Combustion and Emissions Modeling of a Gasoline HCCI Engine Using Model Fuels 2009-01-0669
To address the growing need for accurate predictions of combustion phasing and emissions for development of advanced engines, a more accurate definition of model fuels and their associated chemical-kinetics mechanisms are necessary. Wide variations in street fuels require a model-fuel blending methodology to allow simulation of fuel-specific characteristics, such as ignition timing, emissions, and fuel vaporization. We present a surrogate-blending technique that serves as a practical modeling tool for determination of surrogate blends specifically tailored to different real-fuel characteristics, with particular focus on model fuels for gasoline engine simulation. We start from a palette of potential model-fuel components that are based on the characteristic chemical classes present in real fuels. From this palette, components are combined into a surrogate-fuel blend to represent a real fuel with specific fuel properties. Detailed chemical-kinetics mechanisms for each component have been assembled either from literature sources or through custom development. These mechanisms have been validated against fundamental kinetics experiments, for each fuel component. For prediction of combustion phasing and emissions, as well as the validation of the surrogate-blending methodology, we have used the multi-zone engine model as implemented in CHEMKIN-PRO. The model has been applied to simulating engine data for three surrogate-fuel blends and for a market, unleaded, regular gasoline fuel, using the surrogate composition determined from our methodology. To better model the stratification in the engine due to crevice and boundary-layer cooling effects, the cold-flow compression process is simulated using KIVA-3V  up to 700 K, while the effect of fuel chemistry is still negligible. From the results of this simulation, zonal information is extracted for use in the multi-zone model. Predicted ignition timing, heat release, NOx and unburnt hydrocarbon emissions are compared with engine data over a wide range of inlet temperatures. Together, the surrogate-fuel-blending methodology and the multi-zone engine-combustion model prove to be an efficient and effective means of investigating HCCI gasoline combustion for realistic fuels using detailed chemical kinetics.