| With the rapid development of China’s automobile industry,the number of motor vehicles has increased year by year,and the surge in the number of automobiles has caused serious exhaust pollution problems.Motor vehicle exhaust seriously threatens the physical and mental health of the people.Nitrogen oxides（NOX）in the exhaust gas are the main reason for the formation of photochemical smog;particulate matter（PM）emitted by the exhaust gas will be deposited in the bronchus and lungs after being inhaled by the human body,causing various respiratory diseases.Studying the emission characteristics of vehicle exhaust pollutants and evaluating the effectiveness of exhaust gas aftertreatment devices can provide theoretical basis and scientific guidance for controlling and reducing exhaust emissions.Heavy-duty diesel vehicles are the main contributors to nitrogen oxides（NOX）and particulate matter（PM）.Therefore,this article focuses on the emission of NOX and PM in the exhaust of heavy diesel vehicles,and conducts a comparative experiment on whether a heavy diesel vehicle is equipped with an aftertreatment device,focusing on exploring the effect of the aftertreatment device on the removal of particulate matter and the particulate trap DPF).This study used Portable Emission Measurement System（PEMS,Portable Emission Measurement System）to conduct road measurement on 4 NationalⅤheavy-duty diesel vehicles,focusing on the emissions of NOX and PM in vehicle exhaust from two aspects of driving conditions and aftertreatment devices feature.At the same time,the utility of the particle trap DPF is evaluated,the particle removal efficiency of the DPF is analyzed,the average particle size of the particulate matter before and after the modification is compared,and the particulate emission list after the DPF modification is established.Experimental results show that NOX emissions of heavy-duty diesel vehicles are negatively correlated with vehicle speed.The average NOX emissions on urban roads are the highest,suburban road emissions are in the middle,and highway emissions are the lowest.The emission of particulate matter also has a negative correlation with vehicle speed.The emissions on different roads are shown as:urban road>suburban road>highway.Under the conditions of frequent acceleration and deceleration,the instantaneous emission peaks of NOX and PM both increased significantly.By comparing whether to install after-treatment devices,it was found that for experimental vehicles with similar vehicle condition information,the NOX and PM emissions of heavy-duty diesel vehicles with after-treatment devices SCR and DPF reduced by91.5%and 95.3%,respectively.The effectiveness evaluation of DPF shows that the removal efficiency of PN by DPF is greater than that of PM under any working conditions.The removal efficiency of PM under accelerated conditions is 98.2%higher than that under idle conditions93.8%.The average diameter of the particulate matter under accelerated conditions is 82.5nm,which is larger than the diameter of the particulate matter under idle conditions of 59.5nm.According to the Shenzhen DPF retrofit plan,DPF was installed on 200 heavy-duty diesel vehicles in use.The results of the emission list show that the modified heavy-duty diesel vehicles emit 0.12 tons of PM2.5 per year and can reduce PM2.5 emissions by 3.04 per year Ton. |
