Digital colour image processing based measurement of premixed CH4 + air and C2H4 + air flame chemiluminescence

The experimental investigation of flame properties based on digital colour analysis has been conducted. In particular, the practicality of obtaining physical flame chemiluminescence characteristics through the inherent colour-filtering architecture employed in the digitisation of flame images was demonstrated. This is important as radical emission signals is an effective non-intrusive tool for deriving a number of useful combustion properties. In this study, a processing procedure was introduced which allows commercial digital colour camera to be transformed into a semi-quantitative device for radiation-based combustion diagnostics. Results have shown that the digitised primary colour outputs can be abstractly related to various emanating radicals in premixed CH4 + air and C2H4 + air flames. Both the RGB and HSV colour models were applied and each was found to be effective in tackling different issues in the overall make-up of the colour processing scheme. HSV-based numerical identity was able to recognise the appropriate RGB signal related to the radical chemiluminescence-induced digital colouration. From the recognised flame colour regime, the validity of the observed B and G signal correlation to emission characteristics of CH∗ and C2∗ radiation was conclusive by comparing with the results from the well-established spectrometry and optically filtered imaging methods. The abstract colour signals depicted similar radical chemiluminescence behaviour variations along with changes in equivalence ratio, reactant composition, and the increase of heat-release in the reactant flow.