Patent Application
20150247641
The application relates generally to gas turbine engines and, more particularly, to combustion systems for gas turbine engines.
Combustion systems of gas turbine engines provide power to the aircraft for various conditions during flight and on ground. Some conditions, such as idle or taxiing, require lower power from the combustion system, while other conditions, such as taking-off and altitude cruising require higher power from the combustion system. Fuel injectors, depending if they inject more or less fuel for high or low power, may produce unwanted by-products of combustion.
In one aspect, there is provided a gas turbine engine comprising: a combustion system comprising: a secondary annular combustor and a primary annular combustor in fluid communication with the secondary combustor and converging thereto; a secondary fuel injector associated with the secondary annular combustor; a primary fuel injector associated with the primary annular combustor, the primary fuel injector delivering a maximum fuel amount to the primary annular combustor; a fuel conduit network fluidly connected to the secondary fuel injector and the primary fuel injector; and an electronic control unit (ECU) controlling fuel delivery to the secondary and primary fuel injectors via the fuel conduit network based on at least one input, the ECU allowing fuel to be delivered to the secondary fuel injector in assistance to the primary fuel injector only when the at least one input requires a fuel amount higher than a maximum fuel amount delivered by the primary fuel injector.
In another aspect, there is provided a method of actuating a combustion system for a gas turbine engine, the method comprising, in sequence: delivering fuel only to a primary fuel injector of a primary combustor of a combustion chamber including communicating secondary and primary combustors in response to a first input requiring a fuel amount lower than a maximum fuel amount delivered by the primary fuel injector; and delivering fuel to a secondary fuel injector of the secondary combustor in assistance to delivering fuel to the primary fuel injector of the primary combustor in response to a second input requiring a fuel amount higher than a maximum fuel amount delivered by the primary fuel injector.
Reference is now made to the accompanying figures in which:
Turning now to
The combustion chamber 20 comprises a main lobe for the secondary combustor 22 and a smaller lobe for the primary combustor 21. The combustion chamber 20 may be unitary or made of several parts joined to each other. The secondary 22 and primary combustors 21 are annular and converge to each other in this example. The secondary combustor 22 in this example is arranged generally parallel to an axis of the engine, while the primary combustor 21 is disposed radially outward of the secondary combustor 22. The primary combustor 21 in this example is disposed on along a primary combustor axis A1 which intersects with a secondary combustor axis A2 parallel to the engine axis 11 at an acute angle a of 25°. It is contemplated that the angle α could be comprised between 20° and 30° in another example.
The primary and secondary combustors 21, 22 are arranged in series. Although forming distinct combustion zones or chambers, the primary combustor 21 and the secondary combustor 22 are in fluid communication with each other. Exhaust gases from the primary combustor 21 reach the secondary combustor 22 before being evacuated via a single outlet 24 of the secondary combustor 22. A size of the primary combustor 21 may be determined to enable full combustion before the exhaust gases reach the secondary combustor 22.
The combustion chamber 20 includes a plurality of air inlets. A primary series of air inlets 25 is disposed on the primary combustor 21 and a secondary series of air inlets 26 is disposed on the secondary combustor 22. The air inlets 25, 26 allow external air to feed the combustion. Additional air is carried through porous walls of the combustion chamber 20.
An assembly of primary fuel injectors 28 is associated with the primary combustor 21, and a secondary fuel injector assembly 29, distinct from the primary fuel injector 28, is associated with the secondary combustor 22. The primary and secondary fuel injectors 28, 29 in use atomize fuel from a source delivered to them by associated primary and secondary fuel conduits 34, 35. The primary fuel injector 28 may be a series of discrete in-line or other suitable configuration fuel nozzles, while the secondary fuel injector assembly 29 may be an annular ring injector comprised of a much higher number of, typically smaller, fuel injection points such that effectively a continuous annular ring of fuel is injected into the secondary combustor, or other suitable configuration fuel nozzles. In one embodiment, the primary fuel injector 28 includes 6 to 9 injectors and the secondary fuel injector 29 includes between 60 and 70 injectors. It is contemplated that the primary fuel injectors 28 may also be ring injector, or may employ another suitable configuration. The secondary fuel injector 29, in one example, may be substantially as described in co-pending applications Ser. Nos. 13/795,058, 13/795,082, 13/795,089 and 13/795,100, the entirety of each of which is hereby incorporated by reference.
