Patent Publication Number: US-2022213838-A1

Title: Air system switching system to allow aero-engines to operate in standby mode

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a divisional of U.S. patent application Ser. No. 16/366,293 filed Mar. 27, 2019, the entire content of which is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The disclosure relates to operation of a multi-engine aircraft and, more particularly, to operation of engine air systems for such a multi-engine aircraft. 
     BACKGROUND 
     Bleed air produced by a gas turbine engine is compressed air from the compressor stage that is used for engine functions (such as cooling of turbines and to help seal bearing cavities, for example) and is also used for aircraft functions (such as engine starting, cabin pressure, pneumatic systems, pressurizing liquid tanks, etc.). Engine bleed air can be derived from the high pressure or the low pressure compressor stage, depending on the air pressure requirements and the engine operating condition. Low pressure stage air is typically used during high power engine operation, and high pressure stage air may be used during descent and other low power engine operations. 
     Bleed air may be used within an engine for engine functions such as bearing cavity sealing and cooling of various engine components. Improvement is desirable to optimize operation of the efficiency of compressed air systems. 
     SUMMARY 
     There is accordingly provided a method of operating a multi-engine aircraft having two or more gas turbine engines, the method comprising: in flight, operating a first engine of the gas turbine engines in a powered mode to provide motive power to the aircraft; in flight, operating a second engine of the gas turbine engines in either a powered mode to provide motive power to the aircraft or in a standby mode to provide substantially no motive power to the aircraft; when operating the second engine in the powered mode, bleeding pressurized air from a first bleed location of a compressor section of the second engine; and when operating the second engine in the standby mode, bleeding pressurized air from a second bleed location of the compressor section of the second engine and supplying the pressurized air to a bleed air system of the second engine, the second bleed location of the compressor section being downstream of the first bleed location relative to main gas flow through the compressor section of the second engine. 
     The method defined above and herein may also further comprise one or more of the following features, in any combination, and in whole or in part. 
     In flight, switching the second engine between the powered mode and the standby mode. 
     Operating a switching valve of an air switching system of the second engine, the switching valve operable to fluidly interconnect an inlet of the bleed air system with the first bleed location or the second bleed location. 
     Using an input selector switch of the bleed air system to operate the bleed valve. 
     Reducing fuel consumption of the multi-engine aircraft by switching, in flight, the second engine from the powered mode to the standby mode. 
     Supplying the pressurized air bled from the first bleed location to the bleed system of the second engine during the powered mode. 
     Maintaining the pressurized air from the bleed system within the second engine during the standby mode and the powered mode. 
     Using the pressurized air from the bleed system of the second engine to pressurize seals and/or cool one or more components of the second engine. 
     Maintaining a power output differential between the first engine operating in the powered mode and the second engine operating in the standby mode, defined as a percentage of a second engine power to a first engine power, of between 20% and 95%. 
     When operating the second engine in the standby mode, maintaining a rotational speed of the second engine in the range of 40 to 70% of a rotational speed of the first engine operating in the powered mode. 
     Switching the second engine from the powered mode to the standby mode by: opening an actuated valve within a high pressure inlet of the second engine to automatically close a normally open check valve within a low pressure inlet of the second engine. 
     Sensing the second engine power output and the first engine power output; and communicating an open signal to the actuated valve when the motive power output differential is below a threshold value. 
     There is also provided, in accordance with another aspect, a multi-engine aircraft comprising: a first engine drivingly engaged to a common rotatable load to provide motive power to the multi-engine aircraft; and a second engine drivingly engaged to the common rotatable load and having a control system, the control system operating the second engine in either a powered mode or a standby mode, the second engine providing motive power to the multi-engine aircraft in the powered mode by driving the common load, and the second engine providing substantially no motive power to the multi-engine aircraft in the standby mode; the second engine having an air switching system in communication with and controlled by the control system; the air switching system of the second engine including a switching valve in communication with the control system, the air switching valve having: a low pressure inlet in communication with a first bleed location in a compressor of the second engine; a high pressure inlet in communication with a second bleed location in the compressor of the second engine, the second bleed location being downstream of the first bleed location relative to main gas flow through the compressor of the second engine; and a switch outlet fluidly connected to either the first bleed location or the second bleed location, the switch outlet fluidly connected to one or more components of the second engine in need of compressed air; wherein the switching valve is displaceable between at least a first position and a second position, the first position interconnecting the lower pressure inlet and the switch outlet, and the second position interconnecting the high pressure inlet and the switch outlet. 
