Patent Application
20230417184
The present disclosure relates to engines, in particular precooled engines, such as of the type which may be used in aerospace applications, and to methods of operating such engines. The present disclosure also relates to aircraft, flying machines and aerospace vehicles comprising such engines.
Efficient air-breathing propulsion for flight from low speed to high Mach (e.g. above Mach 2.5) can require the integration of several engine types (for example, an air-breathing engine and a rocket engine, or a turbomachinery based engine and a ramjet) into a single system, with carefully managed transitions between the various modes of operation provided by the different engine types, as thrust falls in one mode while thrust in another mode rises. The Mach number at which these transitions between different modes of operation occurs is largely a result of temperature limitations. For example, where a system is configured to operate using turbomachinery and a ramjet, typically there will be a transition from turbomachinery to ramjet operation at a flight speed where neither mode is optimised. This is because if, for example, material temperature limits in the turbomachinery are hit early and throttling thus occurs at lower supersonic speeds, well before the ramjet kicks in to produce good thrust performance, this results in a gap/deficiency in overall thrust performance, in which the propulsion system struggles to provide sufficient thrust to continue acceleration. If the temperature of the intake air entering the engine could be controlled (i.e. reduced below stagnation), then the transition point for a given engine mode could be at higher Mach. This would allow the various engine modes to be better optimised, and for greater flexibility of operation through the transition speeds. It could even allow for some engine modes to be removed completely. One means to achieve control of the air temperature entering the engine is by precooling using a heat exchanger (a “precooler”).
High Mach/hypersonic platforms are anticipated to employ precooled turbofan/jet engines for primary vehicle propulsion. A conventional turbofan or jet engine in isolation cannot typically reach hypersonic velocities due to the elevated enthalpy of the freestream flow causing the engine's operation to be restricted by practical limitations, such as a compressor's temperature limits. The use of a precooler allows the inlet flow to be cooled such that the turbofan/jet may be run at both subsonic flight velocities and at velocities which are beyond its typical operating envelope. By extending this envelope to high Mach regimes, the propulsion system will then be able to undertake a mode transition whereby a ramjet is activated within the bounds of efficient space envelope and performance. This can provide a flexible operation since the engine may operate in any mode and also transition between them. However, the use of a precooler can cause increased pressure losses, resulting in engine efficiency losses.
The present disclosure seeks to alleviate, at least to a certain degree, the problems and/or address at least to a certain extent, the difficulties associated with the prior art.
According to a first aspect of the disclosure, there is provided an engine comprising: an air inlet configured to receive air; a first heat exchanger arrangement arranged downstream of the air inlet, having a first heat exchanger inlet configured to receive at least a portion of the air received by the air inlet, and being configured to cool the air received by the first heat exchanger inlet; one or more turbomachinery components arranged downstream of an outlet of the first heat exchanger arrangement, and being configured to receive air; a first flow path arranged to extend from the air inlet to the first heat exchanger inlet; a second flow path arranged to extend from the air inlet to the one or more turbomachinery components, the second flow path bypassing the first heat exchanger inlet; and a flow control arrangement comprising a first portion and a second portion, the first and second portions being configured to be movable relative to one another to selectively obstruct the second flow path.
Advantageously, such an engine can provide that when operating at relatively high flight speeds, for example above approximately Mach 1.5, substantially all of the air entering the engine via the air inlet is caused to flow along the first flow path such that it is caused to enter the first heat exchanger, to be precooled therein; and when operating at relatively low flight speeds, for example at or below approximately Mach 1.5, for example at subsonic flight speeds, that a first portion of the air entering the engine via the air inlet is caused to flow along the first flow path such that it is caused to be precooled in the first heat exchanger, whilst a second portion of the air entering the engine via the air inlet is caused to flow along the second flow path such that it is caused to bypass the first heat exchanger to not be precooled therein. For example, at a low flight speed that is between subsonic to approximately Mach 1.5, full precooling of all of the air flow is not needed, and it would be more efficient to precool only a portion of the air, to advantageously reduce the total inlet pressure loss at such lower flight speeds, resulting in a more efficient engine. At such low flight speeds, the second flow path may thus advantageously provide for a portion of the air flow to bypass the first heat exchanger arrangement. At higher flight speeds, for example above approximately Mach 1.5, the flow control arrangement may advantageously provide for the second flow path to be obstructed/blocked, by movement of the first and second portions thereof, to cause substantially none of the air flow to bypass the first heat exchanger arrangement. Advantageously, the relatively movable first and second portions of the flow control arrangement can provide for this as they are configured to selectively obstruct the second flow path. By providing for selective/optional precooler bypassing/circumvention, such an engine may advantageously be employed in high Mach/hypersonic platforms with improved efficiency, by reducing pressure losses and increasing the pressure recovery factor (PRF).
Optionally, said first and second portions are movable relative to one another to provide at least one inlet flow aperture into the second flow path upstream of the first heat exchanger inlet.
Advantageously, such a flow control arrangement can selectively provide for the second flow path, to permit at least a portion of the air entering the engine via the air inlet, when the engine is in use, to bypass the precooler. In designing the engine, the size of the at least one inlet flow aperture may be chosen to determine the relative ratio between the amount of air received by the air inlet which may flow along the first flow path, and the amount of air received by the air inlet which may flow along the second flow path when the second flow path is un-obstructed.
Optionally, the engine is configured to be operated in a first mode at a first operating flight speed, and in a second mode at a second operating flight speed, wherein the second operating flight speed is greater than the first operating flight speed, and wherein said first and second portions are configured to be moved to selectively obstruct the second flow path when the engine is operating in the second mode, and wherein the first and second portions are configured to provide the at least one inlet flow aperture into the second flow path when the engine is operating in the first mode.
Advantageously, such an engine can provide that at lower flight speeds, a portion of the air flow bypasses the first heat exchanger arrangement, to reduce pressure losses, resulting in improved engine efficiency.
Optionally, the first operating flight speed is between approximately Mach 1 to Mach 3 and/or the second operating flight speed is between approximately Mach 1 to Mach 3. Optionally, the first operating flight speed is less than approximately Mach 1.5, and the second operating flight speed is greater than or equal to approximately Mach 1.5.
Optionally, the flow control arrangement is configured to be arranged in a first position in which the first portion and the second portion are arranged to provide the at least one inlet flow aperture, and a second position in which the first portion and the second portion are arranged to obstruct the at least one inlet flow aperture. The first and second positions may be referred to as “open” and “closed” positions respectively of the flow control arrangement, such that when the flow control arrangement is “open”, air is permitted to flow along the second flow path to bypass the first heat exchanger arrangement, and when the flow control arrangement is “closed”, air is prevented from flowing along the second flow path.
Optionally, the first portion and the second portion are configured such that when the flow control arrangement is in the first “open” position and the engine is in use, a first portion of the air entering the engine via the air inlet is caused to flow along the first flow path, and a second portion of the air entering the engine via the air inlet is caused to flow along the second flow path.
Optionally, the first portion of air may comprise between approximately 50% to 95% of the air entering the engine via the air inlet, and/or the second portion of air may comprise between approximately 5% to 50% of the air entering the engine via the air inlet. For example, the first portion of air may comprise approximately 70% of the air entering the engine via the air inlet, and the second portion of air may comprise approximately 30% of the air entering the engine via the air inlet.
Optionally, the flow control arrangement is configured to be arranged in one or more intermediate positions between the first and second positions, wherein in one or more of said intermediate positions, the first and second portions are arranged to at least partially obstruct the second flow path.
