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Exhaust particulate emissions from a 4-cylinder, 2.25 liter spark ignition engine were measured and characterized. A single-stage ejector-diluter system was used to dilute and cool the exhaust sample for measurement. The particulate measurement equipment included a condensation nucleus counter and a scanning mobility particle sizer. Exhaust measurements were made both upstream and downstream of the catalytic converter using three different fuels. Unlike particulate emissions in diesel engines, spark ignition exhaust particle emissions were found to be highly unstable. Typically, a stable “baseline” concentration on the order of 105 particles/cm3 is emitted. Occasionally, however, a “spike” in the exhaust particle concentration is observed. The exhaust particle concentrations observed during these spikes can increase by as much as two orders of magnitude over the baseline concentration.

Experiments were undertaken to determine some of the characteristics of exhaust particulate emissions in two port fuel injected spark ignition engines. A 2.3L 1993 GM Quad-4 engine and a 4.6L 1994 Ford V8 were tested. Sampling and dilution were accomplished through the use of a single-stage, low residence-time ejector diluter; dilution ratios were maintained at approximately 15:1. Number concentration was measured with a TSI 3020 condensation nucleus counter, and size distributions were measured using two scanning mobility particle sizers. The Quad-4 engine was used to determine the effects of the catalytic converter and deposit control additives on particulate emissions. The catalyst was found to remove particles with an efficiency as high as 78% at low power conditions (∼7 kW), dropping steeply with power, reaching a minimum value of approximately 10% at moderate power conditions (∼18 kW).