High-speed filtered Rayleigh scattering thermometry in premixed flames through narrow channels

Abstract

High-speed filtered Rayleigh scattering at 10 kHz repetition rate for time-resolved temperature measurements in premixed flames propagating in mm-high channels is demonstrated for the first time. The instrument relies on a pulse burst laser with a 200 ns temporal width, and a CCD camera operated in subframe burst gate mode to achieve high signal to noise ratio despite the limited optical access. A 10-inch-long iodine cell acts as a molecular filter and the laser, which is seeded using an external cavity diode laser and operated in a temporally stretched mode, is wavelength-tuned to the peak of a strong iodine absorption line. A CCD camera, operated in the sub-frame burst gating mode with the help of an external slit configuration, is used as the detector to achieve improved camera noise performance. Filtered Rayleigh scattering temperature measurements in premixed flat flames stabilized over a McKenna burner indicate an instrument precision of 3%. Temperature measurements in the products region are within 3% of measurements obtained with conventional Rayleigh scattering. The system's capabilities are demonstrated through time-resolved temperature measurements in a premixed methane-air flame propagating in a 1.5 mm-high rectangular channel designed to study flame quenching in flame arrestors. Surface scattering from the optical windows and the channel surfaces is successfully suppressed and time-resolved temperature profiles are obtained for both quenching and no-quenching events.