Atomization of a G-DI spray with air dissolved in gasoline and mono-component fuels

A spray from a GDI multi-hole injector is used to investigate and compare the atomization results from different fuels in which air has been dissolved to promote the atomization. The spray is injected in air at atmospheric conditions; five fuels are tested, two commercial gasolines with known distillation curves, and three monocomponent fuels, n-pentane n-hexane and n-heptane. The fuel is heated up to a constant temperature, between 30° and 120°C, and pressurised at 50 bars, a relatively low pressure used to improve the accuracy of the droplet sizing by PDA, thus allowing higher sensibility in detecting small variations of the measured quantity for better comparison among the results. This work follows and completes a previous similar study on flash boiling, where no air had been dissolved into the fuels, and more fuels were tested. The global spray behaviours, like spray penetration and spreading angle, are illustrated by photographic results. Then the atomization is accurately measured by Phase Doppler Anemometry and results are analysed and compared. The spray droplet characteristics are measured at 45mm of axial distance from the injector tip in 13 different radial positions; after data post-processing the average velocity and diameters results are plotted, both as time evolution in a fixed position, and as radial profiles during the quasisteady injection period. When no air has been dissolved into the fuel, the temperature increase gives negligible effects up to the initial distillation or boiling point of each fuel, above which stronger variations are observed, with the typical spray collapse at increasing temperature. When the fuel injected is saturated with air dissolved in it, the effects observed are very similar to those caused by flash boiling, but they start and become observable at temperature that is about 20 degrees lower. The major effects are the spray collapse, with a narrower shape, generally finer and more homogeneous atomization, and a remarkable lack of larger droplets, which results in a better atomization of the initial droplets of the spray