Soot formation in turbulent swirl-stabilized spray flames in a model combustor fueled with n-butanol/Jet A-1 blends

Abstract

Information on sooting characteristics of n-butanol/middle distillate fuels from well-described spray flames is lacking but desirable as a benchmark which could help in better interpretation of the reciprocating engine data and can be used in numerical simulation validation efforts. The effects of n-butanol addition to turbulent swirl-stabilized JetA-1 spray flames were studied experimentally in a model gas turbine combustor with 94 mm × 94 mm cross-section and 188 mm length. n-Butanol was added in concentrations of 10% and 20% by energy content such that the total thermal power output was maintained at 10 kW in the globally fuel lean flames. Spray droplet size distributions and velocity fields were obtained using a Fraunhofer diffraction based droplet sizer and stereoscopic particle image velocimetry, respectively. Spatially resolved soot volume fraction and mean primary particle sizes were measured with auto-compensating laser-induced incandescence. Measurable differences in droplet size distributions were observed with n-butanol addition. Flow fields were similar in all flames. Time-averaged soot volume fraction peaks were observed in all flames at radial positions of approximately 0 mm and 27 mm and axial heights of approximately 20 mm and 40 mm, respectively. Soot production decreased monotonically throughout the flames with n-butanol addition. Primary soot particle diameters were generally within the range of 25 to 50 nm. Potential mechanisms explaining the changes observed with n-butanol substitution in jet fuel are discussed.