Temperature imaging of elevated pressure flames using planar laser induced fluorescence

This paper reports on the temperature imaging of elevated pressure flames using planar Two Line Atomic Fluorescence, TLAF, of gallium. The technique was applied in laminar and turbulent flames with and without soot particles. Two tunable laser sheets at 417 nm and 403 nm were used to record two Planar Laser Induced Fluorescence of gallium simultaneously. Gallium nanoparticles were generated by laser ablation and seeded into the flames using nitrogen as the carrier gas. The planar flame temperature was extracted from the ratio of the fluorescence intensity emitted at 403 nm (anti-Stokes process) and 417 nm (Stokes process). The temperature was calibrated by Rayleigh scattering thermometry in a laminar flame with near-unity cross section relative to air. The results exhibited good agreement with those obtained by Rayleigh scattering, with a maximum deviation of ∼ 130 K for laminar flames under atmospheric and elevated pressures, up to 6 bars. The temperature image of a turbulent flame, Re ∼ 4000, was derived based on the calibration factor determined in the laminar flame. The reliability of the TLAF thermometry was further confirmed by imaging the planar temperature field in a sooting flame under high pressure of 5 bars. The findings underscore TLAF's robustness in mitigating soot interference, enabling precise planar temperature imaging, particularly under turbulent and high-pressure conditions. This research enhances the understanding of TLAF's potential in diverse combustion scenarios, contributing to advancements in high-pressure flame diagnostics.