Soot Observations and Exhaust Soot Comparisons from Ethanol-Blended and Methanol-Blended Gasoline Combustion in a Direct-Injected Engine

Particulate formation was studied under homogeneous-intent stoichiometric operating conditions when ethanol-blended (E10) or methanol-blended (M20) gasoline fuel was injected during intake stroke of a 4-stroke direct-injected engine. The engine was tested at wide open throttle under naturally aspirated conditions for a speed-load of 1500 rev/min and 9.8 bar indicated mean effective pressure. In-cylinder soot observations and exhaust soot measurements were completed for different fuel rail pressures, injection timings, coolant and piston temperatures of the optical engine. Fuel delivery settings were tested with both single and split injections during intake stroke. The target piston temperature of the optical engine was attained using pre-determined number of methane port fuel injection firing cycles. Overall, the in-cylinder soot observations correlated well with the engine-out soot measurements. A warmer cylinder head favored soot reduction for both fuels. A hot piston resulted in more soot than a warm piston, with a high fuel rail pressure. The two alcohol blends showed contrasting differences in their inclination for particulate formation. At the tested injection timing, a smaller and larger first split percent of fuel injection favored soot reduction for E10 and M20 respectively, compared to single injection operation.