Patent Description:
Gas turbine engines, such as those utilized in commercial and military aircraft, include a compressor section that compresses air, a combustor section in which the compressed air is mixed with a fuel and ignited, and a turbine section across which the resultant combustion products are expanded. The expansion of the combustion products drives the turbine section to rotate. As the turbine section is connected to the compressor section via a shaft, the rotation of the turbine section further drives the compressor section to rotate. In some configurations, a fan is also connected to the shaft and is driven to rotate via rotation of the turbine.

The compression process of the gas turbine engine results in a rise in the temperature of the gas at the compressor exit due to increasing pressure and component inefficiencies. At certain elevated pressures, the compressed air may become hotter than desirable for the purposes of turbine cooling and it is desirable to cool the compressed air prior to being used as a cooling fluid within the gas turbine engine. The waste heat that is generated (extracted) from this cooled cooling air is imparted to the exhaust flow and expelled without providing additional work. Waste heat is a source of loss (inefficiency) in a thermodynamic cycle, and reduction of waste heat in an engine therefore increases the efficiency of the engine.

<CIT> and <CIT> both disclose gas turbine engines including a means for recovering waste heat and an auxiliary power unit.

According to a first aspect, a waste heat management system according to claim <NUM> is provided.

Optionally, embodiments of the waste heat management systems may include that the APU system is integrated with the turbine engine.

Optionally, embodiments of the waste heat management systems may include that the APU system is integrated within the turbine engine.

Optionally, embodiments of the waste heat management systems may include a switch valve configured to selectively direct a working fluid to the heat recovery heat exchanger and the secondary heat recovery heat exchanger.

Optionally, embodiments of the waste heat management systems may include that the working fluid is directed to the heat recovery heat exchanger when the gas turbine engine is in an on state and wherein the working fluid is directed to the secondary heat recovery heat exchanger when the gas turbine engine is in an off state.

Optionally, embodiments of the waste heat management systems may include that the waste heat recovery system includes a turbine and wherein the APU system is operably connected to the turbine of the waste heat recovery system.

Optionally, embodiments of the waste heat management systems may include that the generated work is at least one of mechanical work and electrical power.

Optionally, embodiments of the waste heat management systems may include a switch valve configured to selectively direct a working fluid through the APU system.

According to one embodiment, a waste heat management system is provided. The waste heat management system includes a cooling duct, a waste heat recovery system having a heat rejection heat exchanger thermally connected to a portion of the cooling duct, the heat rejection heat exchanger being a working fluid-to-air heat exchanger, a recuperating heat exchanger being a working fluid-to-working fluid heat exchanger, a heat recovery heat exchanger being a working fluid-to-exhaust heat exchanger, an auxiliary power unit (APU) system having a secondary heat recovery heat exchanger that is a working fluid-to-APU exhaust heat exchanger, and a working fluid within the waste heat recovery system configured to flow through the recuperating heat exchanger, the heat rejection heat exchanger, and at least one of the heat recovery heat exchanger and the secondary heat recovery heat exchanger.

Optionally, embodiments of the waste heat management systems may include that the working fluid is supercritical CO<NUM> (sCO<NUM>).

Optionally, embodiments of the waste heat management systems may include a switch valve configured to selectively direct the working fluid to the heat recovery heat exchanger and the secondary heat recovery heat exchanger.

Optionally, embodiments of the waste heat management systems may include that the APU system comprises an APU blower arranged between the APU burner and the secondary heat recovery heat exchanger.

Optionally, embodiments of the waste heat management systems may include that the waste heat recovery system comprises a turbine and wherein the APU system is operably connected to the turbine of the waste heat recovery system.

The foregoing features and elements may be executed or utilized in various combinations without exclusivity, unless expressly indicated otherwise.

As illustratively shown, the gas turbine engine <NUM> is configured as a two-spool turbofan that has a fan section <NUM>, a compressor section <NUM>, a combustor section <NUM>, and a turbine section <NUM>. The illustrative gas turbine engine <NUM> is merely for example and discussion purposes, and those of skill in the art will appreciate that alternative configurations of gas turbine engines may employ embodiments of the present disclosure. The fan section <NUM> includes a fan <NUM> that is configured to drive air along a bypass flow path B in a bypass duct defined within a nacelle <NUM>. The fan <NUM> is also configured to drive air along a core flow path C for compression and communication into the combustor section <NUM> then expansion through the turbine section <NUM>. Although depicted as a two-spool turbofan gas turbine engine in the disclosed non-limiting embodiment, it should be understood that the concepts described herein are not limited to use with two-spool turbofans as the teachings may be applied to other types of turbine engines.

In this two-spool configuration, the gas turbine engine <NUM> includes a low speed spool <NUM> and a high speed spool <NUM> mounted for rotation about an engine central longitudinal axis A relative to an engine static structure <NUM> via one or more bearing systems <NUM>. It should be understood that various bearing systems <NUM> at various locations may be provided, and the location of bearing systems <NUM> may be varied as appropriate to a particular application and/or engine configuration.

