Experimental Investigation of Superheated Fuel Spray Characteristics for D.I.S.I Engines

The flash boiling by fuel heating is a useful method to control the time spatial spray characteristics such as atomization of droplets, vaporization and air-fuel mixture concentration. It is one of the important phenomena for a direct injection gasoline engine (D.I.S.I) as a next generation powertrain. This report focuses on flash boiling spray using fuel heating. The purpose of this study is to understand its physical phenomena with scattered light method, schlieren photography, and Super High Spatial Resolution Photography (SHSRP). Fuel is iso-octane and injectors are a single hole nozzle and a multi hole nozzle. These are used for the basic phenomenon analysis. The influence on spray shape can be shown by schlieren photography. Spray droplet diameter and spray dispersion at the nozzle exit are observed by super high spatial resolution photography that is our original development technique. This is the first time that this SHSRP is applied to the measurement of the heating spray. As a result, spray dispersion and atomization were controlled by superheated degree and improved drastically by flash boiling. It was clarified that fuel spray shape greatly varied by heating more than saturated temperature and not only fine atomization of the whole spray, but also decreasing of spray core region. In the case of multi hole nozzle, depending on a spray target, interference between adjacent sprays occurs because of flush boiling, as a result, a compact air-fuel mixture cloud was formed. It was clarified that the evaporation of liquid spray does not decrease in the case of flush boiling spray when interference between adjacent sprays occurs. In the heating condition that is slightly lower than critical temperature, a shock wave “MACH DISK” was confirmed at nozzle exit by SHSRP technique though the detailed analysis has just begun.