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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.

This study investigates the potential of controlling premixed charge compression ignition (PCCI) 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 a medium engine load of 9 bar net IMEP and was also found to be effective to prevent excessive rates of pressure rise. Parameters used in the experiments were guided from the KIVA-CHEMKIN code with a reduced primary reference fuel (PRF) mechanism including injection timings, fuel percentages, and intake valve closing (IVC) timings for dual-fuel PCCI combustion. The engine experiments were conducted with a conventional common rail injector (i.e., wide angle and large nozzle hole) and demonstrated control and versatility of dual-fuel PCCI combustion with the proper fuel blend, SOI and IVC timings.

Single-cylinder engine experiments were used to investigate a fuel reactivity controlled compression ignition (RCCI) concept in both light- and heavy-duty engines and comparisons were made between the two engine classes. It was found that with only small changes in the injection parameters, the combustion characteristics of the heavy-duty engine could be adequately reproduced in the light-duty engine. Comparisons of the emissions and performance showed that both engines can simultaneously achieve NOx below 0.05 g/kW-hr, soot below 0.01 g/kW-hr, ringing intensity below 4 MW/m2, and gross indicated efficiencies above 50 per cent. However, it was found that the peak gross indicated efficiency of the baseline light-duty engine was approximately 7 per cent lower than the heavy-duty engine. The energy balances of the two engines were compared and it was found that the largest factor contributing to the lower efficiency of the light-duty engine was increased heat transfer losses.

Many concepts of premixed diesel combustion at reduced temperatures have been investigated over the last decade as a means to simultaneously decrease engine-out particle and oxide of nitrogen (NO ) emissions. To overcome the trade-off between simultaneously low particle and NO emissions versus high "diesel-like" combustion efficiency, a new dual-fuel technique called Reactivity Controlled Compression Ignition (RCCI) has been researched. In the present study, particle size distributions were measured from RCCI for four gasoline:diesel compositions from 65%:35% to 84%:16%, respectively. Previously, fuel blending (reactivity control) had been carried out by a port fuel injection of the higher volatility fuel and a direct in-cylinder injection of the lower volatility fuel. With a recent mechanical upgrade, it was possible to perform injections of both fuels directly into the combustion chamber.

In-cylinder blending of gasoline and diesel to achieve Reactivity Controlled Compression Ignition (RCCI) has been shown to reduce NOX and particulate matter (PM) emissions while maintaining or improving brake thermal efficiency as compared to conventional diesel combustion (CDC). The RCCI concept has an advantage over many advanced combustion strategies in that the fuel reactivity can be tailored to the engine speed and load allowing stable low-temperature combustion to be extended over more of the light-duty drive cycle load range. Varying the premixed gasoline fraction changes the fuel reactivity stratification in the cylinder providing further control of combustion phasing and pressure rise rate than the use of EGR alone. This added control over the combustion process has been shown to allow rapid engine operating point exploration without direct modeling guidance.

Dual-fuel combustion using port-injected gasoline with a direct diesel injection has been shown to achieve low-temperature combustion with moderate peak pressure rise rates, low engine-out soot and NOx emissions, and high indicated thermal efficiency. A key requirement for extending high-load operation is moderating the reactivity of the premixed charge prior to the diesel injection. Reducing compression ratio, in conjunction with a higher expansion ratio using alternative valve timings, decreases compressed charge reactivity while maintain a high expansion ratio for maximum work extraction. Experimental testing was conducted on a 13L multi-cylinder heavy-duty diesel engine modified to operate dual-fuel combustion with port gasoline injection to supplement the direct diesel injection. The engine employs intake variable valve actuation (VVA) for early (EIVC) or late (LIVC) intake valve closing to yield reduced effective compression ratio.