NO Sensor for Practical Gas Turbine Engines Using Ammonia Hydrogen Fuel Blends

Ammonia-hydrogen fuel blends are a promising route for carbon-free gas turbine operation. One important challenge for their practical use is the formation of nitric oxide emissions, which must be accurately quantified and controlled. In this work, a nitric oxide sensor based on scanned wavelength direct absorption spectroscopy is developed for ammonia-hydrogen combustion conditions. The sensor uses a mid-infrared quantum cascade laser from Alpes Lasers tuned near 5.2 µm, and scans across three transitions: two water lines at 1936.21 and 1937.94 cm⁻¹ for thermometry and one nitric oxide line at 1937.02 cm⁻¹ for nitric oxide quantification. Spectral line selection is supported by a chemical reactor network in Ansys Chemkin Pro that combines a perfectly stirred reactor and a plug flow reactor to represent the toroidal jet stirred reactor facility, and by absorbance simulations in SpectraPlot using the HITEMP2010 database. These calculations establish expected water and nitric oxide signals, water interference, and the small contribution from room humidity. The analysis framework uses dual line water thermometry to obtain path-averaged temperature and then applies the Beer-Lambert relation to recover water and nitric oxide mole fractions from the integrated absorbances. The sensor architecture is implemented in an optical layout that can be aligned to multiple facilities and includes reference and etalon channels together with a wavemeter for wavenumber calibration. Initial validation is carried out in an atmospheric static cell with known nitric oxide mixtures, followed by measurements in the exhaust of a toroidal jet stirred reactor operating at atmospheric pressure. Emission-only tests confirm that broadband exhaust emission is a minor correction that can be removed in post-processing. The resulting sensor concept is intended to provide a transferable platform for future measurements in more complex ammonia-based combustor and engine experiments.