A flexible diesel spray model for advanced injection strategy

Abstract

Diesel engine has witnessed an increasingly stringent emission regulation due to its concomitant serious environmental pollution problems. Various advanced injection strategies have been proposed to cope with the emissions issues of diesel engine, but also increase the difficulty for evaluating spray tip penetration (Stip). Meanwhile the time dependence characteristics of Stip in multiple-injection is still unknown so far. Gaining a thorough understanding of Stip is extremely important to assess the spray mixing process and further adjust injection and combustion strategy to maximize the efficiency of diesel engines. Therefore, this paper aims to develop a flexible spray model for the quick and robust prediction of Stip under various advanced injection strategies and study the time dependence characteristics of Stip in multiple-injection. First a reduced analytical expression of effective injection velocity is derived based on the assumption of transient quasi-steady jet. Then a variable Stokes number (St) depending upon the change of injection velocity is formulated. Next a single injection spray model is developed by embedding the effective injection velocity in an existing analytical spray model. Meanwhile, the multiple-injection spray model is established with a penetrating enhancement coefficient (EC) introduced to correct its time dependence characteristics of Stip. Finally, the newly developed Stip models are validated experimentally under varied injection strategies. The results show that the newly developed Stip models could flexibly apply to various advanced injection strategies, and for the multiple-injection strategy, the first injection quantity and the dwell time are two major impact factors to the second injection.