The low speed spool <NUM> includes an inner shaft <NUM> that interconnects the fan <NUM> of the fan section <NUM>, a first (or low) pressure compressor <NUM>, and a first (or low) pressure turbine <NUM>. The inner shaft <NUM> is connected to the fan <NUM> through a speed change mechanism, which, in this illustrative gas turbine engine <NUM>, is as a geared architecture <NUM> to drive the fan <NUM> at a lower speed than the low speed spool <NUM>. A combustor <NUM> is arranged in the combustor section <NUM> between the high pressure compressor <NUM> and the high pressure turbine <NUM>. A mid-turbine frame <NUM> of the engine static structure <NUM> is arranged between the high pressure turbine <NUM> and the low pressure turbine <NUM>. The mid-turbine frame <NUM> may be configured to support one or more of the bearing systems <NUM> in the turbine section <NUM>. The inner shaft <NUM> and the outer shaft <NUM> are concentric and rotate via the bearing systems <NUM> about the engine central longitudinal axis A which is collinear with their longitudinal axes.

The core airflow through core airflow path C is compressed by the low pressure compressor <NUM> then the high pressure compressor <NUM>, mixed and burned with fuel in the combustor <NUM>, then expanded over the high pressure turbine <NUM> and low pressure turbine <NUM>. The mid-turbine frame <NUM> includes airfoils <NUM> (e.g., vanes) which are arranged in the core airflow path C. The turbines <NUM>, <NUM> rotationally drive the respective low speed spool <NUM> and high speed spool <NUM> in response to the expansion of the core airflow. It will be appreciated that each of the positions of the fan section <NUM>, the compressor section <NUM>, the combustor section <NUM>, the turbine section <NUM>, and geared architecture <NUM> or other fan drive gear system may be varied. For example, in some examples, the geared architecture <NUM> may be located aft of the combustor section <NUM> or even aft of the turbine section <NUM>, and the fan section <NUM> may be positioned forward or aft of the location of the geared architecture <NUM>.

The gas turbine engine <NUM> in one example is a high-bypass geared aircraft engine. In some such examples, the engine <NUM> has a bypass ratio that is greater than about six (<NUM>), with an example being greater than about ten (<NUM>). In some examples, the geared architecture <NUM> is an epicyclic gear train, such as a planetary gear system or other gear system, with a gear reduction ratio of greater than about <NUM> and the low pressure turbine <NUM> has a pressure ratio that is greater than about five (<NUM>). In one non-limiting example, the bypass ratio of the gas turbine engine <NUM> is greater than about ten (<NUM>:<NUM>), a diameter of the fan <NUM> is significantly larger than that of the low pressure compressor <NUM>, and the low pressure turbine <NUM> has a pressure ratio that is greater than about five (<NUM>:<NUM>). The low pressure turbine <NUM> pressure ratio is pressure measured prior to inlet of low pressure turbine <NUM> as related to the pressure at the outlet of the low pressure turbine <NUM> prior to an exhaust nozzle. In some examples, the geared architecture <NUM> may be an epicycle gear train, such as a planetary gear system or other gear system, with a gear reduction ratio of greater than about <NUM>:<NUM>. It should be understood, however, that the above parameters are only for example and explanatory of one non-limiting example of a geared architecture engine and that the present disclosure is applicable to other gas turbine engines including turbojets or direct drive turbofans or turboshafts.

The fan section <NUM> of the gas turbine engine <NUM> is designed for a particular flight condition -- typically cruise at about <NUM> Mach and about <NUM>,<NUM> feet (<NUM>,<NUM> meters). The low fan pressure ratio as disclosed herein according to one non-limiting example is less than about <NUM>. "Low corrected fan tip speed" is the actual fan tip speed in ft/sec divided by an industry standard temperature correction of [(Tram °R) / (<NUM> °R)^<NUM> whereby T(K) = T(°R) * (<NUM>/<NUM>). The "Low corrected fan tip speed" as disclosed herein according to one non-limiting example is less than about <NUM> ft / second (<NUM> meters/second).

Gas turbine engines generate substantial amounts of heat that is exhausted from the turbine section <NUM> into a surrounding atmosphere. This expelled exhaust heat represents wasted energy, and can be a large source of inefficiency in gas turbine engines.

Turning now to <FIG>, a schematic illustration of a gas turbine engine <NUM>, including a compressor section <NUM>, a combustor section <NUM>, and a turbine section <NUM>, all of which are connected via a primary fluid flow path, is shown. The gas turbine engine <NUM> may have, for example, a similar structure and configuration as that shown and described with respect to <FIG>, although such structure is not to be limiting and such systems will include, at least, various additional components as described herein. The turbine cooling air is employed to provide cooling to the turbines and other components of the gas turbine engine <NUM>.

