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.
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.
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
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.