Effect of Pressure on the Micro-explosion of Water/Oil Emulsion Droplets Over a Hot Plate

Abstract

The purpose of the present investigation is experimentally to study the micro-explosion behavior of water/oil emulsion droplets over a hot plate in general, and the effect of pressure on this droplet/plate system in particular. The technological relevance of this study stems from the interest in direct injection high-compression-ratio engines because droplet/wall interaction is believed to be an important process within these engines, and because water/oil emulsion is most suitable for application with the heavier oils used by them. From the fundamental viewpoint it is not clear a priori that insights gained from results of freely falling droplets can be readily applied to the present system. This is because droplet gasification behavior over a hot plate (commonly known as the Leidenfrost phenomenon) is a nonmonotonic one. Specifically, for a droplet originally in contact with the plate, with increasing plate temperature the droplet lifetime will first decrease, then increase rapidly as the droplet attempts to levitate itself by its outgoing vapor, and finally decrease gradually when it is in the totally levitated mode. Furthermore, a change in pressure not only will shift the transition plate temperatures for the different gasification modes, but it can also conceivably alter the nucleation mode of the more » superheated water microdroplets depending on whether the emulsion droplet is in physical contact with the plate. « less