A test method for matching restrictor holes in aircraft fuel tank inerting systems

Abstract

The present application belongs to the technical field of aircraft fuel systems, and particularly relates to a flow restriction orifice matching test method for an aircraft fuel tank inerting system. The method comprises: constructing an aircraft fuel tank inerting system, the aircraft fuel tank inerting system comprising a small flow inerting branch, a medium flow inerting branch, and a large flow inerting branch arranged in parallel, the small flow inerting branch being provided with a small flow restriction orifice, the medium flow inerting branch being provided with a medium flow restriction orifice, and the large flow inerting branch being provided with a large flow restriction orifice, the aircraft fuel tank inerting system having a small flow mode, a medium flow mode, and a large flow mode; determining the matching order of the small flow restriction orifice, the medium flow restriction orifice, and the large flow restriction orifice; determining the qualification criteria for the small flow mode, the medium flow mode, and the large flow mode, respectively; and sequentially performing flow restriction orifice matching according to the matching order and the corresponding qualification criteria. The present application saves time for flow restriction orifice matching and simplifies the steps of the flow restriction orifice matching test.

Description

Technical Field

[0001] The present application belongs to the technical field of aircraft fuel systems, and in particular relates to a flow restriction orifice matching test method for an aircraft fuel tank inerting system. Background Art

[0002] Aircraft fuel system fires or explosions are one of the leading causes of aircraft accidents. The fire and explosion resistance of aircraft fuel systems is directly related to aircraft survivability and vulnerability, as well as aircraft utilization, costs, and crew safety. Aircraft fuel tank inerting technology can effectively address these fire and explosion issues.

[0003] The flow distribution of nitrogen-rich gas in existing aircraft fuel tank inerting is generally divided into several flow modes. Different flow modes achieve aircraft fuel tank inerting through corresponding inerting branches. The inerting branches are provided with flow limiting holes. The size of the flow limiting hole is an important factor affecting the inerting effect of aircraft fuel tanks. If the flow limiting hole size is too large, the flow rate corresponding to the flow mode will be too large, resulting in the problem of wasting engine bleed air. If the flow limiting hole size is too small, the flow rate corresponding to the flow mode will be too small, reducing the inerting efficiency of the inerting system for the fuel tank.

[0004] Therefore, it is desired to have a technical solution to overcome or at least alleviate at least one of the above-mentioned deficiencies of the prior art. Summary of the Invention

[0005] The purpose of this application is to provide a flow restriction orifice matching test method for an aircraft fuel tank inerting system to solve at least one problem existing in the prior art.

[0006] The technical solution of this application is:

[0007] A test method for matching flow restriction holes in an aircraft fuel tank inerting system, comprising:

[0008] An aircraft fuel tank inerting system is constructed, the aircraft fuel tank inerting system comprising a small flow inerting branch, a medium flow inerting branch, and a large flow inerting branch arranged in parallel, the small flow inerting branch being provided with a small flow limiting hole, the medium flow inerting branch being provided with a medium flow limiting hole, and the large flow inerting branch being provided with a large flow limiting hole, the aircraft fuel tank inerting system having a small flow mode, a medium flow mode, and a large flow mode;

[0009] Determine the matching order of small flow limiting holes, medium flow limiting holes, and large flow limiting holes;

[0010] Determine the eligibility criteria for small flow mode, medium flow mode, and large flow mode respectively;

[0011] According to the matching order and the corresponding qualification criteria, the flow limiting holes are matched in sequence.

[0012] Preferably, the aircraft fuel tank inerting system further comprises:

[0013] An air separation device, the air separation device having an inlet pipeline and an outlet pipeline, the air separation device being connected to an air source via the inlet pipeline, the inlet pipeline being provided with an inlet pressure sensor and an inlet pressure regulating valve, and the outlet pipeline being provided with a flow sensor and an oxygen concentration sensor;

[0014] A fuel tank, wherein the fuel tank is provided with a fuel tank pressure sensor;

[0015] The two ends of the small flow inerting branch are respectively connected to the outlet pipeline of the air separation device and the oil tank;

[0016] The two ends of the medium flow inerting branch are respectively connected to the outlet pipeline of the air separation device and the oil tank, and the medium flow inerting branch is also provided with a medium flow cut-off valve;

[0017] The two ends of the large flow inerting branch are respectively connected to the outlet pipeline of the air separation device and the oil tank, and a large flow cut-off valve is also provided on the large flow inerting branch;

[0018] A controller is used to collect data fed back by various sensors and control the inlet pressure regulating valve, the medium flow cut-off valve and the large flow cut-off valve.

