Distributed propulsion system and method for low altitude aircraft based on supercritical co2

Abstract

The application belongs to the technical field of aviation power system, and discloses a distributed propulsion system and method for low-altitude aircraft based on supercritical CO2, wherein the system comprises a high-speed start / generator, a SCO2 power device, a system controller, a power distributor, a lithium battery and an electric propulsion unit; the SCO2 power device drives the high-speed start / generator to operate and generate electricity, the generated electricity is provided to the lithium battery and the electric propulsion unit through the power distributor, the system controller collects signals of the high-speed start / generator and the lithium battery, and the system controller controls the high-speed start / generator, the SCO2 power device, the power distributor and the lithium battery; the SCO2 power device is a structure for converting heat energy of external heat carriers into kinetic energy. The application can be used for manned aircraft and unmanned aerial vehicles adopting rotor take-off and thrust cruise, the system state is not affected by flight height and environmental air pressure, and the output power has the advantage of small attenuation with the change of the flight height of the aircraft.

Description

Technical Field

[0001] This invention belongs to the field of aviation propulsion system technology, and relates to a distributed electric propulsion system for low-altitude aircraft based on supercritical carbon dioxide power, specifically to a distributed propulsion system and method for low-altitude aircraft based on supercritical CO2. Background Technology

[0002] With the advent of the low-altitude economy, the development of low-altitude manned / unmanned aerial vehicles (UAVs) has been rapid. Currently, most of these UAVs use a battery-powered technology, with motors driving lift propellers to provide lift. However, due to the limitations of battery energy density, battery-powered low-altitude UAVs cannot operate for extended periods, thus hindering their development.

[0003] Furthermore, the power requirements of low-altitude vertical takeoff and landing (VTOL) aircraft are characterized by the need for significant power output during takeoff and landing, followed by a substantial reduction in power output during the cruise phase. Generally, the power requirement during takeoff is 4-5 times that during cruise. Therefore, a flexible and adaptable aircraft power plant with a high peak-to-average power ratio (PAPR) represents a new development requirement. Moreover, traditional turboshaft engines are inefficient, with small turboshaft engines typically having an efficiency below 25%. Therefore, developing more efficient aircraft power systems is also a crucial requirement for the development of the low-altitude economy. Summary of the Invention

[0004] To address the aforementioned issues, this invention proposes a distributed propulsion system and method for low-altitude aircraft based on supercritical CO2. This system can generate electricity from supercritical carbon dioxide to drive distributed electric thrusters, providing thrust and featuring high efficiency and long range.

[0005] Technical solution of the present invention:

[0006] A distributed propulsion system for low-altitude aircraft based on supercritical CO2 includes a high-speed starter / generator, an SCO2 power unit, a system controller, a power divider, a lithium battery, and an electric propulsion unit. The SCO2 power unit drives the high-speed starter / generator to generate electricity, which is then supplied to the lithium battery and the electric propulsion unit via the power divider. The system controller collects signals from the high-speed starter / generator and the lithium battery, and controls the high-speed starter / generator, the SCO2 power unit, the power divider, and the lithium battery. The SCO2 power unit is a structure that converts the thermal energy of an external heat transfer fluid into kinetic energy.

[0007] Furthermore, the SCO2 power unit includes a closed-loop gas path, which is arranged between the heat exchanger and the drive unit. The gas in the closed-loop gas path exchanges heat with the heat transfer fluid at the heat exchanger and becomes a hot gas flow, which drives the drive unit to operate. The drive unit then drives the high-speed starter / generator to generate electricity.

[0008] Furthermore, the SCO2 power unit includes a compression unit and a cold-end heat exchanger. The drive unit is the SCO2 turbine, and the heat exchange unit is the hot-end heat exchanger. After the gas in the closed-loop gas circuit completes heat exchange in the hot-end heat exchanger, it first enters the SCO2 turbine to do work, then enters the cold-end heat exchanger to dissipate heat, and after being pressurized by the compression unit, it returns to the hot-end heat exchanger.

[0009] Furthermore, the compressor, SCO2 turbine, and high-speed starter / generator are coaxial. During the start-up phase, the high-speed starter / generator acts as a starter to drive the compressor, causing the airflow in the closed-loop air circuit to begin circulating.

