Patent Description:
Gas turbine engines have been employed in a variety of applications, including aircraft, marine and industrial applications such as in the oil and gas industry. Various emissions standards have been set by government agencies and gas turbine engine vendors have strived to improve the emissions of their products to meet the standards. One technology employed in gas turbine engines has been known as Dry Low Emissions (DLE) combustors. DLE combustors generally utilize a pre-mixer assembly to pre-mix fuel and air prior to the fuel-air mixture being ejected into a combustion section for ignition. Conventional, pre-mixer assemblies have been known to include both pilot pre-mixers and main pre-mixers. Pilot pre-mixers generally mix fuel and air to a desired ratio that is ejected into the combustion chamber for use during engine start-up, and lower power operations, but is also continuously ejected during all operation modes. Main pre-mixers, on the other hand, generally mix fuel and air to produce a lean fuel-air mixture that is ejected into the combustion chamber across power operations. Generally, only some of the main pre-mixers are fueled at lower power conditions, while all of the main pre-mixers are fueled at higher power conditions. When a flame is ignited for the pilot mixture, combustion products from the pilot provide an ignition source to the main pre-mixer flames to achieve combustion within the system. <CIT> discloses a premixing fuel nozzle assembly for gas turbine engine combustors.

To address problems in the conventional art, the present inventors have devised techniques for providing a furcating pilot flame into the combustor so as to provide better spread of the pilot fuel-air mixture to the main pre-mixers. According to one aspect, the present disclosure is directed to a pre-mixer assembly for a gas turbine engine. The pre-mixer assembly includes a housing having a combustion chamber side and a pre-mixer side, a plurality of main pre-mixers connected to the housing, each main pre-mixer having an outlet on the combustion chamber side of the housing for dispensing a main pre-mixer fluid mixture to a combustion chamber of a combustor, and at least one pilot pre-mixer connected to the housing. In addition, each pilot pre-mixer includes a pilot body, including: an internal mixing chamber; a first end on an upstream side of the internal mixing chamber; a second end on a downstream side of the internal mixing chamber; a fuel injector at the first end and communicable with the internal mixing chamber; a plurality of first oxidizer inlet ports arranged to provide an oxidizer agent from outside of the pilot body to the internal mixing chamber; and a plurality of pilot outlet ports at the second end and communicable with the internal mixing chamber, each of the plurality of pilot outlet ports having an outlet on the second end for dispensing a pilot fluid mixture into the combustion zone of the combustor.

According to another aspect, the present disclosure is directed to a pilot pre-mixer for a gas turbine engine, comprising: a pilot body, including: an internal mixing chamber; a first end on an upstream side of the internal mixing chamber; a second end on a downstream side of the internal mixing chamber; a fuel injector at the first end and communicable with the internal mixing chamber; a plurality of first oxidizer inlet ports arranged to provide an oxidizer agent from outside of the pilot body to the internal mixing chamber; and a plurality of pilot outlet ports at the second end and communicable with the internal mixing chamber, each of the plurality of pilot outlet ports having an outlet on the second end for dispensing a pilot fluid mixture into a combustion zone of a combustor.

Additional features, advantages, and embodiments of the present disclosure are set forth or apparent from consideration of the following detailed description, drawings and claims. Moreover, it is to be understood that both the foregoing summary and the following detailed description are exemplary and intended to provide further explanation without limiting the scope of the disclosure as claimed. The invention as such is defined in the appended claims.

The foregoing and other features and advantages will be apparent from the following, more particular, description of various exemplary embodiments, as illustrated in the accompanying drawings, wherein like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements.

Various embodiments are discussed in detail below. While specific embodiments are discussed, this is done for illustration purposes only. A person skilled in the relevant art will recognize that other components and configurations may be used without departing from the spirit and scope of the present disclosure.

Generally, conventional pilot pre-mixers include a single outlet port that produces a centralized flame directed straight from the pre-mixer outlet. With this arrangement, combustion products from the pilot are not efficiently mixed with the main pre-mixer mixture and the centralized pilot flame does not provide sufficient stability of the main pre-mixer flame. Additionally, a rich fuel-air mixture from the pilot remains in the centerline of the pilot and does not efficiently mix with the main pre-mixer fuel-air mixture. This results in higher NOx (Nitrogen Oxides) emissions. Thus, there exists a need to provide better stability to the main pre-mixer flame to ensure lower NOx emissions. The present disclosure addresses these problems by providing techniques for a better spread of the pilot fuel-air mixture towards the main pre-mixers inside the combustion chamber for more efficient burning.

