Characterisation of diesel exhaust particle number and size distributions using mini-dilution tunnel and ejector-diluter measurement techniques

This paper presents the characteristics of diesel exhaust particle number and size distributions. These were measured for different engine load conditions from 10% to 100% of full engine load at a maximum torque of constant speed, using mini-dilution tunnel and sampling (MDTS) and ejector-diluter and sampling (EDS) systems. The exhaust particles sampled were analysed using a scanning mobility particle sizer (SNIPS). In general, the particle number concentration increased with increasing engine load using both measurement systems. Comparing the particle number and volume concentrations, the MDTS system measures a lower level in the nanoparticle range, D-p < 50 nm, but a higher level in the accumulation mode size range, 50 < D-p < 670 nm, than the EDS system. The measurements also showed that the MDTS system shifted the particle count median diameter (CMD) to larger particle diameter and the particle number size and volume distribution for all engine load conditions. It is mainly because the mini-dilution tunnel leads to the particle transformations of nucleation and condensation taking place simultaneously when the exhaust particle emissions are cooled and diluted. However, the effect of coagulation on the total number particle concentration was shown to be negligible. On the other hand, the EDS measurement system can minimise the particle transformations taking place on the exhaust particle number and size distributions during the heated dilution process. Hence, the EDS measurement system can provide more reliable diesel exhaust particle number and size distributions than MDTS measurement system. (C) 2003 Elsevier Ltd. All rights reserved.