Effect of a Preprocessing Method on Inverting Chemiluminescence Images of Flames Burning Substitute Natural Gas

Abstract A preprocessing scheme utilizing multi-division of the ROI (region of interest) in a chemiluminescence image duringinversion is proposed. The resulting inverted image shows the flame’s structure, which can be useful for studying combustioninstability. The flame structure is often quantitatively visualized with PLIF (planar laser-induced fluorescence) images as well. The chemiluminescence image, which is a line-integral of the flame, needs to be preprocessed before inversion, mainlydue to the inherent noise and the assumption of axisymmetry during the inversion. The feasibility of the multi-division preprocessing technique has been tested with experimentally-obtained OH PLIF and OH * chemiluminescence images of jetand swirl-stabilized flames burning substitute natural gas (SNG). It turns out that the technique outperforms two conventionalmethods, specifically, the technique without preprocessing and the one with uni-division, reconstructing the SNG flame structures much better than its two counterparts when compared using corresponding OH PLIF images. The characteristicsof the optimum degree of polynomials to be applied for curve-fitting of the flame region data for the multi-division methodinvolving two flames has also been investigated.