Optionally, the flow control arrangement is arranged downstream of the air inlet.
Optionally, the air inlet is configured for the flow of subsonic, supersonic and/or hypersonic air.
Optionally, the air inlet, the flow control arrangement, the first heat exchanger arrangement and the one or more turbomachinery components are arranged along and to be centred on a longitudinal axis of the engine. The longitudinal axis of the engine may be at least partially curved.
Optionally, the one or more turbomachinery components comprises a compressor. The one or more turbomachinery components may further comprise a turbine configured to drive the compressor. Optionally, the engine further comprises an air-breathing combustion chamber configured to receive compressed air from the compressor and for the combustion of air and fuel. The engine may further comprise an augmentation system such as a reheat or afterburner system. The engine may further comprise one or more exhaust nozzles, such as one or more variable area nozzles.
The engine may comprise an air-breathing jet engine, wherein the one or more turbomachinery components may comprise a compressor and a turbine.
Optionally, said first and second portions are configured to be movable relative to one another axially along a longitudinal axis of the engine, rotationally about said longitudinal axis and/or pivotally, to provide for said at least one inlet flow aperture.
Optionally, said first and second portions are arranged concentrically relative to one another with respect to a longitudinal axis of the engine and are movable relative to one another along said longitudinal axis to provide for said at least one inlet flow aperture.
Optionally, the at least one inlet flow aperture comprises an annular gap between the first and second portions.
Advantageously, the at least one inlet flow aperture comprising an annular gap can provide for air to flow along the second flow path with minimal flow turning required, thus preserving the dynamic head of the flow and hence minimising pressure losses, resulting in improved engine efficiency.
Optionally, said first and second portions are shaped such that when the flow control arrangement is in the second “closed” position, the first and second portions together form a generally continuous generally conical shaped structure, with no annular gap therein, i.e. with no annular gap between the first and second portions.
Advantageously, such a flow control arrangement may be configured to slow down the flow of incoming air received by the air inlet, for example to slow it from a supersonic flight speed to a subsonic flight speed, causing a conical shock wave to form at the apex of the conical shaped structure.
Optionally, said first portion is generally conical and is arranged concentrically inside the second portion, which is generally annular and comprises an outer surface that is generally in the form of a truncated cone. Optionally, the first portion is configured to be movable relative to the second portion with respect to the longitudinal axis of the engine, or vice versa. Optionally, the first portion is at least partially hollow. Optionally, the first portion is filled with a honeycomb filler material, to advantageously improve its specific stiffness properties.
Optionally, said first and second portions are shaped such that when the first portion or the second portion is moved towards the air inlet (i.e. in the upstream/forwards direction), an outer surface of the first portion is arranged to bear against an inner surface of the second portion to obstruct the second flow path, and conversely when the same one of the first portion or the second portion is moved away from the air inlet (i.e. in the downstream/rearwards direction), said annular gap is provided between the outer surface of the first portion and the inner surface of the second portion.
Optionally, said first and second portions are shaped such that when the first portion or the second portion is moved away from the air inlet (i.e. in the downstream/rearwards direction), an outer surface of the first portion is arranged to bear against an inner surface of the second portion to obstruct the second flow path, and conversely when the same one of the first portion or the second portion is moved towards the air inlet (i.e. in the upstream/forwards direction), said annular gap is provided between the outer surface of the first portion and the inner surface of the second portion.
Optionally, said first portion comprises at least one vane configured to be pivotable relative to said second portion, in order to provide for the at least one inlet flow aperture.
Optionally, said at least one vane is configured to be moved into a closed position in which said at least one vane is arranged to obstruct the second flow path, and an open position in which said at least one vane is arranged to provide the at least one inlet flow aperture.
Optionally, said first portion comprises a plurality of vanes angularly spaced apart from one another about a longitudinal axis of the engine. Optionally, each of the vanes is hingedly connected to a relatively fixed portion of the first portion to provide for pivotal movement of each of the respective vanes relative to the relatively fixed portion of the first portion and also relative to said second portion.
Optionally, said first and second portions are arranged concentrically relative to one another with respect to a longitudinal axis of the engine, the first portion comprising at least one first aperture and the second portion comprising at least one second aperture, the first and second portions being rotatable relative to one another about said longitudinal axis to align said at least one first aperture with said at least one second aperture to provide the at least one inlet flow aperture.
Optionally, said first and second portions are generally conical and are shaped to generally correspond with one another, such that by being arranged concentrically relative to one another, one of the first and second portions is nested inside the other one of the first and second portions. Optionally, the first and second portions are rotatable relative to one another into a first “closed” position in which the at least one first and second apertures are arranged to be misaligned with respect to one another, to obstruct the second flow path, and into a second “open” position in which they are aligned with respect to one another to provide the at least one inlet flow aperture. Optionally, the at least one first and second apertures each comprises a slot, the slots being angularly spaced apart from one another relative to the longitudinal axis of the engine. Optionally, the at least one first apertures cover/extend over approximately half of the circumference or surface area of the first portion, and the at least one second apertures cover/extend over approximately half of the circumference or surface area of the second portion.
Optionally, the first heat exchanger arrangement is generally annular, and the second flow path is arranged to extend generally parallel to a longitudinal axis of the engine through the centre of the generally annular first heat exchanger arrangement.
Optionally, the first heat exchanger arrangement comprises a generally cylindrical annular heat exchanger or a generally conical annular heat exchanger through which air is configured to flow from the first heat exchanger inlet to the first heat exchanger outlet in a generally radial direction that is perpendicular to the longitudinal axis of the engine.
Optionally, the first heat exchanger arrangement comprises a plate heat exchanger.
Optionally, the first heat exchanger arrangement comprises a plurality of tubes for the flow of a heat transfer medium in heat exchange with the air received by the first heat exchanger inlet, wherein the first flow path is arranged to extend around and/or between said tubes.
Optionally, the first heat exchanger arrangement comprises a plurality of heat exchanger modules, the plurality of heat exchanger modules being arranged to be generally centred on and arranged along a longitudinal axis of the engine. Optionally, the modules are generally annular. Optionally, at least one of the plurality of heat exchanger modules is arranged to overlap with at least one other one of the plurality of heat exchanger modules relative to the longitudinal axis of the engine. The plurality of heat exchanger modules may be arranged to be in fluid communication with one another. The plurality of heat exchanger modules may be arranged in series and/or in parallel relative to the longitudinal axis of the engine.
Optionally, each of the plurality of heat exchanger modules may comprise a plurality of tubes for the flow of a heat transfer medium in heat exchange with the air received by the first heat exchanger inlet. The first heat exchanger arrangement may be configured such that air is configured to flow around and/or between the plurality of tubes as it flows through the first heat exchanger arrangement. The plurality of tubes may be arranged to be each wound in a respective path that gradually widens or tightens about the longitudinal axis of the engine and each spaced apart from one another in rows along the longitudinal axis of the engine. For example, the plurality of tubes may be arranged in involute spiral paths, which may extend circumferentially about the longitudinal axis of the engine.
Advantageously, the modular structure of the first heat exchanger arrangement provides that the engine may be configured such that the flow of a heat transfer medium in one or more of the heat exchanger modules may be modulated or completely turned off separately (i.e. independently from the flow of a heat transfer medium in the other heat exchanger modules). Additionally, the heat exchanger modules of the engine may provide that a proportion of the air may pass through each heat exchanger module and be cooled by a heat transfer medium in the first heat exchanger arrangement. Advantageously, this may further provide for improved optimisation, flexibility and control of the temperature profile of the air flowing through the engine.
