Numerical analysis of exhaust gas dispersion from moving vehicles

The exhaust gas dispersion from the tailpipes of moving vehicles was studied by applying the CFD software package FLUENT 6.1.22TM.The distributions of air flow,turbulence kinetic energy and CO2 concentration in the wake behind a truck were solved by the eddy dissipation model and the species transport equation.The simulated results matched very well with the available experimental results.Analyzing the effects of vehicle speeds,temperature at the outlet of exhaust pipe and turbulence kinetic energy on CO2 dispersion showed that due to the relatively small diameter and flow rate,there was the less effect of the jet from the exhaust pipe on the air flow in the wake.Because the maximum concentration gradient existed at the outlet of the exhaust pipe,the CO2 concentration decreased with increasing distance from the rear of the truck.The horizontal and vertical concentration increased with increasing vehicle speed;higher vehicle speed induced a lower CO2 concentration at the same location in the wake.The effective scope of the temperature difference between exhaust pipe and external environment in the scope of 0.75 times the truck length.Maximum turbulence kinetic energy in the wake benefits pollutant dispersion.