[0010] Furthermore, the SCO2 power unit also includes a high-temperature regenerator, a low-temperature regenerator, and a flow valve. The compression unit includes the SCO2 main compressor and the SCO2 repressurizer. The gas from the SCO2 turbine enters the hot end of the high-temperature regenerator and the low-temperature regenerator successively. Then, it is split into two gas streams by the flow valve. One gas stream dissipates heat through the cold end heat exchanger, is then pressurized by the SCO2 main compressor, and then enters the cold end of the low-temperature regenerator and the hot end inlet of the high-temperature regenerator. The other gas stream is pressurized by the SCO2 repressurizer and enters the hot end inlet of the high-temperature regenerator. The hot end outlet of the high-temperature regenerator is connected to the inlet of the hot end heat exchanger.

[0011] Furthermore, the SCO2 main compressor compresses the CO2 gas flow after the cold-end heat exchanger, operating near the critical point, and typically has relatively low compression work. The SCO2 recompression compressor compresses the CO2 gas after the cryogenic regenerator, operating further away from the critical point, and is relatively larger in size. Using both the SCO2 main compressor and the SCO2 recompression compressor allows for inconsistent flow rates at the cold and hot ends of the cryogenic regenerator, thus avoiding pinch-up problems and preventing heat transfer degradation.

[0012] Furthermore, the gas in the closed-loop gas circuit is carbon dioxide.

[0013] A method for operating a distributed propulsion system for a low-altitude aircraft based on supercritical CO2 is described. During the start-up phase, a lithium battery powers a high-speed starter / generator, which in turn drives a compressor to circulate the gas in a closed-loop gas path. Simultaneously, a heat transfer fluid begins to flow in a heat exchanger, heating the gas in the closed-loop gas path and creating a high-temperature airflow that performs work on the SCO2 turbine. When the SCO2 turbine reaches a set speed, the high-speed starter / generator switches to power generation mode, and the SCO2 turbine drives the high-speed starter / generator to generate electricity, providing power to the lithium battery and the electric propulsion unit.

[0014] The beneficial effects of this invention are as follows:

[0015] 1. This invention provides a distributed electric propulsion system for low-altitude vertical take-off and landing aircraft. With the configuration of lithium batteries, the system has certain energy storage characteristics and the system power has the characteristics of peak-to-average power ratio. It can be used in manned and unmanned aircraft that adopt rotor take-off and landing and thrust cruise.

[0016] 2. This invention reduces the number of shafts used. By mounting the main compressor, repressurizer, turbine, and starter / generator on the same shaft, the traditional gear reduction transmission device is eliminated, greatly simplifying the system structure.

[0017] 3. This invention adopts the closed-loop thermoelectric conversion technology principle. Compared with traditional turbine power plants, the system state is not affected by flight altitude and ambient air pressure, and the output power has the advantage of small attenuation with changes in flight altitude.

[0018] 4. The supercritical carbon dioxide power generation technology of this invention has the characteristics of small turbine size and high efficiency, which has great benefits for the miniaturization and advancement of airborne equipment.

[0019] 5. The bearing of this invention adopts a gas dynamic pressure bearing, which eliminates the oil lubrication mechanism of the rolling bearing in the traditional airborne turbine power system, reducing weight and achieving the requirement of maintenance-free operation. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments of this invention, the drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort.

[0021] Figure 1 This invention relates to a distributed propulsion system for low-altitude aircraft based on supercritical CO2.

[0022] Among them, 1-high-speed starter / generator, 2-SCO2 power unit, 3-closed-cycle power generation unit, 4-system controller, 5-lithium battery, 6-motor, 7-ducted fan, 8-electric propulsion unit, 9-power distributor, 10-starter, 11-AC / DC rectifier, 12-SCO2 main compressor, 13-bearing, 14-SCO2 repressurizer, 15-SCO2 turbine, 16-hot end heat exchanger, 17-high temperature regenerator, 18-low temperature regenerator, 19-cold end cooler, 20-flow valve. Detailed Implementation

[0023] This section describes embodiments of the present invention, used to explain and illustrate the technical solutions of the present invention. Unless otherwise specified, the embodiments and features described herein can be combined with each other.

