Auxiliary torch ignition

A torch igniter includes an auxiliary fuel injector; an ignition source; and an igniter body carrying the auxiliary fuel injector and the ignition source. The igniter body includes an auxiliary combustion chamber having a side wall extending axially from a first end wall to a second end wall. In some examples, at least a portion of the side wall includes a distributed pattern of cooling apertures, with each of the cooling apertures extending obliquely from an outer surface of the side wall to an inner surface of the side wall. In some examples, the second end wall defines a fluid outlet leading to an outlet tube in fluid communication with the primary combustion chamber, at least a portion of the outlet tube including a distributed pattern of dilution apertures.

TECHNICAL FIELD

This specification generally relates to combustor assemblies for gas turbine engines that incorporate auxiliary torch ignition systems to facilitate ignition in a main combustion chamber.

BACKGROUND

The gas turbine engine is the preferred class of internal combustion engine for many high power applications. Fundamentally, the gas turbine engine features an upstream rotating compressor coupled to, and typically driven by, a downstream turbine, with a combustion chamber residing in-between the two rotary components. A torch igniter is a device that may be used to ignite the primary combustor of a gas turbine engine. In some applications, the torch igniter has advantages over conventional spark igniters, because it can provide larger amounts of energy release to the main combustor, and thus, is capable of lighting the engine in a more reliable manner. To achieve this, the torch igniter requires an auxiliary source of fuel and air, as well as an ignition source. Auxiliary air flow is typically obtained from the plenum downstream of the engine's compressor or from an external source of compressed air; and the auxiliary fuel is obtained from the fuel-metering unit or manifold or from an independent fuel source. Air flow requirements to operate the torch igniter may vary under different conditions, but are often significantly less than the air flow requirements of the primary combustor. On a typical engine, much like a conventional spark igniter, there can be two or more torch igniters for redundancy.

SUMMARY

In one aspect, a gas turbine combustor assembly includes: a primary combustion chamber in fluid communication with a primary fuel injector and a primary air inlet; and a torch ignitor coupled to the primary combustion chamber. The torch igniter includes: an auxiliary fuel injector; an ignition source; and an igniter body carrying the auxiliary fuel injector and the ignition source. The igniter body includes an auxiliary combustion chamber having a side wall extending axially from a first end wall to a second end wall, at least a portion of the side wall including a distributed pattern of cooling apertures, with each of the cooling apertures extending obliquely from an outer surface of the side wall to an inner surface of the side wall, so as to cause fluid entering an interior cavity of the auxiliary combustion chamber through the cooling apertures to form a fluid film along the inner surface.

In some examples, the combustor assembly further includes a premixing cup residing within the interior cavity of the auxiliary combustion chamber. In some examples, the premixing cup includes a cylindrical wall radially surrounding the auxiliary fuel injector and an auxiliary air inlet, the cylindrical wall of the premixing cup protruding axially outward relative to the first end wall of the auxiliary combustion chamber through a portion of the interior cavity to delineate a premixing zone radially inward of the cylindrical wall and a recirculation zone radially outward of the cylindrical wall, with the ignition source residing on the side wall of the auxiliary combustion chamber at a position proximate the recirculation zone

In some examples, the auxiliary combustion chamber is substantially cylindrical in shape, with the side wall having a circular cross-section of constant diameter, and the first and second end walls being substantially planar.

In some examples, the second end wall defines a fluid outlet leading to an outlet tube in fluid communication with the primary combustion chamber. In some examples, the igniter body further includes an outer shell surrounding at least a portion of the auxiliary combustion chamber, the outer shell including a fluid inlet coaxially aligned with the outlet tube. In some examples, the igniter body includes a fluid annulus formed between an inner surface of the shell and an outer surface of the auxiliary combustion chamber, the annulus directing fluid from the fluid inlet across the outer surface of the auxiliary combustion chamber towards the first end wall.

In some examples, the second end wall of the auxiliary combustion chamber defines a fluid outlet leading to an outlet tube in fluid communication with the primary combustion chamber, at least a portion of the outlet tube including a distributed pattern of dilution apertures, with each of the dilution apertures configured to direct fluid in cross-flow with heated gas exiting the auxiliary combustion chamber through the outlet tube.

