Reduction of Numerical Parameter Dependencies in Diesel Spray Models

Abstract

Numerical grid and time-step dependencies of discrete droplet Lagrangian spray models are identified. The two main sources of grid dependency are due to errors in predicting the droplet-gas relative velocity and errors in describing droplet-droplet collision and coalescence processes. For reducing grid dependency due to the relative velocity effects, a gas-jet theory is proposed and applied to model diesel sprays. For the time-step dependency, it is identified that the collision submodel results in drop size variation in the standard spray model. A proposed spray model based on the gas-jet theory is found to improve the time-step independency also along with the mesh independency. The use of both Eulerian (collision mesh) and Lagrangian (radius of influence) collision models along with the gas-jet theory is found to provide mesh-independent results.

Simulating low temperature diesel combustion with improved spray models

“…Spray models based on a complete Eulerian approach for both the liquid and gas phases have also been of interest. However, both of these approaches have limitations when using coarse numerical meshes in predicting the spray structure, penetration and drop sizes, as shown by Abani et al [1] for LDEF-based models, and by Abraham [2] for the Eulerian approach. Coarse meshes are desired in order to reduce computer times for detailed multi-dimensional spray simulations.…”

“…In both methods, adequate resolution of the flow near the nozzle is required down to sizes the order of the injector-hole size for better spray predictions. In addition, it was shown by Abani et al [1] that even with an adequate resolution, the drop sizes are predicted poorly due to the failure of standard collision models, which are based on O'Rourke and Bracco's collision approach [3] that uses the cell volume as the collision volume. These models over-predict the penetration of sprays.…”

A gas jet superposition model for CFD modeling of group-hole nozzle sprays

“…In addition, Abani et al (2008a-c) used a ROI (radius-of-influence) collision model and a mean collision time model to reduce numerical dependencies in the collision model (Abani et al, 2008c). used the new spray models of Abani et al (2008b) (i.e., the gas jet model, ROI collision model, and the mean collision time model) to reduce numerical dependencies in modeling group-hole nozzles. They validated the models using experimental spray penetration and SMD (Sauter mean diameter) distributions and successfully demonstrated reduced numerical dependencies in comparison to conventional spray models.…”

Development and validation of a reduced chemical kinetic model for dimethyl ether combustion

“…62 Thus, accurate chemical kinetic mechanisms are of great impor- 63 tance for simulation of advanced engine combustion concepts [3]. 64 Dimethyl ether (DME) is a promising alternative fuel for com- 65 pression ignition engines since it can provide low PM or soot emis- 66 sions and be synthesized from emerging renewable energy 67 sources, such as biomass and existing fossil fuel sources [4]. 68 Furthermore, DME offers favorable combustion characteristics 69 including easily auto-ignited due to a high cetane number and 70 soot-free combustion due to the easy vaporization and no car- 71 bon-carbon bond [5].…”