The Influence Of Road Environmental Variables On Vehicle Exhaust Plume Chasing Test Method

On-road vehicle emissions are important source of urban air pollutants,and the transportation sector may account for more than 30%of the emitted NOx in some city.With the rapid increase of vehicle ownership in China,traffic related air pollution has become a more and more serious problem in air pollution control.At present,some commonly used road pollutant emission detection methods generally have the problems of efficiency and flexibility,which can not meet the detection needs of illegal high emission vehicles in the actual situation.Therefore,more advanced detection methods are urgently needed to meet the needs of vehicle management departmentsOn-road mobile chasing method is developed to mesure the exhaust emissions of road vehicles in recent years.Vehicles equipped with rapid-responce pollutant analyzers can be used to measure the exhaust emissions of target vehicles when following them.However,there are still few studies on the environmental variables that affect mobile chasing test.In this paper,equipment such as anemometer and lidar was added to the mobile test platform to collect more environmental data and to detect heavy-duty diesel trucks equipped with portable emission measurement systems(PEMS)that can accurately test vehicle emission results.The short-period emission factor calculation method used in the analysis preserved the transient characteristics of environmental variables and clearly showed the error characteristics of the mobile chasing test affected by the environmental variables,and the cause analysis of error performance based on the original data.The simulation of the experimental process refering to vehicle outflow field simulation separated the relevant environmental variables,and further clarified the influence of each environmental factor on the basis of verifying some test results.The results of the conjoint PEMS-chasing tests and numerical simulation showed that distance had less effect on the emission factor measurement results,and the high driving speed would lead to a significant reduction in emission factors of chasing test results,while the crosswind might cause a significant change in the distribution characteristics of the flow field,resulting in abnormally high NO_X emission factors in the test.The study is significant to the error research and optimization of the mobile chasing method.