Challenges in Modeling the Liquid Phase in Direct-Injection Diesel Engines

The fuel spray in direct-injection Diesel engines has a structure that includes an intact liquid core which sheds drops from it. The drops then vaporize in the hot ambient and subsequently the vapor penetrates. In current models for such sprays, the intact liquid core is not well represented. Typically, drop dynamics that include collisions and coalescence and secondary breakup, and heat and mass transfer are modeled within the framework of a Lagrangian representation of the liquid phase and an Eulerian representation of the gas phase. Recently, serious limitations related to the numerical treatment of the drop dynamics which, in turn, affect the computed liquid penetration and vaporization rates have been found. In this work, these limitations will be discussed. Results of computed and measured liquid penetrations will be presented for a wide range of Diesel conditions. It has also been shown that, under conditions where the liquid penetration is short relative to the penetration of the overall jet and the mass of fuel in the chamber that is in liquid phase is small relative to the total mass of fuel present, the liquid phase may be represented by a Virtual Liquid Source (VLS) model. The model will be described and results presented showing comparisons between computed and measured results.