Auxiliary power unit fuel system and control method, and aircraft

Abstract

This invention discloses a fuel system and control method for an auxiliary power unit (APU) and an aircraft. In the APU fuel system, a fuel module pressurizes fuel from the fuel inlet and transmits it to a fuel distributor; a controller controls the rotation of the fuel pump in the fuel module; the fuel distributor, when its inlet pressure is greater than a first opening pressure and less than a second opening pressure, transmits fuel through a first fuel manifold to a return valve and a pre-combustion stage nozzle; the fuel distributor, when its inlet pressure is greater than the second opening pressure, transmits fuel through a second fuel manifold to the main combustion stage nozzle; the return valve is connected to the fuel inlet via a return oil pipe; the controller also controls the return valve to open or close, ensuring that the fuel supply from the first fuel manifold to the pre-combustion stage nozzle is the ignition fuel quantity for the APU. The technical solution provided by this invention ensures successful startup of the APU at high altitudes.

Description

Technical Field

[0001] This invention relates to the field of flight technology, and more particularly to a fuel system for an auxiliary power unit and its control method, and an aircraft. Background Technology

[0002] Auxiliary power units (APUs) are the onboard power units of aircraft and other aircraft besides the main power units. They are generally small gas turbine engines. Their main functions are to provide compressed air for starting the main engine, providing compressed air for the aircraft's environmental control system, providing ground power for the aircraft's electrical system, and providing backup power in the event of a main engine failure. Modern aircraft are all equipped with APUs, and their importance is becoming increasingly apparent.

[0003] Modern aircraft fly at increasingly higher altitudes. When an aircraft experiences a power failure at high altitudes, it needs to urgently activate the auxiliary power unit (APU) to ensure the aircraft's power supply and restart the power system. Therefore, the high-altitude restart performance of the APU is directly related to aircraft safety. However, existing APUs have poor high-altitude restart performance, posing a risk of APU restart failure at high altitudes. Summary of the Invention

[0004] This invention provides a fuel system and control method for an auxiliary power unit, as well as an aircraft, to ensure successful startup of the auxiliary power unit at high altitudes.

[0005] In a first aspect, embodiments of the present invention provide a fuel system for an auxiliary power unit, comprising: a controller, a fuel module, a fuel distributor, a return valve, a pre-combustion stage nozzle, and a main combustion stage nozzle;

[0006] The fuel module is used to pressurize the fuel at the fuel inlet and then transmit it to the fuel distributor; the controller is electrically connected to the fuel module and is used to control the rotation of the fuel pump of the fuel module; the fuel distributor is connected to the pre-combustion stage nozzle and the return valve respectively through a first fuel main pipe, and is used to transmit the fuel to the return valve and the pre-combustion stage nozzle when the inlet pressure of the fuel distributor is greater than the first opening pressure and less than the second opening pressure; the fuel distributor is connected to the main combustion stage nozzle through a second fuel main pipe, and is used to transmit the fuel to the main combustion stage nozzle when the inlet pressure of the fuel distributor is greater than the second opening pressure;

[0007] The return valve is connected to the fuel inlet via a return oil pipe; the controller is also used to control the return valve to open or close when the fuel distributor transmits the fuel to the first fuel manifold, so that the amount of fuel supplied from the first fuel manifold to the pre-combustion stage nozzle is the amount of ignition fuel for the auxiliary power unit.

[0008] Secondly, embodiments of the present invention provide a control method for the fuel system of an auxiliary power unit, applicable to the fuel system of any auxiliary power unit provided in any embodiment of the present invention, comprising:

[0009] The controller receives the start command of the auxiliary power unit and controls the fuel pump of the fuel module to rotate according to the start command, so that the fuel module transmits fuel to the fuel distributor;

[0010] During the ignition phase of the auxiliary power unit, the controller controls the inlet pressure of the fuel distributor to be greater than the first opening pressure and less than the second opening pressure through the fuel module, so that the fuel distributor transmits the fuel to the return valve and the pre-combustion stage nozzle through the first fuel manifold.

[0011] During the operation of the auxiliary power unit, the controller controls the inlet pressure of the fuel distributor to be greater than the second opening pressure through the fuel module, so that the fuel distributor transmits the fuel to the main combustion stage nozzle through the second fuel manifold;

[0012] When the fuel distributor transmits the fuel to the first fuel manifold, the controller is also used to control the reflux valve to open or close, so that the amount of fuel supplied from the first fuel manifold to the pre-combustion stage nozzle is the amount of ignition fuel for the auxiliary power unit.

[0013] Thirdly, embodiments of the present invention also provide an aircraft, including an auxiliary power unit; and a fuel system for the auxiliary power unit provided in any embodiment of the present invention.

[0014] In this invention, the fuel pump of the fuel module in the auxiliary power unit's fuel system rotates under the control of a controller, pressurizing the fuel at the fuel inlet and transmitting it to the fuel distributor. When the inlet pressure of the fuel distributor is greater than a first opening pressure but less than a second opening pressure, it transmits fuel to the return valve and the pre-combustion stage nozzle through the first fuel manifold; when the inlet pressure is greater than the second opening pressure, it transmits fuel to the main combustion stage nozzle through the second fuel manifold. Specifically, when the fuel distributor transmits fuel to the first fuel manifold, the return valve can be controlled to open or close, ensuring that the fuel supply from the first fuel manifold to the pre-combustion stage nozzle is the ignition fuel quantity for the auxiliary power unit, and allowing excess fuel to flow back to the fuel inlet through the return pipe via the return valve. During the ignition phase, the auxiliary power unit provides the ignition fuel quantity through the pre-combustion stage nozzle. Because the ignition fuel quantity for the auxiliary power unit at high altitudes is extremely small, this embodiment can adjust the fuel supply from the fuel distributor to the pre-combustion stage nozzle via the return valve to prevent over-discharge. The return valve is designed to meet the minimum required amount of ignition fuel, ensuring successful high-altitude ignition of the auxiliary power unit, while also accommodating the large fuel volume demands of the auxiliary power unit, thus expanding its operational envelope. Furthermore, the fuel returned to the fuel inlet by the return valve can be reused by the fuel module, improving fuel efficiency. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the fuel system of an auxiliary power device provided in an embodiment of the present invention;

