Single-shot 3D flame diagnostic based on volumetric laser induced fluorescence (VLIF)

Abstract

We demonstrate single-shot three-dimensional (3D) flame measurements based on volumetric laser-induced fluorescence (VLIF). For this effort, the excitation laser beam was expanded into a “slab” with a height of 40mm and thickness of 10mm to excite the CH radicals in the target flames. The volumetric LIF signals were then simultaneously captured by five intensified cameras, and the images were fed into a tomographic algorithm as inputs to obtain the 3D distribution of CH. The results show that single-shot 3D measurements with sufficient accuracy can be obtained in a volume of 9.3×9.3×32.7mm3 with an excitation pulse energy of ∼10mJ. With a total of five intensified cameras, 3D measurements were obtained with a voxel size of 0.15mm over a total of 64×64×224≈106 voxels, which can be further improved by the use of additional cameras or advanced tomographic inversion techniques. Comparison with PLIF measurements suggested that the spatial resolution of the CH-based VLIF technique to characterize the flame surface was about 0.4mm. Measurements were first performed on stable laminar flames, for comparison and validation against PLIF, and then on turbulent jet flames, to illustrate the feasibility and accuracy of VLIF for instantaneous 3D flame measurements and motivate further investigation.