Analysis of uncertainties in instantaneous soot volume fraction measurements using two-dimensional, auto-compensating, laser-induced incandescence (2D-AC-LII) |
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Authors: | B M Crosland M R Johnson and K A Thomson |
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Abstract: | Laser-induced incandescence (LII) is an optical measurement technique capable of measuring soot volume fraction over a wide
range of conditions. However, development of two-dimensional auto-compensating LII (2D-AC-LII) in the literature has been
limited and until now, instantaneous measurements have not been demonstrated. In this paper, we successfully demonstrate instantaneous
2D-AC-LII soot volume fraction (SVF) measurements in an ethylene-air co-annular diffusion flame. Results were then used to
support a detailed uncertainty analysis based on a Monte-Carlo simulation. Agreement between both the instantaneous and average
SVF measurements with published data from attenuation measurements under identical conditions was found to be good. Uncertainties
are discussed both in terms of an overall accuracy of the SVF measurement, which is strongly dominated by uncertainty in the
optical properties of soot, and the comparative uncertainties with optical properties fixed. The uncertainty in an instantaneous
2D determination of SVF for a comparative measurement is dominated by photon shot noise, and in regions of high soot volume
fraction it is below 25% (95% confidence interval). Shot noise uncertainty could be further reduced with additional pixel
averaging at the expense of spatial resolution. This diagnostic shows significant promise for quantitative planar soot concentration
measurements within turbulent flames. |
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