Penetration and combustion characterization of cavitating and non-cavitating fuel injectors under diesel engine conditions

This work investigates the effects of cavitation on spray characteristics by comparing measurements of liquid and vapor penetration as well as ignition delay and lift-off length. A smoothed-inlet, converging nozzle (nominal KS1.5) was compared to a sharp-edged nozzle (nominal K0) in a constant-volume combustion vessel under thermodynamic conditions consistent with modern compression ignition engines. Within the near-nozzle region, the K0 nozzle displayed larger radial dispersion of the liquid as compared to the KS1.5 nozzle, and shorter axial liquid penetration. Moving downstream, the KS1.5 jet growth rate increased, eventually reaching a growth rate similar to the K0 nozzle while maintaining a smaller radial width. The increasing spreading angle in the far field creates a virtual origin, or mixing offset, several millimeters downstream for the KS1.5 nozzle. Remarkably, this mixing offset appeared to globally influence the liquid penetration and lift-off stabilization location over a wide range of operating conditions. When this offset was removed, OH chemiluminescence-derived lift-off lengths for the two nozzles essentially collapsed. An Eulerian multiphase mixture model, with Large-Eddy Simulations (LES) combining internal and external flow predicted the trends in spreading angle in the region close to the injector. The K0 simulation showed cavitation zones along walls downstream of the nozzle inlet with some dispersion into the center of the jet before the nozzle exit. With a slightly diverging nozzle (as measured), the K0 simulation also indicated that low pressure zones draw ambient gas just inside the nozzle exit, which, combined with cavitation dynamics, should be considered as a potential contributor to the initial growth rate.