Under-Expanded Jets Characterization by Means of CFD Numerical Simulation Using an Open FOAM Density-Based Solver

Among the others, natural gas (NG) is regarded as a potential solution to enhance the environmental performance of internal combustion engines. Low carbon-to-hydrogen ratio, worldwide relatively homogeneous distribution and reduced price are the reason as, lately, many researchers efforts have been put in this area. In particular, this work focuses on the characterization of the injection process inside a constant volume chamber (CVC), which could provide a contribution to the development of direct injection technologies for a gaseous fuel. Direct injection of a gaseous fuel involves the presence of under-expanded jets whose knowledge is fundamental to achieve the proper mixture formation prior to the combustion ignition. For this reason, a density based solver was developed within the OpenFOAM library in order to simulate the jet issued from an injector suitable for direct injection of methane. The numerical investigations are supported by an experimental campaign performed with aims of schlieren technique. The results obtained shed more light on the structure of under-expanded jets, the shock waves present, the flow field generated and the evolution of the mixing activity depending on the injection parameters.