REAL-TIME EVOLUTION OF NOZZLE INTERNAL FLOW AND SPRAY BREAKUP UNDER HIGH FUEL TEMPERATURE AND HIGH AMBIENT PRESSURE

Injector nozzle internal flow and the following spray atomization considerably affect combustion characteristics and emissions from diesel engines. This study focuses on the instantaneous cavitation evolution inside the diesel injector nozzle. The aim is to study how the nozzle internal flow influ- ences the real-time near-filed diesel spray evolution and its atomization characteristics. A high-speed camera coupled with a microscope was employed to capture the instantaneous cavitation evolution inside an optical quartz nozzle under high fuel temperature and high ambient pressure conditions. The area-based cavitation fraction was used to quantify the cavitation intensity in the nozzle. Re- sults show that increasing fuel temperature leads to less residual fuel left in the nozzle at the end injection due to a reduction of fuel viscosity; consequently, gas bubbles increase at the next injection event. Compared with the saturated vapor pressure changing with the temperature, the size of the initial bubbles has a greater influence on the development of subsequent cavitation strength. The influence of back pressure on the cavitation strength is weaker than that of temperature. The rela- tionship between the instantaneous cavitation intensity and the spray cone angle is linear.