In some examples, the igniter body further includes a fluid swirler residing at an entrance to a premixing cup residing within the auxiliary combustion chamber. In some examples, the fluid swirler includes an axial fluid swirler including a circumferential pattern of swirl opening surrounding an outlet of the auxiliary fuel injector.

In some examples, the torch igniter further includes a shielding device configured to at least partially shield the ignition source from fluid flow through the auxiliary combustion chamber. In some examples, the shielding device is coupled to an inner surface of the auxiliary combustion chamber proximate the ignition source, and includes a curved, convex surface.

In another aspect, a gas turbine combustor assembly includes: a primary combustion chamber in fluid communication with a primary fuel injector and a primary air inlet; and a torch ignitor coupled to the primary combustion chamber. The torch igniter includes: an auxiliary fuel injector; an ignition source; and an igniter body carrying the auxiliary fuel injector and the ignition source. The igniter body includes an auxiliary combustion chamber having a side wall extending axially from a first end wall to a second end wall, the second end wall defining a fluid outlet leading to an outlet tube in fluid communication with the primary combustion chamber, at least a portion of the outlet tube including a distributed pattern of dilution apertures, with each of the dilution apertures configured to direct fluid in cross-flow with heated gas exiting the auxiliary combustion chamber through the outlet tube.

In some examples, the combustor assembly further includes a premixing cup residing within an interior cavity of the auxiliary combustion chamber. In some examples, the premixing cup includes a cylindrical wall radially surrounding the auxiliary fuel injector and an auxiliary air inlet, the cylindrical wall of the premixing cup protruding axially outward relative to the first end wall of the auxiliary combustion chamber through a portion of the interior cavity to delineate a premixing zone radially inward of the cylindrical wall and a recirculation zone radially outward of the cylindrical wall, with the ignition source residing on the side wall of the auxiliary combustion chamber at a position proximate the recirculation zone.

In some examples, the auxiliary combustion chamber is substantially cylindrical in shape, with the side wall having a circular cross-section of constant diameter, and the first and second end walls being substantially planar.

In some examples, the second end wall defines a fluid outlet leading to an outlet tube in fluid communication with the primary combustion chamber. In some examples, the igniter body further includes an outer shell surrounding at least a portion of the auxiliary combustion chamber, the outer shell including a fluid inlet coaxially aligned with the outlet tube. In some examples, the igniter body includes a fluid annulus formed between an inner surface of the shell and an outer surface of the auxiliary combustion chamber, the annulus directing fluid from the fluid inlet across the outer surface of the auxiliary combustion chamber towards the first end wall.

In some examples, at least a portion of the side wall of the auxiliary combustion chamber includes a distributed pattern of cooling apertures, with each of the cooling apertures obliquely canted relative to an inner surface of the side wall so as to cause fluid entering an interior cavity of the auxiliary combustion chamber through the cooling apertures to form a fluid film along the inner surface.

In some examples, the igniter body further includes a fluid swirler residing at to an entrance to a premixing cup residing within the auxiliary combustion chamber. In some examples, the fluid swirler includes an axial fluid swirler including a circumferential pattern of swirl opening surrounding an outlet of the auxiliary fuel injector.

In some examples, the torch igniter further includes a shielding device configured to at least partially shield the ignition source from fluid flow through the auxiliary combustion chamber. In some examples, the shielding device is coupled to an inner surface of the auxiliary combustion chamber proximate the ignition source, and includes a curved, convex surface.

In yet another aspect, a method of operating a gas turbine combustor assembly includes the steps of: mixing auxiliary fuel and air flows in an auxiliary combustion chamber to form an auxiliary fuel/air mixture; igniting the auxiliary fuel/air mixture to form an auxiliary flow of heated fluid; directing the auxiliary flow of heated fluid through the auxiliary combustion chamber towards a primary combustion chamber; while directing the auxiliary flow of heated fluid, receiving a flow of cooling fluid, and directing the cooling fluid so as to form a film of cooling fluid along an inner surface of the auxiliary combustion chamber and dilute the auxiliary flow of heated fluid; and igniting a primary air/fuel mixture in a primary combustion chamber of the gas turbine combustor assembly with the diluted auxiliary flow of heated fluid from the auxiliary combustion chamber.