Optionally, at least a portion of the first flow path is arranged between the flow control arrangement and an outer housing of the engine.
Optionally, the flow control arrangement comprises at least a portion that is generally in the shape of a cone or a truncated cone and/or an axisymmetric curved shape.
Advantageously, such a flow control arrangement may be configured to slow down the flow of incoming air received by the air inlet, for example to slow it from a supersonic flight speed to a subsonic flight speed.
Optionally, the engine further comprises an actuator arrangement for actuating the flow control arrangement, to cause the first and second portion to move relative to one another to selectively obstruct and un-obstruct the second flow path.
Optionally, the actuator arrangement comprises one or more active actuators such as one or more fueldraulic, hydraulic, pneumatic, ball-screw and/or electric actuators and/or one or more passive actuators. Optionally, the actuator arrangement may be configured to be passively actuated by utilising the variation between at least two different local air pressures in the engine.
Optionally, the flow control arrangement comprises one or more inconel nickel alloys and/or ceramic composites, to advantageously improve the maximum operating temperature of the flow control arrangement.
Optionally, the engine may further comprise a plurality of turning vanes configured to direct the flow of air into and out of the first heat exchanger arrangement. Advantageously, this may provide for the air flow to be directed into and out of the first heat exchanger arrangement. Said plurality of turning vanes may be configured to turn the air flow through an angle of approximately 90 degrees, to guide the air flow from generally along a longitudinal axis of the engine to generally along a radial direction of the engine, or vice versa.
Optionally, the engine may further comprise a separator duct arranged on the outside of the first heat exchanger arrangement. Advantageously, the separator duct may prevent debris and large particles that may be ingested into the air inlet from impacting on the heat exchanger arrangement.
Optionally, the engine further comprises: a second heat exchanger arrangement arranged upstream of the first heat exchanger arrangement, having a second heat exchanger inlet configured to receive at least a portion of the air received by the air inlet, and being configured to cool the air received by the second heat exchanger inlet; and a third flow path arranged to extend from the air inlet to the second heat exchanger inlet; wherein the at least one inlet flow aperture is positioned between the first and second heat exchanger arrangements.
Advantageously, such an engine can provide that when operating at relatively low flight speeds, for example at or below approximately Mach 1.5, a first portion of the air entering the engine via the air inlet is caused to flow along the first flow path such that it is caused to be precooled in the first heat exchanger arrangement, a second portion of air is caused to flow 35 along the third flow path such that it is caused to be precooled in the second heat exchanger arrangement, and a third portion of air is caused to flow along the second flow path such that it bypasses the first heat exchanger arrangement. This is advantageous because at relatively low flight speeds, full precooling of all of the air entering the engine via the air inlet is not needed, so it would be more efficient to precool only a portion of the air, leaving some of the air (i.e. that which flows along the second flow path) uncooled, to advantageously reduce the total inlet pressure loss at such lower flight speeds, resulting in a more efficient engine. Together, the first and second heat exchanger arrangements may be referred to as constituting a “modular heat exchanger arrangement”, and such an engine thus advantageously provides for selective bypassing of one or more modules in a modular heat exchanger arrangement by providing for selective bypassing/circumvention of one or more modules. Such an engine may thus advantageously be employed in high Mach/hypersonic platforms with improved efficiency, by reducing pressure losses and increasing the pressure recovery factor (PRF). Furthermore, since the at least one inlet flow aperture is positioned between the first and second heat exchanger arrangements, and the second flow path is arranged to bypass the first heat exchanger arrangement (which is arranged downstream of the second heat exchanger arrangement), the location of the at least one inlet flow aperture advantageously allows the air flow to settle upstream of the one or more turbomachinery components whilst also allowing for the possibility of access for a diagonal rocket thrust strut to pass through to the wingtip.
Optionally, the first and second heat exchanger arrangements are arranged to be spaced apart from one another along a longitudinal axis of the engine.
Optionally, the flow control arrangement comprises at least one butterfly valve. Optionally, said first portion of the flow control arrangement comprises a respective disc of each of the at least one butterfly valves configured to rotate within and relative to said second portion of the flow control arrangement, to selectively obstruct the second flow path, the second portion comprising an outer structure of each of the at least one butterfly valves.
Advantageously, butterfly valves are lightweight and may be less prone to jamming under mechanical distortion of the first and/or second heat exchanger arrangements.
Optionally, the flow control arrangement comprises a plurality of butterfly valves angularly spaced apart from one another relative to a longitudinal axis of the engine.
Optionally, the plurality of butterfly valves comprises a first set of butterfly valves configured to be rotated in a first direction and a second set of butterfly valves configured to be rotated in a second direction that is opposite to the first direction, wherein the first and second sets of butterfly valves are arranged alternately with respect to one another about the longitudinal axis of the engine.
Advantageously, rotating alternate butterfly valves in opposite directions can eliminate outlet swirl.
Optionally, the first and second heat exchanger arrangements are generally annular and are arranged along and generally centred on a longitudinal axis of the engine, and are each configured for air to flow therethrough in a generally radial direction that is perpendicular to a longitudinal axis of the engine, and the plurality of butterfly valves are arranged adjacent a bore of the first and/or second heat exchanger arrangements.
Optionally, the engine further comprises a generally cylindrical perforated drum configured to support the first and second heat exchanger arrangements, the flow control arrangement being attached to said drum.
Optionally, the first and second heat exchanger arrangements are generally annular and are arranged within an outer housing of the engine; a first portion of the second flow path is arranged to extend generally parallel to the longitudinal axis of the engine between the outer housing and the second heat exchanger arrangement; a second portion of the second flow path is arranged to extend generally perpendicular to said longitudinal axis in said gap between the first and second heat exchanger arrangements; and a third portion of the second flow path is arranged to extend generally parallel to said longitudinal axis through the centre of the generally annular first heat exchanger arrangement.
Optionally, the first heat exchanger arrangement is configured to be supplied with a heat transfer medium for undergoing heat transfer with the air received by the first heat exchanger inlet. The heat transfer medium may be any fuel type, any gas, any liquid, and/or any cryogenic fluid, for example, the heat transfer medium may be helium, kerosene, ammonia or hydrogen. The heat transfer medium may comprise a fuel, or the heat transfer medium may comprise a fluid that is different to and separate to (i.e. fluidly isolated from) a fuel used in the engine. The heat transfer medium may comprise a fluid that is different to and separate to (i.e. fluidly isolated from) a fuel used in the engine, and the engine may further comprise a third heat exchanger arrangement configured to provide for heat transfer between said heat transfer medium and said fuel. The fuel may comprise hydrogen. The fuel may be provided in liquid form or cryogenic form, for example, the fuel may comprise liquid hydrogen.
Optionally, the first heat exchanger arrangement may be configured such that air is configured to flow into and through the first heat exchanger arrangement substantially along the radial direction of the engine, i.e. to flow substantially perpendicular to the longitudinal axis of the engine.
According to a second aspect of the disclosure, there is provided a method of operating an engine according to the first aspect of the disclosure, the method comprising: causing air to flow along the first flow path such that at least a portion of the air received by the air inlet is cooled in the first heat exchanger arrangement by undergoing heat exchange with a heat transfer medium configured to flow through the first heat exchanger arrangement, before flowing downstream to the one or more turbomachinery components;
Optionally, the heat transfer medium is helium, kerosene, ammonia or hydrogen.
