Patent Application
20200056551
The disclosure relates generally to turbine engines for aircraft and more specifically to optimizing idle operation of such engines for advanced applications.
Relatively high idle speed results in excessive thrust at idle which makes aircraft taxing more difficult and can consume aircraft braking capacity, which in some cases may restrict takeoff capability. The high idle speeds raise the engine exhaust gas temperature (EGT) to the point where for some engines it is the highest EGT the engine experiences. These high temperatures necessitate the use of higher temperature capable, more expensive materials for some exhaust system parts. Furthermore, accommodations made to reduce idle speeds, such as compressor geometry changes, can be detrimental to high power efficiency.
Idle speeds are constrained by several factors. First, compressor and turbine efficiencies are low at idle speeds, far below those at engine design speed. The power available to accelerate the spool is only the turbine power in excess of that required to power the compressor, such excess power is relatively low near idle. Second, fuel must be added to generate excess power. The fuel addition raises the combustor exit air temperature, thus reducing the air density entering the fixed turbine geometry. This increases the back pressure on the compressor before the spool can accelerate so the engine operating point moves up the constant speed line toward the stall line. This loss of stall margin constrains the rate at which fuel can be added and so the rate at which a spool can accelerate. Requirements for acceleration time from idle to full power can thus contribute to the need for a relatively high idle speed.
An embodiment of an engine assembly includes a combustion turbine engine having at least a first compressor spool, a first turbine spool, a first shaft connecting the first compressor spool and the first turbine spool, and a combustor disposed in a working gas flow path between the first compressor spool and the first turbine spool. A first controller is programmed with a surge map, and configured to operate the combustion turbine engine in a range extending between a first suppressed idle mode, a second base idle mode, and a maximum takeoff power rating mode. An idle speed suppressor includes at least one idle assist motor connected to the first shaft of the combustion turbine engine. A second controller is configured to manage operation of the idle speed suppressor relative to the combustion turbine engine during times of minimum power demand, such that operating the idle speed suppressor increases a compressor speed in the first suppressed idle mode relative to a compressor speed in the second base idle mode.
An embodiment of a method of operating an engine assembly includes operating a combustion turbine engine having at least a first compressor spool, a first turbine spool, a first shaft connecting the first compressor spool and the first turbine spool, and a combustor disposed in a working gas flow path between the first compressor spool and the first turbine spool. Operation of the combustion turbine engine is performed in part according to a compressor surge map, in a range extending between a first suppressed idle mode, a second base idle mode, and a maximum takeoff power rating mode. In at least the first suppressed idle mode, the combustion turbine engine supplemented with an idle speed suppressor, including at least one idle assist motor connected to the first shaft of the combustion turbine engine. The idle speed suppressor is operated relative to the combustion turbine engine during times of minimum power demand, such that operating the idle speed suppressor increases a compressor speed in the first suppressed idle mode relative to a compressor speed in the second base idle mode without increasing engine thrust.
Engine 10 includes low spool 30 including low-pressure rotor 22 with a shaft connecting a low pressure portion of compressor 14 and a low pressure portion of turbine 18, as well as high spool 32 which includes high pressure rotor 20 having a coaxial shaft connecting high pressure portion of compressor 14 to a high pressure portion of turbine 18.
As illustrated in
In operation, air flow F enters compressor 14 through fan 12 and is split into core flow Fp and bypass flow Fs. Air flow Fp is compressed by the rotation of compressor 14 driven by high-pressure rotor 20. The compressed air from compressor 14 is further divided, with a large portion going to combustor 16, and a smaller portion employed for cooling components exposed to high-temperature combustion gases, such as stator vanes, as described below. Compressed air and fuel are mixed an ignited in combustor 16 to produce high-temperature, high-pressure combustion gases Fp. Combustion core gases Fp exit combustor section 16 into turbine section 18. Stator stages 28 properly align the flow of combustion gases Fp for an efficient attack angle on subsequent rotor stages 26. The flow of combustion gases Fp past rotor stages 26 drives rotation of both high-pressure rotor 20 and low-pressure rotor 22. High-pressure rotor 20 drives at least the high-pressure part of compressor section 14, as noted above, and low-pressure rotor 22 drives at least the low-pressure part of compressor 14 as well as fan 12 to produce thrust Fs from gas turbine engine 10. In this example, engine 10 has two spools, low pressure spool 30 and high pressure spool 32.
