Phenomenological models of the transient processes of diesel spray tip penetration

Abstract

The multiple-injection strategy that has been used widely in diesel engines usually features a short duration for each injection pulse, which makes the start-of-injection (SOI) and end-ofinjection (EOI) transients increasingly important for sprays in an injection event. Owing to the needle movement, spray developments during the transient processes are quite different from the spray at the quasi-steady state. In this paper, considering the sac pressurization processes during the SOI transients and effects of ''entrainment wave'' after the EOI, a theoretical zerodimensional (0-D) model for the entire development processes of spray tip penetration is deduced. Then, the model is validated against the experimental spray data using a constant volume chamber and high-speed shadowgraphy. The model and experimental results demonstrate that the spray tip penetration has a t 3/2 dependence at the initial stage of injection rather than the t dependence suggested by the Hiroyasu model. Later, the spray tip penetration has a t 3/4 dependence owing to the spray breakup, a t 1/2 dependence with the completion of sac pressurization, and a (t-t i ) 1/4 dependence after two injection durations from the SOI 1 .