A COMPREHENSIVE STUDY ON THE INFLUENCE OF RESOLVING AN INJECTOR ORIFICE AND THE INFLUENCE OF CREATING STRIPPED OFF DROPLETS ON SPRAY FORMATION USING THE VSB2 SPRAY MODEL

Artikel i vetenskaplig tidskrift, 2021

With respect to simulating fuel sprays applied to direct injection engines, few studies in literature have investigated resolving the injector orifice and how this may influence spray predictions for high pressure and temperature diesel engine-like conditions. In this work, we used the stochastic blob and bubble (VSB2) spray model to conduct simulations in which fuel is injected into a constant volume combustion vessel. The injector orifice is resolved into nine cells. The boundary conditions were the same as the Engine Combustion Network (ECN) noncombusting case for n-dodecane (ECN, 2020). Two simulation meshes were compared with experimental data: (1) injector orifice resolved and (2) injector orifice unresolved (grid cells in the orifice region equal orifice diameter). The resolved orifice mesh showed a liquid penetration length slightly higher and closer to experimental values. Spray predictions for an asymmetrical injection velocity was compared for both meshes. Finer structures near the leading edge of the spray (for mixture fraction and temperature fields) seen in the resolved mesh were missing in the unresolved mesh. Resolving the orifice requires a change in the core of the mesh, which also influences the results. The influence of creating new child blobs (liquid parcels are referred to as blobs in this work) stripped off from a parent blob by secondary breakup was also studied. The simulation results suggested that for high pressure and temperature diesel engine-like conditions, the influence of creating new child blobs is insignificant.