[0019] Preferably,

[0020] After the aircraft fuel tank inerting system is started on the ground, the air separation unit is preheated, and after the preheating is completed, the system enters the medium flow mode;

[0021] During the aircraft climbing and cruising phases, the aircraft fuel tank inerting system enters a low-flow mode;

[0022] During the aircraft's descent phase, the aircraft fuel tank inerting system enters high-flow mode;

[0023] In low-flow mode, the aircraft fuel tank is inerted via the low-flow inerting branch;

[0024] In the medium flow mode, the medium flow cut-off valve is opened to inert the aircraft fuel tank via the low flow inerting branch and the medium flow inerting branch;

[0025] In the high flow mode, the high flow cut-off valve is opened, and the aircraft fuel tank is inerted through the low flow inerting branch and the high flow inerting branch.

[0026] Preferably, the first qualification criterion for the low flow mode is: the oxygen concentration of the nitrogen-rich gas in the low flow mode is between O1±0.3%, wherein O1 is the oxygen concentration corresponding to the low flow mode.

[0027] Preferably, the second qualification criterion for the medium flow mode is: the oxygen concentration of the nitrogen-rich gas in the medium flow mode is between O2±0.3%, wherein O2 is the oxygen concentration corresponding to the medium flow mode.

[0028] Preferably, the third qualification criterion of the large flow mode is: the nitrogen-rich gas flow rate in the large flow mode is in the descending stage of the design cross section of the aircraft fuel tank inerting system, and the pressure of the fuel tank relative to the atmospheric environment is P min kPa~(P min +2) kPa, where P min The minimum negative pressure designed for aircraft fuel tank inerting systems.

[0029] Preferably, the small flow limiting hole matching process is as follows:

[0030] S1. Determine the initial dimensions of the three flow restriction holes and install the aircraft fuel tank inerting system;

[0031] S2. Start the aircraft fuel tank inerting system and introduce high-temperature gas into the aircraft fuel tank inerting system through the gas source to preheat the air separation unit;

[0032] S3. After the air separation unit is fully preheated, the aircraft fuel tank inerting system enters the medium flow mode;

[0033] S4. Adjust the air separation unit inlet pressure to a second pressure, where the second pressure is the bleed air pressure after the ground auxiliary power unit (APU) is started;

[0034] S5. After the inlet pressure stabilizes, record the nitrogen-rich gas flow rate and oxygen concentration at the outlet of the air separation unit in the medium flow mode;

[0035] S6. Set the wheel load to air and the aircraft fuel tank inerting system to low flow mode;

[0036] S7, adjusting the air separation unit inlet pressure to a first pressure, where the first pressure is the minimum bleed air pressure when the aircraft is cruising at high altitude;

[0037] S8. After the inlet pressure stabilizes, record the nitrogen-rich gas flow rate and oxygen concentration at the outlet of the air separation unit in the low-flow mode;

[0038] S9. Compare the oxygen concentration of the nitrogen-rich gas in the low flow mode with the first qualification criterion. If the first qualification criterion is not met, perform the following steps:

[0039] S9.1. Turn off the aircraft fuel tank inerting system;

[0040] S9.2. Adjust the low-flow restrictor orifice size and reinstall the aircraft fuel tank inerting system;

[0041] S9.3. Adjust the size of the medium flow restrictor orifice and reinstall the aircraft fuel tank inerting system. Return to step S2.

[0042] Repeat steps S2-S9 until the first qualification criterion is met and the small flow limiting hole matching is completed.

[0043] Preferably,

[0044] In step S9.2, the process of adjusting the size of the low flow limiting hole specifically includes:

[0045] S9.2.1. If the oxygen concentration of the nitrogen-rich gas in the low-flow mode is higher than O1 + 0.3%, reduce the size of the low-flow restrictor orifice;

[0046] S9.2.2 If the oxygen concentration of the nitrogen-rich gas in the low-flow mode is lower than O1-0.3%, increase the size of the low-flow restrictor orifice.

[0047] Preferably,

[0048] In step S9.3, the process of adjusting the size of the medium flow limiting hole specifically includes:

[0049] S9.3.1. If the oxygen concentration of the nitrogen-rich gas in the medium flow mode is between O2 ± 0.3%, if the small flow rate limiting orifice size is reduced, the medium flow rate limiting orifice size shall be increased; if the small flow rate limiting orifice size is increased, the medium flow rate limiting orifice size shall be decreased;

[0050] S9.3.2 If the oxygen concentration of the nitrogen-rich gas in the medium flow mode is higher than O2 + 0.3%, if the small flow rate limiting orifice size is reduced, the medium flow rate limiting orifice size shall be reduced or kept unchanged; if the small flow rate limiting orifice size is increased, the medium flow rate limiting orifice size shall be reduced;

[0051] S9.3.3. If the oxygen concentration of the nitrogen-rich gas in the medium flow mode is lower than O2-0.3%, when the small flow rate limiting orifice size is reduced, the medium flow rate limiting orifice size is increased; when the small flow rate limiting orifice size is increased, the medium flow rate limiting orifice size is increased or remains unchanged.

