Experimental Approach on Concentration Measurements of NO in Hydrogen Combustion Based on Heterodyne Laser Absorption Spectroscopy Using Quantum Cascade Lasers

Experimental determination of NO and \(H_2O\) production during hydrogen combustion applying laser absorption spectroscopy will be performed in the High Enthalpy Shock Tunnel Gottingen of the German Aerospace Center. The combustion process forming these species within the propulsion unit of a small scale wind tunnel model is to be studied. A novel experimental approach to obtain absorption spectra of both species in the infrared region within \(\mu \)-second range is reported. This technique is based on the use of frequency combs generated with quantum cascade lasers. This method enables multi-species measurements of absorption spectra from which concentrations can be inferred. The generated frequency combs are within the \(1760\,\pm \,30\,\mathrm cm^{-1}\) wavenumber region which features strong NO and \(H_2O\) spectral lines allowing characterization of these species. The technique, the application in short duration ground testing and its calibration procedure will be reported.