A study on the evolution of secondary nanoparticles in a diesel engine exhaust is presented, coupling the large eddy simulation (LES) and the Taylor expansion method of moments (TEMOM), with the aim to reveal the differences in total particle number concentration, volume concentration and geometric mean diameter of diesel engines from Canada, Singapore, European, USA, Russia, China and Japan. The investigated aerosol system involved nanoparticle diffusion, nucleation, coagulation and condensation. The nucleation model is the binary homogeneous nucleation of water-acid system, which is valid for the engine exhaust dilution conditions. Considering the particle diameter range in the particle evolution, the free molecule regime coagulation formula is used. The particle condensation growth rate is obtained by calculating the arrival and loss of acid molecules at the entire particle surface. Five different diesel fuel sulfur contents, 10, 15, 30, 50, 350 mg/kg, are chosen as the initial conditions to investigate the particle evolution. It is shown that particles mainly form in the exhaust shear layer while the maximum values of particle number concentration and particle diameter appear in the downstream 0.6 m from the tailpipe. It is obvious that the fuel sulfur content has a significant effect on the formation of secondary nanoparticles. The total particle number concentration and total volume concentration are about four and six orders of magnitude smaller in the lowest fuel sulfur standard than those in the highest fuel sulfur standard, respectively.

large eddy simulation  /  Taylor expansion method of moments  /  exhaust  /  homogeneous nucleation  /  low fuel sulfur content  /  nanoparticles