Laser Diagnostics for High Pressure, Optically Thick, Particle-Laden Combustion Environments

The development of future commercial combustors as well as the redesign of current models relies heavily on diagnostic information collected on operating combustors. Key diagnostic information includes spatially resolved temperature maps, as well as maps of mass and energy transport coefficients. Diagnostics in commercial combustors are hampered by the presence of particulates such as soot which greatly increases the flame luminosity. Additionally, such combustors operate at high pressure. To address the diagnostic needs in these challenging environments, we propose the application of a non-resonant, spatially-resolved, non-intrusive, laser diagnostic to commercial combustors for the measurement of temperature and thermal diffusivity. The frequency-based technique provides a measure of temperature and transport properties independent of any amplitude fluctuations of the signal due to laser intensity fluctuations, beam steering, or beam extinction. The technique requires only minimal optical access and produces a spatially coherent signal that makes discrimination against background luminosity and scattering easy. In a particle-laden, high pressure combustor, the signal will have measurable contributions from both the gas-phase constituents and the soot particles without the need of a tunable laser system. The detected signal increases quadratically with pressure and can be employed for either point or line measurements.