According to a third aspect of the disclosure, there is provided an engine, comprising: an air inlet configured to receive air; a first compressor configured to receive air; a first heat exchanger arrangement configured to cool air; the first compressor and the first heat exchanger arrangement being arranged downstream of the air inlet and being arranged along and generally centred on a longitudinal axis of the engine, and the first compressor having a radial direction that is perpendicular to said longitudinal axis; a first flow path arranged to extend through the first heat exchanger arrangement and an inner radial portion of the first compressor; and a second flow path arranged to extend through an outer radial portion of the first compressor, the second flow path bypassing the first heat exchanger arrangement.
Advantageously, such an engine can provide that air flowing through/around the inner radial portion of the compressor may be cooled more than air flowing through/around the outer radial portion of the compressor. Accordingly, such an engine can provide that all of the heat and temperature reduction capability of the first heat exchanger arrangement can be applied to/directed to only cool the air which really needs to be cooled, without doing any superfluous cooling, thus resulting in reduced pressure losses and hence improved overall engine efficiency. Furthermore, by providing enhanced cooling of the air which is configured to flow through the inner radial portion of the first compressor, leaving the air flowing through the outer radial portion of the first compressor either relatively uncooled or cooled to a lesser degree, this provides significant stress related to the first compressor, and especially to roots of its blades. This is because in general, keeping the inner radial portion and hence roots of said blades (i.e. a “hub section” of the first compressor) cool will provide a significant advantage to the engine's turbomachinery, because the inefficiency of the first compressor would otherwise typically manifest itself in flows along an inner wall of the first compressor as high temperature with lower pressure, this central area of the first compressor being where the rotating parasitic mass of the first compressor's blades meet a supporting/heavy thermally unresponsive disc/shaft of the first compressor. Thus, since the first compressor is configured to operate across both the first and second flow paths, such an engine advantageously provides an opportunity for the lower engine core air temperature to cool the first compressor itself, despite the outer radial portion thereof being in a relatively high temperature air flow. Thus, advantageously, blades of the first compressor may conduct heat away from relatively hotter blade tips towards relatively cooler but more highly mechanically stressed blade roots (i.e. from the radial outer portion to the radial inner portion). Advantageously, the highly stressed radial inner portion, which typically carries all the parasitic stress of the blades may thus be running at a significantly cooler temperature. In turn, this may advantageously reduce the inlet temperature of a second compressor in the engine, thus allowing said second compressor to generate an increased pressure ratio and flow, thus increasing the engine's overall specific thrust significantly more than if all of the air flow entering the engine via the air inlet were to be cooled in the first heat exchanger arrangement. Furthermore, this will also serve to better protect any bearing chambers, rotating machinery discs and seals etc. in the engine. In addition, when the engine is a bypass engine (i.e. an engine having a non-zero bypass ratio), this can enable the precooling action of the first heat exchanger arrangement to be directed more efficiently at the part of the engine's operating cycle that is causing specific thrust reduction/limitation, as the operational/flight speed of the engine increases, thus resulting in improved engine efficiency.
Optionally, the engine further comprises one or more turbomachinery components configured to receive air and arranged downstream of the first compressor, and one or more exhaust nozzles arranged downstream of the one or more turbomachinery components; wherein the first and second flow paths are arranged to extend from the air inlet to the one or more exhaust nozzles.
Optionally, the first flow path is arranged to extend through the one or more turbomachinery components, and the second flow path is arranged to bypass the one or more turbomachinery components. In other words, the engine may be a bypass engine, i.e. an engine having a bypass ratio (“BPR”), which is the ratio of the mass flow rate of the second flow path to the mass flow rate of the first flow path, that is greater than zero. Advantageously, such an engine can offer an improved level of specific thrust whilst also offering a moderate specific fuel consumption. Optionally, the bypass ratio is between 0.5 and 1.
Optionally, the engine further comprises a generally cylindrical outer casing within which the first compressor and the first heat exchanger arrangement are arranged. Optionally, the engine further comprises a generally cylindrical inner casing arranged concentrically inside the outer casing and within which the first heat exchanger arrangement is arranged. Optionally, at least a portion of the first flow path is arranged to extend through the centre of the generally cylindrical inner casing, and at least a portion of the second flow path is arranged to extend between the inner and outer casings.
Optionally, the first compressor comprises a plurality of blades angularly spaced apart from one another and each arranged to extend generally along said radial direction, wherein each of the blades has a root and a tip, the root being arranged closer to said longitudinal axis than the tip, such that at least a portion of the first flow path is arranged to extend adjacent the roots of the blades, and at least a portion of the second flow path is arranged to extend adjacent the tips of the blades.
Optionally, the first heat exchanger arrangement is arranged upstream of the first compressor.
Optionally, the first heat exchanger arrangement is arranged downstream of the first compressor and upstream of the one or more turbomachinery components.
Optionally, the engine further comprises a second heat exchanger arrangement configured to cool air arranged downstream of the air inlet and being arranged along and generally centred on said longitudinal axis; wherein the second flow path is arranged to extend through the second heat exchanger arrangement; such that the first heat exchanger arrangement is configured to cool a first portion of air received by the air inlet, and the second heat exchanger arrangement is configured to cool a second portion of air received by the air inlet, the first portion of air being configured to flow along the first flow path, and the second portion of air being configured to flow along the second flow path. The second heat exchanger arrangement may be arranged upstream of the first compressor. The second heat exchanger arrangement may be arranged downstream of the first compressor and upstream of the one or more turbomachinery components.
Advantageously, such an engine may provide that substantially all of the air entering the engine via the air inlet is cooled, but that the air flowing along the first flow path through the inner radial portion of the first compressor may be selectively cooled to a greater extent than the air flowing along the second flow path through the outer radial portion of the first compressor. The amount of a heat transfer medium flowing through the second heat exchanger arrangement may be controlled to be selectively reduced relative to the amount of a heat transfer medium flowing through the first heat exchanger arrangement, and/or stopped entirely, to selectively reduce the cooling capacity/effect of the second heat exchanger arrangement compared with that of the first heat exchanger arrangement. This may be done at high flight speeds/low operational speeds of the engine, for example at above approximately Mach 1.5, and/or in different modes of operation of the engine, to reduce or entirely stop the amount of precooling being performed on the air flowing along the second flow path, or to entirely stop the air flowing along the second flow path from being precooled.
Optionally, the engine further comprises a flow control arrangement configured to selectively control the amount of a heat transfer medium flowing through the second heat exchanger arrangement for undergoing heat transfer with said second portion of the air.
Advantageously, such an engine may provide for the cooling action of the second heat exchanger arrangement to be reduced relative to the cooling action of the first heat exchanger arrangement, or stopped entirely, to reduce or entirely stop the amount of precooling being performed on the air flowing along the second flow path, to advantageously focus the cooling on the inner radial portion of the first compressor, resulting in thermodynamic and mechanical advantages as discussed above, and thus leading to improved engine efficiency.
Optionally, the one or more turbomachinery components comprises a second compressor, at least one combustion chamber, and at least one turbine, the second compressor being configured to operate at a higher air pressure than the first compressor.
Optionally, the first heat exchanger arrangement is arranged upstream of the second compressor.
Optionally, the at least one combustion chamber comprises an air-breathing combustion chamber configured to receive compressed air from the second compressor and for the combustion of air and fuel, and a rocket combustion chamber for the combustion of fuel and oxidant, wherein the air-breathing combustion chamber and the rocket combustion chamber are configured to be operated independently.
Optionally, the engine further comprises a ramjet.
