Femtosecond Laser Absorption Spectroscopy for Simultaneous Temperature and NH Concentration Measurements in An Ammonia/Hydrogen Flame

A femtosecond ultraviolet laser absorption diagnostic for simultaneous temperature and NH concentration measurements is developed and demonstrated in an atmospheric ammonia/hydrogen flame produced by a Hencken burner. The diagnostic system provides high-accuracy, calibration-free, single-shot measurement of NH based on the (0, 0) band of the A3Π-X3Σ- electronic transition near 336 nm with an acquisition rate of 156 Hz. Theoretical NH absorbance is simulated using a line-by-line model. NH and temperature profiles along the flame central axis are measured. An estimated NH detection limit of 1.3 ppm was achieved. This diagnostic enables quantitative and time-resolved NH and temperature measurement, providing a new method for probing ammonia reaction kinetics in combustion and chemical synthesis.