Study On The Air Quality Models For Highway Tunnel With Shaft Ventilation

The diffusion of the automobile exhaust gases is limited inside a highway tunnel due to the relative closed space,which forms the air pollution in the highway tunnel and has a risk to the healthy of drivers and the safety of the vehicles driving.The problem of the air pollution in tunnel will be more serious when the tunnels are longer.In this thesis,the focus is on the problem of air pollution in highway tunnel with shaft ventilation.First,according to the atmospheric diffusion equation,air quality model for highway tunnel is established and the sensitivity of the parameters in the model is analyzed.Then,the different atmospheric diffusion models of the mountain and valley terrain are compared based on the terrain condition of the drain outlet.On the basis of the models,concentration distribution of the air pollutants in Qinling Zhongnanshan highway tunnel is simulated,and the environmental impact of the shafts exhaust emission is predicted.According to the structural characteristics of the highway tunnel and diffusion condition inside the highway tunnel,one-dimension air quality model for the concentration of pollutants inside highway tunnel is established based on the atmospheric diffusion equation. With finite-volume method,we get the numerical solution from the air quality model by using difference scheme.Then,stability and conservation of the discrete equation are discussed.Besides,the sensitivity of the parameters in the model is carried out.The simulated results indicate that the pollutant emission rate from motor vehicles and the wind speed along the tunnel are the key factors which affect the concentration distribution of the pollutants in the tunnel.For the highway tunnel with ventilation shafts,ventilation parameter is a very important factor to reduce the pollutant concentration inside the tunnel.Although initial concentration and boundary concentration inside the tunnel can also influence the pollutant concentration,these are less important,and pollutant deposition on the road and wall inside the tunnel can be also negligible.As an engineering example,the air quality inside the Qinling Zhongnanshan highway tunnel and the impact of shafts exhaust emission are simulated using the models presented in the thesis.It turns out that CO is the primary air pollutant in the tunnel,the concentration of CO is slightly higher than those of HC and NO_x.During the rush hour of traffic condition in the long-term operation(in 2025),the maximum concentration of CO,HC and NO_x are 211.44mg/m~3,30.12 mg/m~3 and 88.34 mg/m~3,respectively.All of them do not exceed the permitted design standard values.The concentration reduction rates are different for the three shafts,and the reduction rate for the third shaft(fara way from entrence of the tunnel) is the most remarkable.The results also show that the concentration of the pollutant emitted by vehicles increases with the increase of distance,and the atmospheric environment condition has a noticeable effect on the pollutants concentration.