To capture the waste heat within the gas turbine engine <NUM> and convert such waste heat to work, a waste heat recovery heat exchanger <NUM> is connected to a compressor bleed port <NUM> and a turbine inlet <NUM>. The waste heat recovery heat exchanger <NUM> provides a hot flow path <NUM> that connects the compressor bleed port <NUM> to the turbine inlet <NUM>. As such, the hot flow path <NUM> bypasses the combustor section <NUM>. In one non-limiting example, the compressor bleed port <NUM> is located at or downstream of an aft most compressor stage of the compressor section <NUM>. Further, in some examples, the turbine inlet <NUM> is arranged at or upstream of the upstream-most turbine stage of the turbine section <NUM>.

As the air from the compressor bleed port <NUM> is passed through the waste heat recovery heat exchanger <NUM>, a portion of the heat in the bypassed air may be extracted at the waste heat recovery heat exchanger <NUM>. The heat extracted from the hot flow path <NUM> provides the air at the turbine inlet <NUM> to be at an appropriate pressure and temperature to be used to cool portions of the turbine section <NUM>. The waste heat recovery heat exchanger <NUM> extracts heat from the air bled from the compressor section <NUM> and provides the extracted heat to a waste heat recovery system <NUM>. The waste heat recovery system <NUM> is configured to use the waste heat to generate work and provide the generated work to one or more engine systems within the gas turbine engine <NUM>. The waste heat recovery heat exchanger <NUM> includes the hot flow path <NUM> (may be a first fluid path) that connects the compressor bleed port <NUM> to the turbine inlet <NUM>, and a cold flow path <NUM> (may be a second fluid path) that connects an inlet <NUM> of the waste heat recovery system <NUM> and an outlet <NUM> of the waste heat recovery system <NUM>.

Within the waste heat recovery heat exchanger <NUM>, heat is transferred from air within the hot flow path <NUM> to working fluid within the cold flow path <NUM>. The cold flow path <NUM> is connected to the waste heat recovery system <NUM>. In some examples, the waste heat recovery system <NUM> is configured as a supercritical CO<NUM> (sCO<NUM>) Brayton cycle. The waste heat recovery system <NUM> converts the extracted heat into work (e.g., rotational work and/or electrical) which is provided to at least one additional engine system of the gas turbine engine <NUM>. The waste heat recovery system <NUM> includes a working fluid (e.g., sCOz) that is retained and used within a closed-loop system (e.g., within the waste heat recovery system <NUM>). The waste heat recovery system <NUM> recuperates waste heat and expands the sCO<NUM> working fluid below the supercritical pressure during a working cycle. Such expansion of the sCO<NUM> is referred to as an overexpanded recuperating work recovery cycle.

In the illustrative configuration, included within the waste heat recovery system <NUM> is a turbine <NUM> with an inlet <NUM> connected to an output of the waste heat recovery heat exchanger <NUM>. The turbine <NUM> is configured to expand the heated working fluid and expels the heated working fluid through a turbine outlet <NUM>. The turbine <NUM> may be configured to expand the working fluid beyond an expansion that would place the working fluid back at, or just above, the supercritical point prior to a beginning of a working fluid cycle. This expansion may be referred to as overexpansion. As a result of the overexpansion, a secondary compressor <NUM> and a second heat rejection heat exchanger <NUM> are, optionally, included within the working cycle of the waste heat recovery system <NUM> to return the working fluid (sCO<NUM>) to a pressure and temperature required to achieve a supercritical state at the beginning of a working cycle.

From the turbine <NUM>, the expelled working fluid is passed through a relatively hot passage of a recuperating heat exchanger <NUM>. The working fluid is then passed to a relatively hot passage of a first heat rejection heat exchanger <NUM>. After passing through the first heat rejection heat exchanger <NUM>, the working fluid is passed to the secondary compressor <NUM> and the second heat rejection heat exchanger <NUM>. The working fluid is then passed to an inlet <NUM> of a compressor <NUM> (alternately referred to as a working fluid compressor <NUM>). The compressor <NUM> is configured to compress the working fluid and direct the compressed working fluid from a compressor outlet <NUM> to a cold passage of the recuperating heat exchanger <NUM>. In practical terms, the location of the inlet <NUM> of the working fluid compressor <NUM> is referred to as the start of the working fluid cycle.

During operation of the waste heat recovery system <NUM>, the compressor <NUM> compresses the working fluid, and passes the compressed working fluid through the recuperating heat exchanger <NUM> and the waste heat recovery heat exchanger <NUM>, causing the compressed working fluid to be heated. The heated working fluid is provided to the inlet <NUM> of the turbine <NUM> and expanded through the turbine <NUM>, driving the turbine <NUM> to rotate. As described above, the turbine <NUM> is configured to overexpand the working fluid beyond a point that would return the working fluid to the state of the working fluid at the beginning of the cycle. The rotation of the turbine <NUM> drives rotation of the compressor <NUM>, the overexpansion compressor <NUM>, and an output shaft <NUM>. The output shaft <NUM> is mechanically connected or coupled to one or more additional turbine engine systems. The coupling of the output shaft <NUM> provides work to the connected systems using any conventional means for transmitting rotational work. Additionally, in some examples and configurations, the rotational work can be converted into electricity and used to power one or more engine or aircraft systems. By way of example, transmitting rotational work can include a drive shaft, a gear system, an electrical generator and distribution system, or any similar structure(s). In the illustrated example, the working fluid is a CO<NUM> fluid that is maintained at or above a supercritical point throughout the entirety of the working cycle. Due to being maintained at or above the supercritical vapor dome, the waste heat recovery system <NUM> may be referred to as a supercritical CO<NUM> cycle (sCO<NUM> cycle).

