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

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 zerodimensional 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 quasisteady 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.

Automated summary

The study investigates the influence of the start and end injection transients on spray behavior and establishes a theoretical model for the entire spray tip penetration development process, validated through experiments. Four key time points and five stages in the spray development process are analyzed.