The present disclosure generally relates to a pre-mixer assembly for use in, for example, a Dry Low Emissions (DLE) type combustor of a gas turbine engine. More particular, the disclosure generally relates to a pilot pre-mixer that provides a pre-mixed fuel-air mixture to a combustion chamber in a manner that directs the flow of the fuel-air mixture closer to main pre-mixers than with the conventional pilot pre-mixer. In the present disclosure, a pilot pre-mixer has a fuel injector to which a fuel input thereto is injected into a mixing chamber of the pilot pre-mixer, and also has air inlet ports that provide air from outside of the pilot pre-mixer into the mixing chamber to mix with the fuel. The fuel injector is generally conical shaped and ejects the fuel from a tip thereof. The air inlet ports are arranged such that some of them are located upstream of the fuel injector tip. Others of the air inlet ports are arranged with their center aligned with the tip of the fuel injector. With this arrangement, the air from the air inlet ports impinge on the fuel being ejected from the tip to prevent a low velocity at the tip, and also provide an outward flow of the fuel-air mixture at the tip toward an outer wall of the mixing chamber. Thus, a more efficient mixing of the fuel and air can be obtained without the need for internal swirlers in the mixing chamber.

The fuel and air mixture continues to be further mixed in the mixing chamber as it travels downstream, possibly with additional air from additional air inlet ports, until it reaches a plurality of outlet ports formed at a downstream end of the pilot pre-mixer. The plurality of outlet ports divide the fuel-air mixture into branches where it continues to be mixed within a channel of the outlet ports. The outlet ports are arranged at a radially outward angle so as to provide the fuel-air mixture away from a center of the pilot pre-mixer. The pilot fuel-air mixture is then ejected from the outlet ports into the combustion chamber for ignition.

In operation, at start-up and low power operations, the fuel-air mixture from the pilot only may be ignited, whereas at other operating conditions, a fuel-air mixture may also be ejected from main pre-mixers that are also part of the pre-mixer assembly. The fuel-air mixture from the main pre-mixers is generally ignited by a flame from the already burning pilot pre-mixer fuel-air mixture. To obtain a more stable flame for the main pre-mixers, the outlets of the pilot pre-mixer are arranged at the radial angle so as to disperse the pilot fuel-air mixture in close proximity to one or more of the main pre-mixers. This is in contrast to prior art systems in which the pilot fuel-air mixture is not directed towards the main pre-mixers, but is generally directed straight into the combustion chamber.

Referring now to the drawings, <FIG> is a schematic partially cross-sectioned side view of an exemplary high by-pass turbofan jet engine <NUM>, herein referred to as "engine <NUM>," as may incorporate various embodiments of the present disclosure. Although further described below with reference to a turbofan engine, the present disclosure is also applicable to turbomachinery in general, including turbojet, turboprop, and turboshaft gas turbine engines, including marine and industrial turbine engines and auxiliary power units. As shown in <FIG>, engine <NUM> has a longitudinal or axial centerline axis <NUM> that extends there through for reference purposes. In general, engine <NUM> may include a fan assembly <NUM> and a core engine <NUM> disposed downstream from the fan assembly <NUM>.

The core engine <NUM> may generally include a substantially tubular outer casing <NUM> that defines an annular inlet <NUM>. The outer casing <NUM> encases or at least partially forms, in serial flow relationship, a compressor section having a booster or low pressure (LP) compressor <NUM>, a high pressure (HP) compressor <NUM>, a combustion section <NUM>, a turbine section including a high pressure (HP) turbine <NUM>, a low pressure (LP) turbine <NUM> and a jet exhaust nozzle section <NUM>. A high pressure (HP) rotor shaft <NUM> drivingly connects the HP turbine <NUM> to the HP compressor <NUM>. A low pressure (LP) rotor shaft <NUM> drivingly connects the LP turbine <NUM> to the LP compressor <NUM>. The LP rotor shaft <NUM> may also be connected to a fan shaft <NUM> of the fan assembly <NUM>. In particular embodiments, as shown in <FIG>, the LP rotor shaft <NUM> may be connected to the fan shaft <NUM> by way of a reduction gear <NUM> such as in an indirect-drive or geared-drive configuration. In other embodiments, although not illustrated, the engine <NUM> may further include an intermediate pressure (IP) compressor and turbine rotatable with an intermediate pressure shaft.

As shown in <FIG>, the fan assembly <NUM> includes a plurality of fan blades <NUM> that are coupled to and that extend radially outwardly from the fan shaft <NUM>. An annular fan casing or nacelle <NUM> circumferentially surrounds the fan assembly <NUM> and/or at least a portion of the core engine <NUM>. In one embodiment, the nacelle <NUM> may be supported relative to the core engine <NUM> by a plurality of circumferentially-spaced outlet guide vanes or struts <NUM>. Moreover, at least a portion of the nacelle <NUM> may extend over an outer portion of the core engine <NUM> so as to define a bypass airflow passage <NUM> therebetween.

