To investigate the combustion characteristics of hollow-cone spray flames somewhat similar to those occurring in the primary zone of gas turbine combustion chambers or within oil burners, a swirl-stabilized combustor was designed. The combustor is circular in cross section, with a swirl plate and fuel nozzle axis coinciding with the axes of the combustor. Separate swirl and dilution air flows are distributed into the combustor that pass through honeycomb flow straighteners and screens. A kerosene spray was generated by a simplex atomizer with a nominal initial-spray-angle of 30 degrees. Swirling air with swirl number of 1.5 was produced from a swirl plate. A Phase Doppler Particle Analyzer (PDPA) was used to measure the drop size, mean and rms values of axial drop velocity with and without combustion. Air and fuel flow rates and other conditions were kept identical for reacting and non-reacting cases to investigate effects of combustion alone on the spray. A thermocouple was used to measure the average uncorrected temperature in this turbulent spray flame. A water-cooled stainless-steel gas sampling probe was designed to be used with a gas chromatograph (GC) to measure the gaseous species concentrations in this combustor.
Results for mean axial drop velocity profiles indicate widening of the spray, with slight increase in the magnitudes of the peak drop velocities due to combustion. No measurements of this type are possible inside the hollow-cone spray due to burning of fuel droplets within the flame zone. Root-Mean-Square (RMS) values of drop velocity fluctuations decrease due to combination of increase in gas kinematic viscosity and elimination of small drops at high temperatures. Sauter Mean Diameter (SMD) radial profiles at all axial locations increase with combustion as compared to the no-combustion case due to preferential burning of small drops. At the initial stages of combustion near the atomizer, the gas species concentration changes due to droplet evaporation, decomposition of fuel, reaction, and mixing with extra air. At the end of the visible flame zone, away from the nozzle, no significant amounts of methane and hydrogen have been observed. The gas concentration profiles at this axial position are flat within the burned gas zone. The species concentration profiles measured in the burned gas zone near the nozzle and along the spray centerline axis are similar to those of turbulent gaseous-fuel diffusion flame.