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

In the framework of the Argon Power Cycle, millisecond-pulsed hydrogen gas injections into a high-pressure, room temperature nitrogen or argon ambient are investigated. Instantaneous Rayleigh scattering is used to quantify the hydrogen mole fraction in the ensuing jets. 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 (compressible) choked flow theory. The linear dependence of the Rayleigh signal on the number density is experimentally validated and the validity for the assumed constant number density throughout the mixing jet is presented. The evolution of mole fraction is presented for both nitrogen and argon ambient gases, and pressure ratios of 2.5 and 10. Quasi-steady behavior is shown in both axial and radial direction, while self-similar behavior is already observed 3 mm from the nozzle (\(x/d_\textrm{e} = 5.5\)).