Referring now to <FIG>, a chart <NUM> illustratively shows a state of a working fluid throughout a working cycle of a waste heat recovery system. For example, chart <NUM> may represent a state plot of a working fluid within the waste heat recovery system <NUM> shown in <FIG>. The chart <NUM> illustrates the relationship of temperature with respect to entropy of the working fluid. Initially, the working fluid starts at or above a peak of a vapor dome <NUM> at a starting point <NUM>. The vapor dome <NUM> represents an upper boundary above which the working fluid is at the corresponding supercritical point. Reference will be made, for explanatory purposes, with respect to the waste heat recovery system <NUM> shown in <FIG>. For example, the starting point <NUM> is the state of the working fluid at, for example, the inlet of the compressor <NUM>, prior to the working fluid undergoing compression by the compressor <NUM>.

As noted, the working fluid is compressed in the compressor <NUM>, causing the temperature and pressure of the working fluid to increase, while also imparting a minimal increase in the entropy of the working fluid until the working fluid is expelled from the compressor <NUM>. Point <NUM> of the chart <NUM> represents the state of the working fluid at the compressor outlet <NUM>. After exiting the compressor <NUM>, the working fluid is passed through the recuperating heat exchanger <NUM>, where the temperature and entropy of the working fluid are increased to point <NUM>, at an outlet of the recuperating heat exchanger <NUM>.

The working fluid is then passed from the outlet of the recuperating heat exchanger <NUM> to the waste heat recovery heat exchanger <NUM>. Within the waste heat recovery heat exchanger <NUM>, the entropy and temperature of the working fluid are increased to a point <NUM> on chart <NUM>. The point <NUM> represents the state of the working fluid at the outlet of the waste heat recovery heat exchanger <NUM> and at the inlet <NUM> of the turbine <NUM>. Further, the point <NUM> represents the peak temperature and entropy of the working fluid in the cycle.

As power is extracted from the working fluid in the turbine <NUM>, the temperature and pressure of the working fluid will drop. The pressure is reduced below the level of the start of the cycle (point <NUM>) and needs to be compressed back up to the pressure at the starting point <NUM>. The overexpansion in the turbine <NUM> allows for additional work extraction compared to expanding to the pressure of the start of the cycle (point <NUM>). After work has been extracted by the turbine <NUM>, the overexpanded working fluid is provided to the recuperating heat exchanger <NUM> and a portion of the excess heat is transferred from the expanded working fluid to working fluid between points <NUM> and <NUM> of the chart <NUM> (representative of the cycle). The state of the working fluid at the outlet of the recuperating heat exchanger <NUM> and the inlet of the first heat rejection heat exchanger <NUM> is illustrated at point <NUM>.

To improve operations of the waste heat recovery system <NUM>, the waste heat recovery system <NUM> employs the second heat rejection heat exchanger <NUM> to return the state of the working fluid to as close to the starting point <NUM> as possible. Due to the overexpansion at the turbine <NUM>, the pressure of the working fluid at an outlet of the heat rejection heat exchanger <NUM> (point <NUM>) is lower than required to maintain the working fluid at a supercritical point at the start of the working fluid cycle. To address this, the working fluid is pressurized in the secondary compressor <NUM>. The pressurization results in a pressure and temperature of the working fluid at an outlet (point <NUM>) of the secondary compressor <NUM> being above that which is required to maintain the supercritical state of the working fluid. The second heat rejection heat exchanger <NUM> is used to transfer waste heat in a similar manner as the first heat rejection heat exchanger <NUM>, and returns the working fluid to the inlet <NUM> of the working fluid compressor <NUM>. The waste heat can be transferred into any number of heat sinks within the gas turbine engine including, but not limited to, fan duct air, ram air, fuel, and a transcritical CO<NUM> refrigeration cycle. The multiple stages of compression, with heat rejection in between, creates an intercooled compression that increases the bottoming cycle efficiency.

In the illustrated example presented in chart <NUM> of <FIG>, the starting point <NUM> of the cycle is immediately at the vapor dome <NUM>. In practical examples, the starting point can be targeted at slightly above the vapor dome in order to prevent minor variations during operation and other practical considerations from causing the working fluid to fall below the vapor dome <NUM>.