<FIG> is a cross sectional side view of an exemplary combustion section <NUM> of the core engine <NUM> as shown in <FIG>. As shown in <FIG>, the combustion section <NUM> may generally include an annular type combustor assembly <NUM> having an annular inner liner <NUM>, an annular outer liner <NUM> and a bulkhead <NUM> that extends radially between upstream ends <NUM>, <NUM> of the inner liner <NUM> and the outer liner <NUM> respectfully. As shown in <FIG>, the inner liner <NUM> is radially spaced from the outer liner <NUM> with respect to engine centerline axis <NUM> (<FIG>) and defines a generally annular combustion chamber <NUM> therebetween. In particular embodiments, the inner liner <NUM> and/or the outer liner <NUM> may be at least partially or entirely formed from metal alloys or ceramic matrix composite (CMC) materials.

As shown in <FIG>, the inner liner <NUM> and the outer liner <NUM> may be encased within an outer casing <NUM>. An outer flow passage <NUM> may be defined around the inner liner <NUM> and/or the outer liner <NUM>. The inner liner <NUM> and the outer liner <NUM> may extend from the bulkhead <NUM> towards a turbine nozzle or inlet <NUM> to the HP turbine <NUM> (<FIG>), thus at least partially defining a hot gas path between the combustor assembly <NUM> and the HP turbine <NUM>. A pre-mixer assembly <NUM> may extend at least partially through the bulkhead <NUM> and provide a main mixer fuel-air mixture <NUM> to the combustion chamber <NUM>, as well as a pilot pre-mixer fuel-air mixture <NUM> to the combustion chamber <NUM>.

During operation of the engine <NUM>, as shown in <FIG> and <FIG> collectively, a volume of air as indicated schematically by arrows <NUM> enters the engine <NUM> through an associated inlet <NUM> of the nacelle <NUM> and/or fan assembly <NUM>. As the air <NUM> passes across the fan blades <NUM>, a portion of the air as indicated schematically by arrows <NUM> is directed or routed into the bypass airflow passage <NUM>, while another portion of the air as indicated schematically by arrow <NUM> is directed or routed into the LP compressor <NUM>. Air <NUM> is progressively compressed as it flows through the LP and HP compressors <NUM>, <NUM> towards the combustion section <NUM>. As shown in <FIG>, the now compressed air as indicated schematically by arrows <NUM> flows across a compressor exit guide vane (CEGV) <NUM> and through a pre-diffuser <NUM> into a diffuser cavity <NUM> of the combustion section <NUM>.

The pre-diffuser <NUM> and CEGV <NUM> condition the flow of compressed air <NUM> to the pre-mixer assembly <NUM>. The compressed air <NUM> pressurizes the diffuser cavity <NUM>. The compressed air <NUM> enters the pre-mixer assembly <NUM> and, as will be discussed below, into a plurality of main pre-mixers <NUM> and a plurality of pilot pre-mixers <NUM> within the pre-mixer assembly <NUM> to mix with a fuel <NUM>. As will be described in more detail below, the main pre-mixers <NUM> and the pilot pre-mixers <NUM> are retained by a housing <NUM> and pre-mix fuel <NUM> and compressed air <NUM> within an array of main pre-mixers <NUM> and pilot pre-mixers <NUM> to provide a resulting main pre-mixer fluid (fuel/air) mixture <NUM> and a pilot pre-mixer fluid (fuel/air) mixture <NUM> respectively, exiting from the pre-mixer assembly <NUM> into combustion chamber <NUM>. The fuel-air mixtures <NUM>, <NUM> are then ignited and burned within the combustion chamber <NUM> and generate combustion gases <NUM>.

Typically, the LP and HP compressors <NUM>, <NUM> provide more compressed air to the diffuser cavity <NUM> than is needed for combustion. Therefore, a second portion of the compressed air <NUM> as indicated schematically by arrows <NUM>(a) may be used for various purposes other than combustion. For example, as shown in <FIG>, compressed air <NUM>(a) may be routed into the outer flow passage <NUM> to provide cooling to the inner and outer liners <NUM>, <NUM>. In addition or in the alternative, at least a portion of compressed air <NUM>(a) may be routed out of the diffuser cavity <NUM>. For example, a portion of compressed air <NUM>(a) may be directed through various flow passages to provide cooling air to at least one of the HP turbine <NUM> or the LP turbine <NUM>.

