Heterodyne Dual Frequency Comb Laser Absorption Spectroscopy Measurements in Supersonic Combustion

Abstract

Experimental determination of NO and H2O production during hydrogen combustion applying laser absorption spectroscopy has been performed in the High Enthalpy Shock Tunnel Göttingen of the Ger- man Aerospace Center. The combustion process forming these species within the propulsion unit of a small scale wind tunnel model was experimentally studied. A novel experimental approach to obtain absorption spectra in the infrared region within µ-seconds is reported. This technique is based on the use of quantum cascade lasers generated frequency combs and enables multi-species measurements at high acquisition rates. The generated frequency combs are within the 1740±20 cm−1 wavenumber region which features strong NO and H2O spectral lines allowing for the spectral characterization of these species. The technique and its underlying physics, the application in short duration ground testing and the needed calibration work is discussed.