Patent Description:
Aircraft engines, for instance turbofan-type gas turbine engines, may be provided with high bypass ratios for increased propulsive efficiency and reduced fuel consumption. However, when an aircraft is provided with an engine with a high bypass ratio, there may be a measurable difference between the thrust provided at take-off and the thrust provided while climbing and at higher altitudes. For instance, the flow of gases through the exhaust nozzle may be choked (i.e. flowing at the speed of sound), preventing further thrust from being provided. If the aerodynamic or mechanical limit of the fan has been reached, for instance while the aircraft is climbing or has reached a high altitude, it cannot rotate any faster to provide a desired increase in thrust. <CIT>, <CIT>, <CIT> and <CIT> disclose arrangements of the prior art.

In one aspect of the invention, there is provided a method for operating an engine according to claim <NUM>.

In another aspect of the invention, there is provided a system for operating an engine according to claim <NUM>.

In a further aspect of the invention, there is provided an engine system according to claim <NUM>.

The following optional features may be applied to any of the above aspects.

The at least one condition for heat application-based thrust may comprise at least one of an aircraft altitude, a Mach number, a rotational speed of the engine, and a flight phase. Applying the heat source (e.g., applying heat) may comprise applying the heat source to at least one conductive surface in the engine and heating the bypass air through convection heat-transfer from the at least one conductive surface to the bypass air. The heat source may be an induction heater and applying the heat source to the at least one conductive surface may comprise inductively heating the at least one conductive surface. Applying the heat source (e.g., applying heat) to the at least one conductive surface of the engine may comprise applying the heat source to at least one existing engine surface (e.g., a common, conventional or structural surface of the engine). Applying the heat source to at least one existing engine surface may comprise applying the heat source to at least one of a radially outer surface of a mixer nozzle, a radially outer surface of the engine core, a radially inner surface of an engine casing surrounding the engine core and an engine bypass strut. Applying the heat source to the at least one conductive surface of the engine may comprise applying the heat source to at least one engine surface (e.g., an additional, non-structural or dedicated heating surface) dedicated to heating the bypass air. Applying the heat source may comprise powering the heat source with at least one of a battery, a hydrogen fuel cell, and an auxiliary power unit. Powering the heat source may comprise drawing power from an existing power source in the engine (e.g., a common power source for powering engine components, an aircraft or aircraft components).

The present disclosure is directed to methods and systems for operating an engine. <FIG> illustrates an example engine <NUM> of a type provided for use by an aircraft in subsonic flight. The engine <NUM> of <FIG> is a turbofan engine that generally comprises, in serial flow communication, a fan <NUM> through which ambient air is propelled toward an inlet <NUM>, a compressor section <NUM> for pressurizing the air, a combustor <NUM> in which the compressed air is mixed with fuel and ignited for generating an annular stream of hot combustion gases, and a turbine section <NUM> for extracting energy from the combustion gases, which are mixed by a mixer <NUM> and exit via an exhaust nozzle <NUM>. High-pressure rotor(s) of the turbine section <NUM> (referred to as "HP turbine <NUM>") are mechanically linked to high-pressure rotor(s) of the compressor section <NUM> (referred to as "HP compressor <NUM>") through a high-pressure shaft <NUM>.

According to the illustrated example, the engine <NUM> is provided in the form of a multi-spool engine having a high pressure (HP) spool and a low pressure (LP) spool independently rotatable about axis <NUM>. However, it is understood that a multi-spool engine could have more than two spools. It should also be noted that the embodiments described herein also consider the use of single-spool engines.

Low-pressure rotor(s) of the turbine section <NUM> (referred to as "LP turbine <NUM>") are mechanically linked to the low-pressure rotor(s) of the compressor section <NUM> (referred to as "LP compressor <NUM>") and/or the fan <NUM> through a concentric low-pressure shaft <NUM> (referred to as an "LP shaft <NUM>") extending within the high-pressure shaft <NUM> and rotating independently therefrom. The high pressure components (HP turbine <NUM>, HP compressor <NUM>, HP shaft <NUM>) form the high pressure spool (referred to as "HP spool"), while the low pressure components (LP turbine <NUM>, LP shaft <NUM>, LP compressor <NUM>) form the low pressure spool (referred to as "LP spool"). In the shown embodiment, the fan <NUM> extends forwardly from the LP shaft <NUM> and is mechanically coupled thereto to be driven by the LP turbine <NUM>. The rotational speed of the fan <NUM>, generally referred to as N1, is thus limited by the rotational speed of the LP spool, while the HP spool rotates at a second rotational speed generally referred to as N2.