     There is also provided, in accordance with another aspect, a multi-engine aircraft comprising: a first gas turbine engine for providing a first engine power output; and a second engine for providing a second engine power output, the second engine having a bleed air system and a compressed air switching system including: an switching valve having: a low pressure inlet in communication with a first bleed location in a compressor of the second engine; a high pressure inlet in communication with a second bleed location in the compressor of the second engine, the second bleed location being downstream of the first bleed location relative to main gas flow through the compressor of the second engine; and a switch outlet in communication with a bleed air system of the second engine; and wherein the switching valve is displaceable between at least first and second positions, the first position interconnecting the lower pressure inlet and the switch outlet, and the second position interconnecting the high pressure inlet and the switch outlet. 
     The multi-engine aircraft defined above and herein may also further comprise one or more of the following features, in any combination, and in whole or in part. 
     Tithe compressed air switching system is actuable between a powered mode and a standby mode, the switching valve in the first position in the powered mode and the switching valve in the second position in the standby mode. 
     A control system for controlling the second engine and/or the compressed air switching system thereof, the control system actuating the switching valve to switch between the first position and the second position. 
     The switching valve comprises: a compressed air manifold having: a check valve within the low pressure inlet being normally open when a pressure of air bled from the first bleed location exceeds a manifold air pressure; and an actuated valve within the high pressure inlet for switching between the powered mode and the standby mode. 
     The actuated valve is a solenoid valve in communication with the control system, the control system including a second engine power output sensor and a first engine power output sensor. 
     The air bleed system of the second engine communicates with an engine operation system including one of: an air pressure operated oil retention seal; an air cooled engine component; and a turbine. 
     The low pressure inlet comprises a low pressure plenum. 
     The first engine includes a bleed air system feeding an aircraft operation system including one of: an engine starting system; an anti-icing system; a water system pressurization system; a hydraulic system reservoir pressurization system; an aircraft cabin pressurization system; a cabin air conditioning system; and a wing boundary layer separation enhancement system. 
     Further details of these and other aspects of the subject matter of this application will be apparent from the detailed description included below and the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a schematic view of a multi-engine aircraft; 
         FIG. 1B  is a schematic representation of an exemplary multi-engine system for the aircraft of  FIG. 1A , showing axial cross-sectional views of two gas turbine engines; 
         FIG. 2  is a schematic axial cross-sectional view of one of the gas turbine engines of  FIG. 1B , for the multi-engine aircraft of  FIG. 1A ; 
         FIG. 3  is the schematic axial cross-sectional view of  FIG. 2 , showing the air switching system of the present disclosure; 
         FIG. 4  is an enlarged axial cross-section view of the compressor section of the gas turbine engine of  FIG. 2 , showing the air system switching system of  FIG. 3  operating in a first mode; 
         FIG. 5  is an enlarged axial cross-section view of the compressor section of the gas turbine engine of  FIG. 2 , showing the air system switching system of  FIG. 3  operating in a second mode. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1A  depicts an exemplary multi-engine aircraft  1 , which in this case is a helicopter. The aircraft  1  may however also be a fixed-wing aircraft. The aircraft  1  includes at least two gas turbine engines  10 , labeled in  FIG. 1A  as “ENGINE 1” and “ENGINE 2”. These two engines may be interconnected, in the case of the depicted helicopter application, by a common gearbox to form a multi-engine system  50  as shown in  FIG. 1B . 
       FIG. 1B  illustrates a schematic representation of an exemplary multi-engine system  50  that may be used as a power plant for the aircraft  1 . The multi-engine system  50  comprises two or more gas turbine engines  10 . The multi-engine system  50  may manage the operation of the engines  10 , as will be described in further detail below. The multi-engine system  50  may be used as a dual engine powerplant for an aircraft, such as a helicopter. In addition to airborne applications, the multi-engine system  50  may be used in marine and/or industrial applications. 
     More particularly, the multi-engine system  50  of this embodiment includes first and second turboshaft engines  10  each having a respective transmission  38  which are interconnected by a common output gearbox  40  to drive a common load  44 . In one embodiment, the common load  44  may comprise a rotary wing of a rotary-wing aircraft. For example, the common load  44  may be a main rotor of the helicopter  1 . Depending on the type of the common load  44  and on the operating speed thereof, each of turboshaft engines  10  may be drivingly coupled to the common load  44  via the output gearbox  40 , which may be of the speed-reduction type. 
