Research On NO_x Emission Characteristics And Evaluation Methods Of China Ⅵ Heavy Duty Vehicles

Mobile source pollution control has become an important part of air pollution prevention and control.China has now fully implemented the China Ⅵ heavy-duty vehicle emission standard,which tightens the NO_x emission limits and introduces vehicle monitoring technologies such as whole-vehicle PEMS testing and remote OBD.At present,scholars at home and abroad have conducted less research on the NO_x emission characteristics of China Ⅵ heavy-duty vehicles,and the applicability of different emission testing and evaluation methods needs further study.In this paper,we adopt PEMS to test the emission characteristics of China Ⅵ heavy-duty vehicles under actual driving,and also study the applicability of three testing methods,namely PEMS,road remote sensing and remote OBD,in evaluating the NO_x emissions of China Ⅵ heavy-duty vehicles,and construct emission evaluation models based on road remote sensing and remote OBD data,respectively.The main conclusions of the paper are as follows.（1）The NO_x emission level of China Ⅵ heavy-duty vehicles is significantly reduced compared with that of China V heavy-duty vehicles,in which the NO_x emission factor of heavy-duty diesel vehicles is reduced by 72%～91%and that of heavy-duty natural gas vehicles is reduced by about 67%～89%.When driving on urban roads,the NO_x emission control of China Ⅵ natural gas vehicles has a significant advantage compared with China Ⅴ natural gas vehicles,while the NO_x emission control of China Ⅵ diesel vehicles is better when driving on high-speed roads.（2）With the PEMS test results as the true value,the average error of road remote sensing test is about 4.79%,and the NO/CO₂ ratio is more accurate compared with NO concentration when using road remote sensing for the evaluation of heavy-duty diesel vehicles.The NO concentration of China Ⅵ vehicles was significantly higher than that in the normal state of the aftertreatment after the aftertreatment failure,but the NO concentration distribution before and after the aftertreatment failure of China V vehicles was relatively less different.Using the multi-factor combination evaluation method of driving conditions,NO/CO₂ ratio and NO concentration can improve the accuracy of road remote sensing to identify high emission vehicles.（3）The comparison of remote OBD and PEMS test results found that NO_x concentration and vehicle speed have high accuracy,but their data integrity needs further improvement.By constructing an emission evaluation model based on remote OBD data,the NO_x emission level of in-use vehicles can be effectively evaluated.（4）The three test methods have good complementarity in NO_x emission regulation.PEMS test results have higher accuracy and data integrity and are suitable for single-vehicle emission characterization,remote OBD data integrity is lower than that of PEMS test,which can be used for long-term vehicle emission regulation,and road remote sensing test has lower data accuracy,but its test cost is lower and is suitable for high emit vehicle that cannot be monitored by remote OBD vehicle screening.