The present study focuses on multi-cylinder, light-duty engine operation at light load conditions while maintaining efficiency and emissions. As the same engine should be able to run at high load conditions as well, the choice of fuel and combustion strategy should support over a wide range of speed-load operation. This is achieved by utilizing partially premixed combustion [PPC] of gasoline, which is a combination of homogeneous mixture operation of the fully premixed charge and a direct injection, where the fuel is injected during or slightly before the combustion event, like in standard diesel combustion. The engine load in gasoline PPC operation is controlled by limiting the number of injections and injected fuel amount, whereas desirable combustion phasing is achieved by controlling the injection timing. The effect of injector included angle was also studied in the present work with the objective of operating at the lowest possible load in this type of combustion.
As the fuel effects also significantly alter the combustion behavior due to changes in the auto-ignition characteristics, the current study focused on low load operation using various RON gasoline fuels in a multi-cylinder engine.
The use of a 2-EthylHexyl Nitrate [EHN] cetane improver is also emphasized in this research for operation at light load conditions with lower octane fuels. By changing the amount of cetane improver in standard gasoline, it is possible to alter the octane number of the fuel and potentially resolve engine startability issues. A reaction kinetics model for EHN was developed and used to study HCCI operation in a light-duty, single-cylinder engine at light load conditions. 96 RON gasoline was used as the base fuel. The results indicate that the current EHN mechanism predicts combustion phasing and nitrogen oxides [NOx] and carbon-monoxide [CO] emission trends of available HCCI experiments fairly well. Direct injection engine experiments performed at the Argonne National Laboratory with 87 AKI gasoline and 0.4% by volume of EHN additive were also used to validate the newly developed EHN mechanism. An additive-PRF map was generated that provides information about the effective PRF number of mixtures of gasoline and EHN additive.