Experiments and Modeling of Dual-Fuel HCCI and PCCI Combustion Using In-Cylinder Fuel Blending 2009-01-2647
This study investigates the potential of controlling premixed charge compression ignition (PCCI and HCCI) combustion strategies by varying fuel reactivity. In-cylinder fuel blending using port fuel injection of gasoline and early cycle direct injection of diesel fuel was used for combustion phasing control at both high and low engine loads and was also effective to control the rate of pressure rise. The first part of the study used the KIVA-CHEMKIN code and a reduced primary reference fuel (PRF) mechanism to suggest optimized fuel blends and EGR combinations for HCCI operation at two engine loads (6 and 11 bar net IMEP). It was found that the minimum fuel consumption could not be achieved using either neat diesel fuel or neat gasoline alone, and that the optimal fuel reactivity required decreased with increasing load. For example, at 11 bar net IMEP, the optimum fuel blend and EGR rate for HCCI operation was found to be PRF 80 and 50%, respectively. Engine experiments using a dual-fuel PCCI strategy with port fuel injection of gasoline and early cycle multiple injections of diesel fuel with a conventional diesel injector (i.e., wide angle and large nozzle hole) were performed. The experimental results confirmed that an extension of the PCCI operating regime is possible when optimized fuel blends are used. At the 11 bar operating point, NOx and soot were ~0.01 g/kW-hr and ~0.008 g/kW-hr, respectively. That is, US 2010 heavy duty emissions regulations are easily met without after-treatment while achieving 50% thermal efficiency.