[0016] Figure 2 This is a schematic diagram of the fuel system of another auxiliary power device provided in an embodiment of the present invention;

[0017] Figure 3 A schematic flowchart illustrating a control method for a fuel system of an auxiliary power unit provided in an embodiment of the present invention;

[0018] Figure 4 A flowchart illustrating another method for controlling the fuel system of an auxiliary power unit provided in an embodiment of the present invention;

[0019] Figure 5 A schematic diagram of the curve for obtaining the current return oil volume of the reflux valve provided in an embodiment of the present invention;

[0020] Figure 6 This is a schematic diagram of the structure of an aircraft provided in an embodiment of the present invention. Detailed Implementation

[0021] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the present invention, and not all of the structures.

[0022] In existing technologies, the power plants of aircraft and other aircraft generally include a main propulsion system and an auxiliary power unit (APU). As aircraft fly at increasingly higher altitudes, when the main propulsion system fails at high altitudes, the APU needs to be activated to restart the main propulsion system and provide electrical power to the aircraft during the main propulsion failure. Therefore, the high-altitude restart performance of the APU is crucial. However, in developing this invention, the inventors discovered that the higher the flight altitude, the smaller the amount of ignition fuel required to ignite the APU. Existing technologies struggle to control the formation of such a small amount of ignition fuel, easily leading to unsuccessful ignition at high altitudes and limiting the aircraft's flight altitude.

[0023] To address the altitude limitations of auxiliary power units (APUs) during in-flight start-up and improve their high-altitude start-up performance, this invention provides a fuel system for the APU, such as... Figure 1 As shown, Figure 1 This is a schematic diagram of the structure of a fuel system for an auxiliary power unit provided in an embodiment of the present invention. The fuel system for the auxiliary power unit includes: a controller 11, a fuel module 12, a fuel distributor 13, a return valve 14, a pre-combustion stage nozzle 16, and a main combustion stage nozzle 15.

[0024] Fuel module 12 is used to pressurize the fuel at the fuel inlet and then transmit it to fuel distributor 13; controller 11 is electrically connected to fuel module 12 and is used to control the rotation of fuel pump in fuel module 12; fuel distributor 13 is connected to pre-combustion stage nozzle 16 and return valve 14 through first fuel main pipe 21, and is used to transmit fuel to return valve 14 and pre-combustion stage nozzle 16 when the inlet pressure of fuel distributor 13 is greater than the first opening pressure and less than the second opening pressure; fuel distributor 13 is connected to main combustion stage nozzle 15 through second fuel main pipe 22, and is used to transmit fuel to main combustion stage nozzle 15 when the inlet pressure of fuel distributor 13 is greater than the second opening pressure;

[0025] The return valve 14 is connected to the fuel inlet via the return oil pipe 23; the controller 11 is also used to control the return valve 14 to open or close when the fuel distributor 13 transmits fuel to the first fuel main pipe 21, so that the amount of fuel supplied from the first fuel main pipe 21 to the pre-combustion stage nozzle 16 is the amount of ignition fuel for the auxiliary power unit.

[0026] The auxiliary power unit (APU) provides compressed air for starting the aircraft's main engine, for the aircraft's environmental control system, for the aircraft's electrical system, and as backup power in case of main engine failure, thus ensuring safe flight. In this embodiment, the fuel system of the APU is improved to control the amount of ignition fuel to a minimum when starting the APU at high altitude, ensuring a safe start. The fuel system includes a controller 11, a fuel module 12, a fuel distributor 13, a return valve 14, a pre-combustion stage nozzle 16, and a main combustion stage nozzle 15. The controller 11 is electrically connected to the fuel module 12. Specifically, the fuel inlet refers to the inlet of the APU's fuel system supplied with fuel from the aircraft's fuel tank or a ground fuel tank via pipeline. The fuel module 12 is connected to this fuel inlet, enabling it to obtain and pressurize the fuel to the pressure required by subsequent equipment. Specifically, the fuel module 12 can regulate the fuel pressure by rotating a fuel pump. In addition to the fuel pump, the fuel module 12 may also include components such as a fuel filter, bypass valve, overflow valve, and fuel filter blockage signal sensor to assist in the fuel pressurization process. The controller 11 is electrically connected to the fuel module 12 and can control the rotation of the fuel pump. Furthermore, the controller 11 can also control the starting of the auxiliary power unit, power regulation, bleed air generator generation, and fuel regulation.

[0027] The fuel module 12 pressurizes the fuel and pumps it into the fuel distributor 13. The fuel distributor 13 is a functional component that distributes the flow of the pressurized fuel from the fuel module 12. The fuel distributor 13 distributes the fuel flow to the pre-combustion stage fuel line and the main combustion stage fuel line. The pre-combustion stage fuel line mainly supplies fuel during the ignition phase of the auxiliary power unit, and the fuel quantity is relatively small; the main combustion stage fuel line mainly supplies fuel after the auxiliary power unit is ignited, and the fuel quantity is relatively large. In this embodiment, the fuel distributor 13 is connected to the pre-combustion stage nozzle 16 and the return valve 14 through the first fuel main pipe 21. Specifically, the first fuel manifold 21 includes a first input end, a first output end, and a second output end, all of which are interconnected. The first input end of the first fuel manifold 21 is connected to the fuel distributor 13, the first output end is connected to the pre-combustion stage nozzle 16, and the second output end is connected to the return valve 14. Thus, the first fuel manifold 21 supplies fuel obtained from the fuel distributor 13 to the pre-combustion stage nozzle 16 and the return valve 14, forming a pre-combustion stage fuel circuit. The fuel distributor 13 is connected to the main combustion stage nozzle 15 via the second fuel manifold 22, which supplies fuel obtained from the fuel distributor 13 to the main combustion stage nozzle 15, forming a main combustion stage fuel circuit.