The compressor section <NUM>, combustor <NUM> and turbine section <NUM> are contained within an engine core <NUM> surrounded by a bypass duct <NUM> carrying bypass air generated by the fan <NUM>. An engine casing <NUM> surrounds the engine core <NUM>, with the bypass duct <NUM> radially defined between the engine casing <NUM> and engine core <NUM>. Illustratively, a plurality of engine bypass struts <NUM> support the engine core <NUM> within the engine casing <NUM>.

Control of the operation of the engine <NUM> can be effected by one or more control systems, for example a controller <NUM>, which is communicatively coupled to the engine <NUM>. The operation of the engine <NUM> can be controlled by way of one or more actuators, mechanical linkages, hydraulic systems, and the like. The controller <NUM> can be coupled to the actuators, mechanical linkages, hydraulic systems, and the like, in any suitable fashion for effecting control of the engine <NUM>. The controller <NUM> can modulate the position and orientation of variable geometry mechanisms within the engine <NUM>, the bleed level of the engine <NUM>, and fuel flow, based on predetermined schedules or algorithms. In some embodiments, the controller <NUM> includes one or more FADEC(s), electronic engine controller(s) (EEC(s)), or the like, that are programmed to control the operation of the engine <NUM>.

Engine <NUM> may operate with a high bypass ratio, i.e. a ratio of the mass flow rate through the bypass duct <NUM> to the mass flow rate entering the engine core <NUM>, for instance to increase propulsive efficiency and thus reduce fuel consumption. One of the drawbacks of increasing the engine bypass ratio is it suffers from a greater difference between the maximum thrust available at take-off and the maximum thrust available at maximum climb due to the reduced jet velocity. This may result in a choked flow at the exhaust nozzle <NUM>, whereby the flow is travelling at the speed of sound (Mach <NUM>). At such speeds, the fan <NUM> may have reached its aerodynamic or mechanical limit (rotating at a maximum rotational speed of the LP spool), for instance while the aircraft is climbing or flying at high altitudes, and may not be able to rotate any faster to increase thrust. It will be understood that the actual location of choked flow may vary in the exhaust nozzle <NUM> and is represented conceptually as occurring at a plane defining the exhaust nozzle <NUM>.

As such, the present disclosure describes systems and methods for providing additional thrust to the engine <NUM> in certain circumstances, by using one or more heat source to increase a temperature of bypass air flowing through the exhaust nozzle <NUM>. The bypass air may be heated at various stages of the engine <NUM>, such as in the bypass duct <NUM> and/or at or near the exhaust nozzle <NUM>. As used herein, a heat source comprises one or more components capable of transferring heat to the bypass air, directly or indirectly. In some embodiments, the heat source comprises a power source of the engine <NUM> such as, but not limited, to a battery, a hydrogen fuel cell, an auxiliary power unit, and combinations thereof. Existing power sources for the engine <NUM>, for instance in engines employing a hybrid powertrain, existing power sources for an aircraft, as well as dedicated power sources for the purposes of acting as a heat source, may be used. In some embodiments, the heat source is an electrical device that converts alternating current (AC) into heat. In some embodiments, the heat source is an electrical device that converts direct current (DC) into heat. In some embodiments, the heat source is operable to directly heat the bypass air. In some embodiments, the heat source is operable to apply heat to one or more conductive surfaces of the engine <NUM> by electromagnetic induction, and the bypass air is heated by convection heating as the bypass air comes in contact with the one or more conductive surface. Other means for heating the bypass air may be contemplated as well.