As shown in more detail in
Idle speed suppressor 36 can include at least one idle assist motor 48 connected to a compressor 14 side of combustion turbine engine 10. Where idle assist motor 48 relies on converting stored power into another form (e.g., hydraulic or compressed air), optional motor drive 50 can be provided. Second controller 52 can be configured to manage operation of idle speed suppressor 36 relative to combustion turbine engine 10 during times of minimum power demand, such as idling while taxiing in from or out to the runway. In general, operating idle speed suppressor 36 increases a speed of at least one stage or spool of compressor 14 while in the first, suppressed idle mode, relative to a corresponding compressor speed when engine 10 operates in the second, base idle mode. In certain embodiments, programming of first controller 46 and second controller 52, among others, can be integrated into a single controller unit.
Idle speed suppressor 36 utilizes various inputs and other data to facilitate steady operation with proper feedback in order to maintain suppressed yet also stable idle during at least part of the taxi or other low-power engine mode. In addition to speed sensor 56 which measures rotation of shaft(s) 44, at least one of first controller 46 and second controller 52 can be configured to control fuel flow 60 to engine 10 (specifically combustor 16) that is specific to the idle suppression mode and the surge map (shown in
As for particular embodiments, idle assist motor 48 can include one or more of a starter/generator, a starter motor, and a dedicated idle assist motor. Though conventional engines are equipped with a dedicated starter or a starter/generator, these are sized to the minimum required to ensure reliable startup and/or power generation in flight. Ordinarily a starter/generator is in generator (power offtake) mode only during operation of the engine due to limitations of component cost, addition to aircraft weight and operability complications. In starter mode, the starter/generator is in power addition mode (assisting with rotating the compressor for example) only during engine lighting and occasionally during in-flight restart. In other words, a starter and a starter/generator only add power to the engine when it is off, and a starter/generator only takes power off of the engine when it is on.
With advances in energy storage, more efficient components and controls, and other technologies, the starter/generator can be enlarged beyond its conventional size to allow for the engine to boost compression (i.e., add power) while the engine is on, so that less fuel is required to maintain the same or less net thrust. This has the effect of suppressing or allowing for lower baseline idle speed as compared to conventional operation.
As such, at least one of the starter and the starter/generator can be operable in an additional idle speed suppression mode while the engine is running, in order to increase a speed of at least one compressor stage during suppressed idle or taxi mode, reducing the load on a turbine driving the at least one compressor stage during suppressed idle or taxi mode.
In certain embodiments, idle assist motor 48 operates at least partially on stored power 62 separate from turbine 18 of combustion turbine engine 10. Stored power 62 can be retained by one or more of a flywheel, a hydraulic reservoir, a battery, and a compressed air tank. In certain embodiments, idle assist motor 48 operates on energy provided by another engine, for example, on operating at higher power levels or an auxiliary power unit (not explicitly shown).
Beyond this, moving to an alternate embodiment shown in
Electric propulsion engine 111 can be configured to operate at least periodically as idle suppressor 136/idle assist motor 148, operating in an idle suppression mode during a suppressed idle and/or taxi mode. Second controller 152 can be configured to manage operation of electric propulsion engine 111 as idle speed suppressor 136 relative to combustion turbine engine 110 during times of minimum power demand, such as idling while taxiing in from or out to the runway. As in the example of
As noted above, in at least the first suppressed idle mode, the combustion turbine engine is supplemented with an idle speed suppressor, including at least one idle assist motor connected to a compressor side of the combustion turbine engine. The idle speed suppressor is operated in conjunction with/relative to the combustion turbine engine during times of minimum power demand, such as during taxi in and out. Operating the idle speed suppressor increases a compressor speed in the first suppressed idle mode relative to a compressor speed in the second base idle mode without increasing engine thrust. This can be done by controlling fuel flow to the engine specific to the idle suppression mode and the surge map while maintaining stability of the engine during the first suppressed idle mode and/or acceleration mode.