[0052] Preferably, the medium flow limiting hole matching process is as follows:

[0053] S10: Compare the oxygen concentration of the nitrogen-rich gas in the medium flow mode with the second qualification criterion. If the second qualification criterion is not met, perform the following steps:

[0054] S10.1. Turn off the aircraft fuel tank inerting system;

[0055] S10.2. Adjust the size of the medium flow restrictor orifice and reinstall the aircraft fuel tank inerting system;

[0056] S10.3. Start the aircraft fuel tank inerting system and introduce high-temperature gas into the aircraft fuel tank inerting system through the gas source to preheat the air separation unit;

[0057] S10.4. After the air separation unit is fully preheated, the aircraft fuel tank inerting system enters the medium flow mode;

[0058] S10.5. Adjust the air separation unit inlet pressure to the second pressure;

[0059] S10.6. After the inlet pressure stabilizes, record the nitrogen-rich gas flow rate and oxygen concentration at the outlet of the air separation unit in the medium flow mode, and return to step S10.

[0060] Repeat step S10 until the second qualification criterion is met, and the medium flow limiting hole matching is completed.

[0061] Preferably,

[0062] In step S10.2, the process of adjusting the size of the medium flow limiting hole specifically includes:

[0063] S10.2.1. If the oxygen concentration of the nitrogen-rich gas in the medium flow mode is higher than O2 + 0.3%, reduce the size of the medium flow restrictor orifice;

[0064] S10.2.2. If the oxygen concentration of the nitrogen-rich gas in the medium flow mode is lower than O2-0.3%, increase the size of the medium flow restrictor orifice.

[0065] Preferably, the large flow limiting hole matching process is as follows:

[0066] S11. Set the wheel load to air and simulate the aircraft climbing and descending according to the designed profile;

[0067] S12. Before the aircraft descends, adjust the air separation unit inlet pressure to a third pressure, where the third pressure is the average bleed air pressure during the aircraft's descent phase;

[0068] S13, during the descent phase, the aircraft fuel tank inerting system enters high-flow mode;

[0069] S14. After the inlet pressure stabilizes, record the minimum pressure of the fuel tank in the high-flow mode, as well as the nitrogen-rich gas flow rate and oxygen concentration at the outlet of the air separation unit;

[0070] S15. Compare the minimum pressure of the fuel tank in the high flow mode with the third qualification criterion. If the third qualification criterion is not met, perform the following steps:

[0071] S15.1. Turn off the aircraft fuel tank inerting system;

[0072] S15.2. Adjust the size of the high-flow restrictor orifice and reinstall the aircraft fuel tank inerting system;

[0073] S15.3. Start the aircraft fuel tank inerting system and introduce high-temperature or room-temperature gas into the aircraft fuel tank inerting system through the gas source to preheat the air separation unit;

[0074] S15.4. After the air separation unit is fully preheated, return to step S11;

[0075] Repeat steps S11-S15 until the third qualification criterion is met, and then proceed to step S16;

[0076] S16: Determine whether the gas introduced by the gas source to the aircraft fuel tank inerting system in the high flow mode is high temperature gas. If so, proceed to step S17; if not, perform the following steps:

[0077] S16.1. Turn off the aircraft fuel tank inerting system;

[0078] S16.2. Start the aircraft fuel tank inerting system and introduce high-temperature or room-temperature gas into the aircraft fuel tank inerting system through the gas source to preheat the air separation unit;

[0079] S16.3. After the air separation unit is fully preheated, return to step S11;

[0080] S17. Turn off the aircraft fuel tank inerting system and complete the matching of the large flow limiting orifice.

[0081] Preferably,

[0082] In step S15.2, the process of adjusting the large flow limiting hole size specifically includes:

[0083] S15.2.1. If the minimum pressure of the fuel tank in the high flow mode during the descent phase is less than P min kPa, increase the size of the large flow restrictor hole;

[0084] S15.2.2 If the minimum pressure of the fuel tank in the high flow mode during the descent phase is greater than (P min +2) kPa, reduce the size of the large flow restrictor hole.

