Patent Application
20120107750
The present invention generally involves a system and method for igniting a combustor. In particular embodiments, the system and method may employ a laser to provide a focused beam for igniting a fuel in the combustor.
Combustors are known in the art for igniting fuel with air to produce combustion gases having a high temperature and pressure. For example, gas turbine systems, aircraft engines, and numerous other combustion-based systems include one or more combustors that mix a working fluid such as air with fuel and ignite the mixture to produce high temperature and pressure combustion gases. Each combustor generally includes an igniter to initiate the combustion which then becomes self-sustaining. In addition, the igniter may be used to re-initiate the combustion when needed. For example, gas turbine systems having multiple combustors may occasionally experience an interruption in combustion in a single combustor which, if not promptly re-ignited, may result in an unanticipated or unscheduled shut down of the gas turbine system. Similarly, aircraft engines occasionally operate under conditions known to create instabilities in the normally self-sustaining combustion and therefore may use an igniter that can quickly and reliably re-initiate combustion when needed.
Various systems are known in the art for igniting combustors. For example, conventional igniters often include a sparkplug that provides a spark inside the combustor to ignite the fuel and air mixture. To effectively operate, the spark produced by the sparkplug must be close enough to the fuel to ignite the fuel. This generally requires either inserting the sparkplug into the combustion chamber to reach the fuel spray or increasing the width of the fuel spray to reach the sparkplug. Inserting the sparkplug into the combustor may interfere with the flow of fuel, air, and combustion gases in the combustor, and increasing the width of the fuel spray to reach the sparkplug may reduce the efficiency of the combustor once combustion is initiated and self-sustaining. Extending the sparkplug into the combustor to initiate combustion and retracting the sparkplug once combustion has been initiated is a useful solution. However, the sparkplug may become inoperable in the event the mechanism for extending and retracting the sparkplug malfunctions.
More recent attempts have been made to incorporate a laser as an ignition source. The laser may be located outside of the combustor and still generate a laser beam having a focal point in the path of a more narrow fuel spray inside the combustor. A window or lens between the laser and the focal point provides a shutter between the combustion gases and the laser to protect the focal lens. However, foreign object debris, oil, fuel, combustion gases, and other contaminants tend to foul the window or lens over time. As the window or lens becomes fouled, the window or lens may refract or distort the laser beam. The refraction or distortion of the laser beam may move the focal point of the laser beam so that the focal point of the laser beam is no longer coincident with the narrow fuel spray, rendering the igniter inoperable. Moreover, the new focal point of the laser beam may result in damage to the combustor and/or the laser. Material fouling of the lens surface can produce rapid heating of the lens surface as a result of absorption of the laser energy by the fouling material. A rapid temperature change at the lens surface can result in permanent degradation or failure of the lens. As a result, an improved system and method for igniting a combustor would be useful.
Aspects and advantages of the invention are set forth below in the following description, or may be obvious from the description, or may be learned through practice of the invention.
One embodiment of the present invention is an ignition system for a combustor. The system includes an access port through a wall of the combustor and a laser outside the combustor and aligned with the access port to generate a beam along a path. A lens in the path of the beam focuses the beam at a focal point inside the combustor, and a shutter has a first position in the path and a second position out of the path.
Another embodiment of the present invention is an ignition system for a combustor. The system includes an access port through a wall of the combustor and a laser outside the combustor and aligned with the access port to generate a beam along a path. A fiber-optic bundle in the path focuses the beam at a focal point inside the combustor.
The present invention may also include a method for igniting a combustor. The method includes generating a beam along a path, focusing the beam to a focal point inside the combustor, and moving a shutter from a first position in the path to a second position outside of the path.
Those of ordinary skill in the art will better appreciate the features and aspects of such embodiments, and others, upon review of the specification.
A full and enabling disclosure of the present invention, including the best mode thereof to one skilled in the art, is set forth more particularly in the remainder of the specification, including reference to the accompanying figures, in which:
Reference will now be made in detail to present embodiments of the invention, one or more examples of which are illustrated in the accompanying drawings. The detailed description uses numerical and letter designations to refer to features in the drawings. Like or similar designations in the drawings and description have been used to refer to like or similar parts of the invention.
Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that modifications and variations can be made in the present invention without departing from the scope or spirit thereof. For instance, features illustrated or described as part of one embodiment may be used on another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents.
Embodiments within the scope of the present invention provide a system and method for igniting a combustor using a laser as the ignition source. The system and method include multiple features that enhance the ability of the laser to effectively and reliably provide an ignition source to the combustor. The system and method may be used with any combustor, including combustors incorporated into gas turbines, aircraft engines, and reciprocating engines.