In certain situations and/or configurations heat exchanger pressure losses and size may be concerns, especially with respect to the first and/or second heat rejection heat exchangers <NUM>, <NUM> shown in <FIG>. In some configurations of the waste heat recovery systems described above (e.g., a supercritical CO<NUM> bottoming cycle concept), if the waste heat is transferred into a fan duct or ram air via a heat rejection heat exchanger to return the working fluid to its starting point temperature, then there is a limited pressure drop available for the cold side of the heat exchanger (e.g., second heat rejection heat exchanger <NUM> shown in <FIG>). A higher pressure drop would allow for a more compact, lighter weight second heat exchanger. Also, in a low fan pressure ratio stream, air will not naturally enter the second heat exchanger without extensive baffling, which can incur additional pressure losses and weight.

It will be appreciated that the configuration of the above described examples is merely for example and explanatory purposes, and other configurations are possible without departing from the scope of the present disclosure. For example, in some configurations, the secondary compressor and/or the second heat rejection heat exchanger, described with respect to <FIG>, may be optional components in the system (e.g., may be removed or not necessary in certain configurations). The cooler exchanger, in some examples, may be arranged within a bypass flow stream that is not part of the hot section of a gas turbine engine. For example, in some examples, the cooler exchanger may be arranged within or along the bypass flow path B in a bypass duct, such as shown in <FIG>. In other examples, the cooler heat exchanger may be arranged within an inlet scoop, such as on a turboshaft engine configuration.

It will be appreciated that the different heat exchangers of the systems described herein may have different functions and/or heat exchangers. For example, in some examples, the waste heat recovery heat exchanger may be a working fluid-to-air heat exchanger, the recuperating heat exchanger may be a working fluid-to-working fluid heat exchanger, and the heat rejection heat exchanger (e.g., heat rejection heat exchanger <NUM>) may be a working fluid-to-exhaust heat exchanger. In some such examples, the heat rejection heat exchanger may be referred to as a waste heat recovery heat exchanger, and may be arranged proximate or near a core nozzle (e.g., downstream from a low pressure turbine of a gas turbine engine).

Turning now to <FIG>, a schematic diagram of a gas turbine engine <NUM> is shown. The gas turbine engine <NUM> may be similar to that shown and described above, and may include a waste heat recovery system <NUM>. The gas turbine engine <NUM> includes an inlet <NUM>, a fan <NUM> with a fan nozzle <NUM>, a low pressure compressor <NUM>, a high pressure compressor <NUM>, a combustor <NUM>, a high pressure turbine <NUM>, a low pressure turbine <NUM>, and a core nozzle <NUM> or nozzle section. A bypass flow path may be defined within a bypass duct defined within a nacelle, as described above.

In this configuration, the waste heat recovery system <NUM> includes a sCO<NUM> flow path <NUM> that may be a closed-loop system of CO<NUM> that is cycled to extract additional work from waste heat of the gas turbine engine <NUM>, such as described above. The waste heat recovery system <NUM> includes (in a flow path/cycle direction) a turbine <NUM>, a recuperating heat exchanger <NUM>, a heat rejection heat exchanger <NUM>, a compressor <NUM>, and a heat recovery heat exchanger <NUM>. The turbine <NUM> is coupled to a power output <NUM> (e.g., a drive shaft) that can output work. For example, the power output <NUM> may be connected to a generator (e.g., to generate electricity) or mechanically connected to a fan to drive rotation of the fan (e.g., mechanical work). In some examples, the heat recovery heat exchanger <NUM> is a full annular or circumferential heat exchanger that is arranged between the low pressure turbine <NUM> and the core nozzle <NUM>, and thus provides a thermal exchanger between a working fluid within the flow path <NUM> and an exhaust of the gas turbine engine <NUM>. The full annular circumferential heat exchanger may be a circular structure arranged about or within a nozzle of the gas turbine engine, as will be appreciated by those of skill in the art.

The configuration of the gas turbine engine <NUM>, and the waste heat recovery system <NUM> thereof, modifies the supercritical CO<NUM> bottoming cycle concept. In some supercritical CO<NUM> bottoming cycle concepts, the heat or thermal energy of the working fluid may be transferred into a fan duct or ram air (e.g., cooling duct <NUM>) via the heat rejection heat exchanger <NUM> to return the working fluid to the starting point temperature. The cooling duct is an airflow path through the gas turbine engine that is separate from a core flow path, and in some examples may be completely separate or may be a portion of air extracted from the core flow path. In some such examples, (e.g., fan duct location) there may be a limited pressure drop available for the cold side of the heat rejection heat exchanger to provide efficient temperature control of the working fluid (e.g., CO<NUM>). A sufficient pressure drop is generated at the heat rejection heat exchanger <NUM>. Such increased pressure drop can allow for a more compact, lighter weight heat rejection heat exchanger. Also, in a low fan pressure ratio stream, air will not naturally enter the heat rejection heat exchanger without extensive baffling, which incurs additional pressure loss and/or volume/weight, and examples described herein can avoid such baffling within the heat rejection heat exchanger.

