Modeling Diesel Engine Injector Flows.

摘要

Models have been developed to assess flow fields inside diesel injector orifice passages in order to increase our understanding of the spray formation process which governs performance and emissions in these engines. Fully viscous, unsteady, and two phase codes have been developed to analyze 2-D and 3-D flows and the effect of turbulence has also been incorporated in the 2-D models. A series of parametric studies have been conducted to characterize unsteadiness in the flow brought about by instabilities of the vena-contracta formed downstream of the orifice inlet lip. Turbulence effects have been investigated extensively and the production of turbulence in the bubble collapse region is evident in the simulations. Including the effects of turbulence improves predictions of the extent of the two-phase region. Large three- dimensional simulations have been conducted to reflect the asymmetric inlet conditions realized in today's diesel injectors. The cross flow which is present at the inlet lip has a dramatic impact on the extent of the cavity and the massflow/velocity distribution at the exit of the orifice. Vortices are formed at the inlet lip; these structures persist the entire length of the passage. The structures elucidated by the calculations have also been observed experimentally in recent work from Delphi Systems. These works have shown that the vortices persist into the spray itself and therefore the simulation of the orifice flow does provide a good predictive tool for subsequent spray development.