[0024] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating directions or positional relationships, are based on the orientation or positional relationships in the accompanying drawings and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or case referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implying the number of indicated technical features. Thus, features defined with "first," "second," etc., may explicitly or implicitly include more than one of those features. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0025] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integrated connections; they can refer to mechanical connections or point connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0026] Example 1:

[0027] A distributed electric propulsion system for low-altitude aircraft based on supercritical carbon dioxide power includes a high-speed generator / propellant 1, an SCO2 power unit 2, a system controller 4, a power divider 9, a lithium battery 5, and an electric propulsion unit 8. The SCO2 power unit 2 drives the high-speed generator / propellant 1 to generate electricity, which is then supplied to the lithium battery 5 and the electric propulsion unit 8 via the power divider 9. The system controller 4 collects signals from the high-speed generator / propellant 1 and the lithium battery 5, and controls the high-speed generator / propellant 1, the SCO2 power unit 2, the power divider 9, and the lithium battery 5. The SCO2 power unit 2 is a structure that converts the thermal energy of an external heat transfer fluid into kinetic energy.

[0028] The SCO2 power unit 2 includes a closed-loop gas path, which is arranged between the heat exchange device and the drive device. After the gas in the closed-loop gas path exchanges heat with the heat transfer medium at the heat exchange device, it becomes a hot gas flow, which drives the drive device to operate. The drive device then drives the high-speed starter / generator 1 to generate electricity.

[0029] The SCO2 power unit 2 includes a compression unit and a cold end heat exchanger 19. The drive unit is the SCO2 turbine 15, and the heat exchange unit is the hot end heat exchanger 16. After the gas in the closed-loop gas path completes heat exchange in the hot end heat exchanger 16, it first enters the SCO2 turbine 15 to do work, then enters the cold end heat exchanger 19 to dissipate heat, and after being pressurized by the compression unit, it returns to the hot end heat exchanger 16.

[0030] The compressor, SCO2 turbine 15 and high-speed starter / generator 1 are coaxial. During the start-up phase, the high-speed starter / generator 1 acts as a starter to drive the compressor, causing the airflow in the closed-loop air circuit to begin circulating.

[0031] The SCO2 power unit 2 also includes a high-temperature regenerator 17, a low-temperature regenerator 18, and a flow valve 20. The compression unit includes the SCO2 main compressor 12 and the SCO2 repressurizer 14. The gas after the SCO2 turbine 15 enters the hot end of the high-temperature regenerator 17 and the low-temperature regenerator 18, and is then split into two gas streams by the flow valve 20. One gas stream is cooled by the cold end heat exchanger 19, then pressurized by the SCO2 main compressor 12, and then enters the cold end of the low-temperature regenerator 18, and then enters the hot end inlet of the high-temperature regenerator 17. The other gas stream is pressurized by the SCO2 repressurizer 14 and enters the hot end inlet of the high-temperature regenerator 17. The hot end outlet of the high-temperature regenerator 17 is connected to the inlet of the hot end heat exchanger 16.

[0032] The SCO2 main compressor 12 compresses the CO2 gas flow after the cold-end heat exchanger. It operates near the critical point and typically has relatively low compression work. The SCO2 recompression compressor 14 compresses the CO2 gas after the low-temperature regenerator. It operates far from the critical point and has a relatively large compressor size.

[0033] Setting up SCO2 main compressor 12 and SCO2 recompressor 14 can achieve inconsistent flow rates at the cold and hot ends of the low-temperature regenerator, thus avoiding pinch-point problems in the low-temperature regenerator and preventing heat transfer deterioration.

[0034] The gas in the closed-loop gas circuit is carbon dioxide, which is in a supercritical state throughout the entire cycle.

[0035] Example 2:

[0036] A method for operating a distributed electric propulsion system for a low-altitude aircraft based on supercritical carbon dioxide power is disclosed. During the start-up phase, the lithium battery supplies power to the high-speed starter / generator, which acts as a starter to drive the compressor, causing the gas in the closed-loop gas path to begin circulating. Simultaneously, the heat transfer fluid begins to flow in the heat exchange device, heating the gas in the closed-loop gas path and forming a high-temperature airflow that performs work on the SCO2 turbine. When the SCO2 turbine speed reaches the set value, the high-speed starter / generator switches to power generation mode, and the SCO2 turbine drives the high-speed starter / generator to generate electricity, providing power to the lithium battery and the electric propulsion unit.

