A 30 Hz CARS System for Concentration and Temperature Measurements in Supersonic, Turbulent, H2/Air Combustion

Abstract

CARS has become perhaps the most common non-intrusive laser diagnostic technique used for the analysis of reacting gas flows.1-4 This paper describes the design and calibration of a dual broadband CARS system assembled to measure single-point, single-shot, temperature and species concentration in a simulated hydrogen-fueled scramjet (Supersonic Combustion RamJET) engine model. No scramjet data are included in this paper. However, the optical system design features driven by the scramjet engine test environment are discussed. During calibration, temperatures and relative concentrations of N2 were derived by fitting single-shot CARS spectra acquired at 30 Hz. This optical system was derived in part from a previous 10 Hz system designed for thermometry only5. Since N2 concentrations were found by spectral fitting, they were not subject to problems of beam steering, or beam attenuation. These problems, common in situations with high turbulence levels and windows, interfere with concentration measurement strategies that depend on acquiring absolute CARS signal intensities. In fuel-rich conditions, single-shot temperatures were also found independently by fitting H2 CARS spectra.