Simulation investigation of effect on nanoparticles discharging pattern of a car caused by a following one on a typical city road

Abstract

Vehicle emission is supposed to contribute a great part to the urban air pollution in China, and many relative studies were carried out on a macro base at “city valley” scale. This article, on the “micro” individual scale otherwise, attempts to explore the fine particles’ spreading process after leaving the tailpipe of a typical car equipped with the inner-combustion engine in city main road through 3D CFD simulation. two geometries of typical cars driving in typical city road were built up with detailed structures: one is one car driving on the main city street and the other is two cars, one followed the former established car, all with a driving speed of 40 km/h. Eulerian multiphase model is adopted to describe the dynamics of the multiphase: air, particles in 10nm diameter, and particles in 70nm diameter. The simulation results show that the diffusion process of 70nm particles is mainly governed by gravity, more than 80% of which concentrate within the region behind the car with a volume of 4.0m in length, 3.0m in height, and 2.0m in horizontal width along the centreline of tailpipe, while the 10nm particles exhibit a wider and more random distribution pattern, it spreads throughout the simulation volume with noticeable volume fraction: above, beneath, and behind the driving car, the high volume fraction regions mostly occur within a volume of 12.0m in length, 4.0m in height, and 4.0m in width associated with the tailpipe. The followed car causes a “compressing and lifting” effect, it is found that the high-volume fraction regions of particles are compressed to, in one hand, move around to the bodies of the two cars, and the other hand move towards the sides of the road. The particles in 70nm diameter are less affected by the followed car than that 10nm, especially the lifting effect of high-volume fraction regions of 10nm particles. This suggests some nonconventional management measures should be taken to control the urban air pollution of vehicles.