Nucleation and coagulation of particulate matter inside a turbulent exhaust plume of a diesel vehicle

The objective of this study is to develop a physical model to accurately predict the nucleation, coagulation, and dynamics of particulate matter emission from diesel-fueled engines. The uniqueness of this research is that measured particulate matter (PM) size distribution data is not required a priori to solve the nucleation/coagulation equations; instead the PM concentration is predicted based on the fuel sulfur content, fuel to air ratio, exhaust flow rate, and the ambient conditions. This study presents the CFD modeling of an exhaust plume dispersed from a stack pipe of a tractor truck powered by a 330 HP diesel engine. This effort uses the k-epsilon eddy dissipation model to predict the CO2 variation concentration coming out of the stack pipe into the ambient. The effect of the recirculation region near the truck walls on dispersion of CO2 is presented. The predicted results showed an excellent agreement with the experimentally measured values of CO2 concentration, dilution ratio, and the temperature in the wind tunnel. It was predicted that the relative concentration of CO2 from the stack dropped rapidly from 1 to 0.01 within a distance of 2.54 m downstream of the exhaust outlet.;Additionally, the simultaneous effects of nucleation, condensation and coagulation are incorporated in predicting the PM emissions from on-road heavy-duty diesel vehicles. It was predicted that the critical nucleus diameter decreased by approximately 30% and the number concentration increased by a factor of 6 with the increase in relative humidity from 10% to 90% for a fuel with 50 ppm sulfur content. Numerical simulations suggested that the condensation effects are very important near the stack. Ignoring the contribution from condensation term decreased PM count median diameter (CND) from 52 nm to 10 nm. The root mean square error in the numerically predicted particle number concentration was within 14.3% of the experimentally measured values. An increase in CMD from 52 nm to 62 nm was predicted for a distance of 0.51 m from the stack exit to 8.56 m from the stack exit, and the number concentration for the same distance decreased from 8.77 E+6 to 2.1 E+5 No./cm 3