Spatially correlated temperature, oxygen, and fuel measurements in a plasma-assisted hydrogen diffusion flame by one-dimensional fs/ps rotational CARS imaging

A two-beam, one-dimensional hybrid fs/ps rotational CARS scheme was applied to a coaxial dielectric barrier discharge burner to spatially resolve and simultaneously measure temperature, relative oxygen concentration, and relative hydrogen concentration. At higher applied voltages, the 1 L/min hydrogen burner produces a collapsed flame with a curved reaction zone to the surrounding quiescent air, extending roughly 5 mm above the burner surface, making this a perfect candidate for single-shot realizations of flame properties with a vertical line CARS imaging technique. Time-delayed probing of the impulsively created Raman coherence allowed for improved dynamic range in regions of high temperature gradients, but also introduced the reliance on collisional modeling. Temperature measurements proved robust with probe delay, but the higher detection limit of oxygen at longer delays encouraged the use of isolated oxygen line calibrations to Hencken burner data in place of collisional modeling. A spatial resolution of 140 μm in the axis normal to the burner surface was adequate for mapping out flame properties along the reaction zone.