[0085] The invention has at least the following beneficial technical effects:

[0086] The present application discloses a flow-limiting hole matching test method for an aircraft fuel tank inerting system. The method constructs an aircraft fuel tank inerting system, clarifies the flow-limiting hole matching sequence in low-flow, medium-flow, and high-flow modes, and defines the qualification criteria for flow-limiting hole matching in different flow modes. Combined with usage scenarios, the method provides an optimal flow-limiting hole matching process, obtains the optimal sizes of different flow-limiting holes, saves flow-limiting hole matching time, and simplifies the flow-limiting hole matching test steps. BRIEF DESCRIPTION OF THE DRAWINGS

[0087] Figure 1 This is a flow chart of a flow restriction orifice matching test method for an aircraft fuel tank inerting system according to one embodiment of the present application;

[0088] Figure 2 It is a cross-sectional schematic diagram of a large flow limiting hole matching according to an embodiment of the present application. DETAILED DESCRIPTION

[0089] In order to make the purpose, technical solutions and advantages of the implementation of this application clearer, the technical solutions in the embodiments of this application will be described in more detail below in conjunction with the drawings in the embodiments of this application. In the drawings, the same or similar reference numerals throughout represent the same or similar elements or elements with the same or similar functions. The described embodiments are part of the embodiments of this application, not all of the embodiments. The embodiments described below with reference to the drawings are exemplary and are intended to be used to explain this application, and should not be understood as limitations on this application. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application. The embodiments of this application are described in detail below in conjunction with the drawings.

[0090] The following is combined with Figure 1 To the attached Figure 2 This application is described in further detail.

[0091] The present application provides a test method for matching flow restriction holes in an aircraft fuel tank inerting system, comprising the following steps:

[0092] Constructing an aircraft fuel tank inerting system, the aircraft fuel tank inerting system including a small flow inerting branch, a medium flow inerting branch, and a large flow inerting branch arranged in parallel, the small flow inerting branch being provided with a small flow limiting hole, the medium flow inerting branch being provided with a medium flow limiting hole, and the large flow inerting branch being provided with a large flow limiting hole, the aircraft fuel tank inerting system having a small flow mode, a medium flow mode, and a large flow mode;

[0093] Determine the matching order of small flow limiting holes, medium flow limiting holes, and large flow limiting holes;

[0094] Determine the eligibility criteria for small flow mode, medium flow mode, and large flow mode respectively;

[0095] According to the matching order and the corresponding qualification criteria, the flow limiting holes are matched in sequence.

[0096] This application describes a test method for matching restrictor orifice flow in aircraft fuel tank inerting systems. To meet the nitrogen-enriched gas requirements for different aircraft operating conditions, the fuel tank inerting system of a certain aircraft features three inerting flow modes: low flow, medium flow, and high flow. These modes achieve different nitrogen-enriched gas flow rates and oxygen concentrations through three different restrictor orifices. After ground startup, the fuel tank inerting system requires preheating the air separation unit. After preheating, the system enters medium flow mode. After takeoff, during the climb and cruise phases, the system enters low flow mode. During descent, the system enters high flow mode.

[0097] In a preferred embodiment of the present application, the aircraft fuel tank inerting system further includes: an air separation unit, a fuel tank, and a controller. The air separation unit has an inlet pipeline and an outlet pipeline. The air separation unit is connected to an air source via the inlet pipeline. The inlet pipeline is equipped with an inlet pressure sensor and an inlet pressure regulating valve, and the outlet pipeline is equipped with a flow sensor and an oxygen concentration sensor. The fuel tank is equipped with a fuel tank pressure sensor. The low-flow inerting branch has two ends connected to the air separation unit outlet pipeline and the fuel tank, respectively. The medium-flow inerting branch has two ends connected to the air separation unit outlet pipeline and the fuel tank, respectively. The medium-flow inerting branch also has a medium-flow shut-off valve. The high-flow inerting branch has two ends connected to the air separation unit outlet pipeline and the fuel tank, respectively. The high-flow inerting branch also has a high-flow shut-off valve. The controller is used to collect data fed back by the various sensors and control the inlet pressure regulating valve, the medium-flow shut-off valve, and the high-flow shut-off valve.

[0098] The present application describes a test method for matching flow restrictors in an aircraft fuel tank inerting system. The three flow modes of the aircraft fuel tank inerting system correspond to different inerting branches. The low-flow inerting branch is a normally open pipeline, the medium-flow inerting branch is controlled by a medium-flow shutoff valve, and the high-flow inerting branch is controlled by a large-flow shutoff valve. Therefore, in the low-flow mode, aircraft fuel tank inerting is achieved through the low-flow inerting branch. In the medium-flow mode, the medium-flow shutoff valve is opened, and aircraft fuel tank inerting is achieved through both the low-flow inerting branch and the medium-flow inerting branch. In the high-flow mode, the large-flow shutoff valve is opened, and aircraft fuel tank inerting is achieved through both the low-flow inerting branch and the large-flow inerting branch.

