Hybrid constraint multi-line absorption spectroscopy for non-uniform thermochemical measurements in axisymmetric laminar and jet flames

Abstract

We propose a novel strategy for the accurate determination of non-uniform thermochemical distributions in axisymmetric flames using line-of-sight laser absorption spectroscopy with the constraints of hybrid information. In this method, the computational fluid dynamics (CFD) simulation or other diagnostic method (e.g., thermocouple measurement) is used to qualitatively characterize the thermochemical properties, whereas the kinetic modelling, chemical equilibrium calculation and thermocouple measurement are used to constrain the range of unknown parameters. Experimental demonstrations were firstly performed in a standard laminar CH4/air premixed flame stabilized on a McKenna burner at different equivalence ratios (Φ = 0.8-1.2). With proper hybrid constraints, multiple solutions are avoided, and the deviation and convergence time can be simultaneously reduced comparing to the conventional method. For further demonstration, this strategy was then applied to a turbulent jet flame to recover the significant thermochemical gradient without the need for tomographic reconstruction techniques.