Referring to <FIG>, there are shown three graphs depicting the effects of applying a heat source to heat bypass air flowing through the bypass duct <NUM> towards the exhaust nozzle <NUM>, at a constant rotational speed (N1) of the fan <NUM>, to increase exhaust gas temperature and thus provide additional thrust. Exhaust gas temperature as defined herein refers to the temperature of the gas leaving the engine at the exhaust nozzle <NUM>. <FIG> illustrates N1 relative to ambient temperature. <FIG> illustrates net thrust relative to ambient temperature. <FIG> illustrates inter-turbine temperature (ITT - also called inter-stage turbine temperature) relative to ambient temperature. As used herein, ITT refers to the temperature of the gases in the engine core <NUM> between the high pressure turbine <NUM> and the low pressure turbine <NUM>, as illustrated in <FIG>. It will be understood that the use of ITT in this example is merely to indicate a temperature for which a thermal limit of the engine is reached. In some embodiments, ITT may be replaced with a surrogate or adjacent temperature, such as T4 (found at the exit of the combustor <NUM>) or T41 (the first stator outlet temperature). In each of <FIG>, the values for N1, net thrust and ITT, respectively, in an ideal scenario are represented by respective dotted lines 201A, 201B, 201C. As shown in <FIG>, these values are each limited by the mechanical N1 limit, represented by lines 202A, 202B, 202C, respectively. However, by applying a heat source to heat the bypass air flowing through the bypass duct <NUM> towards the exhaust nozzle <NUM>, thereby increasing the temperature of the mixed air at the exhaust nozzle <NUM>, net thrust can be increased to line 203B. In addition, as shown in <FIG>, this increase in net thrust may be extended over a wider range of ambient temperatures, thus increasing the range of the thrust limit over a wider range of ambient temperatures for certain circumstances, such as when the aircraft is in max climb. As shown in <FIG>, N1 and ITT do not change after the heat source is applied to the bypass air. Thus, additional thrust is generated for a same N1 and ITT.

Referring to <FIG>, various configurations are shown to heat bypass air flowing through the bypass duct <NUM> towards the exhaust nozzle <NUM>. In these examples, a heat source <NUM> is shown to include a current source <NUM> and a heating element <NUM>. It will be understood that this is for illustrative purposes only and other heat sources may be used instead or in combination therewith.

In some embodiments, and as shown in <FIG>, existing engine surfaces are heated through conduction/induction heating. For instance, heating element(s) <NUM> may be applied to a radially outer surface 34a of the mixer nozzle <NUM>, a radially outer surface 40a of the engine core <NUM> and/or a radially inner surface 44a of the engine casing <NUM>. While <FIG> depicts positioning the heating element <NUM> at the intersection between surfaces 40a and 34a, in other embodiments, such surfaces 34a, 40a may individually or concurrently be heated with separate heating elements <NUM>. In some embodiments, two or more heating elements <NUM> are operatively connected to a same current source <NUM>. Alternatively, or in combination therewith, each heating element <NUM> may be operatively connected to its own current source <NUM>. in some embodiments, heat may be applied to an outer surface 46a of one or more bypass struts <NUM>. Any of the surfaces highlighted in bold in <FIG> may be heated so as to transfer heat convectively to bypass air flowing thereby. Other existing surfaces within the engine <NUM> may be contemplated as well. In some embodiments, and as shown in <FIG>, the conductive surfaces heated by the one or more heat source <NUM> may be one or more new surface <NUM>, i.e. additional geometries, introduced within the engine <NUM>. For instance, a new surface <NUM> may comprise a plurality of fins positioned in the bypass duct <NUM>, upstream from the exhaust nozzle. The new surface <NUM> may also be positioned elsewhere along the bypass duct <NUM>, such as locations <NUM>, <NUM>, and/or <NUM>, for example. The new surface <NUM> may be attached to the inner surface 44a of the engine casing <NUM>, the bypass struts <NUM>, the outer surface 40a of the engine core <NUM>, or any other location suitable for coming into contact with the bypass air without significantly affecting the performance of the engine <NUM>. Other examples of a new surface <NUM> include arrays of fins, tubes, heated wires and the like. Such additional surfaces <NUM> should be designed to be substantially aerodynamic so as to minimize pressure loss, and noise created by their addition and avoid vortex-shedding to the extent possible. The additional surface <NUM> may be heated by a dedicated or existing power source <NUM>, for instance an induction heater or other heater type. All of the embodiments for the power source <NUM> described with reference to <FIG> are also applicable to the new surface <NUM>.