[0037] The system controller controls the power distributor to distribute the power of the entire system. During the takeoff phase, the system needs to output a large amount of power. The system controller controls the aviation lithium battery to supply power to the power distributor. At the same time, the closed-cycle power generation unit also supplies power to the power distributor. The power distributor distributes and adjusts the received electrical energy according to the power requirements of each distributed electric propulsion motor.

[0038] During the cruise phase of the aircraft, the propulsion system does not require a large output of power. The system controller directs the power distributor to charge the distributed electric propulsion motors and aviation lithium batteries. When the aviation lithium batteries reach 100% charge, charging stops, and the power output of the closed-cycle power generation unit is reduced simultaneously.

[0039] The system control manages the power output of the closed-cycle power generation system by controlling the flow rates of the heat transfer fluid and refrigerant. When increased power is required, the system controller controls the flow rate of the heat transfer fluid through the hot-end heat exchanger, thereby controlling the gas temperature before the closed-cycle SCO2 turbine, and ultimately controlling the power output of the power generation unit. Simultaneously, the system controller controls the flow rate of the ram air to meet the inlet temperature requirements of the main compressor. The control strategy is feedback regulation, adjusting the ram air flow rate based on the inlet air temperature of the main compressor.

[0040] The working principle of the closed-loop thermoelectric conversion unit is as follows: The hot-end heat exchanger heats the working fluid in the closed loop, causing the temperature of the heat transfer fluid to decrease and the temperature of the circulating gas in the closed loop to increase. The heated circulating gas undergoes power conversion through SCO2 turbine expansion. The turbine expansion work simultaneously drives the compressor to compress the working fluid and the generator to generate electricity. After the working fluid is expanded by the SCO2 turbine, it becomes a low-pressure working fluid and then enters the hot end of the high-temperature regenerator to exchange heat with the airflow from the cold end of the low-temperature regenerator, achieving the first energy recovery. The low-pressure airflow then enters the low-temperature regenerator after passing through the high-temperature regenerator, where it exchanges heat with the high-pressure airflow from the compressor outlet, achieving the second energy recovery. A diversion valve is installed at the hot end outlet of the low-temperature regenerator. After passing through the cold-end heat exchanger, part of the airflow enters the main compressor for compression and then enters the cold end of the low-temperature regenerator; the other part of the airflow directly enters the recompression compressor for compression. The compressed airflow merges with the high-pressure airflow from the cold end outlet of the low-temperature regenerator after heat exchange and enters the cold end of the high-temperature regenerator. After recovering heat, the heat enters the hot-end heat exchanger, thus completing a full power cycle. The advantage of this two-stage regenerator is that the low-temperature regenerator has a smaller total cold-end flow rate during the regeneration process, thereby avoiding pinch-ups and preventing regeneration deterioration. This allows for the recovery of more heat, thus improving system efficiency. Generally, this two-stage regeneration system can increase system efficiency by about 5% compared to a single-stage regeneration system, a significant improvement.

[0041] 1. In a closed-loop system, the working fluid circulates entirely within the system during the cycle and does not come into contact with the ambient atmospheric pressure. Therefore, it is not affected by environmental pressure and can achieve stable power output at different flight altitudes of the aircraft. In contrast, the output power of a traditional APU decreases significantly with increasing altitude.

[0042] 2. Closed-cycle uses high-pressure supercritical CO2 working fluid for circulation. The density of CO2 working fluid is greatly increased under high pressure. Therefore, the actual physical size of the closed-cycle power generation unit is very small, about 1 / 25 of that of a traditional gas turbine, which plays an important role in the miniaturization of aircraft.

[0043] 3. The compressor compresses the CO2 working fluid near the critical point, at which point the compression work is very small. In a traditional gas turbine, the compression work accounts for about 2 / 3 of the turbine output work, while in a closed-cycle power generation unit, the compressor output work accounts for about 1 / 3 of the turbine output work. Therefore, the closed-cycle power generation unit is very efficient.

[0044] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should be covered within the protection scope of the present invention.