Referring back to <FIG> and <FIG> collectively, the combustion gases <NUM> generated in the combustion chamber <NUM> flow from the combustor assembly <NUM> into the HP turbine <NUM> via inlet <NUM>, thus causing the HP rotor shaft <NUM> to rotate, thereby supporting operation of the HP compressor <NUM>. As shown in <FIG>, the combustion gases <NUM> are then routed through the LP turbine <NUM>, thus causing the LP rotor shaft <NUM> to rotate, thereby supporting operation of the LP compressor <NUM> and/or rotation of the fan shaft <NUM>. The combustion gases <NUM> are then exhausted through the jet exhaust nozzle section <NUM> of the core engine <NUM> to provide propulsive thrust.

Referring now to <FIG>, depicted therein are perspective views of an exemplary pre-mixer assembly <NUM> according to the present disclosure. In <FIG>, pre-mixer assembly <NUM> is seen to include a housing <NUM> that retains a plurality of main pre-mixers <NUM> and a plurality of pilot pre-mixers <NUM> (e.g., 104a, 104b, 104c). The pre-mixer assembly <NUM> includes a combustion chamber side <NUM> from which a fuel-air mixture is ejected from the pre-mixer assembly <NUM> and a pre-mixer side <NUM> in which fuel and air are introduced in the pre-mixer assembly <NUM>. As is commonly known in DLE combustors, the pilot pre-mixers provide a fuel-air mixture <NUM> to the combustion chamber for burning generally at start-up and low power operations, and the main pre-mixers provide a lean fuel-air mixture <NUM> to the combustion chamber for burning at higher power operations. The main pre-mixers <NUM> are generally ignited via a flame that is already burning the pilot pre-mixer fuel/air mixture. As will be discussed in more detail below, but as seen in <FIG>, a first array <NUM> of four main pre-mixers <NUM> may be included with a first pilot pre-mixer 104a centrally located within the first array <NUM>. Similarly, a second array <NUM> of four main-pre-mixers <NUM> may be included with a second pilot pre-mixer 104b centrally located within the second array <NUM>. Alternatively, as seen in <FIG>, a pilot pre-mixer 104c may be located between the first array <NUM> and the second array <NUM> of main pre-mixers <NUM>.

Referring to <FIG>, <FIG> is a perspective view of a pilot pre-mixer <NUM>, <FIG> is a perspective cross sectional view along plane <NUM>-<NUM> shown in <FIG>, and <FIG> is a plan cross sectional view along plane <NUM>-<NUM>. As seen in these figures, the pilot pre-mixer <NUM> includes a pilot body <NUM> that has formed therein an internal mixing chamber <NUM>. In operation, a flow of a fuel-air mixture within the pilot body is from left (upstream) to right (downstream) in <FIG>. Thus, the pilot body <NUM> includes a first end <NUM> on an upstream side of the internal mixing chamber <NUM>, and a second end <NUM> on a downstream side of the internal mixing chamber <NUM>. A fuel injector <NUM> is included at the first end <NUM> and is communicable with the internal mixing chamber <NUM> via a fuel outlet port <NUM> to provide fuel to the internal mixing chamber <NUM>.

The pilot body <NUM> further includes a plurality of first oxidizer inlet ports (air holes) <NUM> arranged to provide an oxidizer agent (e.g. air) from outside of the pilot body <NUM> to the internal mixing chamber <NUM>. As will be described in more detail below, pilot body <NUM> includes a plurality of second oxidizer inlet ports <NUM> located in the body upstream of the first oxidizer inlet ports <NUM>. In exemplary embodiments, the pilot body <NUM> may further include a plurality of third oxidizer inlet ports <NUM> downstream of the first oxidizer inlet ports <NUM>, and a plurality of fourth oxidizer inlet ports <NUM> downstream of the second oxidizer inlet ports <NUM>. As will be described in more detail below, these respective oxidizer inlet ports <NUM>, <NUM>, <NUM> and <NUM> provide for first, second, third and fourth stages of air flow into the pre-mixture. Of course, the number of stages and the number of oxidizer inlet port (air holes) is not limited to those shown in exemplary embodiments described herein, and the number of stages and/or oxidizer inlets per stage, if any, may vary depending on a desired fuel-air mixture to be obtained within the pilot pre-mixer <NUM>.

Referring again to <FIG>, pilot body <NUM> is seen to include a plurality of pilot outlet ports <NUM> at the second end <NUM>. The pilot outlet ports <NUM> are communicable with the internal mixing chamber <NUM>, and each of the plurality of pilot outlet ports <NUM> has an outlet <NUM> on the combustion chamber side <NUM> of the housing <NUM> for dispensing a pilot fuel-air mixture <NUM> into the combustion chamber <NUM> of the combustor.