In other embodiments, and as shown in <FIG>, a combination of existing and new conductive surfaces may be provided to heat the bypass air flowing through the bypass duct <NUM> towards the mixer nozzle <NUM>. In some cases, the same heat source <NUM> may be used to heat more than one conductive surface, while in other cases a plurality of heat sources <NUM> with respective current sources <NUM> and heating elements <NUM> may be provided. In some embodiments, a single current source <NUM> may be used to power multiple heating elements <NUM> for multiple surfaces. Other combinations may be contemplated as well. As the number and size of conductive surfaces increases, the potential for providing a greater amount of heat to the bypass air increases as well due to the greater heat transfer surface area provided by such conductive surfaces. In addition, the energy required is inversely proportional to the surface area of such conductive surfaces, so an increase in surface area may result in more efficient heating of the bypass air. For example, in ideal heat transfer conditions for a typical medium by-pass turbofan in the <NUM>,<NUM>-<NUM>,<NUM> lbf thrust class range, <NUM> MW to <NUM> MW of electrical power may be used to provide an increase of <NUM> to <NUM> Rankine (or <NUM> to <NUM> Kelvin) of the EGT, thus providing between <NUM>% and <NUM>% additional thrust. Referring to <FIG>, there is shown an exemplary method <NUM> for operating an engine <NUM> to provide additional thrust in certain circumstances, the engine having an engine core <NUM>, a bypass duct <NUM>, and an exhaust nozzle <NUM> as described above. Such method <NUM> may be performed by the controller <NUM> in part or in whole.

At step <NUM>, a request is received for an increase in thrust generated by the engine <NUM>. In other words, the engine <NUM> is currently producing a given amount of thrust and the request is for more than the given amount of thrust. The request may come from a power lever of an aircraft, a thrust lever of the aircraft, a combined lever of the aircraft, or any other control mechanism operated by a pilot of the aircraft. In some embodiments, the request is generated by the controller <NUM> or another controller or computing device, such as an aircraft computer, in response to a detected state of the engine <NUM> or detected operating conditions of the aircraft.

At step <NUM>, in response to the receipt of the request at step <NUM>, it is determined if at least one operating condition for heat application-based thrust is met. As used herein heat application-based thrust refers to providing additional thrust by applying a heat source to heat bypass air flowing through the bypass duct towards the exhaust nozzle <NUM>, as described herein. It will be understood that heat application-based thrust differs from other techniques for increasing thrust, such as increasing the speed of the fan <NUM> or the use of an afterburner. In some embodiments, heat application-based thrust may be used in combination with other techniques for increasing engine thrust. According to the invention, the operating condition for heat application-based thrust is a choked state of the exhaust nozzle <NUM>. In some embodiments, the operating conditions for heat application-based thrust are a choked state of the exhaust nozzle <NUM> and the fan <NUM> operating at a mechanical limit. In some embodiments, a choked state of the exhaust nozzle <NUM> is approximated using on-board engine model(s) and based on available inputs from aircraft and/or engine sensors. In some embodiments, a choked state of the exhaust nozzle <NUM> is predetermined and step <NUM> comprises confirming the choked state of the exhaust nozzle <NUM> by reading a flag or field having been set as a result of the predetermined choked state of the exhaust nozzle <NUM>. In some embodiments not being part of the claimed invention, the operating conditions for heat application-based thrust are independent of the choked state of the exhaust nozzle and instead relate to other engine and/or aircraft parameters, for example an available ITT margin as determined from an ITT measurement. The controller <NUM> may consider one or more of an aircraft attitude, a Mach number, a rotational speed of the fan <NUM>, an inlet total pressure, an ITT measurement, temperatures and/or pressures in the gas path, and a flight phase to determine whether at least one operating condition for heat application-based thrust is met.

At step <NUM>, when the one or more operating condition is met, a heat source <NUM> is applied to heat bypass air flowing through the bypass duct <NUM> flowing towards the exhaust nozzle <NUM>. In some embodiments, step <NUM> comprises applying the heat source <NUM> to at least one conductive surface of the engine <NUM> and heating the bypass air through convection heat-transfer from the at least one conductive surface to the bypass air, as discussed above. Alternatively, the bypass air is heated directly by the heat source <NUM>. The amount of energy/heat applied can be modulated from minimum to maximum capacity based on the desired thrust increase.

At step <NUM>, the increase in thrust is generated from an increase in temperature of the bypass air flowing through the bypass duct <NUM> and into the exhaust nozzle <NUM>.

While method <NUM> has been herein described for use when engine thrust is limited by, for instance, the mechanical and thermal limits of the fan <NUM>, it is understood that the method may be used to provide additional thrust under other choked exhaust nozzle <NUM> conditions, pending available energy from the applicable heat source <NUM>.