In still yet another aspect, a gas turbine combustor assembly includes: a primary combustion chamber in fluid communication with a primary fuel injector and a primary air inlet; and a torch ignitor coupled to the primary combustion chamber. The torch igniter includes: an auxiliary fuel injector; an ignition source; and an igniter body carrying the auxiliary fuel injector and the ignition source. The igniter body includes an auxiliary combustion chamber having a side wall extending axially from a first end wall to a second end wall, the side wall defining an interior cavity between the first and second end walls. The igniter body further includes a premixing cup residing within the interior cavity including a cylindrical wall radially surrounding the auxiliary fuel injector and an auxiliary air inlet, the cylindrical wall of the premixing cup protruding axially outward relative to the first end wall of the auxiliary combustion chamber through a portion of the interior cavity to delineate a premixing zone radially inward of the cylindrical wall and a recirculation zone radially outward of the cylindrical wall, with the ignition source residing on the side wall of the auxiliary combustion chamber at a position proximate the recirculation zone.

In some examples, the torch igniter further includes an auxiliary fuel source in fluid communication with a nozzle orifice of the auxiliary fuel injector, the auxiliary fuel source configured to provide a pressurized flow of fuel for injection into the auxiliary combustion chamber by the auxiliary fuel injector; and a bypass line configured to return at least a portion of the pressurized flow of fuel to a main engine fuel manifold.

In some examples, the auxiliary combustion chamber is substantially cylindrical in shape, with the side wall having a circular cross-section of constant diameter, and the first and second end walls being substantially planar.

In some examples, the second end wall defines a fluid outlet leading to an outlet tube in fluid communication with the primary combustion chamber. In some examples, the igniter body further includes an outer shell surrounding at least a portion of the auxiliary combustion chamber, the outer shell including a fluid inlet coaxially aligned with the outlet tube. In some examples, the igniter body includes a fluid annulus formed between an inner surface of the shell and an outer surface of the auxiliary combustion chamber, the annulus directing fluid from the fluid inlet across the outer surface of the auxiliary combustion chamber towards the first end wall.

In some examples, the second end wall of the auxiliary combustion chamber defines a fluid outlet leading to an outlet tube in fluid communication with the primary combustion chamber. In some examples, at least a portion of the outlet tube includes a distributed pattern of dilution apertures, with each of the dilution apertures configured to direct fluid in cross-flow with heated gas exiting the auxiliary combustion chamber through the outlet tube.

In some examples, the igniter body further includes a fluid swirler residing at an entrance to the premixing cup. In some examples, the fluid swirler includes an axial fluid swirler including a circumferential pattern of swirl opening surrounding an outlet of the auxiliary fuel injector.

In some examples, the torch igniter further includes a shielding device configured to at least partially shield the ignition source from fluid flow through the auxiliary combustion chamber. In some examples, the shielding device is coupled to an inner surface of the auxiliary combustion chamber proximate the ignition source, and includes a curved, convex surface projecting towards the premixing cup.

In some examples, at least a portion of the side wall of the auxiliary combustion chamber includes a distributed pattern of cooling apertures, with each of the cooling apertures obliquely canted relative to an inner surface of the side wall so as to cause fluid entering an interior cavity of the auxiliary combustion chamber through the cooling apertures to form a fluid film along the inner surface.

In yet another aspect still, a method of operating a gas turbine combustor assembly includes the steps of: receiving auxiliary flows of fuel and air in a premixing cup of an igniter body of the gas turbine combustor assembly; at least partially mixing the auxiliary fuel and air flows in a premixing zone of the premixing cup, and discharging the auxiliary fuel/air mixture into an auxiliary combustion chamber of the igniter body; directing the discharged auxiliary fuel/air mixture into a primary recirculation zone including an annular space between the premixing cup and an inner surface of the auxiliary combustion chamber; igniting the auxiliary fuel/air mixture at a location proximate the primary recirculation zone to form an auxiliary flow of heated fluid; and igniting a primary air/fuel mixture in a primary combustion chamber of the gas turbine combustor assembly with the auxiliary flow of heated fluid from the auxiliary combustion chamber of the igniter body.

