Multipoint injectors with auxiliary stage

A multipoint combustion system for a gas turbine engine includes a housing defining a pressure vessel. A master injector is mounted to the housing for injecting fuel along a central axis. A plurality of slave injectors are each disposed outward of the master injector for injecting fuel and air in an ignition plume radially outward of fuel injected through the master injector. The master injector and slave injectors are configured and adapted so the injection plume of the master injector intersects with the ignition plumes of the slave injectors. A primary manifold is included within the pressure vessel for distributing fuel to the slave injectors. An auxiliary manifold is in fluid communication with the auxiliary nozzles of the slave injectors for issuing an auxiliary flow of fuel from the auxiliary nozzles that is separate from the fuel flow of the primary manifold.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to gas turbine engines, and more particularly to gas turbine engines utilizing low calorific value fuels.

2. Description of Related Art

Gasification of coal, biomass, and other fuels produces fuel gas that can be used for power production. Fuel gas derived from gasification or other such processes is commonly referred to as low calorific value (LCV) fuel because it typically has significantly lower heating values compared to more traditional fuels. Whereas natural gas typically has a heating value of about 1,000 BTU/Ft3, LCV gas can have a heating value on the order of only about 130 BTU/Ft3and less. LCV gas can be used with or as a replacement for more traditional fuels in applications including internal combustion engines, furnaces, boilers, and the like. In addition to environmental concerns, fluctuating fuel costs and availability drive a growing interest in use of LCV fuels where more traditional fuels, such as natural gas, are typically used.

While there is growing interest in LCV fuels, the low heating value of LCV fuel creates obstacles to its more widespread use. Thus there is an ongoing need for improved LCV fuel combustion systems. For example, the use of LCV fuel in an existing, conventional gas turbine engine requires special considerations regarding the fuel injection system. Flammability of LCV fuel gas can be unknown due to variables in the gasification process, so there is typically an unpredictable flameout limit when lowering fuel flow to operate at reduced power. Due to the relatively low heating value, LCV fuel can require 10 to 12 times the volumetric flow rate of natural gas for which the original engine was designed, which can give rise to capacity complications for traditional combustion systems. Typical gasification systems produce LCV fuel through high-temperature processes, and LCV fuel is often supplied directly from the gasification system. The LCV fuel temperature can be significantly hotter than in conventional fuel systems, which can give rise to further thermal management concerns. Additionally, due to the low calorific value, the fuel can present difficulties in terms of start up and flame stabilization.

Some solutions to these challenges have been proposed, such as using large numbers of small injectors, and allowing for mixing traditional fuel in with LCV fuel. However, the high flow rates needed to provide an adequate supply of LCV fuel lead to significant pressure drop, which is exacerbated by using large numbers of small injectors. High pressure drop can severely impact overall thermal efficiency for gas turbine engines, for example. Start up and flame stabilization challenges persist in typical LCV fuel injection systems.

Such conventional methods and systems have generally been considered satisfactory for their intended purpose. However, there is still a need in the art for combustion systems and methods that allow for improved start up, flame stability, and fuel staging. There also remains a need in the art for such systems and methods that are easy to make and use. The present invention provides a solution for these problems.

SUMMARY OF THE INVENTION

The subject invention is directed to a new and useful a multipoint combustion system for a gas turbine engine. The system includes a housing defining a pressure vessel. A master injector is mounted to the housing for injecting fuel in an injection plume along a central axis defined through the pressure vessel. A plurality of slave injectors are each disposed outward of and substantially parallel to the master injector for injecting fuel and air in an ignition plume radially outward of fuel injected through the master injector. The master injector and slave injectors are configured and adapted so the injection plume of the master injector intersects with the ignition plumes of the slave injectors. Each of the slave injectors is an injector for a low-calorific value fuel as described below. A primary manifold is included within the pressure vessel for distributing fuel to the slave injectors. An auxiliary manifold is in fluid communication with the auxiliary nozzles of the slave injectors for issuing an auxiliary flow of fuel from the auxiliary nozzles that is separate from the fuel flow of the primary manifold.

