Simulation of high pressure, direct injection processes of gaseous fuels by a density-based OpenFOAM solver

Abstract

The direct injection of a gaseous fuel in internal combustion engines involves under-expanded supersonic jets and complex air/fuel fluid-dynamics. Furthermore, with the high pressure ratios between the injector and the cylinder, the gaseous flow usually becomes choked even inside the injector. Knowledge of all these phenomena is essential to achieve a deeper understanding of the air–fuel mixing process that follows, influencing combustion and pollutant formation. In this framework, this study deals with the development and validation of a fully explicit, density-based solver for supersonic compressible flows, using the OpenFOAM library and featuring Runge–kutta fourth order time discretization and the Kurganov central flux splitting scheme. This methodology was applied to analyze the inner and the external flow of an innovative, multi-hole, high pressure injector for heavy-duty vehicle applications. The adoption of multi-hole patterned injectors in gaseous fuel combustion systems is believed to be an efficient way of achieving a better air/fuel mixture and, therefore, improving the combustion reaction. The present work aims to evaluate the reliability of the aforementioned mathematical approach for such kinds of complex flows and, especially, provide a comprehensive characterization of the multi-jet spray. It was found that shock waves in the internal-nozzle deeply modify the flow development and the external Mach disk as shock cells move the mixing activity on a lateral shear layer. It was also observed that a methane cloud grows downstream and, although flammable conditions are present, it later inhibits air recirculation toward the near nozzle zone.