Mechanisms of particulate matter formation in spark-ignition engines. 2. Effect of fuel, oil, and catalyst parameters

A combined experimental and modeling effort was performed in order to under stand how particulate matter (PM) is formed in spark-ignition (SI) internal combustion engines, Fuel type and fuel/air ratio strongly affect particle concentrations. PM emissions vary by up to 6 orders of magnitude between fu els at the same fuel/air ratio. Minimum PM concentrations are emitted at a global fuel/air ratio within 10% of stoichiometric, with the exact value de pending on the particular fuel. Concentrations can increase by more than 3 orders of magnitude when the fuel/air ratio is either increased or decrease d 30% from stoichiometric. Particles derived from oil consumption were foun d to be between 0 and 40% of the PM concentration for the ails used in the present experiments. Differences in PM emissions with and without the catal ytic converter are not statistically significant Particulate number and mas s concentrations plus particle sizes are addressed in this paper, as is the correlation between PM and hydrocarbon (HC) emissions.