In certain embodiments, the pressure vessel includes a pressure dome with a central aperture and a central inlet fitting mounted to the central aperture of the pressure dome, wherein the auxiliary manifold is external to the pressure dome. The primary and auxiliary manifolds can advantageously be thermally isolated from one another. The auxiliary nozzles of the slave injectors can be mounted to the pressure vessel with floating seals to accommodate thermal expansion differentials between the pressure vessel and the auxiliary manifold. The auxiliary manifold can advantageously be flexible for ease of installation and to accommodate thermal expansion differentials for example. The auxiliary manifold can be configured and adapted to issue at least one of natural gas and liquid fuel to the auxiliary nozzles of the slave injectors. The auxiliary manifold can be operatively connected to an external valve to permit purging of the auxiliary manifold and auxiliary nozzles with engine air for complete shutdown of the auxiliary manifold and nozzles.

The invention also provides an injector for a low-calorific value fuel combustion system. The injector includes a nozzle body defining a fuel circuit for injecting low-calorific value fuel. An auxiliary nozzle is mounted to the nozzle body and defines a fuel circuit for injecting at least one of natural gas and liquid fuel.

In accordance with certain embodiments, the auxiliary nozzle is mounted to the nozzle body with a floating seal to accommodate a differential in thermal expansion between the auxiliary nozzle and the nozzle body. The fuel circuit of the nozzle body can be annular and the nozzle body can define an outer air circuit outboard of the fuel circuit of the nozzle body. The auxiliary nozzle can advantageously include a fuel outlet configured and adapted to issue a spray of fuel that diverges away from a longitudinal axis defined by the auxiliary nozzle.

In certain embodiments the nozzle body includes an inner wall and an outer wall outboard of and spaced apart from the inner wall, wherein the fuel circuit of the nozzle body passes through the inner and outer walls. The outer wall can define at least one aperture configured for passage of fuel from the primary manifold into the nozzle body for selective injection of at least natural gas and LCV fuel gas in a proportional mix. The auxiliary nozzle can be inboard of and spaced apart from the inner wall of the nozzle body. It is contemplated that the nozzle body and auxiliary nozzle can define a common longitudinal axis, wherein the auxiliary nozzle and nozzle body each include a respective fuel outlet, and wherein the fuel outlet of the auxiliary nozzle is upstream relative to the outlet of the nozzle body along the longitudinal axis.

These and other features of the systems and methods of the subject invention will become more readily apparent to those skilled in the art from the following detailed description of the preferred embodiments taken in conjunction with the drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made to the drawings wherein like reference numerals identify similar structural features or aspects of the subject invention. For purposes of explanation and illustration, and not limitation, a partial view of an exemplary embodiment of a multipoint combustion system in accordance with the invention is shown inFIG. 1and is designated generally by reference character100. Other embodiments of combustion systems in accordance with the invention, or aspects thereof, are provided inFIG. 2, as will be described. The systems and methods of the invention can be used to supply low temperature fuel to LCV combustors, for example liquid fuel for startup.

Referring now toFIG. 1, a multipoint combustion system100for a gas turbine engine includes a housing102defining a pressure vessel. A master injector124is mounted to the housing102for injecting fuel in an injection plume along a central axis A defined through the pressure vessel. A plurality of slave injectors112are each disposed outward of and substantially parallel to master injector124for injecting fuel and air in an ignition plume radially outward of fuel injected through master injector124. Master injector124and slave injectors112are configured and adapted so the injection plume of the master injector intersects with the ignition plumes of slave injectors112. Each of the slave injectors112is an injector for a low-calorific value fuel as described below. A primary manifold114is included within the pressure vessel for distributing fuel, e.g., low-calorific value gaseous fuel, to slave injectors112. An auxiliary manifold116is in fluid communication with the auxiliary nozzles113of slave injectors112for issuing an auxiliary flow of fuel, e.g., liquid fuel used for starting the ignition sequence of system100, from auxiliary nozzles113. Auxiliary manifold116provides for a separate fuel flow from the fuel flow of primary manifold114.