The system 10 generally includes an access port 24 and a laser 26. The laser is located outside of the combustor 12 and aligned with the access port 24 to generate a beam 28 along a path. The beam 28 has a focal point 30 inside the combustor 12 that is generally coincident with the spray of fuel 18 from the nozzles 16. The access port 24 may comprise any suitable opening that allows the passage of light through a wall 32 of the combustor 12. For example, as shown in
The laser 26 may comprise any suitable laser known in the art for generating a high intensity and focused beam of energy capable of igniting the fuel 18 in the combustor 12. The laser 26 generally comprises a power supply 34, an optical tube 36, a lens 38, and a shutter 40. One or more of these components may be protected by or enclosed within a container 42 proximate to the access port 24. The shutter 40 may be configured to isolate the container 42 from the combustor 12 so the container 42 does not have to withstand the anticipated temperatures and pressures inside the combustion chamber 14. Alternately, the shutter 40 may be movable, and the container 42 may be configured to continuously or intermittently withstand the anticipated temperatures and pressures inside the combustion chamber 14.
The power supply 34 provides sufficient energy for the laser 26 to generate the beam 28. For example, the power supply 34 may provide sufficient power to allow the laser 26 to generate a focused beam 28 on the order of approximately 1 GW/cm2, although the size and capacity of the power supply 34 is not a limitation of the present invention unless specifically recited in the claims. The optical tube 36 connects the laser 26 to the access port 24 and provides an optical path for the beam 28 outside of the combustor 12. As a result, the laser 28 and/or the power supply 34 may be located proximate to or remote from the combustor 12, for example, to facilitate maintenance and replacement of the laser 28 and power supply 34.
The shutter 40 protects the lens 38 and/or other components inside the container 42 from contaminants inside the combustion chamber 14. To protect the lens 38 and/or other components inside the container 42, the shutter 40 may be generally located anywhere between the lens 38 and the focal point 30, such as in, along, or adjacent to the path of the beam 28 and/or proximate to or inside the access port 24, although the specific location of the shutter 40 is not a limitation of the present invention unless specifically recited in the claims. If located proximate to or inside the access port 24, a seal 46, wiper 48, gasket, or similar insulating material may be connected to or in contact with the shutter 40 to provide a temperature and/or pressure barrier between the combustion chamber 14 and the inside of the container 42.
In various embodiments, the shutter 40 may be substantially transparent to or substantially opaque to the beam 28 and may include coatings on one or both sides of the shutter 40 to reduce or prevent contaminants from the combustion chamber 14 from adhering to the shutter 40. As used herein, “substantially transparent to the beam 28” means that at least a portion of the beam 28 passes through the shutter 40 without significant refraction and/or blockage. A substantially transparent shutter 40 may comprise, for example, quartz, sapphire, transparent glass, tempered glass, acrylics, and other suitable transparent materials known to one of ordinary skill in the art. If substantially transparent to the beam 28, the shutter 40 may remain in the path of the beam 28 during operation of the laser 26, allowing at least a portion of the beam 28 to pass substantially unchanged through the shutter 40. It is believed that the beam 28 may be sufficiently focused as it passes through the shutter 40 to oblate small amount of contaminants that adhere to the shutter 40. It is further anticipated that larger amounts of contaminants that adhere to the shutter 40 will absorb sufficient energy from the beam 28 to melt a hole through the shutter 40, thus allowing the laser 26 to continue to operate until the shutter 40 may be repaired or replaced. As used herein, “substantially opaque to the beam 28” means that the barrier 40 blocks or refracts substantially all of the beam 28, preventing at least a majority of the beam 28 from passing through the shutter 40. A substantially opaque shutter 40 may comprise, for example, opaque glass, opaque tempered glass, opaque acrylics, magnesium oxide pressed powder, or other suitable opaque materials known to one of ordinary skill in the art.
Regardless of whether the shutter 40 is substantially transparent to or substantially opaque to the laser beam 28, the shutter 40 may have a first or closed position in the path of the beam 28 and a second or open position out of the path of the beam 28. In the first position, the shutter 40 is generally between the combustion chamber 14 and the lens 38 to enhance protection to the lens 38 and/or other components inside the container 42, as shown in
As shown in
As further shown in
As shown in
The systems 10 described and illustrated in the figures may further provide a method for igniting the combustor 12 that includes generating the beam 28 along a path and focusing the beam 28 to the focal point 30 inside the combustor 12. The method may further include moving the shutter 40 from the first position in the path to the second position outside of the path. In particular embodiments, the method may further include focusing the beam 28 within the fiber-optic bundle 44, moving the shutter 40 from the second position to the first position, and/or sensing the condition of the shutter 40.
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other and examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.