[0028] The fuel module 12 pressurizes the fuel and transmits it to the inlet of the fuel distributor 13, controlling the inlet pressure of the fuel distributor 13. When the inlet pressure of the fuel distributor 13 is greater than the first opening pressure and less than the second opening pressure, the channel connecting the fuel distributor 13 to the first fuel main 21 (pre-combustion stage fuel circuit) is open, and the fuel distributor 13 transmits fuel to the pre-combustion stage nozzle 16 and the return valve 14. The second opening pressure is greater than the first opening pressure. When the inlet pressure of the fuel distributor 13 is greater than the second opening pressure, the channel connecting the fuel distributor 13 to the second fuel main 22 (main combustion stage fuel circuit) is open, and the fuel distributor 13 transmits fuel to the main combustion stage nozzle 15. It should be noted that when the inlet pressure of the fuel distributor 13 is greater than the second opening pressure, the channel connecting the fuel distributor 13 to the first fuel main 21 is closed.

[0029] The main function of the pre-combustion stage nozzle 16 is to atomize the fuel supplied by the pre-combustion stage fuel circuit and inject it into the combustion chamber during the ignition stage of the auxiliary power unit, so that it can be ignited and burned. The amount of fuel is relatively small. The main combustion stage nozzle 15 mainly functions to continue to supply fuel after the auxiliary power unit is ignited, and to atomize the fuel supplied by the main combustion stage fuel circuit and inject it into the combustion chamber for ignition and combustion. The amount of fuel is relatively large.

[0030] Because the pre-combustion stage nozzle 16 requires a relatively small amount of fuel, a return valve 14 is added to the pre-combustion stage fuel circuit in this embodiment. The return valve 14 is connected to the fuel inlet via a return oil pipe 23. Therefore, when the fuel supplied to the pre-combustion stage fuel circuit by the fuel distributor 13 is greater than the ignition fuel quantity for the auxiliary power unit, the excess fuel can be returned to the fuel module 12 via the return valve 14 and the return oil pipe 23. This ensures that the fuel quantity supplied to the pre-combustion stage nozzle 16 is not excessive, ensuring that the fuel quantity obtained by the pre-combustion stage nozzle 16 is the ignition fuel quantity for the auxiliary power unit, thus improving the ignition success rate of the auxiliary power unit. Furthermore, the excess fuel returned to the fuel module 12 allows it to be utilized during the operation of the auxiliary power unit, preventing fuel waste. In this embodiment, the return valve 14 can be opened and closed under the control of the controller 11, thereby controlling the amount of returned fuel and further improving the control accuracy of the ignition fuel quantity. As the aircraft's altitude increases, the amount of ignition fuel required for the auxiliary power unit (APU) becomes extremely low. This embodiment utilizes the return valve 14 to achieve this minimal ignition fuel quantity, ensuring the APU receives the necessary amount and thus increasing the aircraft's altitude. Furthermore, the main combustion stage nozzle 15 is compatible with the APU's high fuel requirements, expanding the APU's operational envelope and further enhancing the user experience.

[0031] In this embodiment of the invention, the fuel pump of the fuel module in the auxiliary power unit's fuel system rotates under the control of a controller, pressurizing the fuel at the fuel inlet and transmitting it to the fuel distributor. When the inlet pressure of the fuel distributor is greater than a first opening pressure but less than a second opening pressure, it transmits fuel to the return valve and the pre-combustion stage nozzle through the first fuel manifold; when the inlet pressure is greater than the second opening pressure, it transmits fuel to the main combustion stage nozzle through the second fuel manifold. Specifically, when the fuel distributor transmits fuel to the first fuel manifold, the return valve can be controlled to open or close, ensuring that the fuel supply from the first fuel manifold to the pre-combustion stage nozzle is the ignition fuel quantity for the auxiliary power unit, and allowing excess fuel to flow back to the fuel inlet through the return pipe via the return valve. During the ignition phase, the auxiliary power unit provides the ignition fuel quantity through the pre-combustion stage nozzle. Because the ignition fuel quantity for the auxiliary power unit at high altitudes is extremely small, this embodiment can adjust the fuel supply from the fuel distributor to the pre-combustion stage nozzle via the return valve to prevent over-discharge. The return valve is designed to meet the minimum required amount of ignition fuel, ensuring successful high-altitude ignition of the auxiliary power unit, while also accommodating the large fuel volume demands of the auxiliary power unit, thus expanding its operational envelope. Furthermore, the fuel returned to the fuel inlet by the return valve can be reused by the fuel module, improving fuel efficiency.

[0032] The above is the core idea of ​​this invention. The technical solutions in the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0033] The pre-combustion stage nozzle 16 can be connected to the combustion chamber and is used to atomize and inject fuel transmitted from the first fuel manifold 21 into the combustion chamber during the ignition phase of the auxiliary power unit; the main combustion stage nozzle 15 can be connected to the combustion chamber and is used to atomize and inject fuel transmitted from the second fuel manifold 22 into the combustion chamber during the operation phase of the auxiliary power unit.

