Soot distribution and particle emissionsin a swirl combustor at elevated temperaturesand pressures

An experimental investigation is conducted to examine soot distribution and particulate matter (PM) emissions in the pilot swirl flame of a centrally staged combustor at elevated temperatures (up to 650 K) and pressures (up to 0.5 MPa). The study employs comprehensive optical diagnostics, including two-dimensional laser-induced incandescence, particle image velocimetry, and simultaneous OH/kerosene planar laser-induced fluorescence, complemented by the scanning mobility particle sizer measurements. Results demonstrate that soot predominantly forms near the inner shear layer of the primary recirculation zone but is suppressed by high flow velocities and OH oxidation. Increasing combustor inlet pressure and temperature significantly enhances soot formation, triggering a distribution transition from hollow cone mode to solid cone mode. Under transitional operating conditions, intermittent shifts between these modes correlate with the sporadic presence of OH radicals in the primary recirculation zone. Statistical analysis of exhaust PM reveals nucleation mode dominance in the size distribution, with particle number concentrations and geometric mean diameters increasing at higher pressures. Both in-flame soot and exit PM volume fractions exhibit power-law relationships with pressure, though their temperature sensitivities differ, potentially due to distinct post-flame soot evolution processes. This work highlights the critical role of turbulence−soot interactions in governing soot formation and PM emissions, providing vital insights under engine-relevant conditions.