According to a fourth aspect of the disclosure, there is provided a method of operating an engine according to the third aspect of the disclosure, the method comprising: causing air to flow along the first flow path such that at least a first portion of the air received by the air inlet is configured to flow adjacent the inner radial portion of the first compressor and is cooled in the first heat exchanger arrangement by undergoing heat transfer with a heat transfer medium configured to flow through the first heat exchanger arrangement; and causing air to flow along the second flow path such that at least a second portion of the air received by the air inlet is configured to flow adjacent the outer radial portion of the first compressor and to bypass the first heat exchanger.
Optionally, the heat transfer medium is helium, kerosene, ammonia or hydrogen.
According to a fifth aspect of the disclosure, there is provided an engine, comprising: an air inlet configured to receive air; a first heat exchanger arrangement arranged downstream of the air inlet and configured to cool at least a portion of the air received by the air inlet; a first compressor arranged downstream of the first heat exchanger arrangement and configured to receive and compress at least a portion of the air cooled by the first heat exchanger arrangement; a second heat exchanger arrangement arranged downstream of the first compressor and configured to cool at least a portion of the air compressed by the first compressor; and a second compressor arranged downstream of the second heat exchanger arrangement and configured to receive and compress at least a portion of the air cooled by the second heat exchanger arrangement, the second compressor being configured to operate at a higher air pressure than the first compressor.
Such an engine can provide that substantially all of the air flow entering the engine via the air inlet is configured to be precooled by the first heat exchanger arrangement, and then to be intercooled by the second heat exchanger arrangement between the two compression stages in the first and second compressors. Advantageously, intercooling the air flow in the second heat exchanger allows for the second high pressure compressor to produce more work, by removing the waste heat from the first compression stage performed by the first low pressure compressor. Advantageously, performing both intercooling and precooling on the air flow (i.e. cooling the air both before and after the first compression stage in the first compressor) provides for reduced pressure losses, improved flexibility in operating the engine at different speeds, and improved overall engine efficiency.
Optionally, the first and second heat exchanger arrangements and the first and second compressors are arranged along and generally centred on a longitudinal axis of the engine, and the first and second heat exchanger arrangements are both generally annular and are configured for air to flow therethrough in a generally radial direction that is perpendicular to said longitudinal axis of the engine.
Optionally, the first and/or second heat exchanger arrangements each comprises a plurality of heat exchanger modules arranged along said longitudinal axis of the engine.
According to a sixth aspect of the disclosure, there is provided a method of operating an engine according to the fifth aspect of the disclosure, the method comprising: causing air to enter the engine via the air inlet;
Optionally, the first heat transfer medium and/or the second heat transfer medium comprises helium, kerosene, ammonia or hydrogen.
According to a seventh aspect of the disclosure, there is provided an engine, comprising: an air inlet configured to receive air; a heat exchanger arrangement arranged downstream of the air inlet, the heat exchanger arrangement configured for the flow of a heat transfer medium therethrough to cool air; one or more turbomachinery components arranged downstream of the heat exchanger arrangement and configured to receive air; a first flow path for the flow of air through the engine, arranged to extend from the air inlet to the one or more turbomachinery components via an inlet and an outlet of the heat exchanger arrangement; and an injection arrangement arranged downstream of the air inlet and comprising at least one injector nozzle configured to inject a liquid coolant into the first flow path upstream of the one or more turbomachinery components.
Advantageously, injecting droplets of a liquid coolant into the first flow path upstream of the one or more turbomachinery components can provide for improved cooling of the air, by supplementing/enhancing the cooling action of the heat exchanger arrangement. In particular, droplets of the liquid coolant in the first flow path will absorb heat from air flowing along the first flow path and will thus evaporate, in doing so, cooling the air. In other words, the vaporisation of the droplets will cause a reduction in the air temperature. This is in addition to the cooling of the air that is achieved by placing said air into heat transfer with a heat transfer medium in the heat exchanger arrangement. This combination is particularly advantageous because if the injection arrangement were to be used on its own to cool the air without the heat exchanger also being present in the engine, then the mass of liquid coolant required to provide for sufficient air cooling would be significantly large, and this large mass could potentially negate the benefits of any such cooling, since in aerospace applications for example, it is highly desirable to minimise mass to achieve improved efficiency and reduce fuel consumption. Also, when using coolant injection alone to cool air, there may be difficulties in ensuring that all of the coolant evaporates in time before the air flow enters the one or more turbomachinery components. By combining the injection arrangement with the heat exchanger arrangement, advantageously the injection arrangement can thus aid the cooling action of the heat exchanger arrangement, and vice versa, to provide that at least a portion of the air flowing along the first flow path is cooled as much as possible prior to ingestion in the one or more turbomachinery components. Advantageously, since the heat exchanger is also being used to perform some of said cooling, a lower mass of coolant is required for the injection arrangement.
Also, the injection arrangement can be used effectively to reduce the peak heat transfer requirement of the heat exchanger arrangement by “peak-load loping”, thus enabling the heat exchanger arrangement to be sized for more moderate heat transfer rates rather than for the peak heat transfer rate, thus reducing the size (and hence also the mass) of the heat exchanger and the engine. Furthermore, the combined use of the injection arrangement with the heat exchanger arrangement also enables operational flexibility of the engine, potentially allowing for high vehicle speeds to be accessed for short periods of time, when the engine is applied in a vehicle, for example an aerospace vehicle.
Optionally, the coolant comprises water and/or methanol.
Optionally, the coolant consists of water.
Advantageously based on its latent heat of vaporisation and specific heat capacity, using water as the coolant may provide for optimum cooling of the air to better aid the cooling operation of the heat exchanger arrangement.
Optionally, the injection arrangement is configured to inject the liquid coolant into the first flow path upstream of the heat exchanger outlet.
Advantageously, this can provide that droplets of the liquid coolant have more time to evaporate before the air flow is ingested into the one or more turbomachinery components.
Optionally, the injection arrangement is configured to inject the liquid coolant into the first flow path upstream of the heat exchanger inlet.
It is desirable for the liquid coolant droplets to evaporate by the time that the flow along the first flow path reaches the one or more turbomachinery components. Injecting the liquid coolant into the first flow path upstream of the heat exchanger inlet is thus advantageous because the flow of air through the heat exchanger arrangement will generally be slower than the flow of air into the engine via the air inlet, meaning that more time is available for the droplets to evaporate.
Optionally, the heat exchanger arrangement comprises a plurality of tubes for the flow of the heat transfer medium therethrough, wherein the first flow path is arranged to extend around and/or between said tubes.
Advantageously, when droplets of the liquid coolant are caused to flow from the heat exchanger inlet to the heat exchanger outlet, they can strike the tubes, through inertial effects, causing the droplets to break up and further slowing them down, thus encouraging and increasing the rate of their evaporation.
Optionally, the heat exchanger arrangement and the injection arrangement are both generally annular and are arranged along and generally centred on a longitudinal axis of the engine; at least a portion of the heat exchanger arrangement is arranged concentrically inside at least a portion of the injection arrangement; and the injection arrangement comprises a plurality of injector nozzles angularly spaced apart from one another relative to said longitudinal axis.
Optionally, a portion of the heat exchanger arrangement is arranged concentrically inside at least a portion of the injection arrangement.
Optionally, the at least one injector nozzle is configured to inject the liquid coolant into a portion of the first flow path, such that only a portion of the air configured to flow along the first flow path is configured to be cooled by the liquid coolant.
