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The chemistry of unburned hydrocarbon oxidation in SI engine exhaust was modeled as a function of temperature and concentration of unburned gas for lean and rich mixtures. Detailed chemical kinetic mechanisms were used to model isothermal reactions of unburned fuel/air mixture in an environment of burned gases at atmospheric pressure. Simulations were performed using five pure fuels (methane, ethane, propane, n-butane and toluene) for which chemical kinetic mechanisms and steady state hydrocarbon (HC) emissions data were available. A correlation is seen between reaction rates and HC emissions for different fuels. Calculated relative amounts of intermediate oxidation products are shown to be consistent with experimental measurements.

A one-dimensional model has been developed for the species and energy transfer over a thin (0.1-0.5 mm) layer of liquid fuel present on the wall of a spark-ignition engine. Time-varying boundary conditions during compression and flame passage were used to determine the rate of methanol vaporization and oxidation over a mid-speed, mid-load cycle, as a function of wall temperature. The heat of vaporization and the boiling point of the fuel were varied about a baseline to determine the effect of these characteristics, at a fixed operating point and lean conditions (ϕ = 0.9). The calculations show that the evaporation of fuels from layers on cold walls starts during flame passage, peaking a few milliseconds later, and continuing through the exhaust phase.

Numerical calculations of the fuel spray structure from a high-pressure swirl injector were used to enable the interpretation of experimental observations obtained in hot, hollow-cone fuel sprays issued into sub-atmospheric-pressure environments. The experiments show that the spray becomes narrower, more compact, but with a relatively long penetration depth. Model input parameters, including the droplet size distribution, early vapor production, and initial cone angle, were modified to determine which spray characteristics are important in recreating observed spray structures. A very small mean droplet diameter is needed to recreate the experimentally observed structure of the high-temperature, low-pressure sprays. Vapor addition to the emerging spray is then required to increase the axial penetration and provide the observed vapor core.