The difficulties in making spatially-resolved measurements of soot concentration inside practical combustors, which do not rely on sample extraction techniques, are highlighted. Restricted optical access presents the principal constraint to the adoption of established tomographic techniques. A novel hybrid approach, which combines a traversable laser shielding tube and conventional integrated absorption measurement, is demonstrated in two tubular combustors operating at a range of AFRs, inlet air temperatures and pressures. Measurements are reported which have been taken through existing primary and dilution ports and through additional line-of-sight holes drilled in the liner specifically for that purpose. Distinctive radial profiles of soot volume fraction emerge, reflecting the annular development of richer mixtures, which favour soot formation, downstream of the fuel injector.

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