This invention relates to combustion instability in combustors and more particularly to structure within the combustor selected to suppress combustion instability.
Combustion instability has been one of the most critical phenomena encountered during the development of gas turbine combustors used for propulsion and power generation as well as thrust augmenters, domestic and industrial burners and rocket engines. Because of significant pressure and flow oscillations, these instabilities may cause flame extinction, flashback, structural vibration, significant acoustic noise and even structural damage. As such, in order to develop high efficiency, low emission and compact combustors capable of stable operation over a wide range of operating conditions, it is necessary to formulate control strategies that can mitigate instabilities down to acceptable levels if not eliminating them completely. Passive strategies are preferable; they are less expensive and likely to be more robust.
It is an object of the present invention to demonstrate that the use of low heat conducting materials, also called heat insulating material, located in the flame-anchoring region within a combustor provides passive dynamics suppression over a wide range of operating conditions.
The combustor according to the invention includes a duct through which an air/fuel mixture flows, including a flame-anchoring region. An insulating material is located proximate the flame-anchoring region whereby combustion instability is suppressed. In a preferred embodiment the duct includes a converging region followed by a step expansion region serving as the flame-anchoring region. A suitable insulating material is ceramic block. The duct may also include a constant area region between the converging region and the step expansion region.
a and 2b are illustrations or an original steel block (2a), and a ceramic block (2b).
a and 4b are sound pressure spectrum level maps as a function of equivalence ratio for (a) when the steel block is used at the step, and (b) when the ceramic block was used at the step.
a and 5b are flame chemiluminescence image sequences for (a) when the ceramic block was used at the step and (b) typical unstable operating mode observed when the stainless steel block is used.
A schematic illustration of the backward-facing step combustor system 10 that uses a sudden expansion to anchor the flame is shown in
With reference to
The simple, passive control strategies disclosed in this application are clearly desirable because of their minimal complexity. While active combustion control strategies are able to suppress thermoacoustic instabilities in premixed combustors by disrupting the coupling mechanisms that support these instabilities by using an actuator that modulates the fuel or airflow rate, these strategies require high cost, high speed actuators and add significant complexity to the design of combustors.
The inventors have demonstrated that replacing the combustor section near the flame-anchoring region with materials made of a high heat insulating capability is simple and promising for effective suppression of instability in a passive system.
It is recognized that modifications and variations of the invention will be apparent to those of ordinary skill in the art, and it is intended that all such modifications and variations be included within the scope of the appended claims. These include, but not limited to, combustion tunnels with axisymmetric cross section with overall geometric features similar to those described in this invention.
This application claims priority to provisional application Ser. No. 61/623,177 filed on Apr. 12, 2012, the contents of which are incorporated herein by reference.
Number | Date | Country | |
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61623177 | Apr 2012 | US |