[0099] In this application's restrictor orifice matching test method for aircraft fuel tank inerting systems, the medium flow mode corresponds to the sum of the flow rates through the low-flow and medium-flow inerting branches, while the high flow mode corresponds to the sum of the flow rates through the low-flow and high-flow inerting branches. For this reason, and considering the different activation timings of the three flow modes during flight, the restrictor orifice matching order is determined as follows: first match the low-flow restrictor, then the medium-flow restrictor, and finally the high-flow restrictor.

[0100] The aircraft fuel tank inerting system flow restriction matching test method of this application further obtains acceptance criteria for three flow modes. The primary purpose of the low-flow mode is to fill the fuel tank vapor space with high-quality nitrogen-rich gas to minimize the oxygen concentration in the fuel tank vapor space. This ensures that the tank oxygen concentration meets design requirements even after filling with low-quality nitrogen-rich gas during the aircraft's descent phase. Therefore, the acceptance criteria for flow restriction matching in the low-flow mode should be: the oxygen concentration of the nitrogen-rich gas in the low-flow mode is between O1±0.3%. This is the first acceptance criteria, where O1 is the oxygen concentration corresponding to the low-flow mode. The purpose of the medium-flow mode is to reduce the initial oxygen concentration in the fuel tank vapor space to the design value within a specified time. When the oxygen concentration of the nitrogen-rich gas is O2, the oxygen concentration in the fuel tank is reduced to the design value as quickly as possible. Therefore, the acceptance criteria for flow restriction matching in the medium-flow mode should be: the oxygen concentration of the nitrogen-rich gas in the medium-flow mode is between O2±0.3%. This is the second acceptance criteria, where O2 is the oxygen concentration corresponding to the medium-flow mode. The primary purpose of the high-flow mode is to ensure that the negative pressure of the fuel tank does not exceed the limit, and the secondary purpose is to reduce the oxygen concentration in the fuel tank gas phase space. Once the negative pressure of the fuel tank exceeds the limit, the anti-vacuum valve in the breather box connected to the fuel tank will open, and a large amount of external air will enter the fuel tank gas phase space, and the oxygen concentration in the fuel tank gas phase space cannot be guaranteed. Therefore, the qualified criterion for the matching of the flow restriction hole in the high-flow mode should be: the nitrogen-rich gas flow rate in the high-flow mode should be guaranteed in the descent stage of the design profile of the aircraft fuel tank inerting system, and the pressure of the fuel tank relative to the atmospheric environment should be within P min kPa~(P min +2) kPa, which is the third qualified criterion. The fuel tank has a 2kPa margin relative to the atmospheric pressure to avoid the difference between the test and the actual flight, which may lead to the fuel tank pressure exceeding the limit. min The minimum negative pressure designed for an aircraft fuel tank inerting system. The descent phase corresponding to the design profile of the aircraft fuel tank inerting system has the highest altitude at the start of descent and the fastest average descent speed.

[0101] The aircraft fuel tank inerting system restrictor orifice matching test method disclosed herein involves sequentially performing restrictor orifice matching after determining the restrictor orifice matching sequence and the acceptance criteria for different flow patterns. Prior to restrictor orifice matching, the dimensions of the three restrictor orifices are pre-determined by calculation, and the aircraft fuel tank inerting system is installed. Hollow fiber membranes are preferably used in the air separation unit, as they perform best under high-temperature conditions.

[0102] The operation steps for matching the small flow restrictor hole are as follows: start the aircraft fuel tank inerting system, introduce high-temperature gas into the aircraft fuel tank inerting system, first fully preheat the air separation unit, and after the air separation unit is fully preheated, the aircraft fuel tank inerting system automatically enters the medium flow mode, adjusts the bleed air pressure at the air separation unit inlet to the second pressure, and records the nitrogen-rich gas flow rate and oxygen concentration in the medium flow mode; set the wheel load to air, the aircraft fuel tank inerting system enters the small flow mode, adjusts the bleed air pressure at the air separation unit inlet to the first pressure, and records the nitrogen-rich gas flow rate and oxygen concentration in the small flow mode. The oxygen concentration of the nitrogen-rich gas in the small flow mode is compared with the first qualification criterion. If the first qualification criterion is not met, the aircraft fuel tank inerting system is shut down and the size of the small flow limiting hole is adjusted. The adjustment principle is: if the oxygen concentration in the small flow mode is too high, the size of the small flow limiting hole is reduced; if the oxygen concentration in the small flow mode is too low, the size of the small flow limiting hole is increased. After adjusting the size of the small flow limiting hole, reinstall it; further, the size of the medium flow limiting hole is adjusted. The adjustment principle is: compare the oxygen concentration of the nitrogen-rich gas in the medium flow mode with the second qualification criterion. If the second qualification criterion is met, if the small flow limiting hole is reduced, the size of the medium flow limiting hole is increased; if the small flow limiting hole is increased, the size of the medium flow limiting hole is increased. Reduce the size; if the second qualification criterion is not met, when the oxygen concentration in the medium flow mode is high and the small flow limiting hole is reduced, adjust the size of the medium flow limiting hole as needed; when the oxygen concentration in the medium flow mode is high and the small flow limiting hole is increased, reduce the size of the medium flow limiting hole; if the second qualification criterion is not met, when the oxygen concentration in the medium flow mode is low and the small flow limiting hole is reduced, increase the size of the medium flow limiting hole; when the oxygen concentration in the medium flow mode is low and the small flow limiting hole is increased, adjust the size of the medium flow limiting hole as needed; reinstall the medium flow limiting hole after adjusting the size, and continue the test by reinstalling the small flow limiting hole matching operation steps until the first qualification criterion is met and the small flow limiting hole matching is completed.