In <FIG>, commencement of the pilot outlet ports <NUM> lengthwise along the pilot (i.e., a point where furcation begins), may be a distance L from a tip <NUM> of the fuel outlet port <NUM>. In various embodiments, the length L may be between <NUM>% to <NUM>% of a length D taken from the tip <NUM> of the fuel outlet port <NUM> to a surface of the downstream end <NUM> where outlets <NUM> are located. In the exemplary embodiment shown in <FIG>, the length L can be seen to be about <NUM>% of the length D.

In <FIG>, the length L is depicted as being the same for each of the pilot outlet ports <NUM>. However, in another exemplary embodiment shown in <FIG>, the length L may be different for individual ones of the pilot outlet ports <NUM>. In <FIG>, it can be seen that some of the pilot outlet ports <NUM> may commence at a first length Li, while others of the pilot outlet ports <NUM> may commence at a second length L<NUM>, where L<NUM> < L<NUM>. Thus, some of the pilot outlet ports <NUM> may have a longer channel length than others so as to provide for different fuel-air ratio mixtures to different main mixers.

Referring now to <FIG>, depicted therein is an enlarged view of an exemplary embodiment depicting an arrangement of the fuel injector <NUM>, the fuel outlet port <NUM> into the internal mixing chamber <NUM> and the oxidizer inlet ports <NUM>. As seen in the figure, the plurality of oxidizer inlet ports <NUM> are arranged upstream of the oxidizer inlet ports <NUM> (see <FIG>) and are arranged at an angle <NUM> extending radially inward toward a centerline axis <NUM> of the internal mixing chamber <NUM> from the upstream end <NUM> toward the downstream end <NUM>. In one preferable embodiment, the angle <NUM> may be about <NUM> degrees, while in other exemplary embodiments, the angle <NUM> may range from <NUM> to <<NUM> degrees.

As seen in <FIG>, the fuel injector <NUM> has a conical shaped outer surface <NUM> with a truncated apex thereof forming a fuel nozzle tip <NUM> extending into the internal mixing chamber <NUM> toward the downstream end <NUM>. The fuel outlet port <NUM> is arranged through the tip <NUM>. Fuel is fed to the fuel injector <NUM> by a not shown fuel supply line, and is output into the internal mixing chamber <NUM> via the fuel outlet port <NUM>. In <FIG>, at least a portion of each of the oxidizer inlet ports <NUM> is arranged at an angle to provide a flow of the oxidizer along the conical shaped outer surface <NUM> of the fuel injector <NUM> so as to impinge the oxidizer flow (i.e., the flow of air through the oxidizer inlet ports <NUM>) on a flow of fuel ejected from the fuel outlet port <NUM>. In this manner, an air jet is provided to accelerate the fuel ejected from the fuel outlet port <NUM> into the internal mixing chamber, which aids in the prevention of low velocity in the fuel injection area.

Referring again to <FIG>, in one exemplary embodiment, a centerline axis <NUM> of oxidizer inlet ports <NUM> is seen to be aligned with the fuel nozzle tip <NUM>. In this manner, oxidizer (air) flow entering through the ports <NUM> also helps to avoid low velocity at the fuel injector tip. The interaction of the oxidizer from oxidizer inlet ports <NUM> and the oxidizer from oxidizer inlet ports <NUM> impinge on one another and on the tip <NUM> of fuel injector and cause the air flow and the fuel ejected from the fuel outlet port <NUM> to turn outward towards the wall of the internal mixing chamber <NUM>. This helps to provide a better radial spread of the fuel in the internal mixing chamber <NUM> without the need for swirlers inside the pilot body.

In <FIG>, oxidizer inlet ports <NUM> can be seen to generally include both a cylindrical portion and a slotted portion forming the inlet port <NUM>. However, it can be understood that the oxidizer inlet ports <NUM> may be any other shape, including merely being a cylindrical hole. Regardless of the shape of the oxidizer inlet port <NUM>, a centerline of the inlet port to be aligned with the tip <NUM> constitutes a median of a width W of the inlet port in a horizontal (i.e., upstream to downstream) direction.

Additionally, in the figures, oxidizer inlet ports <NUM>, <NUM> and <NUM> are generally shown as being perpendicular to centerline axis <NUM>. However, in other embodiments, any or all of these oxidizer inlet ports may be angled with respect to the centerline axis <NUM>. For example, some or all of these oxidizer inlet ports may be angled from <NUM> degrees to <NUM> degrees with respect to the centerline axis <NUM>, where an angle from <NUM> to <NUM> degrees would help to reduce wakes from behind the jet flow from the angled inlets and an angle from <NUM> to <NUM> degrees would help to increase the turbulence level of the mixture in the internal mixing chamber.

