Demonstration of a two-line Kr PLIF thermometry technique for gaseous combustion applications

Experiments were performed to demonstrate a dual-wavelength excitation krypton planar laser-induced fluorescence (Kr PLIF)-based 2D temperature imaging technique in a laminar non-sooting CH₄/N₂ diffusion flame. The technique exploits the thermochemical dependence of the overlap integral arising from Kr absorption and excitation laser spectra to yield the temperature without the need to know the local mixture composition. The choice of the two excitation wavelengths is made using the knowledge of the fuel mixture and pressure. The two excitation wavelengths lie within the same 4p⁶S01→→5p[32]₂ transition, and their selection is informed such that the resulting Kr PLIF signal ratio depends primarily on the temperature and negligibly on local composition. Mean temperature fields show excellent agreement when compared to Fluent simulations across different regions of the combustion domain, while the single-shot temperature field exhibits slightly degraded accuracy. Overall, the technique provides very similar figures of merit compared to conventional composition-dependent thermometry approaches and showcases a promising scope for application in complex reacting flows.