Abstract
The method of tomographic imaging using multi-simultaneous measurements (TIMes) for flame emission reconstructions is presented. Measurements of the peak natural CH* chemiluminescence in the flame and luminescence from different vaporised alkali metal salts that were seeded in a multi-annulus burner were used. An array of 29 CCD cameras around the Cambridge-Sandia burner was deployed, with 3 sets of cameras each measuring a different colour channel using bandpass optical filters. The three-dimensional instantaneous and time-averaged fields of the individual measured channels were reconstructed and superimposed for two new operating conditions, with differing cold flow Reynolds numbers. The contour of the reconstructed flame front followed the interface between the burnt side of the flame, where the alkali salt luminescence appears, and the cold gas region. The increased mixing between different reconstructed channels in the downstream direction that is promoted by the higher levels of turbulence in the larger Reynolds number case was clearly demonstrated. The TIMes method enabled combustion zones originating from different streams and the flame front to be distinguished and their overlap regions to be identified, in the entire volume.
Highlights
The inherent nature of practical flames calls for measurement techniques that can provide spatiotemporal information, to enable in-depth understanding of different processes
Oil droplets were used for particle image velocimetry (PIV) data collection from which the volumetric velocity field could be inferred tomographically, and the preheat zone that is marked by vaporisation of the oil droplets was used to track the flame front at the same time
The measurements and reconstructions confirm that the detectable vaporised salt luminescence occurred on the burnt side of the flame
Summary
The inherent nature of practical flames calls for measurement techniques that can provide spatiotemporal information, to enable in-depth understanding of different processes. 3D reconstructions based on simultaneous measurements of CL from flame radicals and electronically excited material-specific molecules and atoms in flame pyrolysis techniques for nanoparticle synthesis will allow the limits and spatial correlation of different zones such as combustion, particle clouds and different fluid streams to be determined in the entire volume. This enables better understanding of the synthesis process which allows us to control it more effectively. TIMes can provide a new perspective for better understanding the stratification process based on 3D experimental flame emission reconstructions which allow the interaction of different streams with each other and with the flame front to be studied
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