Combustors with impingement cooled igniters and igniter tubes for improved cooling of igniters

A combustor for a gas turbine engine is provided, and includes an inner liner; an outer liner circumscribing the inner liner and forming a combustion chamber with the inner liner; a fuel igniter comprising a tip portion configured to ignite an air and fuel mixture in the combustion chamber; and an igniter tube positioning the fuel igniter relative to the combustion chamber, the igniter tube having a plurality of channels configured to direct cooling air toward the tip portion of the fuel igniter.

FIELD OF THE INVENTION

The present invention generally relates to combustors for gas turbine engines, and more particularly relates to combustors with impingement cooled igniters and igniter tubes for improved cooling of igniters.

BACKGROUND OF THE INVENTION

Combustors are used to ignite and burn fuel and air mixtures in gas turbine engines. Known combustors include inner and outer liners that define an annular combustion chamber in which the fuel and air mixtures are combusted. The inner and outer liners are spaced radially inwardly from a combustor casing such that inner and outer passageways are defined between the respective inner and outer liners and the combustor casing. Fuel igniters extend through the combustor casing and the outer passageway, and are coupled to the outer liner by igniter tubes attached to the combustor liner. More specifically, the fuel igniter tubes secure and maintain the igniters in alignment relative to the combustion chamber as well as provide a sealing interface for the igniter between the outer passageway and the combustion chamber.

During operation, high pressure airflow is discharged from a compressor into the combustor. A portion of the airflow enters the combustion chamber, where it is mixed with fuel and ignited by the igniters. Another portion of the airflow entering the combustor is channeled through the combustor outer passageway for attempting to cool the outer liner, the igniters, and diluting a main combustion zone within the combustion chamber. However, over time, continued operation may induce potentially damaging thermal stresses into the combustor that exceed an ultimate strength of materials used in fabricating the components of the combustor. For example, thermally induced transient and steady state stresses may cause low cycle fatigue (LCF) failure of the igniter.

Cooling the igniter, particularly the tip portion of the igniter closest to the combustion process, presents challenges. Some conventional igniters include a plurality of longitudinal slots extending down the length of the igniter to channel cooling air to the vicinity of the tip portion of the igniter. However, this arrangement is not very efficient because it requires a relatively large amount of cooling air to sufficiently cool the tip portion of the igniter. The large amount of air required to effectively cool the tip portion of the igniter in this manner may adversely impact the combustion conditions within the combustion chamber. Particularly, a large amount of cooling air may have a perturbative effect on the ignition process, gaseous emissions, and the temperature distribution of hot gases entering the turbine. In some arrangements, the quantity and manner in which cooling air is admitted into the combustor may result in a barrier formed around the igniter that prevents fuel from reaching the tip portion of the igniter. This can additionally reduce the effectiveness of the igniter for igniting the fuel and air mixture. Moreover, excess cooling air can disrupt the liner cooling film and result in local hot spots immediately downstream of the igniter in the combustor liner.

Accordingly, it is desirable to provide combustors with igniters that are efficiently cooled without adversely interfering with the combustion of the air and fuel mixtures in the combustion chamber. In addition, it is desirable to provide igniter tubes for improved cooling of igniters in combustors. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.

BRIEF SUMMARY OF THE INVENTION

A combustor for a gas turbine engine is provided in accordance with an exemplary embodiment of the present invention. The combustor includes an inner liner; an outer liner circumscribing the inner liner and forming a combustion chamber with the inner liner; a fuel igniter comprising a tip portion configured to ignite an air and fuel mixture in the combustion chamber; and an igniter tube coupling the fuel igniter to the outer liner, the igniter tube having a plurality of channels configured to direct cooling air toward the tip portion of the fuel igniter.

An igniter tube for positioning a fuel igniter with respect to an outer liner of a combustor is provided in accordance with an exemplary embodiment of the present invention. The igniter tube includes an igniter boss having a first end portion for receiving the fuel igniter; a second end portion for coupling the igniter tube to the outer liner; a plurality of channels arranged between the first end portion and the second end portion for directing air toward a tip portion of the fuel igniter.

An igniter tube is provided in accordance with an exemplary embodiment of the present invention for mounting a fuel igniter to an outer liner of a combustor. The igniter tube includes an igniter boss defining a first plurality of holes and configured to be mounted on the annular outer liner; a supporting ring coupled to the igniter boss and defining a second plurality of holes in fluid communication with the first plurality of holes to form a plurality of channels. The plurality of channels is configured to direct cooling air onto an igniter tip of the fuel igniter. The igniter tube further includes a grommet supported by the supporting ring and configured to receive the fuel igniter.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1is a cross-sectional view of a combustor14for a gas turbine engine in accordance with an exemplary embodiment of the present invention. Although the depicted combustor14is an annular combustor, any other type of combustor, such as a can combustor, can be provided. In an exemplary embodiment, the combustor14can form part of, for example, an auxiliary power unit for an aircraft or a propulsion system for an aircraft. The combustor14comprises an inner case18that extends annularly about a central axis17of the combustor14and an outer case20concentrically arranged with respect to the inner case18. The inner and outer cases18and20define an annular pressure vessel24. The combustor14further includes an inner liner30and an outer liner28circumscribing the inner liner30within the annular pressure vessel24. The outer liner28and the inner liner30define an annular combustion chamber32. The outer and inner liners28and30cooperate with outer and inner cases18and20to define respective outer and inner air passageways34and36.

