Development and characterization of a sensitive NO measurement system by wavelength modulation spectroscopy for combustion and emission measurements

Abstract Modern advanced power generation and propulsion systems realize the highest efficiency by achieving combustion reactions at higher temperatures and pressures. One of the challenges that comes with such harsh conditions is NOx emissions. A typical example can be found in combustors in gas turbines, and these need to be quantified. In this work, the concentrations of nitric oxides in combustion products were measured using mid-infrared wavelength modulation spectroscopy (WMS). NO absorption line at 1939.61 cm−1 (5.2 μm) was selected to avoid interference from water. Simulated absorption spectra with a typical combustion product mixture were generated to validate the feasibility of the selected line. The WMS scheme successfully rejected noise from turbulent fluctuations, flame emissions, etc. Peak height of the subtracted 1f normalized 2f signal was useful to quantify integrated absorbances. NO measurement was demonstrated under various conditions of flames at a flat flame burner. Noise equivalent detection limit was 8.4 ppm-m for non-reacting flow. The measurement system shows promise in assisting the development of cleaner and low-emitting advanced power generation and propulsion systems.