CANNEx

The phenomenon of cavitation occurs in high-pressure fuel injectors, extending from their starting point around the nozzle orifice inlet to the exit, where it influences the formation of the emerging spray. The improved spray development is believed to lead to a more complete combustion process, lower fuel consumption, and reduced exhaust gas and particulate emissions. Cavitating holes have proved also their efficiency to limit the risk of coking, i.e. particulates deposit into the injection holes. However, cavitation can decrease the injection process efficiency (discharge coefficient) by limiting the flow rate. It can enhance or limit atomization, depending on the cavitation regime. In addition, imploding cavitation bubbles inside the orifice can cause irreversible damages to the nozzle by material erosion, thus decreasing the life duration and hydraulic performances of the injector. Clearly, an optimum cavitation regime is suitable and it is important to understand the sources and amount of cavitation for more efficient nozzle designs in both Diesel and gasoline applications, including petroleum-based fuels and biofuels. The objective of CANNEx is to deliver new perspectives on cavitation phenomenon to the scientific community, in order to enhance our current knowledge and our ability to control this phenomenon in the context of high injection-pressure applications. To do so, a well-controlled flow will be studied from inside the nozzle to the spray, by using advanced optical diagnostics and efficient numerical tools. Simultaneous visualizations of cavitation inside a transparent nozzle and the liquid jet at nozzle outlet will be performed. The spray will be characterized by using femtosecond ballistic imaging techniques in the near field and an image based drop size technique in the far field. DNS computations incorporating improved cavitation models will be developed and applied to simulate the flow from the nozzle to the emanating jet. Computation and experimental results will be confronted to each other to identify: 1- the relations between cavitation and spray formation , 2- the involved mechanisms. Application to innovative nozzle design is also under the scope of the project as far as these designs will be achievable for transparent nozzles.