[0103] The medium flow restrictor orifice matching procedure is as follows: Compare the oxygen concentration of the nitrogen-rich gas in medium flow mode with the second qualification criterion. If the second qualification criterion is not met, shut down the aircraft fuel tank inerting system and adjust the medium flow restrictor orifice size. The adjustment principle is: if the oxygen concentration in medium flow mode is high, reduce the medium flow restrictor orifice size; if the oxygen concentration in medium flow mode is low, increase the medium flow restrictor orifice size. After adjusting the medium flow restrictor orifice size, reinstall the aircraft fuel tank inerting system, start the aircraft fuel tank inerting system, and introduce high-temperature gas. After the air separation unit is preheated, enter medium flow mode, adjust the bleed air pressure at the air separation unit inlet to the second pressure, and record the nitrogen-rich gas flow rate and oxygen concentration in medium flow mode. Repeat the medium flow restrictor orifice matching procedure until the second qualification criterion is met, and the medium flow restrictor orifice matching is complete.

[0104] The operation steps for matching the large flow restrictor orifice are as follows: set the aircraft wheel load to air, and simulate the aircraft climbing and descending according to the design profile, wherein the atmospheric pressure of the fuel tank changes according to the height corresponding to the design profile; before the aircraft descends, adjust the bleed air pressure at the inlet of the air separation device to the third pressure; during the descent phase, the aircraft fuel tank inerting system enters the large flow mode, and records the minimum pressure of the fuel tank under the large flow mode during the descent phase, as well as the flow rate and oxygen concentration of the nitrogen-rich gas, and compares the minimum pressure with the third qualification criterion. If the third qualification criterion is met, the large flow restrictor orifice is matched. End; If the third qualification criterion is not met, shut down the aircraft fuel tank inerting system and adjust the high-flow orifice size. The adjustment principle is as follows: when the minimum fuel tank pressure is lower than the third qualification criterion, increase the high-flow orifice size; when the minimum fuel tank pressure is higher than the third qualification criterion, decrease the high-flow orifice size. After adjusting the high-flow orifice size, reinstall the aircraft fuel tank inerting system, start the aircraft fuel tank inerting system, and introduce high-temperature or room-temperature gas. After the air separation unit is preheated, repeat the high-flow orifice matching operation steps until the third qualification criterion is met and the high-flow orifice matching is completed. It is understood that to shorten the orifice matching time, the high-flow orifice matching can be performed by introducing room-temperature pressurized gas. After the large-flow orifice size is confirmed, high-temperature pressurized gas can be introduced to confirm the oxygen concentration corresponding to the large-flow mode.

[0105] In a specific embodiment of the present application, Figure 1 , introduce the flow limiting hole matching process in detail:

[0106] S1. Determine the initial dimensions of the three flow restriction holes and install the aircraft fuel tank inerting system;

[0107] S2. Start the aircraft fuel tank inerting system and introduce high-temperature gas into the aircraft fuel tank inerting system through the gas source to preheat the air separation unit;

[0108] S3. After the air separation unit is fully preheated, the aircraft fuel tank inerting system enters the medium flow mode;

[0109] S4. Adjust the air separation unit inlet pressure to a second pressure, where the second pressure is the bleed air pressure after the ground auxiliary power unit (APU) is started;

[0110] The ground auxiliary power unit (APU), similar to a kerosene generator, provides air conditioning and onboard power when the engine is not started, as well as engine starting. Ground inerting air is sourced from environmental control systems. Environmental control bleed air generally comes from two sources: the APU or the engine. APU bleed air pressure is lower than engine bleed air pressure. Lower pressures are associated with more stringent air separation performance assessments. Therefore, the APU bleed air pressure after startup is selected as the matching pressure for medium flow.