Referring to <FIG>, there is illustrated an engine system <NUM>, which is composed of the engine <NUM>, a plurality of sensors <NUM> and a heat source controller <NUM>. It should be understood that certain elements of the engine <NUM>, as shown in <FIG>, are omitted to facilitate understanding. It is also understood that while only one heat source <NUM> is depicted in <FIG>, a plurality of heat sources <NUM> may be provided, as discussed above.

The sensors <NUM> are configured for detecting various parameters for the engine <NUM> and/or aircraft. While the sensors <NUM> are shown as being external to the engine <NUM>, it should be understood that one or more of the sensors <NUM> may form part of the engine <NUM>. In various embodiments, the number, type and positioning of the sensors <NUM> may vary. The sensors <NUM> may be operable to determine that one or more operating condition for a choked state of the exhaust nozzle <NUM> are met, for instance by detecting one or more of an aircraft altitude, a Mach number, a rotational speed, temperatures or pressures of the engine <NUM>, or a flight phase. As such, the sensors <NUM> may include altimeters, speed sensors, temperature sensors, pressure sensors, gyroscopes, as well as others types of sensors. Additionally, although illustrated here as physical sensors that are located at particular locations, it should be understood that in some cases, one or more of the sensors <NUM> can be virtual sensors, that is to say, instruments which make use of measurements from other sensors (physical or virtual) to derive a desired parameter (for example using on-board engine models).

The heat source controller <NUM> may form part of the controller <NUM> and be operable to control the one or more heat sources <NUM> based on, inter alia, information acquired from the sensors <NUM>, which can include applying heat to one or more surfaces in the bypass duct <NUM>. More particularly, applying heat may include diverting power from one or more power sources to one or more heaters, for instance induction heaters, which are positioned proximal to said conductive surfaces to be heated. As discussed above, applying heat to the bypass air in the bypass duct <NUM> may increase the exhaust gas temperature and thus the gas velocity at the exhaust nozzle <NUM>, allowing for more engine thrust to be produced. The heat source controller <NUM> may thus be configured for operating the one or more heats sources <NUM> to selectively increase the thrust of the engine <NUM>. In some embodiments, the engine thrust may be increased by approximately one to three percent, although other percent increases may be contemplated as well.

With reference to <FIG>, an example of a computing device <NUM> is illustrated. For simplicity only one computing device <NUM> is shown but the system may include more computing devices <NUM> operable to exchange data. The computing devices <NUM> may be the same or different types of devices. The heat source controller <NUM> may be implemented with one or more computing devices <NUM>. Note that the heat source controller <NUM> can be implemented as part of a full-authority digital engine controls (FADEC) or other similar device, including electronic engine control (EEC), engine control unit (ECU), and the like.

The methods and systems for operating an engine described herein may be implemented in a high level procedural or object oriented programming or scripting language, or a combination thereof, to communicate with or assist in the operation of a computer system, for example the computing device <NUM>. Alternatively, the methods and systems for operating an engine may be implemented in assembly or machine language. The language may be a compiled or interpreted language. Program code for implementing the methods and systems for operating an engine may be stored on a storage media or a device, for example a ROM, a magnetic disk, an optical disc, a flash drive, or any other suitable storage media or device. The program code may be readable by a general or special-purpose programmable computer for configuring and operating the computer when the storage media or device is read by the computer to perform the procedures described herein. Embodiments of the methods and systems for operating an engine may also be considered to be implemented by way of a non-transitory computer-readable storage medium having a computer program stored thereon. The computer program may comprise computer-readable instructions which cause a computer, or more specifically the processing unit <NUM> of the computing device <NUM>, to operate in a specific and predefined manner to perform the functions described herein, for example those described in the method <NUM>.

Claim 1:
A method for operating an engine (<NUM>), the engine having an engine core (<NUM>), a bypass duct (<NUM>), and an exhaust nozzle (<NUM>), the method comprising:
receiving (<NUM>) a request for an increase in thrust generated by the engine (<NUM>);
in response to receipt of the request, determining (<NUM>) that at least one operating condition for heat application-based thrust is met;
in response to the determining, applying (<NUM>) a heat source (<NUM>) to heat bypass air flowing through the bypass duct (<NUM>) towards the exhaust nozzle (<NUM>); and
generating the increase in thrust from an increased temperature of mixed bypass and core air at the exhaust nozzle (<NUM>); characterised in that the at least one operating condition for heat application-based thrust comprises a choked state of the exhaust nozzle (<NUM>).