Numerical study on evolution of ultrafine particles emitted from vehicle exhaust with multi-dynamical behaviors

Abstract

In this study, a numerical investigation is performed to simulate the evolution process of ultrafine particles emitted from diesel vehicle exhausts. The Taylor expansion method of moments (TEMOM)-CFD coupled model is primarily applied to the non-spherical particles for simultaneously simulating four kinds of particle dynamical behaviors including coagulation, deposition, condensation and nucleation. Compared with previous simulation studies, the developed model shows closer results to the experimental data. The effects of initial particle number, initial particle size, environmental temperature, relative humidity, fuel sulfur content, and exhaust velocity on the evolution process are systematically analyzed. The results show that the increase rate of the geometric mean diameter (GMD) and the increase margin of GMD are proportional to the initial particle number concentration (PNC) and the environmental temperature. When the relative humidity or the fuel sulfur content is higher, the larger increase margin of the GMD appears, but the increase rate of GMD is not affected obviously. Moreover, the initial PNC gives nearly no contributions to the diffusion range. The initial GMD also shows no markedly effects on the decrease rate of the volume concentration. The fuel sulfur content could affect the PNC distribution in a larger region of the flow field, while the environmental relative humidity and temperature have no evident effects on the distribution range of the PNC.