Quantitative Raman imaging investigations of mixing phenomena in high-pressure cryogenic jets

A two-dimensional Raman technique was used to investigate mixing phenomena of cryogenic jets under both supercritical and transcritical conditions. The aim of this study was to enlarge the experimental data basis for modeling purposes and to provide quantitative information to help to improve the design of injectors for high-pressure rocket engine combustion chambers. Cryogenic nitrogen, which served as substitute for liquid O(2), was injected into N(2) at room temperature at pressures up to 6.0 MPa. The liquid N(2) jet could be atomized by a coaxial H(2) flow. Raman scattering was generated with a XeF excimer laser. The resulting signal images were discriminated against background by spectral filtering and preferential detection of light with a polarization corresponding to the polarization of the laser, thus making use of the conserved polarization of the Raman-scattered light. The Raman images were converted into density distributions of N(2) and H(2), respectively, as well as into temperature distributions for a variety of experimental conditions.