Diode Laser Absorption Sensor for Combustion Progress in a Model Scramjet

摘要

The development and use of a tunable diode laser absorption spectroscopy sensor for combustion product water vapor in a hydrogen-fueled model scramjet combustor are presented. A pair of absorption transitions was selected from the combination bands of water vapor near 1.4 μm exploiting telecommunications diode laser and fiber technologies. Wavelength-modulation spectroscopy with detection of the peak second-harmonic signal was used owing to its superior noise-rejection capabilities. The sensor measured temperature and H_2O column density at two axial planes downstream of fuel injection with the absorption line-of-sight positioned at over 40 measurement locations using a translation stage system. The combustion product concentration and the gas temperature were not uniform along the line-of-sight, and the influence of these nonuniformities on the interpretation of the tunable diode laser measurements is discussed. The measurements are compared with published computational fluid dynamics simulations using two different kinetic mechanisms.