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Novel Concepts for Combustion Instability Reduction

Description:

OBJECTIVE: Develop a novel strategy to eliminate or mitigate--preferably passively--combustion instabilities over a wide range of combustor and/or afterburner operating conditions. This concept should concentrate on essentially preventing combustion instabilities in the first place. 

DESCRIPTION: Possible strategies for combustion instability reduction include the design of sufficient fuel circuits to allow manipulation of fuel placement to reduce combustion instabilities. This requires multiple fuel circuit controls and considerable testing to explore how changing the fuel placement can prevent the acoustics. This approach provides a means to alter the acoustics should they arise. Actively controlled approaches in which fuel is manipulated temporally, but out of phase, with the combustion acoustic signature, have proven successful. However, this approach can involve many actuators and adds new sources of unreliability to an already complex system. Also, if instability frequencies are high, fast-acting valves are required, which may themselves fatigue. These approaches also lead to weight and packaging issues. Alternatively, screech liners have been used in augmentors to passively damp acoustic instabilities, and have been proven effective in practice. Acoustic liners generally have limited damping capability below roughly 1000 Hz and tuning them to lower frequencies results in significant issues with weight, size, and packaging. Maintenance of screech liners can be extraordinarily costly. However, a better screech liner is not the objective of this topic. A major challenge with combustor and augmentor development is that the design may need to be modified after engine testing, since typical engine conditions are not easily attained in rig tests. Current design methodologies are limited, especially for next generation military systems, for which boundary conditions such as temperature, operating pressure, velocity/Mach number, turbulence levels and vitiation level (for augmentors), are expected to be more severe, contributing to a higher tendency for combustion instabilities. The local flow conditions in today’s military systems can greatly deviate from the global parameters used to design them. Because of this, improved concepts that capture the local physical phenomena and are robust to changes in operating conditions are needed. This SBIR topic seeks novel concepts that focus on the reduction or prevention of the combustion instability in the first place, or a method to “self correct” the acoustic instability. Small peak-to-peak pressure amplitudes are generally acceptable to most OEMs. The concept should also not cause significant weight gain or complexity to the system. A strong collaboration with the original equipment manufacturers (OEMs) is highly recommended from the inception of this program. 

PHASE I: Show the feasibility for a novel concept for avoiding or reducing combustion instabilities. Develop a strategy for evaluating the idea, through testing and/or analysis, and identifying the key performance parameters necessary to document the concept's ability to avoid or reduce combustion instabilities. Develop an initial transition and business plan. 

PHASE II: In Phase II, the methodology developed in Phase I should be validated for additional conditions approaching those found in practice and for geometries that incorporate geometric features found in practice. In the Phase II effort, steps should be taken to establish requirements for integration of the reduced order model into a standalone design tool that incorporates sufficient details to allow it to successfully predict. The work should be transitioned to interested OEMs. 

PHASE III: Future Phase III efforts should involve further commercialization of strategies developed for incorporation into elevated TRL demonstrations. 

REFERENCES: 

1: Eldredge, J.D. and Dowling A.P., "The absorption of axial acoustic waves by a perforated liner with bias flow," J. of Fluid Mechanics, Vol. 485, pp. 307-335, 2003.

2:  Hathout, J.P., Fleifil, M., Annaswamy, A.M., and Ghoniem, A.F., "Combustion instability active control using periodic fuel injection," J. Prop and Power, Vol. 18 (2), pp. 390-399, 2002.

3:  Heuwinkel, C., et al.,"Establishment of High Quality Database for the Modeling of Perforated Liners," GT-2010-22329, Proceedings of ASME Turbo Expo 2010, Power for Land, Sea and Air, June 14-18, 2010, Glasgow, U.K.

4:  Kinsler, L.E., Frey, A.R., Coppens, A.B., and Sanders, J.V., "Fundamentals of Acoustics," John Wiley and Sons, 4th ed., pp. 284-286, 2000.

KEYWORDS: Augmentor, Combustor, Combustion Instability, Fuel Injection, Combustion Dynamics, Screech, Growl, JP-8, Durability, Analysis 

CONTACT(S): 

Vince Belovich (AFLCMC/LPE) 

(937) 255-4229 

vincent.belovich@us.af.mil 

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