Internal Structure of Vaporizing Pressure-Swirl Fuel Sprays

A computational study was carried out of the atomization and breakup processes of hollow-cone fuel sprays resulting from pressure-swirl injectors which have potential for use in direct-injection gasoline engines. Atomization is described using a method whereby 'blobs' that represents the liquid sheet outside the injector nozzle are injected with sizes equal to the sheet thickness. Breakup of the blobs and the subsequent drops is modeled using a modified Taylor Analogy Breakup (TAB) model in which the originally used χ-squared size distribution for the breakup drops is replaced by a Rosin-Rammler distribution for the considered hollow-cone sprays. The model is implemented in a multidimensional computer code and used to study pressure-swirl atomized sprays. Comparisons of computed and experimentally determined spray characteristics are made and good levels of agreement are obtained. For the engine applications it was of interest to study the spray characteristics and vapor distribution inside a vaporizing spray at elevated ambient pressures and temperatures. It was found that the fuel vapor exhibits a solid-cone distribution in the spray region while the liquid spray keeps a hollow-cone structure. As the ambient pressure is increased, the spray collapses and richer mixtures are found to be present inside of the spray.