[0111] S5. After the inlet pressure stabilizes, record the nitrogen-rich gas flow rate and oxygen concentration at the outlet of the air separation unit in the medium flow mode;

[0112] S6. Set the wheel load to air and the aircraft fuel tank inerting system to low flow mode;

[0113] S7, adjusting the air separation unit inlet pressure to a first pressure, where the first pressure is the minimum bleed air pressure when the aircraft is cruising at high altitude;

[0114] S8. After the inlet pressure stabilizes, record the nitrogen-rich gas flow rate and oxygen concentration at the outlet of the air separation unit in the low-flow mode;

[0115] S9. Compare the oxygen concentration of the nitrogen-rich gas in the low flow mode with the first qualification criterion. If the first qualification criterion is not met, perform the following steps:

[0116] S9.1. Turn off the aircraft fuel tank inerting system;

[0117] S9.2. Adjust the low-flow restrictor orifice size and reinstall the aircraft fuel tank inerting system;

[0118] The process of adjusting the size of the low flow restrictor orifice includes:

[0119] S9.2.1. If the oxygen concentration of the nitrogen-rich gas in the low-flow mode is higher than O1 + 0.3%, reduce the size of the low-flow restrictor orifice;

[0120] S9.2.2. If the oxygen concentration of the nitrogen-rich gas in the low-flow mode is lower than O1-0.3%, increase the size of the low-flow restrictor orifice;

[0121] S9.3. Adjust the size of the medium flow restrictor orifice and reinstall the aircraft fuel tank inerting system. Return to step S2.

[0122] The process of adjusting the size of the medium flow restrictor orifice includes:

[0123] S9.3.1. If the oxygen concentration of the nitrogen-rich gas in the medium flow mode is between O2 ± 0.3%, if the small flow rate limiting orifice size is reduced, the medium flow rate limiting orifice size shall be increased; if the small flow rate limiting orifice size is increased, the medium flow rate limiting orifice size shall be decreased;

[0124] S9.3.2 If the oxygen concentration of the nitrogen-rich gas in the medium flow mode is higher than O2 + 0.3%, if the small flow rate limiting orifice size is reduced, the medium flow rate limiting orifice size shall be reduced or kept unchanged; if the small flow rate limiting orifice size is increased, the medium flow rate limiting orifice size shall be reduced;

[0125] S9.3.3. If the oxygen concentration of the nitrogen-rich gas in the medium flow mode is lower than O2-0.3%, if the small flow rate limiting orifice size is reduced, the medium flow rate limiting orifice size is increased; if the small flow rate limiting orifice size is increased, the medium flow rate limiting orifice size is increased or remains unchanged;

[0126] Repeat steps S2-S9 until the first qualification criterion is met and the small flow limiting hole matching is completed.

[0127] S10: Compare the oxygen concentration of the nitrogen-rich gas in the medium flow mode with the second qualification criterion. If the second qualification criterion is not met, perform the following steps:

[0128] S10.1. Turn off the aircraft fuel tank inerting system;

[0129] S10.2. Adjust the size of the medium flow restrictor orifice and reinstall the aircraft fuel tank inerting system;

[0130] The process of adjusting the size of the medium flow restrictor orifice includes:

[0131] S10.2.1. If the oxygen concentration of the nitrogen-rich gas in the medium flow mode is higher than O2 + 0.3%, reduce the size of the medium flow restrictor orifice;

[0132] S10.2.2. If the oxygen concentration of the nitrogen-rich gas in the medium flow mode is lower than O2-0.3%, increase the size of the medium flow restrictor orifice;

[0133] S10.3. Start the aircraft fuel tank inerting system and introduce high-temperature gas into the aircraft fuel tank inerting system through the gas source to preheat the air separation unit;

[0134] S10.4. After the air separation unit is fully preheated, the aircraft fuel tank inerting system enters the medium flow mode;

[0135] S10.5. Adjust the air separation unit inlet pressure to the second pressure;

[0136] S10.6. After the inlet pressure stabilizes, record the nitrogen-rich gas flow rate and oxygen concentration at the outlet of the air separation unit in the medium flow mode, and return to step S10.

[0137] Repeat step S10 until the second qualification criterion is met, and the medium flow limiting hole matching is completed.