The combustor14includes a front-end assembly38comprising an annularly extending shroud40, at least one fuel injector44, and at least one fuel injector guide46. One fuel injector44and one fuel injector guide46are shown in the partial cross-sectional view ofFIG. 1, although it is appreciated that more fuel injectors and fuel injector guides may be disposed about central axis17in within the combustor14. The fuel injector44may also be coupled with a secondary air swirler (not shown) as is typical practice in gas turbine combustors. The shroud40extends between and is secured to the forwardmost ends of the outer and inner liners28and30. The shroud40includes at least one shroud port48that accommodates the fuel injector44and introduces air into the forward end of the combustion chamber32. The fuel injector44is secured to the outer case20and projects through the shroud port48. The fuel injector44introduces a swirling, intimately blended fuel-air mixture that supports combustion in the combustion chamber32.

A fuel igniter62extends through the outer case20and the outer passageway34, and is coupled to the outer liner28. It will be appreciated that more than one fuel igniter62can be provided in the combustor14, although only one is illustrated inFIG. 1. The fuel igniter62is arranged downstream from the fuel injector44and is positioned to ignite a fuel and air mixture within the combustion chamber32.

The fuel injector62is coupled to outer liner28by an igniter tube64. More specifically, the igniter tube64is coupled within an opening66extending through outer liner28, such that the igniter tube64is concentrically aligned with respect to the opening66of the outer liner28. The igniter tube64maintains the alignment of the fuel igniter62relative to the combustor14and provides for a sealing interface between the igniter62and igniter tube64of the air in the outer passageway34and the combustion chamber32. In one embodiment, the opening66of the outer liner28and the igniter tube64have substantially circular cross-sectional profiles. The igniter tube64is discussed in greater detail below.

During engine operation, airflow exits a high pressure diffuser and deswirl12(partially shown) at a relatively high velocity and is directed into the annular pressure vessel24of the combustor14. The airflow enters the combustion chamber32through openings in the liners28and30, where it is mixed with fuel from the fuel injector44, and the airflow is combusted after being ignited by the fuel igniter62. The combusted air exits the combustion chamber32and is delivered to a turbine (not shown).

FIG. 2is an enlarged isometric cross-sectional view, represented by the dashed box60ofFIG. 1, of the igniter tube64coupled to the outer liner28. As noted above, the igniter tube64mounts the igniter62in the combustor14, and particularly mounts the igniter62such that a tip portion118of the igniter62is exposed to the fuel and air mixture in the combustion chamber32. The tip portion118may be slightly recessed, slightly protuding, or nominally flush with the inner surface of the outer liner28. The igniter tube64includes an igniter boss74, a grommet76, and a supporting ring78extending therebetween. The igniter tube64will be typically manufactured from materials that are similar to those of the inner and outer liners28and30, which are capable of withstanding the temperatures within the combustion chamber32.

The igniter boss74mounts the igniter tube64to the outer liner28. Particularly, an outer diameter82of the igniter boss74is approximately equal to a diameter of the opening66of the outer liner28, and accordingly, the igniter boss74is received in close tolerance within opening66of the outer liner28. In the exemplary embodiment, the igniter boss74has a substantially circular outer diameter corresponding to a diameter of the opening66of the outer liner28. In an alternate embodiment, the igniter boss74is mounted onto a surface of the outer liner28. For example, the igniter boss74may be mounted to an outside surface29or an inside surface27and may be mounted using adhesive, welding, screws, or any other suitable means for affixing the igniter boss74to the outer liner28and providing an adequate sealing interface. The igniter boss74includes a projection80that extends outwardly from the combustion chamber32. The igniter boss74also includes an opening84extending therethrough. In one embodiment, the opening84is substantially circular. The opening84of the igniter boss74is sized to receive the supporting ring78, and the projection80supports the supporting ring78.

The supporting ring78of the igniter tube64includes a first portion79, a second portion81, a third portion83, and a fourth portion85. The first portion79of the supporting ring78is received by and is coupled to the igniter boss74. The second portion81extends generally perpendicularly and radially outwardly from the first portion79. The projection80of the igniter boss74supports the second portion81of the supporting ring78. In an alternate embodiment, the projection of the igniter boss74is directly coupled to the second portion81of the supporting ring78, and thus, the supporting ring78may not include a first portion79. In a further alternate embodiment, the first portion79of the supporting ring78is mounted to or otherwise coupled directly to the outer liner28such that the igniter boss74is omitted. The third portion83of the supporting ring78extends generally perpendicularly from the second portion81. The fourth portion85extends radially inward from the third portion83and is generally parallel to the second portion81.

