Diesel-exhaust aerosol dynamics from the tailpipe to the dilution tunnel

We study, experimentally and theoretically, the dynamics of non-volatile particles emitted from a diesel EURO 3 light-duty vehicle along the transfer tube that conducts exhaust fumes from the tailpipe to the dilution tunnel. Particle agglomeration, diffusional and thermophoretic transport are modeled. For turbulent, but moderate, Reynolds numbers and under steady-state conditions we map the combustion-generated nanoparticle dynamics onto a one-dimensional dynamics of aerosol particles in an ageing chamber. The aggregate fractal dimension, determined self-consistently by comparing mass distributions, varied from 2 to 2.3. The relative importance of aerosol processes is estimated by defining appropriate characteristic time scales. Agglomeration and convection by the bulk motion of the fluid are the dominant processes for inlet number concentrations of the order of 108particles/cm3 and transfer-tube lengths of 6–9 m. Thermophoretic losses are calculated to be non-negligible. For modern vehicles with particulate filters agglomeration is estimated to be negligible, whereas thermophoresis may be significant.