Influence of m-xylene addition to Jet A-1 on spray structure, flow field and soot production in turbulent swirl-stabilized spray flames in a model combustor

Spray combustion of Jet A-1 and a Jet A-1/10% m-xylene blend was investigated to assess the influence of m-xylene addition on the spray characteristics and soot formation in a swirl-stabilized model combustor with dimensions of 94 mm x94 mm cross-section and 188 mm length. Keeping the thermal power output constant at 10 kW, globally fuel lean flames were established for the neat Jet A-1 and 10% m-xylene blend fuels. The velocity field of the model combustor, spray characteristics, and soot volume fraction and primary particle size were measured, respectively, using stereoscopic particle image velocimetry, a Fraunhofer diffraction based droplet sizer, and auto-compensating laser-induced incandescence. Addition of m-xylene to Jet A-1 caused measurable differences in the flow field and the spray characteristics under identical air and fuel flow rates. Soot concentrations were modified throughout the flame by the addition of m-xylene, resulting in significant alterations in the cumulative soot loading within the spray flame envelope. In both flames, peak soot volume fractions were detected in the lower central portion of the combustor at the base of the inner recirculation zone and in the upper portion of the combustor in the fuel shear layer. Our results demonstrate the nontrivial influence of altered distillation characteristics (and other physical properties) of the fuel, induced by m-xylene addition, on flow field structure and spray properties. Potential mechanisms for the influence of changing flow field and spray characteristics, in addition to m-xylene doping of the Jet A-1, on soot processes are discussed. (c) 2020 The Combustion Institute. Published by Elsevier Inc. All rights reserved.