The grommet76of the igniter tube64includes a receiving ring100coupled to an attaching ring102, which extends radially substantially perpendicular from the receiving ring100. The attaching ring102of the grommet76extends radially between the second portion81and the fourth portion85of the supporting ring100and is substantially retained therebetween. An outside diameter of the receiving ring100is less than an inside diameter of the fourth portion85of the supporting ring78. As a result of this arrangement, the grommet76may be able to move laterally with respect to the supporting ring78to accommodate manufacturing tolerances and movements during operation. In an alternate embodiment, the grommet76is fixed to the supporting ring78not movable laterally relative to the supporting ring78, or in a further alternate embodiment, the grommet76is directly coupled to the igniter boss74and the supporting ring78is omitted. The receiving ring100includes a radially divergent portion that defines an opening106. The opening106has a diameter110at a first end112of the receiving ring100that is larger than an inside diameter114at a second end116. Accordingly, the attaching ring102of the grommet76can guide the fuel igniter62into the igniter tube64such that the tip portion118of the igniter tube64extends into the combustion chamber32. The igniter tube64secures the fuel igniter62and maintains the fuel igniter62in alignment relative to the combustor14(FIG. 1). As noted above, although the illustrated embodiment illustrates the supporting ring78, the grommet76, and the igniter boss78as separate pieces, in an alternate embodiment, one or more of the supporting ring78, the grommet76, and the igniter boss78can be integral with one another.

The igniter tube64includes a plurality of channels76for directing air to the fuel igniter62. In the illustrated embodiment, the channels76are defined by a first plurality of holes77and a second plurality of holes75. The projection80of the igniter boss74includes the first plurality of holes77that extend generally perpendicularly through the projection80. The first portion79of the supporting ring78includes the second plurality of holes75that are generally coaxially aligned in fluid communication with the first plurality of holes77in the igniter boss74. During engine operation, as the airflow enters the combustor14, a portion of the airflow is channeled through the outer passageway34of the combustor14(FIG. 1). As shown inFIG. 2, a portion103of the airflow from the combustor14flows through the first plurality of holes77in the igniter boss74and continues through the second plurality of holes75in the supporting ring78. Subsequently, the portion103of airflow directly impinges the fuel igniter62mounted by the igniter tube64and cools the fuel igniter62. The portion103of airflow can particularly be directed to, and cool, the tip portion118of the fuel igniter62. In the illustrated embodiment, the channels76direct the airflow103essentially perpendicularly to the longitudinal axis104of the fuel igniter62, although it can be appreciated that other angles can be provided to cool the igniter tip118of the fuel igniter62.

Some fuel igniters62may have jackets (not shown) completely or partially covering the tip portion118of the fuel igniter62. In these arrangements, the jacket can be at least partially removed to allow access of the cooling air to the tip portion118of the fuel igniter62.

The holes75and77that form the channels76in the igniter tube64can be circular in diameter and circumferentially aligned about the fuel igniter62. The holes75in the first portion79of the supporting ring78and the holes77in the igniter boss74do not have to be the same size and/or shape. For example, one set of holes75or77can be larger than the other set of holes77or75to facilitate alignment. In alternate embodiments, one of the sets of holes75or77can be omitted. For example, the igniter boss74can omit all or portions of the projection80, and the holes77of the supporting ring78can form the channels76. Alternatively, the supporting ring78can omit all or portions of the first portion79, and the holes75of the igniter boss74can form the channels76. Although the illustrated embodiment of the igniter tube64is depicted with three pieces (i.e., the igniter boss74, the supporting ring78, and the grommet76) and two sets of holes75and77, the igniter tube64can have any structural arrangement and combination of holes75and77that enable a portion103of airflow to impinge on the tip portion118of the fuel igniter62.

In an exemplary embodiment, the channels76of the igniter tube64can cool the tip portion118of the fuel igniter62to temperatures less than, for example, 1500° F. In another exemplary embodiment, the channels76of the igniter tube64can cool the tip portion118of the fuel igniter62to temperatures such as, for example, 1200° F. Impingement cooling is more effective than conventional mechanisms, such as slot cooling, for cooling the igniter, and therefore, a reduced amount of air can be used to effectively cool the fuel igniter62. In one exemplary embodiment, the amount of air necessary to cool the fuel igniter62in the combustor14is one third or one fourth of the amount of air necessary to cool igniters in conventional combustors. By reducing the amount of necessary cooling air103through the holes75and77, the function of the igniter62and/or the combustion conditions in the combustion chamber32are not adversely affected. In one exemplary embodiment, ten holes75are provided in the inner portion of the supporting ring78and ten holes77are provided in the igniter boss74. The size of the holes75and77can be, for example, about 0.04 inches (1 millimeter). A greater or fewer number of holes75and77can be provided, as well as different sizes. Different configurations and arrangements of the igniter tube64can be provided as necessary in dependence on the desired temperature of the fuel igniter62and the sensitivity of the combustor14to additional cooling air. Reduced temperatures in the fuel igniter62results in lower thermal stresses and improved life in a cost-effective and reliable manner.