Quantifying the mixing behavior of direct injected hydrogen in high-pressure environments by Rayleigh scattering

Contributing to a sustainable future, a compression-ignition Argon Power Cycle (APC) combustion engine could be an efficient means to use hydrogen as a carbon-free energy carrier. In the APC, hydrogen is burned with oxygen in an argon ambient preventing the formation of nitrogen oxides. A readily available HDEV injector with a straight 0.55-mm orifice and an inward-moving needle controls the mass flow into the constant-volume setup in accordance with (com-pressible) choked flow theory. The mixing capabilities of a milliseconds-duration gaseous jet are investigated using single-shot planar Rayleigh scattering to visualize and quantify the molar fraction of hydrogen in a controlled high-pressure inert nitrogen or argon ambient at room temperature. The linear behavior of the Rayleigh signal on the number density is presented as well as the validity for the assumed constant number density throughout the mixing jet. The evolution of mole fraction is presented for both nitrogen (making this study also relevant for air-breathing engines) and argon ambient gases, and the pressure ratios of 2.5 and 10. The observed jet behavior follows the jet penetration trends found with previous high-speed Schlieren measurements. Quasi-steady behavior is shown in both axial and radial direction, while self-similar behavior is already observed at 3 mm from the nozzle (x/de = 5.5).