A combined experimental and modeling effort was performed in order to understand how particulate matter (PM) is formed in spark-ignition (SI) internal combustion engines. Fuel type and fuel/air ratio strongly affect particle concentrations. PMemissions vary by up to 6 orders of magnitude between fuels 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 depending on the particular fuel. Concentrationscan increase by more than 3 orders of magnitude when the fuel/air ratio is either increased or decreased 30 from stoichiometric. Particles derived from oil consumption were found to be between 0 and 40 of the PM concentration for the oils used in thepresent experiments. Differences in PM emissions with and without the catalytic converter are not statistically significant. Particulate number and mass concentrations plus particle sizes are addressed in this paper, as is the correlation between PM andhydrocarbon (HC) emissions.
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