A Standard Burner for High Pressure Laminar Premixed Flames: Detailed Soot Diagnostics

Soot formation and oxidation in high-pressure combustion is of high practical relevance but still sparsely investigated because of its experimental complexity. In this work we present a high-pressure burner for studying sooting premixed flames at pressures up to 30 bar. An optically accessible vessel houses a burner that stabilizes a rich premixed ethylene/air flame on a porous sintered stainless-steel plate. The flame is surrounded by a non-sooting rich methane/air flame and an air coflow for reducing temperature gradients, buoyancy-induced instabilities, and heat loss of the innermost flame. Spectrally-resolved soot pyrometry was used for determining gas temperatures. These were introduced into model functions to fit the temporal signal decay curves obtained from two-color time-resolved laser-induced incandescence (TiRe-LII) measurements for extracting soot volume fractions and mean particle size as a function of height above burner and gas pressure. The derived mean particle sizes and soot concentrations were compared against thermophoretically sampled soot analyzed via transmission electron microscopy (TEM) and laser extinction measurements at 785 nm, respectively. Soot volume fractions derived from LII peak signal intensities need to be corrected for signal attenuation at the high soot concentrations present in the investigated flame. From the various heat conduction models employed in deriving mean soot particle diameters from TiRe-LII, the Fuchs model gave remarkably good agreement with TEM on sampled soot at various heights above the burner.