Effect of Swirl and Fuel Pulsation on Flow Dynamics, Flame Structure and Droplet Motion in Swirl-Stabilized Spray Flames

This paper describes an experimental investigation of the role of swirl distribution in a co-annular swirl-stabilized spray combustor for passive control of flame structure using kerosene fuel. Three distinctly different flames have been examined. A low shear, a high shear, and a counter-rotating swirling flow flame have been examined. The droplet dynamics and flowfield associated with the low and high shear co-rotating swirl configurations under isothermal and combustion conditions have been examined using a phase Doppler interferometric techniques. The high-shear swirl configuration was found to decrease droplet diameter in the shear region, indicating secondary atomization of larger size droplets due to strong shear effects in the flow. Droplet mean and turbulence characteristics were obtained. In order to simulate oscillations in the flow pulsations were introduced into the fuel flow in order to excite instabilities in the burner. The role of swirl distribution was determined on the attenuation of this imposed instability. Swirl distribution was found to be effective in reducing the instability. Instabilities at the forcing and harmonic frequencies are found to be up to 5 dB more powerful in the counter-rotating flow, demonstrating the role of swirl on flame structure and the associated combustion instability in swirl-stabilized spray combustors. The airflow distribution in the burner was also found to play an important role on the alleviation of combustion instability.