<FIG> depicts an enlarged view of an exemplary embodiment depicting an arrangement of the pilot outlet ports <NUM> on the downstream end <NUM>. As seen in the figure, pilot outlet ports <NUM> are shown to include an angular portion that is angled radially outward toward the downstream end at a desired angle <NUM>. The desired angle can be set based a desired mixture of the pilot fuel-air mixture with the main mixers. In exemplary embodiments, the angle of the angular portion may range from zero to, for example, <NUM> degrees with respect to the centerline axis <NUM> of the internal mixing chamber <NUM>. By splitting the internal mixing chamber <NUM> into multiple pilot outlet ports <NUM>, center peak fuel profiles that otherwise occur in a single outlet of the prior art can be diverted into channels that provide a mixing length for fuel and air mix better. For example, in the prior art system having a single centrally located pilot fuel air mixture, the hottest burn (central peak) occurs far from the main pre-mixer flames. On the other hand, the high temperature burn from the pilot pre-mixer of the present disclosure is located in closer proximity to the main pre-mixer flame. Splitting the flow passages and providing direction to the flow ensures that the pilot fuel-air mixture can be better directed toward the main mixers to provide better stability to the main pre-mixer flames.

In another exemplary embodiment (not shown), the pilot outlet ports <NUM> may be formed in a helical shape extending in the downstream direction from an entrance <NUM> of the outlet port to the outlet <NUM>. Such an arrangement can provide for greater fuel-air mixing in the pilot outlet port <NUM> due to its longer length. Additionally, as shown in <FIG>, the outlets <NUM> of the pilot pre-mixer <NUM> may direct the flow of the fuel-air mixture exiting the outlet <NUM> in a tangential direction <NUM>. This can provide additional mixing downstream between the main mixers and the pilot mixers due to the tangential flow imparted by the helical pilot outlet ports.

<FIG> is a partial cross-sectional view taken along plane <NUM>-<NUM> in <FIG> at an entrance <NUM> to each of the pilot outlet ports <NUM>. As seen in <FIG>, a divider is formed of a plurality of ribs <NUM> for dividing the fuel-air mixture flow from the internal mixing chamber <NUM> into separate flows at the entrance <NUM> for each of pilot outlet ports <NUM>. <FIG> depicts an X-shaped divider including four ribs <NUM> owing to there being four pilot outlet ports <NUM> for the particularly depicted embodiment. Of course, the number of ribs dividing the flow of the fuel-air mixture depends on the number of pilot outlet ports <NUM>, which may be more or less than the four depicted in the figure.

Referring now to <FIG>, various arrangements of the outlets <NUM> from the pilot pre-mixer <NUM> into the combustion chamber with respect to the main pre-mixers <NUM> will be described. Each of <FIG> are plan views perpendicular to the combustion chamber side <NUM> of housing <NUM>, and depict an arrangement of four main pre-mixers <NUM> (as main pre-mixer array <NUM>) and one pilot pre-mixer <NUM>. Of course, other arrangements can be implemented and the foregoing are merely exemplary embodiments. In the plan view of <FIG>, outlets <NUM> for pilot pre-mixer <NUM> are seen to be arranged in a pilot pre-mixer outlet array <NUM>, where the array in <FIG> constitutes four outlets <NUM> equally spaced about a center <NUM> of the pilot pre-mixer. Of course, the present disclosure is not limited to four outlets <NUM> or the array shown in <FIG>, and any other arrangements could be implemented instead. In <FIG>, a plurality of lines <NUM> are seen to connect a center <NUM> of a main pre-mixer <NUM> with a center <NUM> of another main pre-mixer <NUM>. For example, line 150a-b can be seen to connect the center <NUM> of main pre-mixer 102a with the <NUM> center of main pre-mixer 102b. Another line <NUM> is seen to connect a center <NUM> of pilot pre-mixer <NUM> with a centerpoint <NUM> of each line <NUM>. For example, line 152a-b can be seen to connect the center <NUM> of pilot pre-mixer <NUM> with the centerpoint <NUM> of line 150a-b. The lines <NUM> and <NUM> are utilized to demonstrate a directional alignment of outlets <NUM> with respect to the main pre-mixers <NUM>. In the arrangement of <FIG>, for the pilot pre-mixer outlet array <NUM> shown, a center of each of the outlets <NUM> are seen to be aligned along a respective line <NUM> such that a flow of the fuel-air mixture exiting the outlets <NUM> is dispersed between two respective main pre-mixers. For example, the flow from outlet 130a can be dispersed between main pre-mixers 102a and 102b in <FIG>.

