Patent Application
20150128600
This invention is directed generally to turbine engines, and more particularly to fuel system for turbine engines.
Typically, gas turbine engines include a plurality of injectors for injecting fuel into a combustor to mix with air upstream of a flame zone. The fuel injectors of conventional turbine engines may be arranged in one of at least three different schemes. Fuel injectors may be positioned in a lean premix flame system in which fuel is injected in the air stream far enough upstream of the location at which the fuel/air mixture is ignited that the air and fuel are completely mixed upon burning in the flame zone. Fuel injectors may also be configured in a diffusion flame system such that fuel and air are mixed and burned simultaneously. In yet another configuration, often referred to as a partially premixed system, fuel injectors may inject fuel upstream of the flame zone a sufficient distance that some of the air is mixed with the fuel. Partially premixed systems are combinations of a lean premix flame system and a diffusion flame system.
During operation, fuel is injected into the combustion chamber through the injectors into three or four stages, such as a pilot nozzle, an A-stage, a B-stage, and a C-stage (for configurations having tophat injection or pilot premix features). The pilot nozzle may also be formed from premix and diffusion stages. The pilot nozzle provides fuel that is burned to provide a mini-diffusion flame injector and also provides stability for the premixed A-, B-, and C-stages. Often turbine engines are run using high levels of airflow, thereby resulting in lean fuel mixtures with a flame temperature low enough to prevent the formation of a significant amount of NOx. However, because lean flames have a low flame temperature, lean flames are prone to high CO production. And because excess CO production is harmful, a need exists to limit CO emissions.
Turbine engines often operate at higher fuel to air ratios at partial loads rather than at full load. However, turbine engines are designed for full loads. Thus, nozzles designed to run at full load run excessively lean at partial loads. Inlet guide vanes (IGVs) can be used to reduce air flow through the engine at partial loads, thereby increasing the fuel to air ratio and enabling the engine to operate more efficiently through a larger range of loads. However, IGVs may only be used to restrict air flow a limited amount.
Fuel staging is used to control fuel injection at loads below which IGVs may be used effectively. Fuel staging is a process of emitting fuel from less than all of the injectors in a fuel system. By reducing the number of injectors through which fuel is ejected, the amount of fuel passed through the injectors during operation of the turbine engine at partial loads is increased, and thus, burnout is improved. However, using fuel staging requires duplicative auxiliary piping, orifice fuel flow meters, pressure sensors, temperature sensors, and sensors for determining pressure differences. Thus, a need exists for creating efficiencies in a fuel system while maintaining acceptable engine dynamics and NOx emissions.
A fuel system for a turbine engine for improving the efficiency in a fuel system where a major stage and secondary stage can be combined and held to a relatively constant fuel ratio while maintaining acceptable engine dynamics and NOx emissions is disclosed. The fuel system may be formed from a first premix injector assembly stage positioned upstream from a combustor basket, whereby the first premix injector assembly stage is a secondary injector system. The fuel system may be formed from a first primary injector assembly stage, which is a main injector system, positioned downstream from the first premix injector assembly. The first premix injector assembly stage and the first primary injector assembly stage may be coupled together such that the fuel system is capable of emitting fuel into a combustor of the turbine engine via the first premix injector assembly stage and the primary injector assembly stage simultaneously.
The fuel system for a turbine engine may include a first premix injector assembly stage comprising at least one injector positioned upstream from a combustor basket, whereby the first premix injector assembly stage is a secondary injector system. The fuel system may also include a first primary injector assembly stage comprising at least one injector positioned downstream from the first premix injector assembly, whereby the first primary injector assembly is a main injector system. The first premix injector assembly stage and the first primary injector assembly stage may be positioned such that a distance between the first premix injector assembly stage and a flame in the combustor is greater than a distance between the first primary injector assembly stage and the flame in the combustor. The first premix injector assembly stage and the first primary injector assembly stage may be coupled together such that the fuel system is capable of emitting fuel into a combustor of the turbine engine via the first premix injector assembly stage and the primary injector assembly stage simultaneously.
