The Research On Motor Vehicle Exhaust Emission Of PM_2.5 Dispersion In Kunming City

With the acceleration of the urbanization in our country,the air quality is getting more and more attention.The proliferation of traffic vehicles,lead to energy consumption,emission,noise pollution and other issues also appear frequently.In addition to CO and NOx gaseous pollutants,the motor vehicle exhaust components also contain solid particulate pollution.Studies have shown that PM2.5(dynamic particle diameter less than 2.5μm)pollution is most serious.In recent years,the relevant departments to carry out a large number of studies of urban motor vehicle exhaust pollutant diffusion distribution work.But the study in view of the plateau mountainous city of complicated terrain about the area streets flow field and pollutant concentration filed is few.City of plateau mountainous due to its high altitude,low pressure,and the relatively large surface roughness and other special topography and meteorological conditions lead to the motor vehicle exhaust diffusion has its unique rule.Existing research is mainly focused on the simplified 2d or 3d street canyon internal flow filed and the analysis of the pollutants concentration near the building,there is little analysis of the spread distribution about motor vehicle exhaust pollutant in the surrounding blocks.In addition,the building height is uneven around the street canyon in the actual conditions,it also have a certain influence on pollutant concentration distribution.Therefore,it is necessary to study the motor vehicle exhaust distribution characteristics in the road along the wind direction under the condition of reality.This article is intended for high altitude mountainous city(regarding Kunming,Yunnan Province as the research object),including models of Kunming city with the scale of 1:3000.The wind tunnel flow field was adjusted according to the results of Wujiaba wind profile,so as to simulate the local flow field characteristics under neutral conditions in the wind tunnel model by arranging roughness elements segment,adjusting air bar and wind speed,achieving the on-site wind profile exponent similar to the wind tunnel simulation.Three typical road in Kunming urban area(style angle 0°,45° and 90°)as the wind tunnel experiments research object,using ethylene(C2H4)as a tracer,simulates the spread distribution of motor vehicle exhaust emission about PM2.5(include the dust)under the condition of different angle.The results showed that 300m range from the research road shoulder are under the influence of PM2.5,and pollutant concentration in general with the increase of sampling point distance showed a trend of decline.Using CATIA 3d modeling and ICEM meshing the model,using FLUENT software to simulate the spread of PM2.5 under the condition of angle 45.It also use the visualization post-processing software of Tecplot to analyze the wind speed and pollutant concentration field at different section of the field.Analysis results show that motor vehicle exhaust pollutant concentration along the city road is related to the building layout.The results of numerical simulation tallies with the results of the wind tunnel experiment.The relative error of the simulation value and experiment value between 1.99%and 9.81%,the error value is less than 10%,has a good consistency.According to the flow filed and concentration filed simulation results are in good agreement with wind tunnel experimental results under the condition of 45 angle.This paper established the simulation of the distribution of PM2.5 diffusion numerical model and the algorithm is suitable for the plateau mountainous city.In order to further explore the influence factors of pollutant diffusion characteristics,analyzed the influence of the wind speed,atmospheric pressure and the temperature on PM2.5 diffusion process.Simulation results show that the pollutant source and other conditions unchanged,the pollutant concentration under the condition of 3m/s is significantly higher than the low wind speed of 0.6m/s of the corresponding points,and the pollutant concentration gradient change of the former was obviously higher than that of the latter.The pollutant concentration under normal atmosphere pressure of 101.325kPa is higher 1.6%～26.5%than 80.390kPa,average higher 18.1%.And the pollutant concentration under temperature of 273.15K is higher-12.5%～21.0%than 296.15K,average higher 5.2%.