Abstract
High-pressure direct injection of the fuel into the cylinder is as a promising approach to increase the performance of gaseous fueled internal combustion engines (ICEs). Nevertheless, a direct injection (DI) strategy increases the number of degrees of freedom for optimal mixture formation. Computational Fluid Dynamics (CFD) can support this optimization process. Compared to liquid sprays, the phenomena involved in the evolution of gaseous jets are less complex to understand and model, however the numerical simulation of a high pressure gas jet is not a simple task. At high injection pressure, the gas at the nozzle exit is under-expanded and a large series of shocks occurs due to the effect of compressibility. To simulate and capture this phenomenon, grid resolution, computational time-step, discretization scheme, and turbulence model, need to be properly set. In this paper, the injection of argon at high-pressure (100 bar) in a cylindrical chamber is simulated using the CFD solver Fluent, with main focus on the characteristics of the under-expanded region. CFD results are validated through the comparison with high-definition, time-resolved measurements of gas jet mass distribution using x-ray radiography performed at the Advanced Photon Source (APS) at Argonne National Laboratory. The simplest nozzle geometry, consisting of one hole with a diameter of 1 mm and directed along the injector axis, is evaluated. An optimized computational grid is generated, with higher resolution in the under-expanded region. Results show good agreement between CFD and x-ray data. The mass distribution within the jet is well predicted by numerical simulations. The influence of turbulence model and discretization order is shown. Finally, pressure, temperature and mixing characteristics for the injected gas are illustrated in the under-expanded region.