The first premix injector assembly stage and the first primary injector assembly stage may be coupled together via a fuel manifold such that fuel supplied to the fuel manifold is distributed to the first premix injector assembly stage and the first primary injector assembly stage. A tuning orifice plate may be positioned inline with the first premix injector assembly stage to regulate a fuel ratio of the combined first premix injector assembly stage and the first primary injector assembly stage. In at least one embodiment, the first premix injector assembly stage may be positioned upstream from a preswirler positioned within the fuel system. The first primary injector assembly stage is positioned at the preswirler or may be positioned downstream from the preswirler.
The fuel system may be configured such that the first premix injector assembly stage may inject between about 10 percent and about 20 percent of the total fuel injected into the combustor. The first primary injector assembly stage may be configured to inject between about 25 percent and about 45 percent of the total fuel injected into the combustor. The fuel system may also include a pilot stage formed from at least one injector positioned downstream from the first premix injector assembly stage. In at least one embodiment, the pilot stage may be configured to inject less than 10 percent of the total fuel injected into the combustor.
In another embodiment, the fuel system may also include a second primary injector assembly stage comprising at least one injector positioned downstream from the first premix injector assembly, whereby the second primary injector assembly is a main injector system. The first primary injector assembly stage may emit at least 40 percent of a total fuel injected by the main injectors of the fuel system. In another embodiment, the first primary injector assembly stage may emit at least 50 percent of a total fuel injected by the main injectors of the fuel system.
An advantage of the fuel system is that the fuel system can combine primary and secondary fuel injector assembly stages while maintaining acceptable engine dynamics and NOx emissions, thereby eliminating the need for duplicative auxiliary piping, orifice fuel flow meter, pressure sensor, temperature sensor, and sensors for determining pressure differences.
These and other embodiments are described in more detail below.
The accompanying drawings, which are incorporated in and form a part of the specification, illustrate embodiments of the presently disclosed invention and, together with the description, disclose the principles of the invention.
As shown in
The fuel system 10 for a turbine engine may include a first premix injector assembly stage 18 formed from one or more injectors 26 positioned upstream from the combustor basket 20, as shown in
The fuel system 10 may also include a first primary injector assembly stage 22 formed from one or more injectors 28 positioned downstream from the first premix injector assembly, whereby the first primary injector assembly is a main injector system, as shown in
The first premix injector assembly stage 18 and the first primary injector assembly stage 22 may be coupled together via a fuel manifold 32, as shown in
The fuel system 10 may also include a pilot stage 38 formed from one or more injectors 40 positioned downstream from the first premix injector assembly stage 18. In at least one embodiment, the pilot stage 38 may be configured to inject less than 10 percent of the total fuel injected into the combustor 24.
In another embodiment, the fuel system 10 may also include a second primary injector assembly stage 42 formed from one or more injectors 44 positioned downstream from the first premix injector assembly stage 18, whereby the second primary injector assembly is a main injector system. The first primary injector assembly stage 22 may emit at least 40 percent of a total fuel injected by the main injectors of the fuel system 10. In another embodiment, the first primary injector assembly stage 22 may emit at least 50 percent of a total fuel injected by the main injectors of the fuel system 10.
The fuel system 10 is that the fuel system 10 can combine primary and secondary fuel injector assembly stages 14, 16, such as the first premix injector assembly stage 18 and the first primary injector assembly stage 22 while maintaining acceptable engine dynamics and NOx emissions, thereby eliminating the need for duplicative auxiliary piping, orifice fuel flow meter, pressure sensor, temperature sensor, and sensors for determining pressure differences.
During operation, the combined primary and secondary fuel injector assembly stages 14, 16, such as the first premix injector assembly stage 18 and the first primary injector assembly stage 22, may be activated at the same time and operated at the same fuel ratio through the engine loads, such as between 40 percent load and 100 percent load, as shown in
The foregoing is provided for purposes of illustrating, explaining, and describing embodiments of this invention. Modifications and adaptations to these embodiments will be apparent to those skilled in the art and may be made without departing from the scope or spirit of this invention.
