Numerical simulation of the formation of pollutant nanoparticles in the exhaust twin-jet plume of a moving car

The concentration and size of particulate matter (PM) in atmosphere have a severe impact on human health. Diesel vehicle engines generate great abundant nanoparticles. The large eddy simulation (LES) was combined with the equations of nucleation and coagulation to study the flow structure and the formation of pollutant nanoparticles H2SO4droplets in the flow around an on-road two tailpipes sedan. The effects of different ambient wind speeds and exhaust gas speeds on the particle number concentration and size distributions have been studied. The results show that the ratio of the ambient wind velocity to exhaust gas velocity greatly affect the flow structure, and further affect the nanoparticle concentration and size distribution. A higher ambient wind speed reduces the formation rate of nanoparticles and increases nanoparticle size. This study contributes to a better understanding of the number concentration and size distribution of nanoparticles which form through a nucleation process and transform as the subsequent coagulation after the formation.