[0034] The specific control process of the auxiliary power unit's fuel system includes the ignition stage and the subsequent operating stage. This embodiment includes two nozzles: a pre-combustion stage nozzle 16 and a main combustion stage nozzle 15. Both nozzles atomize fuel and inject it into the combustion chamber. The pre-combustion stage nozzle 16 atomizes the ignition fuel in the pre-combustion stage fuel circuit and injects it into the combustion chamber, completing the ignition start-up process of the auxiliary power unit. Afterward, the fuel system continues to provide power to the auxiliary power unit by atomizing the ignition fuel in the main combustion stage fuel circuit and injecting it into the combustion chamber through the main combustion stage nozzle 15.

[0035] Figure 2This is a schematic diagram of the fuel system of another auxiliary power unit provided in an embodiment of the present invention. Optionally, the fuel system of the auxiliary power unit may further include: a shut-off valve 17; the shut-off valve 17 is disposed in the transmission channel between the fuel module 12 and the fuel distributor 13, and is used to open and close the connection between the fuel module 12 and the fuel distributor 13 under the control of the controller 11.

[0036] In this embodiment, a shut-off valve 17 can also be installed between the outlet of the fuel module 12 and the inlet of the fuel distributor 13. The controller 11 is electrically connected to the shut-off valve 17 and controls its opening and closing. When the fuel module 12 needs to pump fuel into the fuel distributor 13, the controller 11 controls the shut-off valve 17 to open; when the fuel system stops working and the fuel module 12 is no longer needed to pump fuel into the fuel distributor 13, the controller 11 controls the shut-off valve 17 to close. The shut-off valve 17 can prevent fuel leakage from the fuel module 12 to the fuel distributor 13 when the fuel system is not needed, effectively improving the reliability of the fuel system.

[0037] Optionally, the controller 11 can be specifically used to control the conduction area of ​​the return valve 14 so that the amount of fuel supplied from the first fuel main 21 to the pre-combustion stage nozzle 16 is the amount of ignition fuel for the auxiliary power unit. In this embodiment, in addition to controlling the amount of fuel supplied from the first fuel main 21 to the pre-combustion stage nozzle 16 by controlling the opening and closing of the return valve 14, the return fuel quantity can also be adjusted by adjusting the conduction area (valve port flow area) of the return valve 14. This allows for further precise adjustment of the return fuel quantity, achieving a minimum value for the ignition fuel quantity of the auxiliary power unit, ensuring that the auxiliary power unit starts at high altitudes.

[0038] To provide a more detailed explanation of the control process of the fuel system for the auxiliary power unit, this invention provides a description of the start-up process of the auxiliary power unit:

[0039] First, the auxiliary power unit receives a start command. Optionally, the controller 11 can receive the start command, and optionally, the controller 11 can also be used to obtain the current ignition fuel quantity of the auxiliary power unit based on the current ambient temperature and pressure. Because environmental parameters such as the aircraft's flight altitude, flight Mach number, and current temperature can all affect the current ignition fuel quantity of the auxiliary power unit, this embodiment summarizes all the above environmental factors into two environmental parameters: temperature and pressure. The current ignition fuel quantity is determined based on the temperature and pressure of the environment in which the auxiliary power unit is currently located. Specifically, the controller 11 may include sensing components such as temperature sensors and pressure sensors, which can detect the current ambient temperature and pressure. The controller can also pre-store a fuel reference table. As shown in Table 1, Table 1 is a reference table of temperature, pressure, and ignition fuel quantity of the auxiliary power unit provided in this embodiment of the invention. Different temperatures T or different pressures P correspond to different ignition fuel quantities D. For example, when the temperature is T1 and the pressure is P1, the ignition fuel quantity is D1; ​​when the temperature is T2 and the pressure is P2, the ignition fuel quantity is D3. When the temperature is the same but the pressure is different, the corresponding ignition fuel quantity will also be different. For example, when the temperature is T1, the ignition fuel quantity at pressure P1 is D1, and the ignition fuel quantity at pressure P2 is D2. The required ignition fuel quantity for the current environment can be obtained according to a pre-stored fuel reference table. It should be noted that the above reference table can be obtained experimentally based on the characteristics of the auxiliary power system. Optionally, this data can be obtained before the auxiliary power system leaves the factory for user convenience.

[0040] Table 1: Comparison of Temperature, Pressure, and Ignition Fuel Quantity of Auxiliary Power Unit

[0041] Temperature T (°C) Pressure P (pa) Ignition fuel quantity D (L) T1 P1 D1 T1 P2 D2 T2 P2 D3 … … …

[0042] The controller 11 is also used to control the starter motor of the auxiliary power unit to start, driving the engine rotor of the auxiliary power unit to rotate. When the engine rotor rotates to the specified speed, the ignition exciter of the auxiliary power unit is energized to ignite. In addition, the controller 11 controls the fuel module 12 to start working and controls the shut-off valve 17 to be energized and opened, so that the fuel module 12 delivers fuel to the fuel distributor 13 through the fuel pump.