In the example of <FIG>, the heat rejection heat exchanger <NUM> is arranged within or along a cooling duct <NUM> defined between the fan <NUM> and the fan nozzle <NUM> (e.g., a fan duct). To increase a pressure drop across the heat rejection heat exchanger <NUM> (on the cold side), an optional blower <NUM> is arranged upstream of the heat rejection heat exchanger <NUM>. The optional blower <NUM> may be a fan, turbine, blower, or other air-mover that can generate a pressure drop across the heat rejection heat exchanger <NUM>. The optional blower <NUM> may be electrically, mechanically, or electromechanically driven. In one non-limiting examples, and as shown in <FIG>, the optional blower <NUM> may be operably coupled to the power output <NUM>. In one such example, the power output may be an electrical connection, with an electrical generator driven by a rotated shaft driven by the turbine <NUM>. In other examples, the power output <NUM> may be a rotationally driven shaft that drives rotation and operation of the optional blower <NUM>.

Adding a waste heat recovery system, such as a supercritical CO<NUM> bottoming cycle, to the main engine cycle can improve overall system efficiency and reduce fuel burn. However, such added systems can potentially significantly increase the weight onboard an aircraft. Accordingly, the weight of the added components for the waste heat recovery system can limit the achievable improvement. However, by configuring the waste heat recovery system to have additional functionalities can offset such increased weight. For example, an aircraft needs an auxiliary power unit ("APU") to provide power to aircraft systems when the main engines are shut off. The APU also adds weight to the system, reducing some fuel burn performance while the aircraft is in flight. Thus, by combining the functions of the waste heat recovery system and an onboard APU, improved efficiencies may be achieved.

Turning now to <FIG>, a schematic diagram of a gas turbine engine <NUM> in accordance with an embodiment of the present disclosure is shown. The gas turbine engine <NUM> may be similar to that shown and described above, and may include a waste heat recovery system <NUM>. The gas turbine engine <NUM> includes an inlet <NUM>, a fan <NUM> with a fan nozzle <NUM>, a low pressure compressor <NUM>, a high pressure compressor <NUM>, a combustor <NUM>, a high pressure turbine <NUM>, a low pressure turbine <NUM>, and a core nozzle <NUM>. A bypass flow path may be defined within a bypass duct defined within a nacelle, as described above.

In this configuration, the waste heat recovery system <NUM> includes a working fluid flow path <NUM> (e.g., sCO<NUM> flow path) that may be a closed-loop system of CO<NUM> that is cycled to extract additional work from waste heat of the gas turbine engine <NUM>, such as described above. The waste heat recovery system <NUM> includes (in a flow path/cycle direction) a turbine <NUM>, a recuperating heat exchanger <NUM>, a heat rejection heat exchanger <NUM>, a compressor <NUM>, and a heat recovery heat exchanger <NUM>. The turbine <NUM> is coupled to a power output <NUM> (e.g., a drive shaft) that can output work. For example, the power output <NUM> may be connected to a generator (e.g., to generate electricity) or mechanically connected to a fan to drive rotation of the fan (e.g., mechanical work). In some embodiments, the heat recovery heat exchanger <NUM> is a full annular or circumferential heat exchanger that is arranged between the low pressure turbine <NUM> and the core nozzle <NUM>. In other embodiments, the heat recovery heat exchanger <NUM> may be less than a full annular or circumferential heat exchanger, with one or more sections of heat exchanger disposed at various locations at the outlet of the gas turbine engine <NUM>. The heat recovery heat exchanger <NUM> is configured to provide a thermal exchange between a working fluid within the working fluid flow path <NUM> and an exhaust of the gas turbine engine <NUM>.

In the waste heat recovery system <NUM> of <FIG>, the heat or thermal energy of the working fluid may be transferred into a fan duct or ram air (e.g., a cooling duct <NUM>) via the heat rejection heat exchanger <NUM> to return the working fluid to the starting point temperature. The cooling duct <NUM> is an airflow path through the gas turbine engine that is separate from a core flow path, and in some embodiments may be completely separate or may be a portion of air extracted from the core flow path. In some such embodiments, (e.g., fan duct location) there may be a limited pressure drop available for the cold side of the heat rejection heat exchanger to provide efficient temperature control of the working fluid (e.g., CO<NUM>). In accordance with embodiments of the present disclosure, a sufficient pressure drop may be generated at or for the heat rejection heat exchanger <NUM>. Such increased pressure drop can allow for a more compact, lighter weight heat rejection heat exchanger. Also, in a low fan pressure ratio stream, air will not naturally enter the heat rejection heat exchanger without extensive baffling, which incurs additional pressure loss and/or volume/weight, and inclusion of a blower <NUM> can avoid such baffling within the heat rejection heat exchanger.

