Abstract
The particle size distribution emitted from a modern heavy duty diesel engine was investigated. It was found that the operation of the engine test bed system, primary and secondary dilution system and instruments were stable and that particle size distributions could be measured repeatedly under specific conditions. The particle size distribution was determined at different engine speed and load. The mode in the number distribution was smaller than 25 nm at engine speed 1600 rev./min and between 40–60 nm at 2600 rev./min. Good agreement of size distributions measured by SMPS and ELPI instruments was found in the region of overlap, and with measurements made with an electron microscope and image analyser. Total particle volume concentrations calculated from SMPS and ELPI data agreed well with those estimated from filter mass data. The measured particle size distribution and total number concentration changes with the dilution conditions and humidity of dilution air. The mechanism is being investigated and preliminary results suggest that sulphuric acid is involved in homogeneous nucleation of new particles during the dilution process.