Characterization of Mixture Formation Process of Fuel Jet Injected into Superctirical Environment

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An experimental study was conducted on the mixture formation characteristics of the fuel jet injected into the supercritical environment (temperature and pressure of the ambient gas were both higher than the critical point of the fuel) in a constant volume vessel. The 2-wavelength laser absorption scattering (LAS) technique was adopted to quantitatively measure the spray and mixture properties.In this study, the fuel jet in a Diesel engine or a D.I. gasoline engine, whose combustion chamber environment is supercritical for the fuel, was investigated. Effects of nozzle hole diameter, hole L/D and injection pressure were examined. A comparison was made between a single-pulse injection and a two-pulse split injection. The main results are summarized as follows.As the nozzle hole diameter is decreased, the fuel evaporation is enhanced due to the decrease in the Sauter mean diameter, the amount of air entrained into the fuel jet is decreased, and consequently the equivalence ratio of the vapor phase becomes a little higher. As the injection pressure is increased, the fuel evaporation is enhanced due to the decrease in the Sauter mean diameter, the amount of air entrained is increased, and as a balance of these changes, the equivalence ratio of the vapor phase becomes a little lower. Comparing with the single-pulse injection, the split injection before the start of the second pulse shows smaller Sauter mean diameter, a higher ratio of the vaporized fuel to the total fuel and lower amount of air entrained. As a result, the equivalence ratio of the split injection is higher. After the second pulse injection, the split injection shows smaller Sauter mean diameter, a lower ratio of the vaporized fuel and the similar amount of air entrained comparing with the single-pulse injection. Consequently, the equivalence ratio of the split injection becomes lower.