Modeling of the entire processes of diesel spray tip penetration including the start- and end-of-injection transients

Abstract

The start-of-injection (SOI) and end-of-injection (EOI) transients are important for sprays with multiple-injection strategy. Owing to the change of needle position and sac pressure, the spray behaviors in the transient processes are significantly different from those in the quasi-steady stage. In this study, considering the sac pressurization processes during the SOI transients and effects of ''entrainment wave'' after the EOI, a theoretical zero-dimensional model for the entire development processes of the spray tip penetration (Stip) is summarized. Then, a high-speed CMOS camera and constant-volume chamber are employed to study the spray characteristics and verify the model. The model and experimental results clarify four key time points in the entire development processes of Stip: the sac pressurization time (tp), breakup time (tb), injection duration (ti) and two injection durations (2ti). Five stages can be divided according to these four time points: the acceleration stage (Stip proportion to t1.5), transition stage 1 (t1 or t0.75), quasi-steady stage (t0.5), transition stage 2 (t0.5) and decelerating stage ((t-ti) 0.25). Moreover, the newly developed model is compared with the Wakuri model, the Hiroyasu & Arai model, and the Naber & Siebers model. The results show that all the models can well predict Stip during the quasi-steady stage and transition stage 2 with the optimized model constants. While the other models overpredict Stip in the acceleration and decelerating stages, the newly developed model still works very well.