Temperature and H2O concentration measurements in plasma-assisted NH3 combustion using LAS

To decarbonize high-temperature industries like steel and glass manufacturing, ammonia (NH₃) is studied as an alternative to conventional fuels. However, in certain conditions, ammonia combustion faces several challenges, such as high NO emissions and poor stability, leading to (unburnt) NH₃ emissions. The EM2C laboratory investigates plasma-assisted combustion using Nanosecond Repetitively Pulsed (NRP) discharges to improve NH₃ flame stability and reduce these emissions. For that purpose, we developed a laser absorption spectroscopy diagnostic to map temperature and H₂O concentration in the flame exhaust without disturbing the flow of gasses. By refining the method proposed by Bendana et al., the H₂O lines near 4030 cm⁻¹ are used to quantify combustion efficiency gains from NRP discharges in lean ammonia flames. The tool was validated both numerically on synthetic spectra, and experimentally using a thermocouple, proving effective in measuring the spatially resolved temperature (±50K) and the H₂O mole fraction (relative uncertainty of 7%) in axisymmetrical flames.