[0043] When the fuel module 12 controls the inlet of the fuel distributor 13 to reach the specified oil pressure (first opening pressure), the channel between the fuel distributor 13 and the first fuel manifold 21 is opened. At the same time, the return valve 14 can be opened to transfer excess fuel back to the fuel inlet, ensuring that the fuel supply to the first fuel manifold 21 does not exceed the amount supplied to the pre-combustion stage nozzle 16, and only includes the ignition fuel. The ignition fuel is atomized and injected into the combustion chamber through the pre-combustion stage nozzle 16. It should be noted that for a certain auxiliary power unit, its ignition fuel quantity can be a range. The maximum ignition fuel quantity W_fmax and the minimum ignition fuel quantity W_fmin are obtained based on the overall performance calculation or simulation test of the auxiliary power unit. The maximum ignition fuel quantity W_fmax is the rich ignition boundary of the auxiliary power unit, and the minimum ignition fuel quantity W_fmin is the lean ignition boundary of the auxiliary power unit. These boundaries can be determined by temperature, pressure, and engine control laws. The design of the return oil circuit and return valve 14 should ensure that the maximum return oil capacity reaches (W_fmax-W_fmin), while maintaining a certain pressure before the pre-combustion stage nozzle at the maximum return oil volume, so that the pre-combustion stage nozzle 16 can atomize the fuel effectively. Furthermore, when the return valve 14 is closed, the fuel pressure in the first fuel manifold 21 is less than the opening pressure (second opening pressure) of the main combustion stage oil circuit, where the second opening pressure is greater than the first opening pressure. In a specific example, when starting the auxiliary power unit in low-temperature weather at sea level, the current ignition fuel volume can be the maximum ignition fuel volume, and the controller 11 closes the return valve 14. When starting the auxiliary power unit in high-temperature weather at high altitude, the current ignition fuel volume can be the minimum ignition fuel volume, and the controller 11 opens the return valve 14 to its maximum opening, maximizing the return oil volume. The selection of the current ignition fuel quantity is determined by the current environment of the auxiliary power unit. When the current ignition fuel quantity is the maximum or minimum ignition fuel quantity, the temperature and pressure values ​​of the current environment are close to the boundary. Under normal circumstances, the temperature and pressure of the current environment do not tend to the boundary, and the ignition fuel quantity for starting the auxiliary power unit is between the maximum ignition fuel quantity W_fmax and the minimum ignition fuel quantity W_fmin. When the ignition fuel quantity for starting the auxiliary power unit is between the maximum ignition fuel quantity W_fmax and the minimum ignition fuel quantity W_fmin, the controller 11 needs to adjust the conduction area of ​​the return valve 14 to control the return fuel quantity. Optionally, the controller 11 is also used to obtain the current fuel supply quantity of the fuel pump based on the current ignition fuel quantity, and to obtain the current return fuel quantity of the return valve 14 based on the current fuel supply quantity; the controller 11 is also used to control the current conduction area of ​​the return valve 14 based on the current return fuel quantity.This embodiment can obtain the current fuel supply quantity of the fuel pump based on the current ignition fuel quantity. It should be noted that the current fuel supply quantity of the fuel pump needs to be greater than or equal to the current ignition fuel quantity. The current fuel supply quantity of the fuel pump is determined based on the current ignition fuel quantity and the fuel pressure. The difference between the current fuel supply quantity and the current ignition fuel quantity is used as the current return oil quantity of the return valve 14. This facilitates the determination of the current conduction area of ​​the return valve 14 based on the current return oil quantity, thereby improving the precise control of the current ignition fuel quantity.

[0044] Subsequently, once the fuel is successfully ignited in the combustion chamber, the engine rotor speed continues to increase under the action of the starter motor and turbine. Simultaneously, the controller 11 reduces the conduction area of ​​the return valve 14 until it is completely closed. Then, all the fuel supplied from the first fuel manifold 21 is supplied to the pre-combustion stage nozzle 16, and atomized and injected into the combustion chamber through the pre-combustion stage nozzle 16. This process serves as a transition between the ignition and operation phases of the auxiliary power unit.

[0045] After the transition phase, the controller 11 controls the gear pump speed to continue increasing the fuel supply, so that the inlet pressure of the fuel distributor 13 is greater than the second opening pressure, and the main combustion stage fuel circuit is opened, and the engine rotor speed rises to the rated speed, completing the start-up.

[0046] Based on the same concept, embodiments of the present invention also provide a method for controlling the fuel system of an auxiliary power unit. Figure 3 This is a flowchart illustrating a control method for a fuel system of an auxiliary power unit provided in an embodiment of the present invention, as shown below. Figure 3 As shown, the method in this embodiment includes the following steps:

[0047] Step S101: The controller obtains the start command of the auxiliary power unit and controls the fuel pump of the fuel module to rotate according to the start command, so that the fuel module transmits fuel to the fuel distributor.

[0048] Step S102: During the ignition stage of the auxiliary power unit, the controller controls the inlet pressure of the fuel distributor to be greater than the first opening pressure and less than the second opening pressure through the fuel module, so that the fuel distributor transmits fuel to the return valve and the pre-combustion stage nozzle through the first fuel manifold.

[0049] When the fuel distributor delivers fuel to the first fuel manifold, the controller is also used to control the opening or closing of the return valve so that the amount of fuel delivered from the first fuel manifold to the pre-combustion stage nozzle is the amount of ignition fuel for the auxiliary power unit.

[0050] Step S103: During the operation of the auxiliary power unit, the controller controls the inlet pressure of the fuel distributor to be greater than the second opening pressure through the fuel module, so that the fuel distributor transmits fuel to the main combustion stage nozzle through the second fuel manifold.

[0051] In this embodiment of the invention, the fuel pump of the fuel module in the auxiliary power unit's fuel system rotates under the control of a controller, pressurizing the fuel at the fuel inlet and transmitting it to the fuel distributor. When the inlet pressure of the fuel distributor is greater than a first opening pressure but less than a second opening pressure, it transmits fuel to the return valve and the pre-combustion stage nozzle through the first fuel manifold; when the inlet pressure is greater than the second opening pressure, it transmits fuel to the main combustion stage nozzle through the second fuel manifold. Specifically, when the fuel distributor transmits fuel to the first fuel manifold, the return valve can be controlled to open or close, ensuring that the fuel supply from the first fuel manifold to the pre-combustion stage nozzle is the ignition fuel quantity for the auxiliary power unit, and allowing excess fuel to flow back to the fuel inlet through the return pipe via the return valve. During the ignition phase, the auxiliary power unit provides the ignition fuel quantity through the pre-combustion stage nozzle. Because the ignition fuel quantity for the auxiliary power unit at high altitudes is extremely small, this embodiment can adjust the fuel supply from the fuel distributor to the pre-combustion stage nozzle via the return valve to prevent over-discharge. The return valve is designed to meet the minimum required amount of ignition fuel, ensuring successful high-altitude ignition and starting of the auxiliary power unit, while also accommodating the large fuel demand of the auxiliary power unit, thus expanding its operational envelope. Furthermore, the fuel returned to the fuel inlet by the return valve can be reused by the fuel module, improving fuel efficiency.