In some examples, receiving the auxiliary flow of fuel includes the steps of: directing a pressurized flow of fuel from an auxiliary fuel source to a nozzle orifice of an auxiliary fuel injector in fluid communication with the premixing cup, bypassing the nozzle orifice with at least a portion of the fuel flow, and directing the bypassed portion of the fuel flow to a main engine fuel manifold.

In some examples, receiving the auxiliary flow of air includes directing the air through a fluid inlet. In some examples, the method further includes directing the auxiliary flow of heated fluid through a fluid outlet tube coaxially aligned with the fluid inlet as the auxiliary flow of air is directed through the fluid inlet.

In some examples, the method further includes diluting the auxiliary flow of heated fluid by directing a portion of the auxiliary flow of air in cross-flow with the auxiliary flow of heated flow through a pattern of dilution apertures of the outlet tube.

In some examples, the method further includes cooling a portion of the auxiliary combustion chamber by forming a cooling fluid film along an inner surface of the auxiliary combustion chamber. In some examples, forming the cooling fluid film includes directing a portion of the auxiliary flow of air through a distributed pattern of obliquely canted cooling apertures of the auxiliary combustion chamber

In some examples, at least partially mixing the auxiliary fuel and air flows includes inducing a swirling flow pattern in each of the flows

In some examples, igniting the auxiliary fuel/air mixture includes energizing an ignition source while at least partially shielding the ignition source from the auxiliary fuel/air mixture.

DETAILED DESCRIPTION

In a gas turbine engine, the torch igniter ignites fuel released by combustor nozzles in a combustor of the engine to produce heated combustion products. The heated combustion products are, in turn, expanded through a turbine of the engine to produce torque. Reliable ignition and flame propagation around the primary combustor nozzles in conditions with relatively low air pressure drop (delta P) may require a heightened minimum level of ignition energy provided to the operating envelope. This concern is often exacerbated when the ambient environment is particularly cold. In order to provide sufficient ignition energy across a broad range of operating conditions in different ambient environments, high-quality flame stability/operability of the torch igniter system is desired.

In certain aspects, the present disclosure relates to torch igniter systems that supply high ignition energy by incorporating various combinations of design features in the igniter body. In some implementations, for example, the igniter body includes an auxiliary combustion chamber with a premixing cup that directs a mixture of fuel and air into a recirculation zone proximate an ignition source. The entrance to the premixing cup may include an air swirler to enhance recirculation and mixing of the auxiliary air and fuel flows in the auxiliary combustion chamber.

In some implementations, optimization of the turbulence and swirling components is achieved to sustain the torch igniter flame without having to keep the ignition source on. In some implementations, a torch igniter in accordance with one or more embodiments of the present disclosure can improve cold day combustor light off performance, and provide reliable re-light capability across a wide range of operating conditions by providing high energy release that is enhanced by swirl stabilized combustion in the torch combustor.

Further, certain torch igniter systems of the present disclosure incorporate design features that extend the operational life of components having high-temperature failure mechanisms. For instance, in some implementations, a side wall of the auxiliary combustion chamber includes a pattern of distributed cooling apertures. As discussed in detail below, the cooling apertures can be configured to enable cooling fluid (e.g., air) to contact the inner surface of the auxiliary combustion chamber without adversely affecting the combustion conditions therein (e.g., fuel/air ratio, air/fuel temperatures, air/fuel flow velocities, etc.). As another example, in some implementations, an outlet tube receiving the combustion products from the auxiliary combustion chamber includes a pattern of dilution apertures. The dilution apertures on the outlet tube can be configured to facilitate mixing of a dilution fluid (e.g., air) with the combustion products to effect a temperature change.

FIG. 1is a half, side cross-sectional view of an example gas turbine engine10. The gas turbine engine10is turbojet-type gas turbine that could be used, for example, to power jet aircrafts. However, it is appreciated that the concepts described in the present disclosure are not so limited, and can be incorporated in the design of various other types of gas turbine engines (e.g., turbofan, turboprop, turboshaft, or industrial/marine engines).

