Power plants – Combustion products used as motive fluid – Process
Reexamination Certificate
2001-09-27
2004-01-06
Casaregola, Louis J. (Department: 3746)
Power plants
Combustion products used as motive fluid
Process
C060S725000
Reexamination Certificate
active
06672071
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to gas turbine engines, and more particularly, to methods and apparatus for operating gas turbine engines.
Gas turbine engines typically include high and low pressure compressors, a combustor, and at least one turbine. The compressors compress air which is mixed with fuel and channeled to the combustor. The mixture is then ignited for generating hot combustion gases, and the combustion gases are channeled to the turbine which extracts energy from the combustion gases for powering the compressor, as well as producing useful work to propel an aircraft in flight or to power a load, such as an electrical generator.
Because gas turbine engines must be capable of operating in a plurality of operating conditions, stable burning is essential for engine operation over a wide range of engine operating conditions. More specifically, stable combustion facilitates reducing engine blowout while achieving engine rated thrust or power levels. Furthermore, stable combustion also facilitates reducing engine screech, rumble, or howl. Screech is characterized by high pressure acoustic oscillations at a frequency above 300 Hz., and may be caused by a coupling/feedback mechanism of the combustion process with a natural acoustic transverse mode (radial and tangential) of a combustion chamber defined within the combustor. Rumble or howl is also characterized by high pressure acoustic oscillations, but at frequencies below 300 Hz. More specifically, at such frequencies, combustion instability may be caused by a coupling/feedback mechanism of the combustion process with a natural axial mode of the combustion system. Continued operation with screech, rumble, or howl may cause hardware damage to occur.
To facilitate reducing potentially harmful combustion resonance, at least some known combustors have been modified with extensive and expensive design changes. Such design changes may include the addition of acoustic suppressors that are tuned to facilitate reducing resonant frequencies. Frequent maintenance may occur if a combustion instability persists in a product introduced in the field. Additionally, damage to fuel nozzles, liners, and other combustor components including suppressors may occur with continued operation during combustion instability.
Other known combustors include complex active combustion control systems (ACC) that include a pulsator coupled upstream from a controller that is coupled between the pulsator and the fuel manifold. The pulsator pulses the fuel flow to the fuel manifold at a resonant frequency to enhance combustion stability. The controller receives continuous feedback from the combustor and times the fuel pulsation such that the fuel flow increases at the low portions of the oscillation and decreases at high portions of the oscillation, such that the system serves as a wave cancellation. However, because the controller is downstream from the pulsator, establishing the accurate timing of the controller with respect to the pulsator may be difficult. Furthermore, such systems may provide only limited benefits when spinning tangential modes instead of merely standing acoustic modes are present during engine operations. Moreover, during such conditions, because of the difficulty in establishing the controller timing, the pulsator frequency may become in tune with the resonant frequency, and as a result, may actually increase the resonance of the chamber. If the pulsator can not be set to cancel or detune the resonant frequency, the pulsator is not utilized and an operating range of the combustor may be limited.
BRIEF DESCRIPTION OF THE INVENTION
In one aspect of the invention, a combustion control system for controlling a turbine engine that includes a fuel manifold and a plurality of fuel injectors is provided. The control system includes a fuel pulsator and a controller. The fuel pulsator is coupled in flow communication with the plurality of injectors and the fuel manifold. The controller is coupled to the fuel pulsator such that the pulsator is between the controller and the fuel manifold. The controller is variably selectable and configured to facilitate promoting stable combustion.
In another aspect, a method for controlling an aircraft engine is provided. The engine includes a combustor, a fuel manifold, and a plurality of fuel injectors. The fuel manifold is coupled in flow communication with the fuel injectors for supplying fuel to the combustor. The combustor defines a combustion chamber. The method includes supplying fuel to the combustor fuel injectors through a fuel pulsator and the fuel manifold, wherein the fuel pulsator is coupled to a controller that is upstream from the fuel pulsator; and variably operating the controller to pulse fuel with the fuel pulsator to facilitate promoting stable combustion within the combustion chamber.
In a further aspect, a gas turbine engine is provided that includes a combustor, a fuel manifold, a plurality of fuel injectors, and a fuel control system. The combustor defines a combustion chamber, the plurality of fuel injectors are in flow communication with the fuel manifold. The fuel injectors are configured to supply fuel to the combustion chamber. The fuel control system is coupled to the fuel manifold and the fuel injectors. The fuel control system includes a fuel pulsator and a controller. The fuel pulsator is in flow communication with the fuel manifold, and the controller is coupled to the fuel pulsator such that the pulsator is between the controller and the fuel manifold.
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Andes William Scott
Armstrong Teasdale LLP
Casaregola Louis J.
General Electric Company
Reeser III Robert B.
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