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Gas ingested into the sac of a fuel injector after the injector needle valve closes is known to have crucial impacts on initial spray formation and plume growth in a following injection cycle. Yet little research has been attempted to understand the fate sac gases during pressure expansion and compression typical of an engine. This study investigated cavitation and bubble processes in the sac including the effect of chamber pressure decrease and increase consistent with an engine cycle. A single axial-hole transparent nozzle based on the Engine Combustion Network (ECN) Spray D nozzle geometry was mounted in a vessel filled with nitrogen, and the nitrogen gas pressure was cycled after the end of injection. Interior nozzle phenomena were visualized by high-speed longdistance microscopy with a nanosecond pulsed LED back-illumination. Experimental results showed that the volume of gas in the sac after the needle closes depends upon the vessel gas pressure.

The reaction zone of a diesel fuel jet stabilizes at a location downstream of the fuel injector once the initial autoignition phase is over. This distance is referred to as flame lift-off length. Recent investigations have examined the effects of a wide range of parameters (injection pressure, orifice diameter, and ambient gas temperature, density and oxygen concentration) on lift-off length under quiescent diesel conditions. Many of the experimental trends in lift-off length were in agreement with scaling laws developed for turbulent, premixed flame propagation in gas-jet lifted flames at atmospheric conditions. However, several effects did not correlate with the gas-jet scaling laws, suggesting that other mechanisms could be important to lift-off stabilization at diesel conditions. This paper shows experimental evidence that ignition processes affect diesel lift-off stabilization.