Formation and transformation of volatile nanoparticles from a diesel engine during exhaust dilution

A classic H2SO4-H2O binary homogeneous nucleation model coupled to an aerosol dynamics model, suitable for studying the formation and transformation of volatile nanoparticles (VNPs) during diesel engine exhaust dilution, has been developed. Using the H2SO4-H2O binary homogeneous nucleation model, the nucleation ratio and molecular cluster size were calculated. The effect of aerosol dynamic processes on VNP number size distributions was studied. The effects of fuel sulfur content (FSC) and sampling conditions in the laboratory on VNP number size distributions were also calculated. Our simulations demonstrated that nucleation increased the cluster number concentration and that FSC, temperature and humidity significantly affected the nucleation ratio and molecular cluster size. Coagulation promoted the evolution of cluster-particle size distributions from monodisperse to polydisperse. Soot present in the exhaust can suppress the formation of VNPs. FSC and sampling conditions, like the primary dilution temperature, the primary dilution relative humidity, residence time and the primary dilution ratio have significant effects on VNP number size distributions.