[0052] Optionally, after the controller receives the start command for the auxiliary power unit, it further includes: the controller obtaining the current ignition fuel quantity of the auxiliary power unit based on the current ambient temperature and pressure; the controller is also used to obtain the current fuel supply quantity of the fuel pump of the fuel module based on the current ignition fuel quantity, and to obtain the current return fuel quantity of the return valve based on the current fuel supply quantity; when the fuel distributor transmits fuel to the first fuel manifold, the controller is also used to control the return valve to open or close, so that the fuel supply quantity transmitted from the first fuel manifold to the pre-combustion stage nozzle is the ignition fuel quantity of the auxiliary power unit, including: when the fuel distributor transmits fuel to the first fuel manifold, the controller controls the conduction area of ​​the return valve based on the return fuel quantity, so that the fuel quantity transmitted from the first fuel manifold to the pre-combustion stage nozzle is the ignition fuel quantity of the auxiliary power unit.

[0053] In a specific example, this embodiment details the process of adjusting the conduction area of ​​the return valve using the flow characteristic curve of the gear pump, the characteristic curve of the pre-combustion stage nozzle, and the family of return oil characteristic curves. Specifically, as shown below... Figure 4 As shown, Figure 4 A schematic flowchart of a control method for a fuel system of an auxiliary power unit provided in an embodiment of the present invention is shown below. Figure 4 As shown, the method in this embodiment includes the following steps:

[0054] Step S201: The controller obtains the start command of the auxiliary power unit and controls the fuel pump of the fuel module to rotate according to the start command, so that the fuel module transmits fuel to the fuel distributor.

[0055] Step S202: The controller obtains the current fuel pressure of the pre-combustion stage nozzle corresponding to the current ignition fuel quantity based on the fuel supply quantity-fuel pressure curve of the pre-combustion stage nozzle.

[0056] Step S203: The controller obtains the current fuel supply quantity of the fuel pump corresponding to the current fuel pressure based on the fuel supply quantity-fuel pressure curve of the fuel pump.

[0057] Step S204: The controller obtains the current return oil quantity of the return valve based on the current fuel supply quantity and the current ignition fuel quantity.

[0058] The process of "the controller is also used to obtain the current fuel supply quantity of the fuel pump of the fuel module according to the current ignition fuel quantity, and to obtain the current return oil quantity of the return valve according to the current fuel supply quantity" in the above embodiment may specifically include the above steps S202 to S204.

[0059] Step S205: Based on the family of return oil quantity-fuel pressure curves of the return valve, obtain the current return oil quantity-fuel pressure curve of the return valve corresponding to the current return oil quantity and the current fuel pressure; wherein, the family of return oil quantity-fuel pressure curves includes multiple return oil quantity-fuel pressure curves; different return oil quantity-fuel pressure curves correspond to different conduction areas of the return valve.

[0060] Step S206: Based on the current return oil quantity-fuel pressure curve, obtain the current conduction area of ​​the return valve so that the fuel supply from the first fuel main pipe to the pre-combustion stage nozzle is the ignition fuel quantity of the auxiliary power unit.

[0061] The process described in the above embodiment, "when the fuel distributor transmits fuel to the first fuel manifold, the controller controls the conduction area of ​​the return valve according to the amount of return fuel, so that the amount of fuel transmitted from the first fuel manifold to the pre-combustion stage nozzle is the amount of ignition fuel for the auxiliary power unit", may specifically include the above steps S205 to S206.

[0062] like Figure 5 As shown, Figure 5 This is a schematic diagram of the curve for obtaining the current return oil volume of the reflux valve, provided in an embodiment of the present invention. Figure 5 It includes the fuel supply quantity-fuel pressure curve I of the fuel pump, that is, the flow characteristic curve of the fuel pump. Figure 5 It also includes the fuel supply-fuel pressure curve II of the pre-combustion stage nozzle, that is, the pre-combustion stage nozzle characteristic curve. Figure 5It also includes a family of return fuel volume-fuel pressure curves, that is, a family of return fuel characteristic curves. It is important to note that... Figure 5 The horizontal axis of all curves represents pressure P, and the vertical axis represents fuel quantity Q. All of these curves are pre-installed in the storage unit before the auxiliary power unit is started. Specifically, curve I, representing the fuel pump's fuel supply quantity versus fuel pressure, shows the change in fuel supply quantity as fuel pressure increases when the fuel pump speed is constant; generally, the fuel supply quantity decreases as fuel pressure increases. In this embodiment, the fuel pump speed is pre-set according to the characteristics of the auxiliary power unit. In curve II, representing the pre-combustion stage nozzle's fuel supply quantity versus fuel pressure, the fuel supply quantity increases as the fuel pressure in the first fuel manifold before the pre-combustion stage nozzle increases. Similarly, in the family of return fuel quantity versus fuel pressure curves, the return fuel quantity from the return valve increases as the fuel pressure in the first fuel manifold increases. Figure 5 It can be seen that when the conduction area of ​​the return valve is different, it will be in different return oil quantity-fuel pressure curves. The above-mentioned family of return oil quantity-fuel pressure curves includes multiple return oil quantity-fuel pressure curves with the same trend. Each return oil quantity-fuel pressure curve represents a different conduction area. When the specific return oil quantity-fuel pressure curve is determined, the corresponding return valve conduction area is determined.