In the embodiment of <FIG>, the heat rejection heat exchanger <NUM> is arranged within or along the cooling duct <NUM> defined between the fan <NUM> and the fan nozzle <NUM> (e.g., a fan duct). To increase a pressure drop across the heat rejection heat exchanger <NUM> (on the cold side), an optional blower <NUM> is arranged within the cooling duct <NUM>, illustratively shown upstream from the heat rejection heat exchanger <NUM>, but may be arranged downstream in some embodiment. The optional blower <NUM> may be a fan, turbine, blower, or other air-mover that can generate a pressure drop across the heat rejection heat exchanger <NUM>. The optional blower <NUM> may be electrically, mechanically, or electromechanically driven. In one non-limiting embodiment, the optional blower <NUM> may be operably coupled to the power output <NUM>. In one such example, the power output may be an electrical connection, with an electrical generator driven by a rotated shaft driven by the turbine <NUM>. In other embodiments, the power output <NUM> may be a rotationally driven shaft that drives rotation and operation of the optional blower <NUM>.

In this embodiment, the gas turbine engine <NUM> further includes an integrated APU system <NUM> that is operably connected to the waste heat recovery system <NUM>. The integrated APU system <NUM> includes an APU burner <NUM>, an optional APU blower <NUM>, and a secondary heat recovery heat exchanger <NUM>. The secondary heat recovery heat exchanger <NUM> may be a working fluid-to-APU exhaust heat exchanger. The integrated APU system <NUM>, as illustratively shown in the embodiment of <FIG>, adds a secondary burner (APU burner <NUM>) with a powered fan (APU blower <NUM>), and a secondary CO<NUM> heater heat exchanger (secondary heat recovery heat exchanger <NUM>), to the waste heat recovery system <NUM> of the gas turbine engine <NUM>.

The integrated APU system <NUM> is configured to supply additional heat to the working fluid (e.g., CO<NUM>) of the waste heat recovery system <NUM>. For example, when an aircraft is located on the ground, and the main engines (e.g., gas turbine engine <NUM>) is off, it may not be possible to add additional heat to the working fluid. However, in the present configuration, by having a flow line of the working fluid pass through the secondary heat recovery heat exchanger <NUM>, additional heat can be applied to the working fluid prior to being directed into the turbine <NUM> to generate work.

The integrated APU system <NUM> is configured to generate extra or auxiliary power on an aircraft. The power generated by the integrated APU system <NUM> may be achieved by passing a hot gas from the APU burner <NUM> into the secondary heat recovery heat exchanger <NUM>. The hot combusted gas may pass through the secondary heat recovery heat exchanger <NUM> to enable thermal transfer into the working fluid of the waste heat recovery system <NUM>. Because the integrated APU system <NUM> can be operated even when the main engine (e.g., gas turbine engine <NUM>) is in an off state, the waste heat recovery system <NUM> may be continuously operated to generate work through the power output <NUM>. Specifically, the integrated APU system <NUM> enables the waste heat recovery system <NUM> to become an auxiliary power unit or system of the aircraft, thus potentially eliminating (or shrinking) other APU systems on the aircraft, resulting in weight savings and other benefits.

As shown, the integrated APU system <NUM> may be selectively connected to the waste heat recovery system <NUM> by a switch valve <NUM>. The switch valve <NUM> splits the working fluid flow path <NUM> into a main engine flow path <NUM> and an APU flow path <NUM>. When the gas turbine engine <NUM> is in operation, the switch valve <NUM> is controlled to direct all or most of the working fluid along the main engine flow path <NUM>. However, when the gas turbine engine <NUM> is off, the switch valve <NUM> may be controlled to direct all or most of the working fluid along the APU flow path <NUM>. When the working fluid passes through the main engine flow path <NUM>, the working fluid will pick up heat within the heat recovery heat exchanger <NUM> at the outlet/nozzle of the gas turbine engine <NUM>. When the working fluid passes through the APU flow path <NUM>, the working fluid will pick up heat within the secondary heat recovery heat exchanger <NUM> of the integrated APU system <NUM>. In either case, after passing through the heat recovery heat exchanger <NUM> or the secondary heat recovery heat exchanger <NUM>, the heated working fluid will be directed into the turbine <NUM> to generate work onboard an aircraft.

The switch valve <NUM> may include a fluid and/or pressure regulator that enables selective flow control through one or both the main engine flow path <NUM> and the APU flow path <NUM>. When the waste heat recovery system <NUM> is operated using the APU system <NUM>, the waste heat recovery system <NUM> becomes an APU for the aircraft. In some embodiments, the waste heat recovery system <NUM> with the integrated APU system <NUM> may be the sole APU of an aircraft. In other embodiments, the integrated APU system <NUM> may be a supplemental or additional APU system that allows the reduction of other APU systems on the aircraft. Further, in some embodiments, each engine on an aircraft can include an integrated APU system as described herein, enabling multiple APU systems to be operationally functional on an aircraft. In other configurations, the waste heat recovery system may be integrated into a traditional APU system, with the APU system having an associated turbine and compressor. It will be appreciated that such systems may have more components than that shown in <FIG>, but is a viable configuration, as will be appreciated by those of skill in the art.

