Session: 04-37: Combustion dynamics - experiments II

Paper Number: 129231

129231 - Experimental Investigation on Combustion Instabilities in a Lean Premixed Bluff Body Combustor Producing Acoustically Long Flame 

This paper reports characteristics of combustion instability in a bluff body combustor which produces stable or unstable non-compact flame under the same inlet flow condition (inlet Mach number and equivalence ratio) as the combustor configuration changes (combustor length and blockage ratio). The inlet Mach number is changed over a range of 0.05-0.13 and the equivalence ratio from 0.6 to 0.85, resulting in long flames whose Helmholtz number () ranges between 0.29 to 0.6. For a given inlet flow condition, the combustor length is fixed at 24” or 48”and the exit of combustor is open or partially blocked (56% and 68%) by using circular orifices. Combustion instability with dynamic pressure fluctuation up to 6% of mean pressure is observed over a range of frequency 185-280 Hz. For a given equivalence ratio, the instability frequency is changed only with respect to the inlet flow Mach number regardless of the combustor length or end boundary condition. Simultaneous OH-chemiluminescence imaging of whole flame length and dynamic pressure measurement show that near the bluff body the Rayleigh integral is negative (i.e. the acoustic energy is damped) and it becomes positive thereafter (i.e. the acoustic energy is amplified), resulting in globally amplified acoustic energy in the system and hence thermoacoustic instability.

Presenting Author: Jong Guen Lee University of Cincinnati

Presenting Author Biography: Dr. Lee’s research focuses on combustion and propulsion problems in air-breathing and rocket propulsion systems. He has many years of experience in combustion dynamics in gas turbine, ramjet and augmentor, development of various laser-based optical diagnostic techniques with applications to propulsion systems, combustion control and sensors monitoring the combustion process, turbulent flame propagations and multi-phase combustion processes. Particularly, his research has been focused on the application and development of optical diagnostics which can be used to understand combustion phenomena under realistic operating conditions of combustion devices. He has been collaborating with many major gas turbine/aircraft industries such as GE Aviation, GE Energy, Pratt and Whitney, Siemens-Westinghouse, Solar Turbines as well as the NASA-GRC and DOE NETL in those areas. His research interests also include supersonic combustion, plasma-aided combustion, solid-propellants and combustion of alternative fuels. He has published more than 100 technical papers in those areas.

Authors:

Melvin Ikwubuo University of Cincinnati
Jong Guen Lee University of Cincinnati