Raman imaging of transcritical cryogenic propellants

Abstract

The objective of this research is to explore the atomization and vaporization behavior of cryogenic droplets, jets, and sprays that are injected at a supercritical pressure but subcritical temperature into an environment that is at supercritical pressure and temperature. Lessons learned from developmental experiments have been incorporated into the design of a new high-pressure chamber that is optimized for this study. In preliminary efforts, using an existing pressure vessel not optimized for this purpose, shadowgraph and Raman imaging experiments of transcritical nitrogen jets have been conducted. Shadowgraph imaging of liquid nitrogen jets injected into nitrogen and nitrogen/helium mixtures at pressures below, at, and well above the critical pressure of nitrogen demonstrate the profound effect that transcritical vaporization has on jet structure, atomization, and mixing. Also demonstrated is the profound effect that mixture properties can have on the would-be transcritical interface. Raman imaging diagnostics were evaluated and look promising for use with transcritical jets. The diagnostic was able to distinguish the structural differences between transcritical nitrogen jets injected into helium or nitrogen. The results indicate that Raman imaging will be useful to evaluate vaporization and mixing rates of jets at various conditions.