Study On Road Emission Of Heavy-duty Diesel Vehicles Based On On-board Test Method

With the rapid increase in the number of motor vehicles,motor vehicle pollution has become one of the most prominent and urgent problems in China.Although the relevant laws and regulations on road emission are constantly upgrading,but on-board test method which used for heavy-duty vehicles on road emission measurement has uncertainty in test sample,test condition sequence and test condition proportion.The impact of these uncertain factors on NO_x specific emission calculation results will cause the dispute whether the vehicles reach the standards.Therefore,the development of stable and reliable road test and evaluation method is still the focus of future research.Three representative heavy-duty diesel vehicles are selected to study the influence degree of these uncertain factors on NO_x emissions calculation results.Using portable emission measurement system to collect heavy-duty diesel vehicles real-time on road emissions data,and based on the average window method and NTE method to analysis the influence degree of these uncertain factors on NO_x emissions calculation results respectively,the results are as follows:.Due to the characteristics of the moving average calculation,the average window method can make full use of the on-road emission data.But on the other hand,it is the calculation process of the data repeatedly,which makes the NO_x specific emission of work-based windows are affected greatly by test condition sequence.When the urban road locate in the middle of road test sequence,all high emission conditions data of urban road are calculated repeatedly.What’s more,when the highway or suburban road locate in the end of road test sequence,a lot of low emission conditions did not form work-based windows,so that the NO_x specific emissions of work-based windows are higher.As to the limit of NTE local mode coverage,most of the vehicles operating points are not in the area,and the formation of NTE events requires are difficult to achieve,which lead to the low utilization rate of data,so the NTE events formed mostly in highway,urban road rarely formed NTE events.Test condition proportion can lead to larger variation range of NTE events’NO_x specific emission,but NTE method is not very sensitive to test sample and test condition sequence,the main cause of results difference is the test data itself.In general,average window method and NTE method are not suitable to evaluate Chinese heavy-duty vehicles real road emission,the existing heavy-duty vehicle emission control regulations need to be further improved according to the evaluation methods and test methods,it has important significance in controling heavy-duty vehicles emissions,monitoring emissions scientifically and improving the city air quality.