Without idle speed suppression, the engine would idle at point 202. As fuel is added to accelerate, the engine follows the dashed conventional acceleration trajectory 204, initially up constant speed line 206. Due to spool inertia, addition of fuel initially only increases exhaust temperatures until the additional energy is able to spin up the spool. Thus fuel addition is controlled carefully to maintain the engine along speed line 208 and kept a sufficient distance from surge line 210 as required to avoid the onset of instability. Near the desired final engine speed 214, fuel is reduced to a level needed for steady operation near steady-state line 212 and desired steady-state operating point 214.
The addition of an idle suppression system permits the engine to idle at lower idle speed, here point 218. Instead acceleration follows trajectory 220. The ability to add additional torque to the spool from the idle assist motor frees the engine from having to initially follow constant speed line 206, so surge line 210 need not be approached as quickly during spool-up. Also the total acceleration time from suppressed idle operating point 218 to point 214 can be as fast that from point 202 to point 214 because of the additional power provided by the motor. It also has the effect of reducing a corresponding turbine output speed operating temperature, and/or exhaust temperature as compared to conventional/base idle mode.
Given an instantaneous rotor speed, the shape of the compressor map stored in a controller, and rotary moment of inertia of the spool, the controller balances the spool power to be supplied from fuel addition with power from the idle assist motor to enable the initial acceleration trajectory to be largely independent of the idle constant speed line. The power provided by the idle assist motor may be a significant fraction of the initial off-idle power. This permits the lower idle speed shown with the same or better acceleration time, while also increasing the stall margin.
It will be recognized that the map has been normalized for illustrative purposes, and thus exact trajectories shown in
Discussion of Possible Embodiments
The following are non-exclusive descriptions of possible embodiments of the present disclosure.
An embodiment of an engine assembly includes a combustion turbine engine having at least a first compressor spool, a first turbine spool, a first shaft connecting the first compressor spool and the first turbine spool, and a combustor disposed in a working gas flow path between the first compressor spool and the first turbine spool. A first controller is programmed with a surge map, and configured to operate the combustion turbine engine in a range extending between a first suppressed idle mode, a second base idle mode, and a maximum takeoff power rating mode. An idle speed suppressor includes at least one idle assist motor connected to the first shaft of the combustion turbine engine. A second controller is configured to manage operation of the idle speed suppressor relative to the combustion turbine engine during times of minimum power demand, such that operating the idle speed suppressor increases a compressor speed in the first suppressed idle mode relative to a compressor speed in the second base idle mode.
The assembly of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components:
An engine assembly according to an exemplary embodiment of this disclosure, among other possible things includes a combustion turbine engine comprising a first compressor spool, a first turbine spool, a first shaft connecting the first compressor spool and the first turbine spool, and a combustor disposed in a working gas flow path between the first compressor spool and the first turbine spool; a first controller programmed with a surge map, and configured to operate the combustion turbine engine in a range extending between a first suppressed idle mode, a second base idle mode, and a maximum takeoff power rating mode; an idle speed suppressor including at least one idle assist motor connected to the first shaft of the combustion turbine engine; and a second controller configured to manage operation of the idle speed suppressor relative to the combustion turbine engine during times of minimum power demand, such that operating the idle speed suppressor increases a compressor speed in the first suppressed idle mode relative to a compressor speed in the second base idle mode.
A further embodiment of the foregoing engine assembly, wherein at least one of the first controller and the second controller are configured to control fuel flow to the engine specific to the idle suppression mode and the surge map while maintaining stability of the engine during at least one of idle and acceleration.
A further embodiment of any of the foregoing engine assemblies, wherein the idle assist motor comprises at least one of: a starter/generator, a starter motor, and a dedicated idle assist motor.
A further embodiment of any of the foregoing engine assemblies, wherein at least one of the starter and the starter/generator is operable in an idle speed suppression mode while the engine is running, in order to increase a speed of the first compressor spool during idle or taxi mode, reducing the load on the first turbine spool driving the first compressor spool during idle or taxi mode.