     For example, the gear box  40  may have a plurality of transmission shafts  42  to receive mechanical energy from respective output shafts  11  of respective turboshaft engines  10 . The gear box  40  may be configured to direct at least some of the combined mechanical energy from the plurality of the turboshaft engines  10  toward a common output shaft  42  for driving the common load  44  at a suitable operating (e.g., rotational) speed. It is understood that the multi-engine system  50  may also be configured, for example, to drive accessories and/or other elements of an associated aircraft. As will be described, the gear box  40  may be configured to permit the common load  44  to be driven by either of the turboshaft engines  100  or, by a combination of both engines  10  together. 
     Referring now to  FIG. 2 , the gas turbine engine  10  is of a type provided, in one embodiment, for use in subsonic flight, generally comprising in serial flow communication a compressor section  9  for pressurizing the air, a combustor  8  in which the compressed air is mixed with fuel and ignited for generating an annular stream of hot combustion gases, and a turbine section  5  for extracting energy from the combustion gases. 
     The engine  10  depicted in  FIG. 2  is a turboshaft gas turbine engine, and therefore includes a reduction gearbox and transmission  38  with an output shaft  42  which is configured to provide power output from the engine  10  to the common aircraft gearbox  40  of the multi-engine system  50  of  FIG. 1B . However, it is to be understood that the present disclosure may also be applicable to other types of gas turbine engines, including turboprops and turbofans for example. 
     Referring still to  FIG. 2 , the gas turbine engine  10  includes an air inlet  2  via which air enters the engine  10  before being directed into the compressor section  9  of the engine. In the depicted embodiment, the compressor section  9  includes a low-pressure axial compressor  12  and a high-pressure centrifugal compressor  13 . Compressed air exits the high pressure compressor  13  through a diffuser  6  and is contained within a plenum  7  that surrounds the combustor  8 . Fuel is supplied to the combustor  8  through fuel nozzles fed by a fuel system, wherein the injected fuel from the fuel nozzles is mixed with the compressed air within the combustor  8  thereby causing the fuel-air mixture to be ignited within the combustion chamber. A portion of the compressed air within the plenum  7  is therefore admitted into the combustor  8  through orifices in the side walls to create a cooling air curtain along the combustor walls. A portion of the compressed air is also is used as bleed air for pneumatic systems within and/or external to the engine. The annular stream of hot combustion gases exiting the combustor  8  is directed to a downstream turbine section  5  for extracting energy from the combustion gases before exiting the engine as exhaust. The turbine section  5  may include one or more turbine rotors. In the embodiment of  FIG. 2 , a high pressure turbine  4  drives a high pressure engine shaft to which both the low and high pressure compressors  12  and  13  are connected for driving same, and a low pressure turbine  3  drives a low pressure turbine shaft which is coaxial with the low pressure engine shaft and drives the power output shaft  11 , and the gearbox  38 , of the engine  10 . 
     As will now be described in further detail,  FIGS. 3 to 5  show axial sectional views of the compressor section  9  of the gas turbine engine  10 , in particular the low pressure axial compressor(s)  12  and high pressure centrifugal compressor  13 . While the exemplary embodiment includes an axial compressor and a centrifugal compressor, it is to be understood that other configurations (e.g. two or more axial compressors, two or more centrifugal compressors, a different combination of the two, etc.) is also possible. 
     The present description relates generally to operating a multi-engine aircraft  1 , where a first engine of the gas turbine engines  10  is capable of providing motive power in flight to the aircraft  1  when operating in a “powered mode”, and a second engine of the gas turbine engines  10  can be switched between a powered mode, whereby the second engine also provides motive power to the aircraft, and a lower-power “standby mode”, whereby substantially no (or very little) motive power is provide to the aircraft. The second engine may therefore be switched into, and maintained in, this very low-power standby mode during flight. The low-power standby mode of the second engine includes, but is not limited to a significantly reduced power mode or a so-called “sub-idle” mode in this example. By operating the second engine in this standby mode during flight, fuel consumption of the second engine, and therefore over the overall powerplant, is reduced. The second engine however remains able to return to normal operational power (e.g. full power) if additional power needed by the aircraft. 