Claims

1. A distributed propulsion system for low-altitude aircraft based on supercritical CO2, characterized in that, It includes a high-speed starter / generator (1), an SCO2 power unit (2), a system controller (4), a power divider (9), a lithium battery (5), and an electric propulsion unit (8); the SCO2 power unit (2) drives the high-speed starter / generator (1) to generate electricity, and the generated electrical energy is supplied to the lithium battery (5) and the electric propulsion unit (8) through the power divider (9). The system controller (4) collects signals from the high-speed starter / generator (1) and the lithium battery (5), and controls the high-speed starter / generator (1), the SCO2 power unit (2), the power divider (9), and the lithium battery (5); the SCO2 power unit (2) is a structure that converts the thermal energy of the external heat transfer fluid into kinetic energy.

2. The distributed propulsion system for low-altitude aircraft based on supercritical CO2 according to claim 1, characterized in that, The SCO2 power unit (2) includes a closed-loop gas path, which is arranged between the heat exchange device and the drive device. After the gas in the closed-loop gas path exchanges heat with the heat transfer agent at the heat exchange device, it becomes a high-temperature gas flow, which drives the drive device to operate. The drive device then drives the high-speed starter / generator (1) to generate electricity.

3. A distributed propulsion system for low-altitude aircraft based on supercritical CO2 according to claim 2, characterized in that, The SCO2 power unit (2) includes a compression unit and a cold end heat exchanger (19). The drive unit is the SCO2 turbine (15), and the heat exchange unit is the hot end heat exchanger (16). After the gas in the closed-loop gas path completes heat exchange in the hot end heat exchanger (16), it first enters the SCO2 turbine (15) to do work, then enters the cold end heat exchanger (19) to dissipate heat, and then returns to the hot end heat exchanger (16) after being pressurized by the compression unit.

4. A distributed propulsion system for low-altitude aircraft based on supercritical CO2 according to claim 3, characterized in that, The compressor, SCO2 turbine (15) and high-speed starter / generator (1) are coaxial. During the start-up phase, the high-speed starter / generator (1) acts as a starter to drive the compressor, causing the airflow in the closed-loop air circuit to begin circulating.

5. A distributed propulsion system for low-altitude aircraft based on supercritical CO2 according to claim 3, characterized in that, The SCO2 power unit (2) also includes a high-temperature regenerator (17), a low-temperature regenerator (18), and a flow valve (20). The compression unit includes the SCO2 main compressor (12) and the SCO2 repressurizer (14). The gas after the SCO2 turbine (15) enters the hot end of the high-temperature regenerator (17) and the low-temperature regenerator (18) in succession. Then, it is divided into two gas streams by the flow valve (20). One gas stream is cooled by the cold end heat exchanger (19), then pressurized by the SCO2 main compressor (12), and then enters the cold end of the low-temperature regenerator (18) and then enters the hot end inlet of the high-temperature regenerator (17). The other gas stream is pressurized by the SCO2 repressurizer (14) and enters the hot end inlet of the high-temperature regenerator (17). The hot end outlet of the high-temperature regenerator (17) is connected to the inlet of the hot end heat exchanger (16).

6. A distributed propulsion system for low-altitude aircraft based on supercritical CO2 according to claim 5, characterized in that, The SCO2 main compressor (12) compresses the airflow after the cold end heat exchanger (16). It operates near the critical point and usually has relatively small compression work.

7. A distributed propulsion system for low-altitude aircraft based on supercritical CO2 according to claim 2, characterized in that, The gas in the closed-loop gas circuit is carbon dioxide.

8. A method for operating a distributed propulsion system for low-altitude aircraft based on supercritical CO2, using the distributed propulsion system for low-altitude aircraft based on supercritical CO2 as described in claims 1-7, characterized in that, During the start-up phase, the lithium battery powers the high-speed starter / generator, which in turn drives the compressor to operate, causing the gas in the closed-loop gas path to begin circulating. At the same time, the heat transfer fluid begins to flow in the heat exchanger, heating the gas in the closed-loop gas path and forming a high-temperature airflow that does work on the SCO2 turbine. When the SCO2 turbine reaches the set speed, the high-speed starter / generator switches to power generation mode, and the SCO2 turbine drives the high-speed starter / generator to generate electricity, providing power to the lithium battery and the electric propulsion unit.

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