Numerical Investigation of Non-Reacting and Reacting Diesel Sprays in Constant-Volume Vessels

A numerical investigation on a series of Diesel spray experiments in constant-volume vessels is proposed. Non reacting conditions were used to assess the spray models and to determine the grid size required to correctly predict the fuel-air mixture formation process. To this end, not only computed liquid and vapor penetrations were compared with experimental data, but also a detailed comparison between computed and experimental mixture fraction distributions was performed at different distances from the injector. Grid dependency was reduced by introducing an Adaptive Local Mesh Refinement technique (ALMR) with an arbitrary level of refinement. Once the capabilities of the current implemented spray models have been assessed, reacting conditions at different ambient densities and temperatures were considered. A Perfectly Stirred Reactor (PSR) combustion model, based on a direct integration of complex chemistry mechanisms over a homogenous cell, was adopted. A detailed comparison in terms of auto-ignition time and flame lift-off length is provided. Furthermore, the assumptions of the PSR model were verified by visualizing the mixture fraction variance distribution in the regions where combustion takes place, such that the role of possible interactions between chemistry and turbulence can be estimated.