Understanding Transient Combustion Phenomena in Low-NOx Gas Turbines
Combustion instability is a major issue that impacts the operability of modern, lean-premixed gas turbine engines. Combustion instability occurs when heat release rate fluctuations couple with combustor acoustics in a feedback loop; this manifests as large amplitude pressure oscillations. These pressure oscillations are undesirable because they increase the emissions from the engine, and in the worst-case, cause catastrophic hardware failure from rapid fatigue loading. One way to suppress combustion instability is to redistribute the fuel un-evenly through different nozzles while maintaining the same overall fuel flow rate. This un-even distribution of fuel is called “fuel-staging,” and is widely used in industry for instability suppression. While fuel staging is successful at suppressing instabilities, the mechanism of its operation is not well-researched. Furthermore, gas turbine engines in the field must undergo transients in load as the power demands change throughout the day, and it is not well-understood how these transients in load (and by extension fuel staging) affect combustion instability. The goal of the current work is twofold: One, to understand the mechanisms by which fuel staging suppresses instability and two, to understand how transients in fuel staging affect the instability. Pressure measurements, high-speed flame images, and laser-induced fluorescence are used to capture the combustor and flame dynamics at different operating points.
Culler, W., Chen, X., Samarasinghe, J., Peluso, S., Santavicca, D., O’Connor, J., (2018) “The effect of variable fuel staging transients on self-excited instabilities in a multiple-nozzle combustor,” Combustion and Flame, 194, p. 472-484. Accepted author pre-print available here: Culler_Transients_2018PrePrint-1lhhvef
Culler, W., Chen, X., Peluso, S., Santavicca, D., O’Connor, J., Noble, D., (2018) “Comparison of center nozzle staging to outer nozzle staging in a multi-flame combustor,” ASME Turbo Expo, Oslo, Norway. Accepted author pre-print available here: GT2018-75423_preprint-1s52tff
Chen, X., Culler, W., Peluso, S., Santavicca, D., O’Connor, J., (2018) “Comparison of equivalence ratio transients on combustion instability in single-nozzle and multi-nozzle combustors,” ASME Turbo Expo, Oslo, Norway. Accepted author pre-print available here: GT2018-75427 Draft Revision-x4rw3a
Chen, X., Culler, W., Peluso, S., Santavicca, D., O’Connor, J., (2018) “Effects of equivalence ratio transient duration on self-excited combustion instability time scales in a single-nozzle combustor,” Spring Technical Meeting of the Eastern States Section of the Combustion Institute, State College, PA. Author copy here: ESSCI_2018_Spring_Technical_Meeting_Transient Duration Variation in SNC_Draft_20180122-248o3fa
Sekulich, O., Culler, W., O’Connor, J., (2018) “The effect of non-axisymmetric fuel staging on flame structure in a multiple-nozzle model gas turbine combustor,” Spring Technical Meeting of the Eastern States Section of the Combustion Institute, State College, PA. Author copy here: 20180122_SekulichCuller_EffectOfNonAxisymmsetricFuelStagingOnFlameStructure-186qrly
Samarasinghe, J., Culler, W., Quay, B., Santavicca, D. A., O’Connor, J. (2017) “The effect of fuel staging on the structure and instability characteristics of swirl-stabilized flames in a lean premixed multi-nozzle can combustor.” Journal of Engineering for Gas Turbines and Power, 139(12), 121504. Accepted author pre-print available here: FMANU-GTP-17-1247-2gbhzkr
Culler, W., Samarasinghe, J., Quay, B., Santavicca, D. A., O’Connor, J. (2017) “The effect of transient fuel staging on self-excited instabilities in a multi-nozzle model gas turbine combustor,” ASME Turbo Expo, Charlotte, NC. Accepted author pre-print available here: 20170306TurboExpoTransientsRevision_FINAL-rfwjz8
O’Connor, J., S. Hemchandra, T. Lieuwen, “Combustion Instabilities in Lean Premixed Systems.” Ed. D. Dunn-Rankin and P. Therkelsen, Lean Combustion: Technology and Control, Second Edition.
O’Connor, J., V. Acharya, T. Lieuwen, (2015) “Transverse Combustion Instabilities: Acoustic, Fluid Mechanic, and Flame Processes,” Progress in Energy and Combustion Science, 49, p. 1-39
Impact of Turbulence on Mechanisms of Combustion Instability
Combustion instability is an issue that affects many critical power and propulsion technologies, including jet engines, power-generation gas turbines, rockets, boilers, and process furnaces. Significant questions remain about how turbulence alters flame behavior during instability. In particular, in high-performance engines, does the turbulence/flame interaction change the instability feedback mechanisms and do the present numerical models include the correct physics? This work addresses these questions using a systematic experimental approach to examine various key aspects of combustion instability. Advanced laser diagnostics will be used to image the flowfield and the flame, unlocking the coupling between turbulence and the instability feedback loop.
The technical goal of this project is to understand the impact of turbulence on three critical components of the thermoacoustic feedback loop: the hydrodynamic instability of the flowfield that determines the susceptibility of the flow to external disturbances; the coupling mechanisms that drive heat release rate oscillations; and the mechanism by which these disturbances create heat release rate oscillations in non-flamelet regimes. This systematic approach uses theory-based experimental design to probe the ways in which turbulence impacts flow stability, coupling-mechanism physics, and flame behavior within the framework of combustion instability.
A Fundamental Framework for the Robust Multivariable Stabilization of Time-Delayed Acoustic-Flame Interaction Dynamics, with Application to Gas Turbines
This project is conducted to attenuate the pressure oscillations associated with instability in combustion systems such as gas turbine, rockets, industrial process furnaces, and boilers. The need for controlling combustion instabilities is growing rapidly as society pushes for combustion systems with reduced emissions and increased ability to respond to fluctuating power demands. Gas turbines play an important role in ensuring the resilience of the power grid, where their ability to respond to both slow and rapid demand fluctuations enables them to provide a broad portfolio of ancillary grid services. However, the intermittent, transient operation of these grid-tied generators has not been traditionally considered in their design, which can lead to high-amplitude instability during the above operations. From the study on the instability onset of a laboratory combustor undergoing transient operation, the dramatic increase in combustion-related pressure oscillations by almost an order of magnitude, in less than half a second, highlights the degree to which combustion instability can be disruptive and potentially damaging in gas turbine systems.
The goal of the research is firstly to furnish a fundamental framework for the robust, multivariable, combined passive/active attenuation of combustion instability in a broad range of applications. This framework will take into account the prominent role played by transport delay dynamics in combustion instability, as well as the degree to which uncertainties in factors such as fuel composition and ambient temperature/pressure/humidity affect these delay dynamics. The second goal is to demonstrate the above fundamental framework using a flexible combustion rig as an experimental validation.