Effect of Intake-Air Composition on Gas-Phase and Particulate-Bound HC Emissions from Diesel Engines

The effects of changing the intake-O₂ mole fraction on the emissions of gaseous and particulate-bound hydrocarbons (HC and volatiles, respectively) have been examined using low- and high-swirl prechamber diesel engines. HC and volatile emissions indices increased with decreasing O₂ mole fraction. For most of the test conditions, the effect of intake-air composition on both of these emissions could be explained by variations in the calculated stoichiometric flame temperature, implying that the combustion process in the engines considered was mainly diffusion-controlled. The results also indicated that, at certain operating conditions, a significant fraction of the volatile matter was contributed by sources unrelated to the main combustion event.