Fuel unmixedness effects in a gasoline homogeneous charge compression ignition engine

Abstract Fuel stratification, independent of thermal and residual gas stratification, was studied in a gasoline homogenous charge compression ignition (HCCI) engine. The unmixed charge was created by injecting fuel (iso-octane) into the intake port after being prevaporized and heated to the same temperature as the intake stream. Planar laser-induced fluorescence measurements showed that local equivalence ratios in the charge differed from the mean equivalence ratio by up to 50 per cent for the latest possible injection timing. Experimental results showed little to no change in combustion phasing and performance between prevaporized port (unmixed) or premixed (homogeneous) fuelling. Increases in NO x and CO emissions were observed with the prevaporized port fuelling and are believed to result from the regions richer or leaner than the mean equivalence ratio. These results indicate that fuel stratification in the absence of thermal and residual stratification does not appear to be a viable method for HCCI combustion control for gasoline-type fuels.