In the plan view of <FIG>, a plurality of lines <NUM> are seen to connect a center <NUM> of pilot pre-mixer <NUM> with a center <NUM> of a respective main pre-mixer <NUM>. For example, line 154c is seen to connect the center <NUM> of the pilot pre-mixer <NUM> with the center <NUM> of main pre-mixer 102c. In the arrangement depicted in <FIG>, for the pilot pre-mixer outlet array <NUM> (same as the array <NUM> in <FIG>) shown therein, a center of each of the outlets <NUM> is arranged to be along a respective line <NUM> so as to direct a flow of the fuel-air mixture toward a respective main pre-mixer <NUM>. For example, as seen in the figure, outlet 130c may direct its fuel-air mixture toward main pre-mixer 102c, while outlet 130d may direct its fuel-air mixture toward man pre-mixer 102d.

In the plan view of <FIG>, the alignment of lines <NUM> is the same as that for <FIG> in that each line <NUM> connects the center <NUM> of pilot pre-mixer <NUM> with a respective center <NUM> of a main pre-mixer <NUM>. However, unlike <FIG> where the center of each of the outlets <NUM> is arranged to be on a line <NUM>, in <FIG>, the pilot pre-mixer <NUM> is rotated at an angle <NUM> so that, for the pilot pre-mixer outlet array <NUM> (same array <NUM> as seen in <FIG>) shown in the figure, the center of each of the outlets <NUM> is skewed (offset) from the line <NUM> by the angle <NUM>. In this manner, the fuel-air mixture ejected from the outlets <NUM> can be fed in different proportions to two main pre-mixers. For example, as seen in the figure, outlet 130e-f may direct a portion of its fuel-air mixture toward main pre-mixer 102e and may direct another portion of its fuel-air mixture toward main pre-mixer 102f. Since outlet 130e-f is arranged closer to line 154e than to line 154f, a larger percentage of the fuel-air mixture can be directed toward main pre-mixer 102e than is directed to main-pre-mixer 102f.

<FIG> is a plan view of another arrangement of outlets <NUM> for a pilot pre-mixer <NUM> and main pre-mixers <NUM>. In each of <FIG>, arrangements are depicted with a single outlet <NUM> for a respective main pre-mixer <NUM>. That is, these figures depict four pilot pre-mixer outlets <NUM> working on conjunction with four main pre-mixers <NUM>. In contrast, as shown in <FIG>, the pilot pre-mixer <NUM> may include more than one outlet <NUM> for each pre-mixer. In particular, as seen in the figure, the pilot pre-mixer <NUM> may include two outlets <NUM> directing a fuel-air mixture toward a single main pre-mixer <NUM>. The pilot pre-mixer <NUM> may also include a central outlet <NUM>, providing flow generally perpendicular to the combustion chamber side <NUM>. Of course, the present disclosure is not limited to any of these particular embodiments, and other alternative arrangements of outlets <NUM> and main pre-mixers may be implemented instead.

<FIG> depicts another arrangement of the pilot pre-mixer <NUM> with respect to the main pre-mixers <NUM> that is different from that shown in <FIG>. In <FIG>, the pilot pre-mixer <NUM> is seen with its center <NUM> centrally located with respect to each of the main pre-mixers <NUM> in the array <NUM>. That is, the centers <NUM> of each main pre-mixer <NUM> are each equidistant from the center <NUM> of the pilot pre-mixer. For example, in <FIG>, each of lines <NUM> are the same length, representing that each main pre-mixer is located the same distance from the pilot center <NUM>. Additionally, the centers <NUM> of each main pre-mixer <NUM> are equidistant with one another in the array, where the distance from one center <NUM> of, for example, main pre-mixer 102a to another center <NUM> of, for example main pre-mixer 102b, along each of lines <NUM> are the same. Thus, the four main pre-mixer array <NUM> shown in <FIG>, for example, forms an array centroid that is also located at the same location as the center <NUM>. In <FIG>, the pilot pre-mixer <NUM> is shown with its center <NUM> shifted from being coincident with the array centroid 111a so that the pilot pre-mixer <NUM> is closer to one of the main pre-mixers <NUM>. Of course, the pilot pre-mixer <NUM> can be shifted away from the array centroid 111a in any direction and the present disclosure is not limited to the shift shown in <FIG>. In addition, the pilot pre-mixer <NUM> could be both shifted as shown in <FIG> and rotated as shown in <FIG>.

