Rotational-Vibrational Raman Spectroscopy for Measurements of Thermochemistry in Non-isobaric Environments

Abstract

The present work examines line measurements of pressure, temperature, and density in high speed, non-isobaric flows emanating from an underexpanded jet nozzle. Line images of rotational and vibrational Raman spectra are collected for a 8-mm linear laser probe, and are combined onto the same EMCCD detector. Combining the two techniques allows for a single-shot measurement of major species, pressure, and temperature in a turbulent non-isobaric environment that is chemically reacting. Temperature measurements along the laser test section are extracted from the rotational Raman spectrum, whereas major species densities are measured by examining the intensities of their respective vibrational Raman lines. Pressure can be calculated using an equation of state, in every location along the linear laser probe. The technique feasibility is examined by performing measurements of pressure, temperature and density in a non-reacting underexpanded air jet where the chemical composition is constant and known. Future work will extend the technique to chemically reacting supersonic flows with unknown chemical composition.