     The first engine as described herein may be referred to as a “main” or “primary” engine, and the second engine may be referred to herein as a “reserve” engine. However, it is to be understood that both are capable of operating a full power if desired/necessary. 
     As seen in  FIGS. 3 to 5 , at least the second engine  10  of the aircraft  1  has a compressed air switching system  30  that comprises and is in communication with a switching valve  14 . The switching valve  14  may also be referred to herein as an “input selector switch”  14 . The compressed air switching system  30  may be controlled by the engine control system, such as a full-authority digital engine control (FADEC) system for example. In the example illustrated the input selector switch  14  has three main components, namely, a manifold  15 , a check valve  16 , and a solenoid valve  17 . The manifold  15  has a low pressure inlet  18  including the check valve  16  in communication with a low pressure air plenum  19 . The manifold  15  has a high pressure inlet  20  including the solenoid valve  17  in communication with a high pressure air conduit  21 , derived from the output of the high pressure centrifugal compressor  13 . The manifold  15  conveys low or high pressure air via a manifold outlet  22  in communication with the bleed air system of the engine and aircraft. 
     In the example shown, the combination of the manifold  15 , check valve  16 , and solenoid valve  17  form the switching valve  14 . Other configurations of switching valve  14  will be apparent to those skilled in the art including a poppet valve, a sliding spool valve or a ball valve. 
       FIG. 4  shows the switching valve  14 , and thus the compressed air switching system  30 , in the powered (or “motive”) mode, where the solenoid valve  17  is closed and the check valve  16  is open, thereby connecting the low pressure inlet  18  and the switch outlet  22 . In the powered/powered mode of  FIG. 4 , the low pressure air from the plenum  19  is provided through the manifold  15  into the switch outlet  22 . 
       FIG. 5  shows the switching valve  14 , and thus the compressed air switching system  30 , in the standby mode, where the solenoid valve  17  is open and the check valve  16  is closed, thereby connecting the high pressure inlet  20  and the switch outlet  22 . In the standby mode of  FIG. 5 , the high pressure air from the high pressure air conduit  21  is provided through the manifold  15  into the switch outlet  22 . 
     As shown in  FIG. 4  when the switching valve  14  is in the powered mode, low pressure compressed air is provided to the bleed air system (i.e. the secondary air system) for an engine operation system via the switch outlet  22 . A compressed air passage  23  from the switch outlet  22  leads to an engine shaft  24  wherein the compressed air passage  23  passes through a stationary strut  25  within the gas path. 
     However when the engine speed is lowered to a level at or below idle, such as during “sub-idle” operation, the pressure of compressed air available from the low pressure plenum  19  may be insufficient for engine operations such as engine cooling and maintaining oil seals for the bearing cavities within this engine (i.e. the second engine). “Sub-idle” operation in this sense is understood to mean that the second engine is operating at a bare minimum speed to remain in operation, but engine speed and/or power output may be even lower than in a traditional “idle” operating state. In such sub-idle operations, the switching valve  14  is moved to the standby mode shown in  FIG. 5  (i.e. solenoid valve  17  is open and the check valve  16  is closed). In the standby mode of  FIG. 5 , the high pressure air from the high pressure air conduit  21  is provided through the manifold  15  to the engine operating system to cool the turbines  11 , and maintain oil seals with compressed air of sufficiently high pressure. 
     When the input selector switch  14  is in the powered mode of  FIG. 4 , the engine is operating in a normal flight condition at high power levels to provide a relatively high degree of motive power to the aircraft. During the powered mode, a relatively high quantity of compressed bleed air is provided from the low pressure air plenum  19 . The bleed air in the powered mode is provided to the aircraft operation system at sufficient pressure and quantity for aircraft functions such as cabin pressurization, engine starting, pneumatic systems etc. as well as for the engine operating system to maintain engine functions such as cooling the turbines  11  and maintaining oil seals. 
     When the switching valve is in the standby mode of  FIG. 5 , a relatively low degree of motive power, or substantially no motive power, is provided to the aircraft and a relatively low quantity of aircraft bleed air is provided for the aircraft operation requirements. 
     During the standby mode, the available compressed air is diverted to essential engine functions and is not consumed by aircraft operations. In the standby mode, the second engine power output is less than the first engine power output. In one embodiment, the first engine provides at least 2 times more power output than the second engine. The second engine power output may also be such that a power differential, i.e. a difference between the first engine power and the second engine power, as a percentage of the first engine power, is at least 20%. This differential power between the two engines may however be much greater, for example 40%, 60%, 90%, 95% or greater. Accordingly, in certain embodiments, the power output differential is between 20-95%, or alternately between 40-95%, or alternately still greater than 90%. 