In the foregoing <FIG>, while the pilot body <NUM> may appear to be depicted as a single unit, it is understood that the body may be comprised of multiple component parts. For example, one component part may include an upstream portion that includes the oxidizer inlet ports <NUM> and conical fuel nozzle. Another component part may include a middle portion that includes the internal mixing chamber <NUM> and oxidizer inlet ports <NUM>, <NUM> and <NUM>. Additional component parts may comprise a downstream portion of the body that includes the pilot outlet ports <NUM>. Each of the component parts may then be assembled together to form the pilot body <NUM> depicted in the drawings.

In another aspect, the present disclosure provides for a method of operating a gas turbine engine utilizing the pre-mixer assembly. More particularly, method is practiced by a gas turbine engine has a pre-mixer assembly including a plurality of main pre-mixers for dispensing a main pre-mixer fluid mixture to a combustion zone of a combustor, and at least one pilot pre-mixer having a plurality of pilot outlet ports each having an outlet for dispensing a pilot fluid mixture into the combustion zone of the combustor. According to the present disclosure, the gas turbine engine is operated by a method that provides fuel to a mixing chamber of the pilot pre-mixer, provides a flow of an oxidizer agent to the mixing chamber of the pilot pre-mixer via first oxidizer inlet ports, and mixes, in the mixing chamber the fuel and the flow of the oxidizer agent to produce a pilot fuel-oxidizer mixture. The pilot fuel-oxidizer mixture is then ejected from respective outlets of the plurality of pilot outlet ports into the combustion zone of the combustor, and in the combustion zone of the combustor, the ejected pilot fuel-oxidizer mixture is ignited to produce a plurality of pilot flames from the pilot pre-mixer. In one exemplary aspect, the pilot fuel-oxidizer mixture is directionally ejected from respective ones of the outlets toward a respective main pre-mixer in the combustor. In addition, the method further provides for ejecting a main pre-mixer fuel-oxidizer mixture from respective ones of the plurality of main pre-mixers into the combustion zone of the combustor, wherein the plurality of pilot flames are utilized as an ignition source to ignite the main pre-mixer fuel-oxidizer mixtures of the plurality of main pre-mixers in the combustion zone of the combustor.

In a further aspect of the method, the pilot pre-mixer further includes second oxidizer inlet ports arranged to provide a flow of the oxidizer agent to the mixing chamber. Here, the mixing portion of the method involves, in the pilot pre-mixer, directing the flow of the oxidizer agent from second oxidizer inlet ports along a surface of and toward a tip of a fuel injector from which the flow of the fuel is provided to the mixing chamber, and directing the flow of the oxidizer agent from the first oxidizer inlet ports toward the tip of the fuel injector, wherein the directing the flow of the oxidizer agent from the first oxidizer inlet ports and the directing of the flow of the oxidizer agent from the second oxidizer inlet ports causes a mixture of a fuel-oxidizer fluid at the tip of the fuel injector to circulate outwards toward an outer wall of the mixing chamber.

As discussed above, the pilot of the prior art provides for a low swirl of the fuel air mixture within the pilot pre-mixer, and a generally centrally concentrated flow is projected from the outlet side into the combustion chamber. Thus, the mixedness obtained by the prior art pilot is about <NUM>%. In contrast, in the pilot pre-mixer according to the present disclosure, a non-swirled flow occurs within the pilot pre-mixer. However, additional mixing of the fuel air mixture occurs within the outlet port. At the outlets, therefore, the mixedness spreads out further from the center to mix better with the main pre-mixer flow, such that about <NUM>% mixedness can be achieved.

Similarly, an exit flow progress variable of the fuel air mixture for the conventional low swirl pilot pre-mixer results in a centrally projected flow from the outlet into the combustion chamber and the flow then progresses into a balloon type flow. In contrast, the present disclosure has a flow progress where the fuel-air mixture at the outlet to the combustion chamber projects a smaller flow angularly directed toward the main mixer, and the progress of the flow at remains more concentrated toward the main mixer flames.

Claim 1:
A pilot pre-mixer (<NUM>) for a gas turbine engine (<NUM>), comprising:
a pilot body (<NUM>), including:
an internal mixing chamber (<NUM>);
a first end (<NUM>) on an upstream side of the internal mixing chamber;
a second end (<NUM>) on a downstream side of the internal mixing chamber;
a fuel injector (<NUM>) at the first end and communicable with the internal mixing chamber;
a plurality of first oxidizer inlet ports (<NUM>) arranged to provide an oxidizer agent from outside of the pilot body (<NUM>) to the internal mixing chamber (<NUM>); and
a plurality of pilot outlet ports (<NUM>) at the second end (<NUM>) and communicable with the internal mixing chamber (<NUM>), each of the plurality of pilot outlet ports having an outlet (<NUM>) on the second end (<NUM>) for dispensing a pilot fluid mixture into a combustion chamber (<NUM>) of a combustor (<NUM>).