Technical Report 217, c4e-Preprint Series, Cambridge

Authors: Jochen Dreyer, Radomir I. Slavchov, Eric J. Rees, Jethro Akroyd, Maurin Salamanca, Sebastian Mosbach, and Markus Kraft

Reference: Technical Report 217, c4e-Preprint Series, Cambridge, 2019

Associated Themes:
 

• New regression based methodology (FLiPPID) for performing the inverse Abel transform is reported.
• FLiPPID results in smoother cross-section profiles of the soot temperature and volume fraction obtained from colour-ratio pyrometry experiments.
• Methodology applicable in other experimental techniques where the 2D projection of asymmetric, optically thin objects is recorded.

This letter reports a new regression method based on fitting the line-of-sight projection of a predefined intensity distribution (FLiPPID) to flame images for performing the Abel inversion. The aim is to develop a methodology that is less prone to experimental noise when analysing the projection of antisymmetric objects, in this case co-flow diffusion flame images for colour ratio pyrometry. A regression model is chosen for the light emission intensity distribution of the flame cross-section as a function of the radial distance from the flame centre-line. The forward Abel transform of this model function is fitted to the projected light intensity recorded by a colour camera. For each of the three colour channels, the model function requires three fitting parameters to match the radial intensity profile at each height above the burner. This results in a very smooth Abel inversion with no artefacts such as oscillations or negative values of the light source intensity, as is commonly observed for alternative Abel inversion techniques, such as the basis-set expansion (BASEX) or onion-peeling. The advantages of the new FLiPPID method are illustrated by calculating the soot temperature and volume fraction profiles inside a co-flow diffusion flame, both being significantly smoother than those produced by the alternative inversion methods.

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