As shown, the gas turbine engine10generally facilitates a continuous axial flow of gas. That is, gas generally flows through the engine10in the axially downstream direction indicated by the arrows inFIG. 1. The gas turbine engine10includes an intake12that receives ambient air14and directs the ambient air to a compressor16. The ambient air14is drawn through multiple stages of the compressor16. High-pressure air18exiting the compressor16is introduced to a combustor100. In certain instances, the combustor100is an annular combustor circumscribing the engine's main shaft20or a can-type combustor positioned radially outward of the shaft.

The combustor100includes a combustion shield102, multiple fuel injectors104, a combustor dome106, and a torch igniter system108. At the combustor100, the high-pressure air18is mixed with liquid or gaseous fuel (not shown) and ignited by the torch igniter system108to produce heated combustion products22. The combustion products22are passed through multiple stages of a turbine24. The turbine24extracts energy from the high-pressure, high-temperature combustion products22. Energy extracted from the combustion products22by the turbine24drives the compressor16, which is coupled to the turbine by the main shaft20. Exhaust gas26leaving the turbine24is accelerated into the atmosphere through an exhaust nozzle28to provide thrust or propulsion power or energy for electrical power generation.

FIGS. 2A-2Bshow an example torch igniter200that can be used in the torch igniter system108ofFIG. 1. In certain instances, the torch igniter system108includes multiple, spaced apart torch igniters200. In this example, the torch igniter200includes an igniter body202, an auxiliary fuel injector204, and an ignition source206. The igniter body202includes a main housing208outlining a hollow, substantially cylindrical interior cavity but could be different shape based on physical envelope requirement. The interior cavity of the main housing208receives an auxiliary combustion chamber210. An annular gap between the outer surface of the auxiliary combustion chamber210and the inner surface of the housing208defines a fluid passage212. The fuel injector204and ignition source206are supported by the housing208. The ignition source206, for example, is mounted directly to the housing208, extending through an opening in the housing's side wall. A temperature sensor213(e.g., a thermocouple) is similarly mounted to the housing208. The auxiliary fuel injector204is coupled to the housing208via a mounting bracket214. That is, the mounting bracket214carries the fuel injector204and is directly attached (bolted, in this example) to the front end of the main housing208.

In this example, the auxiliary fuel injector204includes a nozzle orifice216, a fuel inlet line218and a fuel bypass line220. The fuel inlet218is placed in fluid communication with a pressurized source of fuel (not shown). During use, pressurized fuel from the source flows toward the nozzle orifice216via the fuel inlet line218. At least a portion of this fuel flow bypasses the nozzle orifice216and is returned to the main engine fuel manifold by the fuel bypass line220. In some examples, the fuel injector incorporates additional design features for enhancing fuel atomization and increasing fuel turn down ratio to meet fuel flow requirement at all operating conditions without changing the size of the nozzle orifice216, which may otherwise induce coking.

The auxiliary combustion chamber210received within the interior of the main housing208features a cylindrical body including a curved side wall226extending between substantially planar front and rear end walls228,230. The cylindrical body of the auxiliary combustion chamber210defines an axial length “L” and a radial diameter “D”. In some examples, the volume and/or the L/D ratio of the auxiliary combustion chamber210may affect flame stabilization. For example, flame stabilization can be improved by providing the auxiliary combustion chamber210with a volume and/or an L/D ratio that reduces the reference velocity of the fluid (i.e., the theoretical flow velocity of air through an area equal to the maximum cross section of the combustor casing). Improved flame stabilization may enable the torch igniter200to sustain the flame at higher pressure drop conditions, which increases the operating envelope of the primary combustor.