Optionally, when the engine is in operation, a first portion of air is configured to flow along the first flow path, and a second portion of air is configured to flow along the first flow path, the at least one injector nozzle being configured to inject the liquid coolant into one of the first or second portions, such that the other one of the first or second portions of air is not configured to be cooled by the liquid coolant.
Optionally, the injection arrangement comprises at least one first injector nozzle and at least one second injector nozzle arranged downstream of the at least one first injector nozzle.
Optionally, the injection arrangement further comprises one or more actuators configured to actuate the at least one first injector nozzle and the at least one second injector nozzle independently of one another.
Advantageously, this can provide that only a portion of the air being cooled by the heat exchanger arrangement is further cooled by the injection arrangement, e.g. such that a first portion of air being cooled by the heat transfer medium in the heat exchanger arrangement is configured to be further cooled by the injection arrangement, whilst a second portion of air being cooled by the heat transfer medium in the heat exchanger arrangement is configured to not be further cooled by the injection arrangement. For example, a first injector nozzle may be actuated independently of a second injector nozzle to provide for selective cooling in one or more regions/portions of air flow. Advantageously, this can provide that only a portion of the air is further cooled, by applying the injection arrangement to only some of the air flow entering the engine. This is advantageous because for example, at a low flight speed that is between subsonic to approximately Mach 1.5, full cooling of all of the air flow is not needed, and it would be more efficient to further cool using the liquid coolant/injection arrangement only a portion of the air, to advantageously reduce the total inlet pressure loss at such lower flight speeds, resulting in a more efficient engine. Furthermore, the injection arrangement in such an arrangement would therefore be of reduced mass and size and would require a reduced mass of water, thus resulting in improved engine efficiency.
Optionally, the injection arrangement comprises at least one first injector nozzle and at least one second injector nozzle arranged downstream of the at least one first injector nozzle; the at least one first injector nozzle is configured to inject first droplets of the liquid coolant into the first flow path; and the at least one second injector nozzle is configured to inject second droplets of the liquid coolant into the first flow path that have a smaller size than and/or at a lower mass flow rate than the first droplets.
Advantageously, the first droplets are injected further upstream than the second droplets so they have more time to evaporate, to increase the chances of them evaporating by the time the flow reaches the one or more turbomachinery components, and to increase their cooling capability of the air. The smaller and/or slower second droplets are injected further downstream, so that their initial size and/or speed is smaller to increase the chances of them evaporating by the time the flow reaches the one or more turbomachinery components, since they have a shorter distance to travel. Since the first droplets have a larger size and/or higher mass flow rate, they can provide for more cooling than the second droplets, and arranging them upstream of the second droplets provides that as well as providing for more cooling, they will also evaporate in time.
Optionally, the injection arrangement further comprises one or more actuators configured to actuate the at least one first injector nozzle and the at least one second injector nozzle independently of one another.
Optionally, the at least one injector nozzle is further configured to inject an antifreeze into the first flow path.
Advantageously, this may prevent frost formation in and/or on the heat exchanger arrangement.
Optionally, the antifreeze may comprise methanol.
Optionally, the injection arrangement further comprises one or more valves arranged upstream of the at least one injector nozzle and configured to open and close to control the flow of the liquid coolant through the at least one injector nozzle.
Optionally, the injection arrangement further comprises one or more actuators configured to actuate the opening and closing of the one or more valves.
Optionally, the injection arrangement further comprises a coolant supply for supplying the liquid coolant to the at least one injector nozzle. Optionally, the injection arrangement further comprises one or more valves configured to control the supply of the liquid coolant to the at least one injector nozzle from the coolant supply. Optionally, the one or more valves are controlled by one or more actuators, for example an electric pump. Optionally, each of the at least one injector nozzles is associated with its own respective actuator, such that the flow of the liquid coolant through each of the at least one injector nozzle may be controlled (e.g. “turned off” or “turned on”) through each of the respective individual injector nozzles.
According to an eighth aspect of the disclosure, there is provided a method of operating an engine according to the seventh aspect of the disclosure, the method comprising: causing air to flow along the first flow path such that at least a portion of the air received by the air inlet is cooled in the heat exchanger arrangement by undergoing heat exchange with the heat transfer medium, before flowing downstream to the one or more turbomachinery components; and injecting the liquid coolant into the first flow path to supplement the cooling action of the heat transfer medium in the heat exchanger arrangement, to further cool at least a portion of said at least a portion of the air received by the air inlet before it flows downstream to the one or more turbomachinery components.
Optionally, the liquid coolant consists of water.
Optionally, the method further comprises actuating one or more valves arranged upstream of the at least one injector nozzle to control the flow of the liquid coolant through the at least one injector nozzle.
According to a ninth aspect of the disclosure, there is provided an engine, comprising: an air inlet configured to receive air; a heat exchanger arrangement configured downstream of the air inlet, the heat exchanger arrangement configured to cool at least a portion of the air received by the air inlet; one or more turbomachinery components arranged downstream of the heat exchanger arrangement and configured to receive air; and a throttling arrangement arranged upstream of the one or more turbomachinery components and configured to control the mass flow rate of air flow through the heat exchanger arrangement.
Advantageously, this can allow the one or more turbomachinery components (which may be referred to as a “core engine” or “engine core”) to effectively operate at a lower pressure than the air intake arrangement. Also, when employed in a bypass engine (i.e. an engine having a non-zero BPR), this can allow the core engine to effectively operate at a lower pressure than the bypass system, thus permitting the bypass pressure to be increased to up to 1.9 bar, thereby increasing the bypass thrust at high Mach numbers whilst maintaining the non-dimensional operating point of a compressor in the engine constantly to modulate the flow therethrough, to achieve higher thrust at high Mach numbers/high flight speeds. The throttling arrangement also advantageously permits deep throttling of the airbreathing engine at fixed non-dimensional conditions which could be useful for engine starting, ferry flights and aborts.
Optionally, the throttling arrangement is arranged upstream of an outlet of the heat exchanger arrangement.
Optionally, the throttling arrangement is arranged upstream of an inlet of the heat exchanger arrangement.
Optionally, the throttling arrangement comprises one or more valves each configured to be movable into an open position, a closed position, and at least one intermediate position therebetween, to control the flow of air therethrough.
Advantageously, the throttling arrangement may be used to throttle the flow of air through the heat exchanger arrangement. That is, unless all of the one or more valves are completely closed, substantially all of the air received in the engine by the air inlet will be caused to flow into an inlet of the heat exchanger arrangement, such that substantially all of the air received into the engine is cooled by the heat exchanger arrangement, but by varying the size of the opening through each of the one or more valves by moving them between the open and closed positions thereof, the mass flow rate of the air therethrough, and hence the mass flow rate of air through the heat exchanger arrangement, can be reduced/controlled. This can be done to reduce the pressure mismatch in the engine to balance the pressure across the heat exchanger arrangement.
Optionally, the one or more valves comprises a plurality of butterfly valves angularly spaced apart from one another relative to a longitudinal axis of the engine.
Optionally, the plurality of butterfly valves are arranged to be angularly spaced apart from one another relative to a longitudinal axis of the engine in rows spaced apart from one another along said longitudinal axis.
Optionally, the plurality of butterfly valves comprises a first set of butterfly valves configured to be rotated in a first direction and a second set of butterfly valves configured to be rotated in a second direction that is opposite to the first direction, wherein the first and second sets of butterfly valves are arranged alternately with respect to one another about the longitudinal axis of the engine.
Advantageously, rotating alternate butterfly valves in opposite directions can eliminate outlet swirl.
