissions,the pollutant emissions of the three driving curves are relatively low under normal temperature conditions.Under low temperature conditions,emissions of various pollutants increase and further increase with decreasing temperature.Among them,CO emission is higher under CHTC-HT cycle conditions and the lowest under PEMS road spectrum conditions;the change of temperature has little influence on THC emission,and THC emission is little difference under three cycle conditions.As for the transient emissions,under normal temperature conditions,the pollutant emissions from the three curves is relatively stable.In the low-speed urban phase,there are several emission peaks.Among them,the emissions of these three pollutants in PEMS cycle is slightly higher.Under the low temperature condition of-7 ?,it can be seen that the emissions of these three pollutants in CHTC-HT cycle are the highest.Under the low temperature condition of-10 ?,the CO and THC emissions in CHTC-HT cycle are higher than other cycles.In summary,this paper develops an emission test method based on the chassis dynamometer that can reflect the actual driving emissions of gasoline fueled heavy-duty vehicles.The engine bench certification method is converted to the vehicle emission certification method,and a corresponding calculation and evaluation system is established.This method is more precise due to the cold start emissions are included in the vehicle emission evaluation system.Based on this method,the effects of ambient temperature on pollutant emissions from gasoline fueled heavy-duty vehicles and the adaptability of CHTC are further studied.This research has important significance for the improvement of gasoline fuelled heavy-duty vehicle emission standards.