X-ray Diagnostics for Cavitating Nozzle Flow

Cavitation plays a critical role in the internal flow of nozzles such as those used in direct fuel injection systems. However, quantifying the vapor fraction in the nozzle is difficult. The gas-liquid interfaces refract and multiply scatter visible light, making quantitative extinction measurements difficult. X-rays offer a solution to this problem, as they refract and scatter only weakly. In this paper, we report on current progress in the development of several x-ray diagnostics for cavitating nozzle flows. X-ray radiography experiments undertaken at the Advanced Photon Source at Argonne National Laboratory have provided measurements of total projected void fraction in a 500 μm submerged nozzle, which have been directly compared with numerical simulations. From this work, it has been shown that dissolved gases in the liquid also result in the formation of vapor regions, and it is difficult to separate these multiple phenomena. To address this problem, the liquid was doped with an x-ray fluorescent bromine tracer, and the dissolved air substituted with krypton. The fluorescent emission of Br and Kr at x-ray wavelengths provide a novel measurement of both the total void fraction and the dissolved gas component, allowing both cavitation and dissolved gas contributions to be measured independently. [199/200 words].