Publications

Transient cavitation in transparent diesel injectors

Manin, J.; Pickett, Lyle M.; Yasutomi, K.

The flow and cavitation behavior inside fuel injectors is known to affect spray development, mixing and combustion characteristics. While diesel fuel injectors with converging and hydro-eroded holes are generally known to limit cavitation and feature higher discharge coefficients during the steady period of injection, less is known about the flow during transients of needle opening and closing. Multiple injection strategies involve short injections, multiplying the transients and giving them a growing importance as part of the fuel delivery process. In this study, single-hole transparent nozzles were manufactured with the same hole inlet radius and diameter as the Engine Combustion Network Spray D nozzle, mounted to a modified version of a common-rail Spray A injector body and needle. The transients of needle opening and closing were visualized with stereoscopic high-speed microscopy at injection pressures relevant to modern diesel engines. Time-resolved sac pressure was extracted via elastic deformation analysis of the transparent nozzles. Sources of cavitation were observed and tracked, enabling the identification of a gas exchange process after the end of injection with ingestion of chamber gas into the sac and orifice. We observed that the gas exchange contributed widely to disrupting the start of injection and outlet flow during the following injection event.