     The second engine is controlled during idle operation, when the switching valve is in the standby mode, to generate a motive power output differential, defined as a percentage of the second engine power output to the first engine power output, of at least 20%, and may be greater than 90%. It should however be noted that the gas generator speed of the second engine, sometimes referred to as Ng, may however not correspond to the reduced power output of the second engine. Because the power output of the engine can be controlled by other means, such as by controlling variable guide vanes, the gas generator speed of the second engine may be much closer to that of the first engine during operation, even when the above-noted power output differentials remain. 
     To operate the solenoid valve  17 , the solenoid valve  17  is in electric communication with the engine control system that includes sensing the second engine power output and the first engine power output. A comparison is made and a motive power output differential is determined. When the motive power output differential is below a threshold value the control system communicates an open signal to the solenoid actuated valve  17 . 
     When the motive power output differential is reduced below the threshold value, the solenoid valve  17  is actuated to raise the manifold air pressure in the manifold  15  above the air pressure of the low pressure air source  19  which automatically closes the (normally open) one way check valve  16 . As a result the switching valve  14  is switched between the powered mode and the standby mode depending on the signal received from the control system and power output sensors. 
     The control system can control the second engine power output by controlling a plurality of variable guide vanes. While controlling the second engine operation during the standby mode, the rotational speed of the second engine can be maintained in the range of 40-70% of the rotational speed of the first engine, while controlling the variable guide vanes to increase or decrease the second engine power output. 
     Therefore in two possible modes, low motive power (standby mode) and high motive power (powered mode), the method of operating the multi-engine aircraft during flight provides adequate compressed air to the second engine for the engine operation system uses, for example to actuate an air pressure operated oil retention seal, to cool an air cooled engine component, or to cool a turbine. Depending on the most efficient available source of compressed air, the switching valve  14  receives air from the low pressure air plenum  19  or the high pressure air conduit  21 . 
     Accordingly, the present description provides a method of operating an aircraft propulsion gas turbine engine in a multi-engine aircraft, by operating at least one second engine in a powered mode to provide motive power in flight to the aircraft and supplying compressor pressure bleed air to the engine and aircraft, and while in flight operating the second engine in an standby mode to provide little or no motive power to the aircraft, switching to higher pressure bleed air source to provide second engine bleed air while substantially ceasing to supply bleed air to the aircraft. 
     In particular embodiments, the present disclosure includes a method of operating a gas turbine engine including supplying “P2.X” air to pressurize seals and, when engine speed drops below a threshold, switching to higher pressure air source. An air switching system for a secondary air system of a gas turbine engine is therefore provided, which may include a solenoid operated shut off valve, which actuates to switch between first and second bleed air sources, and a check valve. The solenoid valve can be opened and closed, to respectively permit or block higher pressure air (e.g. “P3” air) from being directed to the compressor cavities for cooling and/or sealing purposes. When the engine is operating normally in a powered mode, the solenoid valve is closed and the check valve is open, thereby permitting lower pressure air (e.g. “P2.8” air) to be fed to the compressor cavities for sealing and/or cooling purposes. When the engine is operating in a standby mode with a lower power/speed range (e.g. a “sub-idle” operation as described herein), the solenoid valve is open and the check valve is closed, thereby forcing the higher pressure P3 air to be fed to the compressor cavities for sealing and/or cooling purposes. Accordingly, higher pressure P3 air can be used during sub-idle engine conditions in order to ensure proper engine operation, and switching between the two air system configurations is possible when desired due to the solenoid driven switching valve. Thus, the lowest pressure air source can be selected by the present air switching system for various different engine operating ranges/conditions, to ensure optimal engine operation. 
     The above description is meant to be exemplary only, and one skilled in the relevant arts will recognize that changes may be made to the embodiments described without departing from the scope of the invention disclosed. The present disclosure may be embodied in other specific forms without departing from the subject matter of the claims. The present disclosure is intended to cover and embrace all suitable changes in technology. 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. Also, the scope of the claims should not be limited by the embodiments set forth in the examples, but should be given the broadest interpretation consistent with the description as a whole.