The igniter body202further includes an end cap provided in the form of a bulkhead232bolted to the rear end of the main housing208. The bulkhead232generally closes off the interior cavity of the housing208with the exception of a central through-bore234. As shown, the bore234of the bulkhead232receives an outlet tube236extending from a fluid outlet237at the rear end wall230of the auxiliary combustion chamber210. The outlet tube236conveys heated fluid from the auxiliary combustion chamber210to the primary combustor. Notably, the inner diameter of the bulkhead's bore234is slightly larger than the outer diameter of the outlet tube236, such that a narrow annular gap providing a fluid inlet238is formed therebetween (seeFIG. 2B). The fluid inlet238is in fluid communication with the annular fluid passage212between the housing208and auxiliary combustion chamber210. This configuration places the fluid inlet238and fluid outlet237of the igniter body202in a coaxial arrangement. Thus, a single opening in the outer shell (the main housing208and bulkhead232) of the igniter body202is used to route fluid both to and from the auxiliary combustion chamber210. The design of the bulkhead232is modular and application specific. This coaxial design effectively simplifies the manufacturing and assembly process, provides a compact form factor, and also facilitates crossflow between the two fluid flows. As explained in detail below in connection withFIG. 4, the cross flowing fluid enables incoming auxiliary air flow to be used for cooling and/or dilution purposes.

A premixing cup240resides within the interior of the auxiliary combustion chamber210proximate the chamber's planar front end wall228. The premixing cup240includes an air inlet242and a cylindrical wall244. The air inlet242radially surrounds the auxiliary fuel injector204. The cylindrical wall244circumscribes the air inlet242, and therefore also surrounds the fuel injector204radially. An air swirler246is positioned within the air inlet242. In this example, the air swirler246has a disk-shaped body including a plurality of swirl openings arranged in a circumferential pattern. The swirl openings radially surround the outlet of the auxiliary fuel injector204and are oriented generally axially, at a canted, non-zero angle relative to the longitudinal axis of the auxiliary combustion chamber210. Thus, the swirl openings are arranged to form a flow vortex along the longitudinal axis of the auxiliary combustion chamber210. U.S. Patent Publication No. 2016/0047318, the entirety of which is incorporated herein by reference, describes an axial air swirler suitable for use in conjunction with embodiments of the present disclosure.

The cylindrical wall244of the premixing cup240protrudes axially outward relative to the front end wall228of the auxiliary combustion chamber210to extend through a frontal portion of the auxiliary combustion chamber's interior cavity. The cylindrical wall244delineates two discrete zones within the frontal portion in the auxiliary combustion chamber210—a premixing zone248that is radially inward of the cylindrical wall and a recirculation zone250that is radially outward of the cylindrical wall. The premixing zone248provides a compact area for introducing the auxiliary flow of air to atomized fuel from the fuel injector204, which enhances the degree of fuel/air mixing. When the mixed flow of air and fuel is expelled from the premixing cup440it immediately enters a downstream portion of the auxiliary combustion chamber210. The empty space in the recirculation zone250draws a portion of the fuel/air mixture backwards in the auxiliary combustion chamber towards the chamber's front wall228, creating a turbulent, toroidal flow pattern (seeFIG. 3). This recirculating flow sustains combustion without having to maintain the ignition source206in an “on” condition, because a portion of the ignited air/fuel flow is recirculated back into the incoming fuel flow from the premixing zone248. Even further, the turbulence and recirculation tends to mix the combusting air/fuel with uncombusted air/fuel, which more evenly ignites the air/fuel mixture throughout the auxiliary combustion chamber210. This produces stronger, higher energy combustion.

The diagram ofFIG. 3illustrates how fluid flows through a torch ignitor300, which is similar in construction to the torch igniter200ofFIGS. 2A and 2B. As shown inFIG. 3, an auxiliary flow of air enters an igniter body302of the torch igniter300via a fluid inlet338. The auxiliary air flows from the fluid inlet338into an annular fluid passage312. The fluid passage312directs the auxiliary airflow towards the air inlet of a premixing cup340where it is introduced to an axial air swirler346. The auxiliary air traverses the air swirler346and flows into a mixing zone348defined by a cylindrical wall344of the premixing cup340. In the mixing zone348, the swirling auxiliary airflow meets and mixes with atomized fuel discharged from the auxiliary fuel injector314. The fuel/air mixture flows from the mixing zone348into the remaining area of the auxiliary combustion chamber's interior cavity, including a recirculation zone350radially separated from the premixing zone348by the cylindrical wall344. The fuel/air mixture is energized (e.g., ignited) by the ignition source, which is positioned in the auxiliary combustion chamber310proximate the recirculation zone350. Heated fluid then flows through the auxiliary combustion chamber310towards the fluid outlet337and into the outlet tube336, which leads to the primary combustion chamber.

