Structure of a Hollow-Cone Spray With and Without Combustion

Abstract

A hollow-cone spray with a nominal cone angle of 30 degrees from a pressure-swirl fuel atomizer was used in a swirl-stabilized combustor. The combustor is circular in cross section, with a swirl plate and fuel nozzle axis coinciding with the axes of the chamber. kerosene is injected upward inside the chamber from the fuel nozzle. Separate swirl and dilution air flows are distributed into the chamber that pass through honeycomb flow straighteners and screens. A calculated swirl number of 1.5 is generated with the design swirl plate exit air velocity of 30 degrees with respect to the chamber axis. Effects of swirl and dilution air flow rates on the shape and stability of the flame are investigated. A Phase Doppler Particle Analyzer (PDPA) is used to measure drop size, mean and rms values of axial drop velocity, fuel volume flux, drop velocity and size distributions, and size-classified drop velocity profiles for two cases of with and without combustion and at six different axial locations from the nozzle. For the no-combustion case all air and fuel flow rates were kept at the same values as the combusting spray condition. 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. Root mean square (RMS) values of drop velocity fluctuations decrease due to a 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 due to preferential burning of small drops. Fuel volume flux profiles indicate negligible drop vaporization and/or burning up to a distance of 25mm from the nozzle. Velocity number distributions at different radial points for without combustion at an axial distance of 55mm from the atomizer are symmetric in shape only close to the peak of the mean drop velocity and show a bimodal shape around the maximum mean drop axial velocity gradient. Corresponding number distributions for the combustion case are fairly symmetric and quite different in behavior at all radial positions. Size-classified drop velocity profiles are also plotted and discussed.