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Evaluation of the combustion process in a wall-wetting direct-injection diesel was accomplished by calculation of the apparent rate of heat release from the measured pressure history for several engine speeds, loads, and start-of-combustion timings. At most of the conditions tested, the combustion process seemed to be characterized by transitions from premixed burning to airborne-diffusion burning, and finally to wall-type diffusion burning. Advancing the timing increased the amounts of premixed and airborne-diffusion burning relative to wall burning. The premixed portion of the burn also increased as the engine speed was increased. The results of this study suggest that the diffusion burn in this engine progresses from being mostly airborne at the lightest load to being mostly from the wall at the heaviest load.

To model sprays from pressure-swirl atomizers, the connection between the injector and the downstream spray must be considered. A new model for pressure-swirl atomizers is presented which assumes little knowledge of the internal details of the injector, but instead uses available observations of external spray characteristics. First, a correlation for the exit velocity at the injector exit is used to define the liquid film thickness. Next, the film must be modeled as it becomes a thin, liquid sheet and breaks up, forming ligaments and droplets. A linearized instability analysis of the breakup of a viscous, liquid sheet is used as part of the spray boundary condition. The spray angle is estimated from spray photographs and patternator data. A mass averaged spray angle is calculated from the patternator data and used in some of the calculations.