FIG. 4shows another example torch igniter400. Like the previous examples, torch igniter400includes an igniter body402, an auxiliary fuel injector404, and an ignition source406. The igniter body402includes a main housing408and a bulkhead432enclosing a hollow interior cavity containing an auxiliary combustion chamber410. The bulkhead432includes a central bore434that receives an outlet tube436leading from the auxiliary combustion chamber410. The respective annular gaps between the auxiliary combustion chamber420and the bulkhead432and main housing408define a fluid inlet438leading to a fluid passage412. The interior of the auxiliary combustion chamber410includes a premixing cup440having an air inlet442receiving an air swirler446. The premixing cup440further includes an axially protruding cylindrical wall444delineating a frontal portion of the auxiliary combustion chamber into a mixing zone448and a recirculation zone450.

In this example, the auxiliary fuel injector404incorporates additional design features and control scheme for enhancing fuel atomization and increasing fuel turn down ratio to meet fuel flow requirement at all operating conditions without changing the size of the nozzle orifice, which may otherwise induce coking.

In this example, the curved side wall426of the auxiliary combustion chamber410includes a distributed pattern of cooling apertures452. The cooling apertures452project through the side wall426of the auxiliary combustion chamber410, enabling a portion of the auxiliary air flow traversing the annular fluid passage412to enter the auxiliary combustion chamber410. In this example, each of the cooling apertures452is obliquely canted relative to the inner surface of the chamber's curved side wall426. The angled orientation of the cooling apertures452causes air entering the auxiliary combustion chamber410therethrough to form a fluid film along the chamber's inner surface. The film of auxiliary air adheres to the inner surface of the auxiliary combustion chamber410, and therefore is inhibited from comingling with the air/fuel mixture flowing from the premixing cup440. This allows the auxiliary airflow to cool the auxiliary combustion chamber410without affecting the stoichiometry of the combustion process. The distribution of cooling apertures may vary between different implementations. For example, different implementations may employ more or less cooling apertures without departing from the scope of the present disclosure. Moreover, in some implementations, the distribution of cooling apertures may vary across the length of the auxiliary combustion chamber. For instance, in this example, the density of cooling apertures increases from the front end of the auxiliary combustion chamber410towards the rear end.

In addition to the cooling apertures452, torch igniter400further includes a plurality of dilution apertures454. In this example, the dilution apertures454are located along the outlet tube436that conveys heated fluid from the auxiliary combustion chamber410to the primary combustor. The dilution apertures454are configured to divert a portion of the auxiliary air flow from the annular fluid inlet438. Unlike the cooling apertures452, the dilution apertures454are designed to direct the incoming air into the flowpath of heated fluid exiting the auxiliary combustion chamber through the outlet tube436. For example, the dilution apertures454may be substantially perpendicular to the curved surface of the outlet tube436, as opposed to obliquely canted. The auxiliary air flow mixes with the heated fluid and dilutes the composition, which results in a relatively swift drop in temperature.

While the embodiment ofFIG. 4provides cooling apertures along the auxiliary combustion chamber and dilution apertures along the outlet tube, various other configurations are also contemplated within the scope of the present disclosure. Indeed, either or both of the auxiliary combustion chamber and outlet tube may include cooling and/or dilution apertures in different implementations.

The torch igniter400still further includes a shielding device456residing within the interior cavity of the auxiliary combustion chamber410. The shielding device456is designed to at least partially shield the ignition source406from direct contact with the air/fuel mixture flowing from the premixing cup440. In this example, the shielding device456includes curved body having a convex outer surface facing the premixing cup440. As shown, the shielding device456further includes multiple apertures458distributed along the body that permit a limited portion of the fuel/air mixture to flow passed the tip of the ignition source406. In some implementations, shielding the ignition source406in this way inhibits quenching that tends to occur at relatively cold fuel and air conditions and/or high pressure drop conditions.