In-situ photoacoustic measurement of soot profiles in laminar flames using a high repetition-rate pulsed fibre laser

Humphries, Gordon S. and Roy, Robert and Black, John D. and Lengden, Michael and Burns, Iain S. (2019) In-situ photoacoustic measurement of soot profiles in laminar flames using a high repetition-rate pulsed fibre laser. Applied Physics B: Lasers and Optics, 125 (4). 60. ISSN 0946-2171 (https://doi.org/10.1007/s00340-019-7169-0)

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Abstract

We present a photoacoustic technique for in situ sensing of particulates in reacting flows. The method is demonstrated by measuring soot distribution in laminar flat-flames. The excitation source is a high repetition-rate pulsed fibre laser. The resulting acoustic signals are measured using a uni-directional microphone and lock-in amplifier. Based on an Allan-Werle plot, the detection limit is estimated to be a soot volume fraction of 3 parts-per-billion. Fluence curves are presented, showing a plateau region similar to the behaviour typically observed for laser-induced incandescence. A dependence of the photoacoustic signal on pulse repetition rate is also demonstrated.

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