Date of Graduation


Document Type


Degree Type



Statler College of Engineering and Mineral Resources


Mechanical and Aerospace Engineering

Committee Chair

Mridul Gautam.


The objective of this study was to evaluate the effect of different dilution methodologies on diesel exhaust particle size distributions and concentrations. A two-stage ejector based dilution system was used to dilute the raw exhaust at total dilution ratios of 240 and 504. A naturally aspirated, mechanically controlled, 3-cylinder inline, 0.953 liter Daihatsu Model DM950DTH engine was employed and tests were conducted with and without a wire mesh Diesel Oxidation Catalyst (DOC). Federal Diesel #2 with a sulfur content of 350 ppm was used as the testing fuel. The first dilution method (hot dilution) comprised of hot air dilution in stage 1 and cold air dilution in stage 2. The second method (cold dilution) comprised of cold air dilution in both the stages. A Scanning Mobility Particle Sizer (SMPS), Model 3936 was used for measuring the particle size distributions and concentrations. The engine was operated at four steady state set points, which were selected for a mix of both the volatile and solid particulate matter (PM) fractions in the exhaust stream. At a dilution ratio of 240, the influence of the volatile fraction on the PM size distribution and concentration was comparatively lower in the hot dilution method than the cold dilution method. The cold dilution method resulted in a count median diameter (CMD) of 44.5nm compared to 53.3nm with the hot dilution method when the engine was operating at an intermediate speed and 50% load. A similar trend was observed for the remaining engine set points. The effect of dilution method on PM size distribution and concentrations was not noticeable for a dilution ratio of 504, which indicated that very high dilution ratios have minimal impact. PM concentrations downstream of the DOC showed a reduction in the concentration of nuclei and accumulation mode particles for both the dilution methods. This is possibly indicating the oxidation of PM in the oxidation catalyst.