A further embodiment of any of the foregoing engine assemblies, wherein the idle assist motor operates at least partially on stored power separate from the turbine of the combustion turbine engine.
A further embodiment of any of the foregoing engine assemblies, wherein the stored power is retained by one or more of a flywheel, a hydraulic reservoir, a battery, and a compressed air tank.
A further embodiment of any of the foregoing engine assemblies, wherein power is provided by another engine or an auxiliary power unit.
A further embodiment of any of the foregoing engine assemblies, wherein the engine assembly further comprises an electric propulsion engine operable in series or parallel with the combustion turbine engine.
A further embodiment of any of the foregoing engine assemblies, wherein the electric propulsion engine is configured to operate at least periodically as the idle assist motor, operating in an idle suppression mode during idle or taxi mode.
A further embodiment of any of the foregoing engine assemblies, wherein programming of the first controller and the second controller are integrated into a single controller unit.
An embodiment of a method of operating an engine assembly includes operating a combustion turbine engine having at least a first compressor spool, a first turbine spool, a first shaft connecting the first compressor spool and the first turbine spool, and a combustor disposed in a working gas flow path between the first compressor spool and the first turbine spool. Operation of the combustion turbine engine is performed in part according to a compressor surge map, in a range extending between a first suppressed idle mode, a second base idle mode, and a maximum takeoff power rating mode. In at least the first suppressed idle mode, the combustion turbine engine supplemented with an idle speed suppressor, including at least one idle assist motor connected to the first shaft of the combustion turbine engine. The idle speed suppressor is operated relative to the combustion turbine engine during times of minimum power demand, such that operating the idle speed suppressor increases a compressor speed in the first suppressed idle mode relative to a compressor speed in the second base idle mode without increasing engine thrust.
The method of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components:
A method according to an exemplary embodiment of this disclosure, among other possible things includes operating a combustion turbine engine comprising a first compressor spool, a first turbine spool, a first shaft connecting the first compressor spool and the first turbine spool, and a combustor disposed in a working gas flow path between the first compressor spool and the first turbine spool, operation of the combustion turbine engine being performed in part according to a compressor surge map, in a range extending between a first suppressed idle mode, a second base idle mode, and a maximum takeoff power rating mode; in at least the first suppressed idle mode, supplementing the combustion turbine engine with an idle speed suppressor, including at least one idle assist motor connected to the first shaft of the combustion turbine engine; and operating the idle speed suppressor relative to the combustion turbine engine during times of minimum power demand, such that operating the idle speed suppressor increases a compressor speed in the first suppressed idle mode relative to a compressor speed in the second base idle mode without increasing engine thrust.
A further embodiment of the foregoing method, further comprising: controlling fuel flow to the engine specific to the idle suppression mode and the surge map while maintaining stability of the engine during at least one of the first suppressed idle mode and an acceleration mode.
A further embodiment of any of the foregoing methods, wherein the idle assist motor comprises at least one of: a starter/generator, a starter motor, and a dedicated idle assist motor.
A further embodiment of any of the foregoing methods, further comprising operating at least one of the starter and the starter/generator in an idle speed suppression mode while the engine is running, in order to increase a speed of at least the first compressor spool during at least the first suppressed idle mode, reducing the load on the first turbine spool driving the first compressor spool during at least the first suppressed idle mode.
A further embodiment of any of the foregoing methods, wherein the idle assist motor is operated at least partially on stored power separate from the turbine of the combustion turbine engine.
A further embodiment of any of the foregoing methods, further comprising storing power for operation of the idle assist motor in one or more of a flywheel, a hydraulic reservoir, a battery, and a compressed air tank.
A further embodiment of any of the foregoing methods, further comprising operating an electric propulsion engine in series or parallel with the combustion turbine engine.
A further embodiment of any of the foregoing methods, further comprising operating the electric propulsion unit at least periodically as the idle assist motor.
A further embodiment of any of the foregoing methods, further comprising reducing a corresponding turbine output speed or operating temperature.
A further embodiment of any of the foregoing methods, further comprising reducing a turbine exhaust temperature in the idle suppression mode relative to the base idle mode.
While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.