In some embodiments, the switch valve <NUM> may be a split valve that directs <NUM>% of the working fluid into the main engine flow path <NUM> or the APU flow path <NUM>. In other embodiments, the switch valve <NUM> may be arranged to provide a gradual transition from one flow path to the other, such that, at times, a portion of the working fluid may flow through both the main engine flow path <NUM> and the APU flow path <NUM> simultaneously.

In accordance with embodiments of the present disclosure, and as described above, one or more powered blowers may be added to the waste heat recovery system and integrated APU system. In some embodiments, a powered blower can be arranged in a fan duct, either upstream or downstream of a sCO<NUM> heat rejection heat exchanger. In some embodiments, a powered blower may be arranged to direct heated air from an APU burner through a secondary heat recovery heat exchanger of an integrated APU system. In some configurations, such as an operation with the main engine in an off state, a blower can be employed to generate a pressure drop or delta pressure across the heat rejection heat exchanger The powered blowers may be electrically powered, using power extracted from power generated by the waste heat recovery system (e.g., from the turbine of the waste heat recovery system) and/or from the integrated APU system. In accordance with embodiments of the present disclosure, a portion of the work generated by the waste heat recovery system is used to power and draw air into the heat rejection heat exchanger to allow the needed heat transfer to occur, without the use of baffles.

Advantageously, embodiments of the present disclosure provide for a waste heat recovery system that can generate additional work or power onboard an aircraft, even when the main engine is off. As such, the waste heat recovery system may have a dual-use, for when the main gas turbine engine is on and off. This dual-use configuration can reduce an overall weight for an aircraft that has both an APU to power subsystems while the main engines are off, and a waste heat recovery system for the gas turbine engines to improve engine thermal efficiency while the main engines are on. Combining the two systems reduces the total number of components and weight required, resulting in an overall aircraft fuel burn reduction.

While described above in conjunction with a geared turbofan engine, it is appreciated that the waste heat recovery systems described herein can be utilized in conjunction with any type of turbine engine including a cooled cooling air system with only minor modifications that are achievable by one of skill in the art. The cooled cooling air systems described herein provide a main engine architecture that drives to high pressures by reducing the temperature of the turbine cooling air. Further, the systems described herein provide for recovery of some work from the cooled cooling air system that is normally transferred into a heat sink. Additionally, the mass flow of the CO<NUM> in the system described above, and therefore all the component volumes, may be sized specifically to provide a desired amount of cooling necessary to reduce the temperature of the turbine cooling air. For example, in some configurations and embodiments, the bleed turbine air will be on the order of <NUM>% of core flow. A further benefit of the waste heat recovery systems described herein is that due to the high density and heat capacity of supercritical CO<NUM>, a higher level of compaction can be achieved relative to comparable air systems for cooled cooling air. This is significant for weight and engine integration.

As used herein, the term "about" is intended to include the degree of error associated with measurement of the particular quantity based upon the equipment available at the time of filing the application. For example, "about" may include a range of ± <NUM>%, or <NUM>%, or <NUM>% of a given value or other percentage change as will be appreciated by those of skill in the art for the particular measurement and/or dimensions referred to herein.

It should be appreciated that relative positional terms such as "forward," "aft," "upper," "lower," "above," "below," "radial," "axial," "circumferential," and the like are with reference to normal operational attitude and should not be considered otherwise limiting.

While the present disclosure has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the present disclosure is not limited to such disclosed embodiments. Rather, the present disclosure can be modified to incorporate any number of variations, alterations, substitutions, combinations, sub-combinations, or equivalent arrangements not heretofore described, but which are commensurate with the scope of the present invention as defined by the claims. Additionally, while various embodiments of the present disclosure have been described, it is to be understood that aspects of the present disclosure may include only some of the described embodiments.

Claim 1:
A waste heat management system comprising:
a turbine engine (<NUM>) including:
a compressor section;
a combustor section;
a turbine section; and
a nozzle (<NUM>), wherein the compressor section, the combustor section, the turbine section, and the nozzle define a core flow path that expels through the nozzle;
an auxiliary power unit (APU) system (<NUM>) comprising an APU burner (<NUM>) and a secondary heat recovery heat exchanger (<NUM>); and
a means for recovering waste heat operably connected to the APU system (<NUM>), wherein the APU system (<NUM>) is integrated into a working fluid flow path (<NUM>) of the means for recovering waste heat;
wherein the means for recovering waste heat comprises a waste heat recovery system (<NUM>), the waste heat recovery system being operably connected to the APU system (<NUM>), wherein the APU system is integrated into a working fluid flow path (<NUM>) of the waste heat recovery system; and
wherein the waste heat recovery system (<NUM>) comprises:
a heat recovery heat exchanger (<NUM>) arranged at the nozzle (<NUM>) and the secondary heat recovery heat exchanger (<NUM>) arranged as part of the APU system (<NUM>);
a turbine (<NUM>); and
a compressor (<NUM>);
wherein the turbine and the compressor of the waste heat recovery system are configured to generate work.