Referring to
Referring back to
Having two combustors 21, 22 associated with two distinct fuel injectors 28, 29 may allow operating each combustor 21, 22 at an overall enhanced combustion efficiency which may allow reducing unwanted gas by-products. Referring to
To achieve enhanced combustion efficiency overall, a contribution of each of the combustors 21, 22 to a total power delivered by the combustion chamber 20 may be optimized. For example, as shown in the example of
Turning now to
The method starts at step 42 with the actuation of only the primary combustor 21. Actuation may be based on a first input power request, and may correspond to a command from the cockpit or control system commanding a start to the combustion system 16 or to low power setting, such as ground idle or taxiing in the example described above. Because the input requires a fuel amount lower than a threshold between a lower and a higher power regimes (as discussed in the example above), step 42 is performed by the primary combustor 21 alone. The primary combustor 21 would be actuated alone as long as a the power required by the input is lower than a defined threshold defined between the low and high power modes. The primary combustor 21 is thus actuated, for example by the ECU 23 instructing the divider valve 33 to direct fuel to the primary fuel injector assembly 28 only. Step 42 therefore corresponds to lower power engine regimes, where only the primary combustor 21 is actuated in this example. In one embodiment, the primary combustor 21 is configured to provide an enhanced combustion at the lower power engine regimes, and as such may emit reduced hydrocarbons or other unwanted by-products compared to traditional (single regime) combustors.
From step 42, the method goes to step 44, where in response to a second input power request above a threshold between low and high power regimes, such as a command from the cockpit or control system turning commanding high power operation such as takeoff power, the primary combustor 21 and secondary combustor 22 are actuated. The threshold corresponds to a predetermined fuel amount above which the secondary combustor 22 is to be actuated. In one embodiment, the threshold corresponds to a required fuel amount is higher than the maximum fuel amount which can be delivered by the primary fuel injector assembly 28. Based on the power requested, the ECU 23 may position the divider valve 33 to direct fuel to the secondary fuel injector assembly 29 in addition to the primary fuel injector assembly 28. The amount of fuel delivered to the fuel injectors 28, 29 may be varied by the divider valve 33 controlled by the ECU 23, and may depend on an amount of power required. For example, as higher powers are required, a higher fuel amount may be delivered to the secondary combustor 22. According to the example described above, a majority of the overall fuel supplied to the combustor 20 at step 44 is provided to the secondary combustor 22, the secondary combustor 22 may be configured by design to be optimized for more efficient combustion the higher power engine regimes, which may result in reduced nitride oxides or other by-products produced compared to traditional (single regime) combustors
The dual stage combustion chamber and method described herein allows selectively using different combustion chambers in cooperation to provide complementary power in a selected engine regime. In addition, the combustors may be optimized to operate more efficiently at the selected regimes for which they are configured to operate, and may thus provide an overall enhanced efficiency, and/or reducing unwanted by-products. In addition, having multiple combustion chambers operated in cooperation allows having two flames which may act as a back-up form each other in case one flames out. Because one (in this case, the secondary) combustor may be configured for higher power engine regimes, it may be configured as a lean combustor with a low air ratio.
The above description is meant to be exemplary only, and one skilled in the art will recognize that changes may be made to the embodiments described without departing from the scope of the invention disclosed. For example, the primary combustion chamber can be any suitable configuration. Although an annular primary chamber is described above, primary combustion may instead occur in a plurality of can combustors each with its fuel nozzle and igniter and in communication with the secondary chamber otherwise as described. The combustion chamber could include more than two combustion stages if desired, and any suitable number of combustion stages may be provided. The threshold between low and high power may be determined in any suitable fashion, and the split between fuel supply to combustion stages may be any suitable. Any suitable method of controlling fuel flow to the nozzle systems may be employed. Still other modifications which fall within the scope of the present invention will be apparent to those skilled in the art, in light of a review of this disclosure, and such modifications are intended to fall within the appended claims.
