Hydroxyl Radical Distributions in Shear Coaxial Methane-Oxygen Combustion via Rotational Laser Absorption Tomography

Laser absorption tomography was used to quantify and spatially resolve hydroxyl radical and carbon monoxide concentrations, and temperature in the near-field mixing region for shear and swirl coaxial single element rocket injectors. Two quantum-cascade lasers scanned at 6.25 kHz were used to target a pure rotational absorption line of OH molecule at 18.8 μm and two rovibrational absorption lines of CO near 4.97 μm. Multiplexed, focused laser light was pitched across fuel-rich flames to measure transmitted light intensities with CO and OH absorption. Planar measurements were taken at different heights while the injectors were translated horizontally at constant velocities. A tomographic inversion method was applied to obtain radially-resolved distributions of temperature, CO mole fraction, and OH mole fraction for each axial position or height, yielding quantitative, two-dimensional measurements.