You are here

High-Speed Measurements of Dynamic Flame Stabilization Processes in High-Pressure Combustion Systems

Description:

TECHNOLOGY AREA(S): Air Platform

OBJECTIVE: Develop volumetric, high-repetition-rate techniques to increase the spatial dimensionality of quantitative flame-position and turbulent-velocity-field measurements of unsteady combustion processes in high-pressure combustors.

DESCRIPTION: Combustor and turbine component performance and lifetime are highly sensitive to unsteady temperature, pressure, and velocity perturbations and the coupling of these parameters to heat release. As the pressure and temperature in current and next-generation combustion systems continue to rise, unsteady combustion processes such as thermoacoustic instabilities[1] and blowoff[2] continue to be critical engineering challenges for optimized high-pressure combustor design and operation. These transient processes place strict design requirements on combustor and turbine components, and if not accurately assessed in the design process, can result in over-designed and over-cooled parts, thereby increasing system cost and reducing performance. Predictive modeling and simulation of these behaviors for optimizing system and component design require quantitative high-speed combustion chemistry and fluid dynamics measurements for elucidating flame anchoring and stability physics. Measurements are required under relevant aero-thermodynamic conditions (up to 10 atm, 2200 - 3500 degrees F) to understand the influence of elevated pressure and velocity perturbations on chemistry-turbulence interactions in flame-propagation- and auto-ignition-dominated flames[2]. There is currently minimal understanding of the coupling of these two critical combustion mechanisms which can lead to unsteady flow inside the combustor and at the combustor exit.

Flame propagation is dependent on the velocity field near the flame, the fluid dynamic strain-rate, and the turbulence dynamics. In addition to the velocity field, which necessitates measuring the velocity gradients in all three spatial dimensions, the proposed effort requires measurement of the spatial and temporal evolution of the reacting flame front. Therefore, the proposed effort should develop and apply a three-dimensional technique for high-speed measurements of the velocity field and its gradients synchronously with flame-front orientation. Current state-of-the-art velocimetry techniques provide quantitative information but are limited to small measurement volumes/planes (< 10 mm per side), lines, or points by available techniques[3, 4]. Execution over large measurement volumes (>10 mm per side) becomes particularly challenging at the high repetition rates required (10 to 100 kHz) because the resolvable spatial scales are severely limited by the spatial dynamic range of the measurement techniques. Extension to elevated pressure is required (up to 10 atm), making particle-based velocimetry techniques difficult to implement, because of window and hardware fouling, and seedless techniques as potential alternatives. However, extension to three dimensions is essential for any proposed approach. The characterization of flame propagation processes necessitates the measurement of the spatio-temporal evolution of the flame position synchronous with the velocity field and strain rate. Possible approaches include planar or tomographic laser-induced fluorescence or tomographic chemiluminescence imaging[5]. Purely line-of-sight measurements will not provide sufficient spatial resolution for the required analyses.

The technical merit of the proposed measurement should be demonstrated in an elevated-pressure combustion rig of practical interest, with simultaneous measurements of the spatiotemporal evolution of the flame position. Accurate resolution of relevant temporal and spatial scales must be demonstrated for understanding the influence of flame anchoring physics on unsteady processes including combustion instabilities and blowoff. These measurements will lead to a physics-based understanding of dominant flame stabilization modes at elevated pressures (up to 10 atm) for validation of advanced modeling and simulation approaches. The results of this program will be an improvement to the diagnostics available for three-dimensional combustion measurements, and flame anchoring physics analyses that will be valuable for combustor research and development for predicting performance and enhancing operability, reliability, and sustainability.

PHASE I: Demonstrate high-speed (>1 kHz), three-dimensional velocity measurements along with simultaneous flame orientation measurements in an atmospheric-pressure laboratory scale reacting turbulent flow (2200 - 3500 degrees F). Demonstrate the potential for extension of the technique to confined, elevated pressure combustion systems.

PHASE II: Further develop and apply the technology demonstration in Phase I to an elevated-pressure (up to 10 atm), swirl-stabilized combustion system of practical interest and relevance to combustors. Develop, apply, and deliver hardware and advanced physics-based data analyses software for understanding unsteady combustion processes in high-pressure combustion systems.

PHASE III DUAL USE APPLICATIONS: High-repetition-rate three-dimensional measurement technologies can be used in development and procurement programs for the collection of high-quality quantitative data for validation of design, operation, and performance of military and commercial gas-turbine combustors and turbine test facilities.

REFERENCES:

    • Poinsot, T.J., Trouve, A.C., Veynante, D.P., Candel, S.M., and Esposito, E.J., "Vortex-driven acoustically coupled combustion instabilities," Journal of Fluid Mechanics, Vol. 177, pp. 265–292 (1987).2).

 

    • Lieuwen, T.C., Unsteady Combustor Physics, Cambridge University Press (201

 

    • Elsinga, G.E., Scarano, F., Wieneke, B., and van Oudheusden, B.W., "Tomographic particle image velocimetry," Experiments in Fluids, Vol. 41, pp. 933–947 (2006).

 

    • Danehy, P.M., Bathel, B.F., Calvert, N.D., Dogariu, A., and Miles, R.P., "Three-component velocity and acceleration measurement using FLEET," 30th AIAA Aerodynamic Measurement Technology and Ground Testing Conference, Atlanta GA (2014).

 

  • Böhm, B., Heeger, C., Gordon, R.L., and Driezler, A., "New Perspectives on Turbulent Combustion: Multi-Parameter High-Speed Laser Diagnostics," Flow, Turbulence and Combustion, Vol. 86, pp. 313–341 (2010).

KEYWORDS: combustion instabilities, lean blowoff, velocimetry, high-speed combustion diagnostics, laser-induced fluorescence, tomography

  • TPOC-1: Joseph Miller
  • Phone: 937-255-2668
  • Email: joseph.miller.35@us.af.mil
US Flag An Official Website of the United States Government