Optionally, the throttling arrangement further comprises one or more actuators configured to actuate the movement of the one or more valves.
Optionally, the heat exchanger arrangement comprises a generally annular cylindrical heat exchanger. Optionally, the heat exchanger arrangement comprises a generally annular conical heat exchanger. Optionally, the heat exchanger arrangement comprises a plate heat exchanger. Optionally, the heat exchanger arrangement comprises a plurality of heat exchanger modules.
Optionally, the heat exchanger arrangement is generally annular and is arranged along and generally centred on a longitudinal axis of the engine, and is configured for air to flow therethrough in a generally radial direction that is perpendicular to said longitudinal axis; and the throttling arrangement is arranged on or adjacent a bore of the generally annular heat exchanger arrangement.
Optionally, the heat exchanger arrangement comprises: at least one fluid conduit section for the flow of a heat transfer medium therethrough, wherein said at least a portion of the air received by the air inlet is configured to flow around and/or between said at least one fluid conduit section; and a support structure comprising a generally cylindrical perforated drum structure, to which the throttling arrangement is attached.
Optionally, the heat exchanger arrangement comprises a plurality of heat exchanger modules; and the throttling arrangement comprises a plurality of groups of valves each associated with one of the heat exchanger modules, wherein each of the groups of valves is configured to be actuated independently with respect to the other groups of valves, to independently control the mass flow rate of air flow through its respective heat exchanger module.
Advantageously, this can enable the precooling action of the heat exchanger arrangement to be directed more efficiently at the part of the engine's operating cycle that is causing specific thrust reduction/limitation, as the operational speed of the engine increases, to reduce pressure losses by avoiding superfluously cooling any air that does not need to be cooled, thus resulting in improved engine efficiency.
According to a tenth aspect of the disclosure, there is provided a method of operating an engine according to the ninth aspect of the disclosure, the method comprising: causing air to enter the engine via the air inlet; causing at least a portion of the air received by the air inlet to flow downstream to be cooled in the heat exchanger arrangement by a heat transfer medium; and actuating the throttling arrangement to control the mass flow rate of air flow through the heat exchanger arrangement.
It is to be understood that an engine according to the first aspect of the disclosure may be combined with one or more of the above features of the engines according to the third, fifth, seventh and/or ninth aspects of the disclosure, though said features are not repeated herein, for the sake of conciseness and to avoid repetition.
Similarly, it is to be understood that an engine according to the third aspect of the disclosure may be combined with one or more of the above features of the engines according to the first, fifth, seventh and/or ninth aspects of the disclosure.
It is to be understood that an engine according to the fifth aspect of the disclosure may be combined with one or more of the above features of the engines according to the first, third, seventh and/or ninth aspects of the disclosure.
It is to be understood that an engine according to the seventh aspect of the disclosure may be combined with one or more of the above features of the engines according to the first, third, fifth and/or ninth aspects of the disclosure.
It is to be understood that an engine according to the ninth aspect of the disclosure may be combined with one or more of the above features of the engines according to the first, third, fifth and/or seventh aspects of the disclosure.
According to an eleventh aspect of the disclosure, there is provided an aircraft, flying machine or aerospace vehicle comprising an engine according to any one or more of the first, third, fifth, seventh and/or ninth aspects of the disclosure.
The present disclosure may be carried out in various ways and embodiments of the disclosure will now be described by way of example with reference to the accompanying drawings, in which:
As shown in
Alternative engines which comprise one or more additional means which can be used to supplement and/or replace the cooling action of a precooler heat exchanger, such as that of the precooler heat exchanger 3 shown in
High Mach/hypersonic platforms are anticipated to employ precooled turbofan/jet engines for primary vehicle propulsion. A conventional turbofan or jet engine in isolation cannot typically reach hypersonic velocities due to the elevated enthalpy of the freestream flow causing the engine's operation to be restricted by practical limitations, such as a compressors' temperature limits. The use of a precooler (such as the heat exchanger 3) allows the inlet flow to be cooled such that the turbofan/jet may be run at both subsonic flight velocities and at velocities which are beyond its typical operating envelope. By extending this envelope to high Mach regimes, the propulsion system will then be able to undertake a mode transition whereby a ramjet is activated within the bounds of efficient space envelope and performance. This can provide a flexible operation since the engine may operate in any mode and also transition between them. In the exemplary precooled engine shown in
The flow control arrangement 13 includes an inner structure 14 comprising a generally conical upstream portion 21 having an apex, and an outer structure 15 that is generally annular and includes a tapered outer surface 18 that is generally in the form of a truncated cone. The inner structure 14 is movable relative to the outer structure 15 along the longitudinal axis 19 of the engine 11 and is arranged concentrically inside the outer structure 15. An actuator arrangement (not shown) is configured to control the movement of the inner and outer structures 14, 15 relative to one another, and may comprise, for example, one or more fueldraulic, hydraulic, pneumatic, ball-screw and/or electric actuators. In the example shown, the longitudinal axis 19 is generally linear, though it is also envisaged that said longitudinal axis may be at least partially curved. The inner structure 14 may be filled with a honeycomb filler material, or any other suitable filling means, to advantageously improve its mechanical stiffness. In the position shown in
In this manner, when the flow control arrangement 13 is in the “open” position 140 (see
Precooling only a portion of the air entering the engine 11 may be desirable at low Mach operation of the engine, when full precooling of all of the air flow is not needed, thus leading to a more efficient engine performance, by not doing any superfluous precooling, to advantageously reduce the total inlet pressure loss at lower flight speeds, such as at flight speeds between subsonic and approximately Mach 1.5.
In the examples shown in
In the example shown in
In an alternative example of a flow control arrangement 13 as shown in
When the inner structure 14 is at a first rotational position relative to the outer structure 15 (see
Although the exemplary heat exchanger 3 shown and described in relation to
As shown in the alternative example of an engine 11 shown in
Like the first heat exchanger 3, the second heat exchanger 57 has an inlet 57i and an outlet 570. The first and second heat exchangers 3, 57 are spaced apart from one another along the longitudinal axis 19 of the engine 11 and are arranged with a gap 58 therebetween. The flow control arrangement 13 is arranged in the gap 58 and provides for selective bypassing of the first heat exchanger 3.
As shown in
Specifically, referring back to
Although in the embodiment shown in
An alternative means to cool air upstream of one or more turbomachinery components shall now be described. Bypass engines are a type of engine having one gas stream which passes through the core engine (i.e. the turbomachinery and combustion chamber), and another gas stream which bypasses the core engine (i.e. which flows around the turbomachinery and combustion chamber without being worked on therein). One property of such engines is that they have a bypass ratio (“BPR”), which is the ratio between the mass flow rate of the bypass stream to the mass flow rate entering the engine core, and which may typically be between 0.5 and 1. An engine having a BPR of greater than zero is a bypass engine. Bypass engines advantageously offer a good level of specific thrust whilst also offering a moderate specific fuel consumption. Using a precooler (a precooling heat exchanger arrangement) to cool the air entering an engine is one way to address the reduction in specific power/thrust typically observed at higher flight speeds in such engines. However, if a precooler is used with a bypass engine to cool all of the air flow entering the bypass engine, then as an example, for a BPR of between 0.5 and 1, around 30-50% of the heat transferred by the precooler (through the reduced air temperature) would be in air sent through the bypass (i.e. the gas stream which bypasses the engine core), with insignificant thrust benefit. In fact, at certain conditions where the use of an after burner is required, the lower temperature of precooled air would require more fuel flow to achieve a given/limiting afterburner flame temperature, thus deteriorating the fuel efficiency. This impact would be further exacerbated by an increase in forward speed of the aircraft as the engine needs to “throttle back” further to limit the high pressure compressor and turbine inlet temperatures. This “throttling back” would increase the operating BPR further and can effectively double the designed/intended BPR at high aircraft speeds (e.g. at higher Mach operation). This effect further dilutes the benefits of precooling all of the air entering the engine inlet, leading to inefficiencies in the overall engine operation.
