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Results of two- and three-dimensional computations of combustion of Diesel sprays in a very high-pressure chamber are presented. A wide range of experimental conditions are considered. Peak chamber pressure with combustion range from about 6.0 MPa to about 20 MPa. Computed and measured spray penetrations and chamber pressures are compared and shown to be in adequate agreement. Autoignition is modeled using an equation for a progress variable which measures the local and instantaneous tendency of the fuel to autoignite. High temperature chemistry is modeled using a local equilibrium model coupled to a combination of laminar and turbulent characteristic times. It is shown that scaling rules which were found to apply in vaporizing and non-vaporizing sprays also apply in the combusting sprays. The fuel-air mixing rates and burning rates increase as the ratio of the ambient density to injected density increases.

Results of three-dimensional computations of non-vaporizing and vaporizing Diesel sprays in a very high pressure (up to 18.4 MPa without combustion) environment are presented. These pressures and corresponding density ratios of ambient gas to injected liquid are about a factor of two greater than those in current Diesel engines. The spray model incorporates a line source for drops, heat, mass and momentum exchange between the gas and liquid phases, turbulent dispersion of drops, collisions and coalescences, and drop breakup. The accuracy of the model is assessed by making comparisons of computed and measured spray penetrations. Reasonable agreement is obtained for a broad range of conditions. A scaling for time and axial distance clarifies these results.

In this paper we present photographic and pressure data that describe the autoignition and combustion processes of transient fuel sprays under diesel-like conditions. The results were obtained in a constant-volume vessel that allowed complete optical access to the diesel spray ignition/combustion process. The combination of complete optical access and schlieren/luminosity visualization presents a unique view of the spray. From the data, a narrative of the features of diesel spray autoignition and combustion is constructed. Comparison of events at different gas-phase temperatures shows the effect of shifting the chemical induction time relative to the fluid mechanic transport time. The data show that a key feature of the autoignition process is the formation and shedding of fuel eddies along the edges of the spray jet. These eddies provide an environment conducive to chemical reaction, without the disruptive effects of the spray core fluid mechanics.