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A fuel volatility model based on the major species present in the fuel has been formulated. The model accurately predicts the ASTM distillation curves and Reid Vapor Pressure for hydrocarbon fuels. The model may be used to assess the fuel effects on the extent of evaporation and the vapor composition in the mixture preparation process.

The effects of fuel volatility and degree of enrichment on the starting and warm-up behavior of a modern four-valve spark ignition engine with port-fuel-injection were studied. Quantities of interest are the number of cycles to reach first significant firing, the time scale (τr) for the IMEP development, the decay rate of the IMEP fluctuation, and the RMS fluctuation after 3τr. A selected matrix of fuels that included various volume ratios of indolene/MTBE and iso-octane/n-pentane was used. The amount of fuel injected per cycle was varied from stoichiometric to a fuel equivalence ratio of 1.5. The engine behavior (as quantified by the quantities described in the above) is found to correlate well to a single parameter - the fuel equivalence ratio based on the fuel vapor mass calculated from an isothermal equilibrium flash vaporization of the fuel in the vapor boundary layer of the intake flow at intake manifold temperature.

A sampling system was developed to measure the evolution of the speciated hydrocarbon emissions from a single-cylinder SI engine in a simulated starting and warm-up procedure. A sequence of exhaust samples was drawn and stored for gas chromatograph analysis. The individual sampling aperture was set at 0.13 s which corresponds to ∼ 1 cycle at 900 rpm. The positions of the apertures (in time) were controlled by a computer and were spaced appropriately to capture the warm-up process. The time resolution was of the order of 1 to 2 cycles (at 900 rpm). Results for four different fuels are reported: n-pentane/iso-octane mixture at volume ratio of 20/80 to study the effect of a light fuel component in the mixture; n-decane/iso-octane mixture at 10/90 to study the effect of a heavy fuel component in the mixture; m-xylene and iso-octane at 25/75 to study the effect of an aromatics in the mixture; and a calibration gasoline.