This effect of engine architecture can advantageously be mitigated significantly by the use of partial inlet air flow cooling, as described below in relation to
In the example shown, the first heat exchanger 34 is generally annular such that air is configured to flow from its inlet 34i to its outlet 34o generally inwardly parallel to a radial direction 39 of the first low pressure compressor 35 that is generally perpendicular to the longitudinal axis 38, and is configured to cool a first portion of the air received by the air inlet 32, before said air is then compressed in the first low pressure compressor 35. It is though envisaged that the first exchanger 34 may have any other suitable form, for example it may be a conical and/or modular heat exchanger, or it may be a plate heat exchanger.
An outer radial portion 35 or of the compressor 35 that is generally annular is arranged further apart from the longitudinal axis 38 than an inner radial portion 35ir of the compressor 35 that is generally circular. As shown in
Furthermore, another advantage of the engines shown in
In light of the aforementioned significant mechanical and thermodynamic advantages, it is therefore envisaged that the concept of partial inlet air flow cooling may thus also be applied to non-bypass engines (i.e. engines having a BPR of zero), as discussed below in relation to
Similarly,
In the examples shown in
It is also envisaged that an intercooler may also be used with a precooler more generally, to cool all of the air flow, as shown in
A means to supplement the cooling action of a heat exchanger shall now be described, with reference to
In the example shown in
Advantageously, injecting droplets 71 of a liquid coolant (which in the example described herein consists of water, but which may be any other suitable coolant, for example methanol, or a mixture of water and methanol) into the first flow path upstream of the one or more turbomachinery components provides for improved cooling of the air, by supplementing/enhancing the precooling action of the heat exchanger 3. In particular, the droplets 71 will absorb heat from the air and will thus evaporate, in doing so, cooling the air. In other words, the vaporisation of the droplets 71 will cause a reduction in the air temperature. This is in addition to the cooling of the air that is achieved by placing said air into heat transfer with a heat transfer medium in the heat exchanger 3. This combination is particularly advantageous because if the injection arrangement 67 were to be used on its own to precool the air without the heat exchanger 3 also being present, then the mass of liquid coolant required to provide for sufficient air cooling would be significantly large, and this large mass could potentially negate the benefits of any such cooling, since in aerospace applications for example, it is highly desirable to minimise mass to achieve improved efficiency and reduce fuel consumption. Also, when using coolant injection alone to cool air, there may be difficulties in ensuring that all of the coolant evaporates in time before the air flow enters the one or more turbomachinery components.
By combining the injection arrangement 67 with the heat exchanger 3, advantageously it can thus aid the cooling action of the heat exchanger 3, and vice versa, to provide that the air flowing along the first flow path 70 is cooled as much as possible prior to ingestion in the one or more turbomachinery components 4. Since the heat exchanger 3 is also being used to perform some of said cooling, a lower mass of coolant is required for the injection arrangement 67. Also, the injection arrangement 67 can be used effectively to reduce the peak heat transfer requirement of the heat exchanger 3 by “peak-load loping”, thus enabling the heat exchanger 3 to be sized for more moderate heat transfer rates rather than for the peak heat transfer rate, thus reducing the size (and hence also the mass) of the heat exchanger 3. Furthermore, the combined use of the injection arrangement 67 with the heat exchanger 3 also enables operational flexibility of the engine 72, potentially allowing for high vehicle speeds to be accessed for short periods of time, when the engine 72 is applied in a vehicle, for example an aerospace vehicle.
It is desirable for the droplets 71 to evaporate by the time that the air flow reaches the one or more turbomachinery components 4. Injecting the droplets 71 into the first flow path 70 upstream of the heat exchanger inlet 3i is thus advantageous because the flow of air flow through the heat exchanger 3 is generally slower than the flow of air in the air intake arrangement 2, meaning that more time is available for the droplets 71 to evaporate. In the example described herein, the heat exchanger 3 comprises a plurality of tubes (not shown) for the flow of a heat transfer medium therein, and the air flowing along the first flow path 70 is configured to flow around and/or between said tubes, to undergo heat transfer with the heat transfer medium. Advantageously, when the droplets 71 are flowing from the heat exchanger inlet 3i to the heat exchanger outlet 30, they can strike the tubes, through inertial effects, causing the droplets 71 to break up and further slowing them down, thus encouraging and increasing the rate of their evaporation.
In the example shown in
A means to throttle air flowing through a heat exchanger shall now be described, with reference to
It is also to be understood that while the example shown in
As shown in
In the example shown, the butterfly valves 74 are arranged adjacent to the heat exchanger outlets 3o, 57o in the bore 76 of the generally cylindrical/annular modular heat exchanger arrangement 60 and are attached to the cylindrical perforated drum structure 59. Though, it is also envisaged that the throttling arrangement 73 may be arranged at any other location upstream of said one or more turbomachinery components, for example within a matrix of a heat exchanger between its inlet and outlet, or upstream of the inlet of a heat exchanger.
The butterfly valves 74 may be similar to the butterfly valves 61 described above and shown in
In this manner, the throttling arrangement 73 may be used to throttle the flow of air (i.e. to selectively reduce the mass flow rate of air) through the heat exchanger 3 and/or through the heat exchanger 57. That is, unless the butterfly valves 74 are completely closed, substantially all of the air received into the engine will be caused to flow into the heat exchanger inlets 3i, 57i such that substantially all of the air received into the engine is cooled by the heat exchanger 3 or the heat exchanger 57, but by varying the size of the opening through each of the butterfly valves 74, the mass flow rate of the air therethrough, and hence the mass flow rate of air through the heat exchangers 3, 57 can be reduced/controlled, i.e. throttled. This can be done to reduce the pressure mismatch in the engine to balance the pressure across the heat exchangers—i.e. by controlling the mass flow rate of the air flow, the pressure on either side of the butterfly valves 74 can be changed. Advantageously, this can allow the core engine to effectively operate at a lower pressure than the air intake arrangement. Also, when employed in a bypass engine (i.e. an engine having a non-zero BPR), this can allow the core engine to effectively operate at a lower pressure than the bypass system, thus permitting the bypass pressure to be increased to up to 1.9 bar, thereby increasing the bypass thrust at high Mach numbers whilst maintaining the non-dimensional operating point of a compressor in the engine constantly to modulate the flow therethrough, to achieve higher thrust at high Mach numbers/high flight speeds. The throttling arrangement 73 also permits deep throttling of the airbreathing engine at fixed non-dimensional conditions which could be useful for engine starting, ferry flights and aborts.
Referring now to
It should be understood that one or more of the aforementioned exemplary various means of performing/controlling air cooling in engines may be combined with one another. It should also be understood that the disclosure also includes an aircraft, flying machine or aerospace vehicle comprising any one or more of the exemplary engines and/or heat exchangers and/or air cooling means as described above.
Various modifications may be made to the described embodiment(s) without departing from the scope of the invention as defined by the accompanying claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2018754.8 | Nov 2020 | GB | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2021/083251 | 11/26/2021 | WO |