The pressure vessel of housing102includes a pressure dome108with a central aperture and a central inlet fitting118mounted to the central aperture of the pressure dome108. Auxiliary manifold116is external to pressure dome108. The primary and auxiliary manifolds114and116are advantageously thermally isolated from one another. The auxiliary nozzle113of each respective slave injector112is mounted to the pressure vessel, namely at pressure dome108, with floating seals120to accommodate thermal expansion differentials between the pressure vessel and auxiliary manifold116.

Auxiliary manifold116is advantageously flexible, e.g., for ease of installation and to accommodate thermal expansion differentials. For example, auxiliary manifold116can be a high temperature hose or other suitable conduit with flexibility. Auxiliary manifold116is configured to issue natural gas and/or liquid fuel to auxiliary nozzles113of slave injectors112, or any other suitable type of liquid or gaseous fuel. Auxiliary manifold116is operatively connected to an external valve122, which can be opened to permit purging of auxiliary manifold116and auxiliary nozzles113, for example with engine air, for complete shutdown of auxiliary manifold116and auxiliary nozzles113. So if, for example, a liquid hydrocarbon fuel is used in auxiliary manifold116and nozzles113for startup of system100, after startup the interior of auxiliary manifold116and auxiliary nozzles113can be purged to prevent stagnant liquid fuel from coking therein when system100is operating at full operational temperatures.

Referring now toFIG. 2, one of the slave injectors112is shown in more detail. Slave injectors112are configured for use in low-calorific value fuel combustion systems as described above. Each slave injector112includes a nozzle body126defining a fuel circuit128for injecting low-calorific value fuel. An auxiliary nozzle113is mounted to nozzle body126and defines a fuel circuit130for injecting an auxiliary fuel, for example natural gas or liquid fuel, such as for use in engine startup. Each auxiliary nozzle113is mounted to the respective nozzle body126with a floating seal132, which can be for example a grommet, to accommodate a differential in thermal expansion between auxiliary nozzle113and nozzle body126, e.g., when cold liquid fuel is flowing through auxiliary circuit130, but the overall system is heating up during startup. The auxiliary stage is more suitable than the primary stage for bringing an engine up to power due to the small passage size and relatively high back pressure of the auxiliary stage. The auxiliary stage can be turned down to pilot the LCV fuel operation, or could be flushed and shut down for long term LCV operation using valve122.

Fuel circuit128of nozzle body126is annular and nozzle body126defines an outer air circuit134outboard of fuel circuit128. Each auxiliary nozzle113advantageously includes a fuel outlet136configured and adapted to issue a spray of fuel that diverges away from a longitudinal axis defined by the auxiliary nozzle113.

Nozzle body126includes an inner wall138and an outer wall140outboard of and spaced apart from inner wall138. Fuel circuit128of nozzle body126passes through, e.g., between, inner and outer walls138and140. Outer wall140defines at least one aperture142configured for passage of fuel from primary manifold114into nozzle body126for selective injection of natural gas and LCV fuel gas in a proportional mix, for example. Auxiliary nozzle113is inboard of and spaced apart from inner wall138of nozzle body126.

While described above in the exemplary context of gas turbine engines, those skilled in the art will readily appreciate that the systems and methods described above can be used with any suitable LCV fuel application. Moreover, the systems and methods described above can be used in any suitable non-LCV application without departing from the spirit and scope of the invention.

The methods and systems of the present invention, as described above and shown in the drawings, provide for low calorific value fuel combustion systems with superior properties including improved engine start up and thermal management. While the apparatus and methods of the subject invention have been shown and described with reference to preferred embodiments, those skilled in the art will readily appreciate that changes and/or modifications may be made thereto without departing from the spirit and scope of the subject invention.