[0063] Based on the inlet total temperature and total pressure measured before starting the auxiliary power unit, the controller determines the current ignition fuel quantity W under this intake condition from the lookup table. f Select Q2 = W from the nozzle characteristic curve II pre-installed on the controller. f This determines the current fuel pressure P. c Select the current fuel pressure as P from the pre-installed fuel pump characteristic curve I on the controller. c Given the current fuel supply quantity Q1, calculate the current return fuel quantity Q3 = Q1 - Q2; from the pre-installed return fuel characteristic curve family of the controller, with the current fuel pressure as P... c The current return oil quantity is Q3. Determine the current return oil characteristic curve III, and use this to determine the flow area of ​​the return valve. Adjust the return valve, and use this ignition fuel quantity for ignition start-up.

[0064] This embodiment determines the current return fuel quantity and the conduction area of ​​the return valve by using the flow characteristic curve of the pre-installed fuel pump, the characteristic curve of the pre-combustion stage nozzle, and the family of return fuel characteristic curves. This ensures that the fuel pressure in the first fuel manifold can provide the required ignition fuel quantity to the pre-combustion stage nozzle, thus ensuring the successful start-up of the auxiliary power device.

[0065] Based on the above embodiments, when the fuel distributor transmits fuel to the first fuel manifold, the controller is further configured to control the reflux valve to open or close, so that the fuel supply from the first fuel manifold to the pre-combustion stage nozzle is the ignition fuel quantity for the auxiliary power unit. This may further include: when the ignition fuel quantity is the maximum ignition fuel quantity, the controller controls the reflux valve to close, so that all the fuel in the first fuel manifold is used as ignition fuel; when the ignition fuel quantity is the minimum ignition fuel quantity, the controller controls the reflux valve to open to its maximum conduction area, so that the fuel supply from the first fuel manifold to the pre-combustion stage nozzle is the ignition fuel quantity for the auxiliary power unit. In this embodiment, the fuel supply from the fuel distributor to the first fuel manifold can be the aforementioned maximum ignition fuel quantity. For example, when starting the auxiliary power unit in cold weather at sea level, the current ignition fuel quantity can be the maximum ignition fuel quantity, and the controller closes the return valve; when starting the auxiliary power unit in hot weather at high altitude, the current ignition fuel quantity can be the minimum ignition fuel quantity, and the controller opens the return valve to the maximum opening, so that the return fuel quantity reaches the maximum.

[0066] The present invention also provides an aircraft. Figure 6 A schematic diagram of an aircraft structure provided for an embodiment of the present invention, such as... Figure 6 As shown, the aircraft provided in this embodiment of the invention includes: an auxiliary power unit 31; and a fuel system 32 for the auxiliary power unit provided in any embodiment of the invention. The aircraft in this embodiment solves the problem of insufficient altitude range for in-flight start-up of the auxiliary power unit in existing technologies, improves the high-altitude start-up performance of the auxiliary power unit 31, and ensures successful high-altitude ignition of the auxiliary power unit 31. Optionally, the aircraft in this embodiment can be a large aircraft, a medium-sized aircraft, or a large helicopter, etc. This embodiment does not limit the specific type of aircraft or its usage. Furthermore, as... Figure 6 As shown, the auxiliary power unit 31 and its fuel system 32 can be installed in the tail cone at the rear of the fuselage, so that the auxiliary power unit can provide electricity and compressed air to the aircraft, while ensuring lighting and air conditioning in the cabin and cockpit.

[0067] The aircraft described in any embodiment of the present invention includes the technical features of the fuel system of the auxiliary power unit provided in any embodiment of the present invention, and has the beneficial effects of the corresponding technical features, which will not be repeated here.

[0068] Note that the above description is merely a preferred embodiment of the present invention and the technical principles employed. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and various obvious changes, readjustments, and substitutions can be made without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments, and may include many other equivalent embodiments without departing from the concept of the present invention, the scope of which is determined by the scope of the appended claims.

Claims

1. A fuel system for an auxiliary power unit, characterized in that, include: Controller, fuel module, fuel distributor, return valve, pre-combustion stage nozzle and main combustion stage nozzle; The fuel module is used to pressurize the fuel at the fuel inlet and then transmit it to the fuel distributor; the controller is electrically connected to the fuel module and is used to control the rotation of the fuel pump of the fuel module; the fuel distributor is connected to the pre-combustion stage nozzle and the return valve respectively through a first fuel main pipe, and is used to transmit the fuel to the return valve and the pre-combustion stage nozzle when the inlet pressure of the fuel distributor is greater than the first opening pressure and less than the second opening pressure; the fuel distributor is connected to the main combustion stage nozzle through a second fuel main pipe, and is used to transmit the fuel to the main combustion stage nozzle when the inlet pressure of the fuel distributor is greater than the second opening pressure; The return valve is connected to the fuel inlet via a return oil pipe; the controller is also used to control the return valve to open or close when the fuel distributor transmits the fuel to the first fuel manifold, so that the amount of fuel supplied from the first fuel manifold to the pre-combustion stage nozzle is the amount of ignition fuel for the auxiliary power unit. The controller is also configured to obtain the current ignition fuel quantity of the auxiliary power unit based on the current ambient temperature and pressure; the controller is also configured to obtain the current fuel supply quantity of the fuel pump based on the current ignition fuel quantity, and obtain the current return fuel quantity of the return valve based on the current fuel supply quantity. The controller is also used to control the current conduction area of ​​the return valve based on the current return oil volume.

