Patent Application
20160290651
1. Field
The present disclosure relates to air shrouds for nozzles, more specifically to air shrouds for fuel nozzles such as in gas turbine engine fuel injectors.
2. Description of Related Art
Fuel nozzles allow for mixing of fuel and air for injection into a combustor. Due to the turbulent nature of the flow-field, some of the liquid fuel spray from the fuel nozzle will wet the metal surfaces of the fuel nozzle which are exposed to the hot combustion gases. If the fuel temperature on the surface of the metal is in the proper range (about 200° C. to about 400° C. for jet fuel), then fuel will chemically break down to form carbon deposits on the metal surfaces. This can occur on the exposed surfaces of fuel pre-filmers and/or air-caps (also called air-shrouds). Carbon-formation on these metal surfaces is undesirable because this can adversely affect spray and combustion performance. Also, this carbon can sometimes break free from the metal surface and flow downstream where it can come into contact with the turbine and cause turbine erosion, which shortens the life of the turbine. In other cases, the exposed metal surfaces of the fuel nozzle (most commonly the air-shrouds) are subject to excessive heating from the combustion gases, which can result in thermal erosion or cracking of the metal.
A common method to alleviate either the problem of carbon-formation or thermal-erosion is to add an additional (smaller) air-shroud outboard of the existing air-shroud. This smaller air-shroud is commonly called an air-wipe and serves the function of directing compressor-discharge air downward over the face of the first (larger) air-shroud to either preferentially prevent carbon-formation or alleviate thermal-erosion. In some cases, these air-wipes also experience thermal-erosion and require some method to manage the thermal load. Typically, a series of small holes through the air-wipe are added to provide additional cooler compressor-discharge air in order to reduce the thermal load. Often this will alleviate the problem, but not always. In some cases, it is difficult to get a sufficient amount of additional compressor-discharge air in the vicinity of the air-wipe. In other cases, the thermal loading results in differential thermal expansion of the air-wipe which can result in cracking and reduced life of the fuel nozzle, or possible wear on the turbine due to the air-wipe liberating from the fuel nozzle and traveling downstream through the turbine. Therefore, there is still a need in the art for improved systems to wipe the downstream surface of an air shroud and/or nozzle. The present disclosure provides a solution for this need.
An air shroud for a nozzle includes an air shroud body defining an inlet and an outlet in fluid communication with one another to allow an outer airflow to issue therefrom, the air shroud body defining a downstream surface. A plurality of air wipe channels are defined within the air shroud body, wherein each of the plurality of air wipe channels is in fluid communication with at least one of a plurality of air wipe outlets and air wipe inlets. Each air wipe outlet is defined in the downstream surface of the air shroud body such that air can flow through each air wipe outlet and wipe the downstream surface of the air shroud body.
At least one of the air wipe channels can be straight between the air wipe inlet and the air wipe outlet. In certain embodiments, at least one of the air wipe channels can be defined non-linearly (e.g., such that the flow can deviate from a straight path) between the air wipe inlet and the air wipe outlet. For example, at least one of the air wipe channels can be spiraled around a central axis of the air shroud body.
The air wipe outlets can open in a direction to direct air normally toward a central axis of the air shroud body. In certain embodiments, the air wipe outlets can open in a direction to direct air tangentially relative to a central axis of the air shroud body to swirl airflow about a central axis of the air shroud body.
The air wipe inlets can be defined on an inner surface of the air shroud body. In certain embodiments, the air wipe inlets can be defined on an upstream surface of the air shroud body such that the air wipe channel is defined along the entire length of the air shroud body.
The downstream surface of the air shroud body can be axially angled. For example, the downstream surface of the air shroud body can be conical.
A fuel nozzle includes a nozzle body defining a fuel circuit connecting a fuel inlet to a fuel outlet and including a prefilmer disposed in fluid communication with the fuel outlet, and an air shroud as described above disposed outboard of the prefilmer to direct air toward fuel issued from the nozzle body.
These and other features of the systems and methods of the subject disclosure will become more readily apparent to those skilled in the art from the following detailed description taken in conjunction with the drawings.
So that those skilled in the art to which the subject disclosure appertains will readily understand how to make and use the devices and methods of the subject disclosure without undue experimentation, embodiments thereof will be described in detail herein below with reference to certain figures, wherein:
Reference will now be made to the drawings wherein like reference numerals identify similar structural features or aspects of the subject disclosure. For purposes of explanation and illustration, and not limitation, an illustrative view of an embodiment of an air shroud in accordance with the disclosure is shown in
Referring to
The downstream surface 105 of the air shroud body 101 can be axially angled in the downstream direction. For example, the downstream surface 105 of the air shroud body 101 can be conical (e.g., a chamfered truncated cone shape). This is also contemplated that the downstream surface 105 can have any other suitable profile.
Referring to
The air wipe outlets 109 can be defined and/or open in a direction to direct air normally toward a central axis of the air shroud body 101. In certain embodiments, as shown in
As shown in
Referring to
Referring to
It is contemplated that air shrouds 100, 200 can be manufactured using suitable additive manufacturing techniques or any other suitable manufacturing technique (e.g., casting). Additive manufacturing can allow for complex shaped passages that cannot be formed using traditional manufacturing techniques (e.g., such that the channels can catch airflow from any suitable portion upstream and direct it in any suitable direction downstream).
Referring to
Referring to
As described above, the air wipe 107 provides a wiping airflow that, under some conditions, helps remove fuel off of the downstream surface 105 of the air shroud body 101. Under other conditions (e.g., excessive heat load), the airflow also prevents further thermal erosion of the downstream surface 105. Finally, the web of material 109 between the air wipe passages/outlets 111 provide improved structural support to the air wipe 107. These features can increase the useable lifespan of the assembly and/or the time between required maintenance.
The methods and systems of the present disclosure, as described above and shown in the drawings, provide for air shrouds with superior properties including enhanced wiping for reducing carbon buildup and/or improved thermal management. While the apparatus and methods of the subject disclosure have been shown and described with reference to embodiments, those skilled in the art will readily appreciate that changes and/or modifications may be made thereto without departing from the spirit and scope of the subject disclosure.
