Search Results

A jet and droplet breakup model for high pressure-driven liquid fuel is described and validated for vaporizing sprays, and its performance is evaluated in combination with a recently developed auto-ignition model for reacting sprays under application of a KIVA-3 based code. The breakup model, presented in a previous study for non-evaporating sprays, imitates a cascade of drop breakups whereby the actual disintegration processes reflect the experimentally observed stripping or bag breakup mechanisms. The breakup condition itself is determined by the Taylor drop oscillator dynamics and the droplet injection is governed by a drop size distribution to account for the surface stripping near the nozzle exit. The formation of a fragmented liquid core is the consequence of a drop breakup delay achieved with an appropriate initial drop deformation together with the drop breakup cascade. The model has been validated for vaporizing, non-reacting sprays with experimental data.

The underlying computations examine the spray mean flow and its influence on the fuel distribution under non-reacting conditions, with a particular focus on the application to intermittent, equally-pulsed DI-Diesel sprays. The fuel is injected from the top center of a cylinder in axial direction into quiescent air of 800 K and 120 bar. The fuel flow rates are controlled with the nozzle diameter, keeping the injection pressure constant. The computations have been performed with a KIVA-3 based code on a CRAY-YMP. The spray-induced gas flow interacts with the fuel droplets which leads to an increased collision activity at the tip of the spray and near the nozzle exit, and, via coalescences, results in the formation of larger lumps of fluid. The effect of this droplet clustering has been investigated for various fuel flow rates of continuous and intermittent DI-Diesel sprays.

In this investigation computational methods for the atomization process of a liquid fuel jet and the secondary breakup of droplets have been developed and tested for non-evaporating, solid-cone diesel fuel sprays injected into a cylindrical constant-volume cell using a KIVA-3 based code. The breakup of the liquid fuel is computed based on the Taylor analogy breakup model. In this new approach the droplet breakup process has been improved to account for the different breakup regimes which occur in diesel engine environments. In addition, an appropriate choice of the initial drop deformation parameters allows the simulation of a fragmented liquid core at the nozzle exit. The model enhancements have been tested by comparisons with data from phase doppler anemometry. Specifically, the droplet radius and velocity distributions have been compared over two cross-sections in the near-field region of the spray.