2. The fuel system of the auxiliary power unit according to claim 1, characterized in that, Also includes: Gate valve; The shut-off valve is located in the transmission channel between the fuel module and the fuel distributor, and is used to open and close the connection between the fuel module and the fuel distributor under the control of the controller.

3. The fuel system of the auxiliary power unit according to claim 1, characterized in that, The pre-combustion stage nozzle is connected to the combustion chamber and is used to atomize and inject fuel transmitted from the first fuel manifold into the combustion chamber during the ignition phase of the auxiliary power unit. The main combustion stage nozzle is connected to the combustion chamber and is used to atomize and inject fuel transmitted from the second fuel manifold into the combustion chamber during the operation of the auxiliary power unit.

4. The fuel system of the auxiliary power unit according to claim 1, characterized in that, The controller is specifically used to control the conduction area of ​​the return valve so that the amount of fuel supplied from the first fuel main to the pre-combustion stage nozzle is the amount of ignition fuel for the auxiliary power unit.

5. A control method for the fuel system of an auxiliary power unit, characterized in that, A fuel system suitable for the auxiliary power unit according to any one of claims 1-4, comprising: The controller receives the start command of the auxiliary power unit and controls the fuel pump of the fuel module to rotate according to the start command, so that the fuel module transmits fuel to the fuel distributor; During the ignition phase of the auxiliary power unit, the controller controls the inlet pressure of the fuel distributor to be greater than the first opening pressure and less than the second opening pressure through the fuel module, so that the fuel distributor transmits the fuel to the return valve and the pre-combustion stage nozzle through the first fuel manifold. During the operation of the auxiliary power unit, the controller controls the inlet pressure of the fuel distributor to be greater than the second opening pressure through the fuel module, so that the fuel distributor transmits the fuel to the main combustion stage nozzle through the second fuel manifold; When the fuel distributor transmits the fuel to the first fuel manifold, the controller is also used to control the reflux valve to open or close, so that the amount of fuel supplied from the first fuel manifold to the pre-combustion stage nozzle is the amount of ignition fuel for the auxiliary power unit.

6. The control method for the fuel system of the auxiliary power unit according to claim 5, characterized in that, After the controller receives the start command of the auxiliary power unit, it also includes: The controller obtains the current ignition fuel quantity of the auxiliary power unit based on the current ambient temperature and pressure; the controller is also used to obtain the current fuel supply quantity of the fuel pump of the fuel module based on the current ignition fuel quantity, and to obtain the current return fuel quantity of the return valve based on the current fuel supply quantity. When the fuel distributor delivers fuel to the first fuel manifold, the controller is further configured to control the backflow valve to open or close, so that the amount of fuel delivered from the first fuel manifold to the pre-combustion nozzle is the amount of ignition fuel for the auxiliary power unit, including: When the fuel distributor transmits the fuel to the first fuel manifold, the controller controls the conduction area of ​​the return valve according to the return fuel quantity, so that the amount of fuel transmitted from the first fuel manifold to the pre-combustion stage nozzle is the amount of ignition fuel for the auxiliary power unit.

7. The control method for the fuel system of the auxiliary power unit according to claim 6, characterized in that, The controller is further configured to obtain the current fuel supply quantity of the fuel pump of the fuel module based on the current ignition fuel quantity, and to obtain the current return fuel quantity of the return valve based on the current fuel supply quantity, including: The controller obtains the current fuel pressure of the pre-combustion stage nozzle corresponding to the current ignition fuel quantity based on the fuel supply quantity-fuel pressure curve of the pre-combustion stage nozzle. The controller obtains the current fuel supply of the fuel pump corresponding to the current fuel pressure based on the fuel supply quantity-fuel pressure curve of the fuel pump. The controller obtains the current return oil quantity of the return valve based on the current fuel supply quantity and the current ignition fuel quantity; When the fuel distributor delivers fuel to the first fuel manifold, the controller controls the conduction area of ​​the return valve according to the return fuel quantity, so that the amount of fuel delivered from the first fuel manifold to the pre-combustion stage nozzle is the ignition fuel quantity for the auxiliary power unit, including: Based on the family of return oil quantity-fuel pressure curves of the return valve, obtain the current return oil quantity-fuel pressure curve of the return valve corresponding to the current return oil quantity and the current fuel pressure; wherein, the family of return oil quantity-fuel pressure curves includes multiple return oil quantity-fuel pressure curves; different return oil quantity-fuel pressure curves correspond to different conduction areas of the return valve. Based on the current return oil quantity-fuel pressure curve, the current conduction area of ​​the return valve is obtained so that the fuel supply from the first fuel main to the pre-combustion stage nozzle is the ignition fuel quantity of the auxiliary power unit.

8. The control method for the fuel system of the auxiliary power unit according to claim 5, characterized in that, When the fuel distributor delivers fuel to the first fuel manifold, the controller is further configured to control the backflow valve to open or close, so that the amount of fuel delivered from the first fuel manifold to the pre-combustion nozzle is the amount of ignition fuel for the auxiliary power unit, including: When the ignition fuel quantity is at the maximum ignition fuel quantity, the controller controls the return valve to close, so that all the fuel in the first fuel manifold is used as the ignition fuel quantity. When the ignition fuel quantity is at the minimum ignition fuel quantity, the controller controls the return valve to open to the maximum conduction area, so that the fuel supply from the first fuel main to the pre-combustion stage nozzle is the ignition fuel quantity of the auxiliary power unit.

9. An aircraft, characterized in that, include: Auxiliary power unit; And the fuel system of the auxiliary power unit as described in any one of claims 1-4.

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