Experimental And CFD Study On The Dispersion Of Vehicle Exhaust Pollutants

With the development of China's reform and opening up for 40 years,people's material living standards have been greatly improved,and cars are becoming more and more popular.Nowadays,urban environmental pollution is becoming more and more serious,and the vehicle exhaust pollutants are one of the main sources of urban environmental pollution.Therefore,it is significance to study the diffusion of exhaust pollutants.The pollutant dispersion behavior from the vehicular exhaust plume has a direct impact on human health,particularly to the drivers,bicyclists,pedestrians,people working nearby and vehicle passengers.Based on experimental research.In the underground garage.This paper measures the concentration of NO_X,HC,CO and the distribution of temperature and airflow at different distances from the exhaust pipe when the vehicle is idle in an environment with no wind.In addition,the distribution of PN,Diam,and PM at different distances was measured using a solid particle counter.In order to better verify the impact of driving on human health,the changes in the number and diameter of particulate matter were measured when the vehicle passed pedestrians at two different speeds.Based on the experimental research,this paper also combines numerical simulation analysis.First,the 3D model of the vehicle was drawn using Pro/E,then geometric processing was performed with HyperMesh,and finally imported into Star-CCM+for simulation calculation.The k-?turbulence model is selected during simulation,the mesh type is selected to Trimmed.In order to balance the contradiction between the accuracy of the simulation calculation and the calculation speed,the mesh size of different parts of the vehicle is different,and the resulting network is generated.The number of grids is about 2.5 million.The validity of the model in Star-CCM+software was verified by analyzing the fitting of experimental values and simulated values.The results show that the experimental values and the simulated values have good consistency.As the distance downstream of the exhaust gas centerline increases,the molar fractions of NO_X,HC and CO gradually decrease.For the low ambient wind speed case,the vehicular exhaust jet plume dominates the flow structures and the pollutant dispersion patterns.On the other hand,the dispersion process can be enhanced when the wind speed is much larger than the vehicular exhaust tailpipe velocity.In order to study the range of lateral diffusion of pollutants,two cross-sections were made at 0.5m and 1m from the exhaust pipe.The conclusion is that the lateral diffusion range at 0.5m is only about 0.4m,and the lateral diffusion range at 1m is about 0.55 m.Although the lateral diffusion range is increased,the concentration of pollutants drops rapidly.The experimental results also show that when the vehicle passes through pedestrians at different speeds,the surrounding particulate matter concentration will rise sharply,and the particle diameter will drop sharply.At this time,the health hazard to the human body will increase,and the hazard will increase with the increase of the vehicle speed.Fortunately,this hazard lasts for a short time.