Critical sooting equivalence ratios and subsequent particulate formation during spark-ignition combustion were studied for blends of ethanol, isobutanol (2-methyl-1-propanol), and methylbutenol (2-methyl-3-buten2-ol) with gasoline using premixed prevaporized (PMPV) fueling. The air-fuel mixture was supplied to the engine in a well-mixed gaseous state allowing the chemical sooting tendency of the fuels, as measured by the critical sooting equivalence ratio, to be quantified. The engine was operated at a fixed load and phasing with varying equivalence ratio to determine the critical sooting equivalence ratio and evolution of the particle size distribution (PSD) for each fuel. Each alcohol was splash blended with a gasoline blendstock for oxygenate blending (BOB) at three different blend levels. Ethanol was blended at 10, 20, and 30% by volume (E10, E20, and E30). Isobutanol and methylbutenol blends were matched to ethanol on an oxygen weight percent basis resulting in blends of 16, 32, and 49% and 18, 37, and 56% by volume for isobutanol and methylbutenol, respectively. The results of this work show that increases in alcohol content consistently decreased the chemical sooting tendency and particulate emissions for all alcohol-gasoline blends tested. The level of decrease in particulate on a volume basis can be ordered isobutanol < methylbutenol < ethanol. On an oxygen weight percent basis, the order is ethanol < isobutanol < methylbutenol. The results demonstrate that methylbutenol has a lower chemical sooting tendency than isobutanol, and, given its other properties, is a potentially promising biofuel for blending with gasoline.
