Underexpanded Impinging Gaseous Jet Interaction with a Lubricated Cylinder Surface

The dynamics of the gaseous jet is a major factor affecting the particulate matter and gaseous pollutants formation in the combustion of hydrogen or a hydrogen-rich reformate. Mitigation of particulate matter formation is essential for the sustainability of a novel high-efficiency propulsion cycle with High-Pressure Thermochemical Recuperation which has been developing in the Technion. The latter suffers from elevated particle emissions compared to hydrocarbon fuels combustion in a wide range of operating regimes. An intensified lubricant involvement in the combustion process was found to be the source of the elevated particle formation in a non-premixed reformate and hydrogen combustion. The reported research further analyzes and compares using analytical, empirical, and experimental tools the gaseous impinging underexpanded jet evolution and propagation with a focus on the lubricant vapor entrainment mechanisms from a heated cylinder wall surface into the combustion chamber bulk. Shadowgraph optical imaging was employed to investigate the impinging jet interaction with a heated lubricated surface. Semi-analytical model of the jet development along the piston axis and the cylinder wall after impingement has been derived and validated based on previous publications and the experimental results of this study. The obtained experimental data showed for the first time that the evolving after impingement gaseous fuel vortex climbs over the liner wall and sweeps away the lubricant vapors into the combustion chamber bulk. This entrainment mechanism was found to be stronger compared with the lubricant entrainment in the free-jet region. The lower heating value of the reformate fuel compared to hydrogen requires a longer injection duration and/or higher injection pressure. These contribute to longer and more intensive vortex flow along the cylinder wall, thus explaining the previously observed higher particle formation with the reformate compared to hydrogen. Fundamental principles of the impinging jet interaction with a heated lubricated surface have been discussed. Possible ways of mitigating the lubricant vapor entrainment into the combustion bulk have been suggested.