[0138] S11, set the wheel load to air, and simulate the aircraft according to the design profile (such as Figure 2 Climb and descend as shown;

[0139] S12. Before the aircraft descends, adjust the air separation unit inlet pressure to a third pressure, where the third pressure is the average bleed air pressure during the aircraft's descent phase;

[0140] S13, during the descent phase, the aircraft fuel tank inerting system enters high-flow mode;

[0141] S14. After the inlet pressure stabilizes, record the minimum pressure of the fuel tank in the high-flow mode, as well as the nitrogen-rich gas flow rate and oxygen concentration at the outlet of the air separation unit;

[0142] S15. Compare the minimum pressure of the fuel tank in the high flow mode with the third qualification criterion. If the third qualification criterion is not met, perform the following steps:

[0143] S15.1. Turn off the aircraft fuel tank inerting system;

[0144] S15.2. Adjust the size of the high-flow restrictor orifice and reinstall the aircraft fuel tank inerting system;

[0145] The process of adjusting the size of the high flow restriction orifice includes:

[0146] S15.2.1. If the minimum pressure of the fuel tank in the high flow mode during the descent phase is less than P min kPa, increase the size of the large flow restrictor hole;

[0147] S15.2.2 If the minimum pressure of the fuel tank in the high flow mode during the descent phase is greater than (P min +2) kPa, reduce the size of the large flow limiting hole;

[0148] S15.3. Start the aircraft fuel tank inerting system and introduce high-temperature or room-temperature gas into the aircraft fuel tank inerting system through the gas source to preheat the air separation unit;

[0149] S15.4. After the air separation unit is fully preheated, return to step S11;

[0150] Repeat steps S11-S15 until the third qualification criterion is met, and then proceed to step S16;

[0151] S16: Determine whether the gas introduced by the gas source to the aircraft fuel tank inerting system in the high flow mode is high temperature gas. If so, proceed to step S17; if not, perform the following steps:

[0152] S16.1. Turn off the aircraft fuel tank inerting system;

[0153] S16.2. Start the aircraft fuel tank inerting system and introduce high-temperature or room-temperature gas into the aircraft fuel tank inerting system through the gas source to preheat the air separation unit;

[0154] S16.3. After the air separation unit is fully preheated, return to step S11;

[0155] S17. Turn off the aircraft fuel tank inerting system and complete the matching of the large flow limiting orifice.

[0156] The present invention discloses a flow restriction orifice matching test method for an aircraft fuel tank inerting system. This method addresses the requirements of different aircraft operating conditions and constructs an aircraft fuel tank inerting system with three flow modes. The three flow modes correspond to nitrogen-rich gases with three different oxygen concentrations and flow rates, and the nitrogen-rich gases in the three flow modes are all supplied through flow restriction orifices of different sizes. Since the low-flow inerting branch is a normally open pipeline, it must first be matched with a low-flow flow restriction orifice, followed by a medium-flow restriction orifice and a high-flow restriction orifice. Based on the main purposes of different flow modes, acceptable criteria for matching flow restriction orifices in different flow modes are provided. Furthermore, based on the usage scenarios, an optimal flow restriction orifice matching process is provided, resulting in the optimal sizes of different flow restriction orifices. This saves time in flow restriction orifice matching and simplifies the flow restriction orifice matching test steps.

[0157] The above description is merely a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this application should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. A test method for matching flow restriction holes in an aircraft fuel tank inerting system, characterized in that: include: An aircraft fuel tank inerting system is constructed, the aircraft fuel tank inerting system comprising a small flow inerting branch, a medium flow inerting branch, and a large flow inerting branch arranged in parallel, the small flow inerting branch being provided with a small flow limiting hole, the medium flow inerting branch being provided with a medium flow limiting hole, and the large flow inerting branch being provided with a large flow limiting hole, the aircraft fuel tank inerting system having a small flow mode, a medium flow mode, and a large flow mode; Determine the matching order of small flow limiting holes, medium flow limiting holes, and large flow limiting holes; Determine the eligibility criteria for small flow mode, medium flow mode, and large flow mode respectively; According to the matching order and the corresponding qualification criteria, the flow limiting holes are matched in sequence.

2. The aircraft fuel tank inerting system flow restriction hole matching test method according to claim 1, characterized in that: The aircraft fuel tank inerting system further comprises: An air separation device, the air separation device having an inlet pipeline and an outlet pipeline, the air separation device being connected to an air source via the inlet pipeline, the inlet pipeline being provided with an inlet pressure sensor and an inlet pressure regulating valve, and the outlet pipeline being provided with a flow sensor and an oxygen concentration sensor; A fuel tank, wherein the fuel tank is provided with a fuel tank pressure sensor; The two ends of the small flow inerting branch are respectively connected to the outlet pipeline of the air separation device and the oil tank; The two ends of the medium flow inerting branch are respectively connected to the outlet pipeline of the air separation device and the oil tank, and the medium flow inerting branch is also provided with a medium flow cut-off valve; The two ends of the large flow inerting branch are respectively connected to the outlet pipeline of the air separation device and the oil tank, and a large flow cut-off valve is also provided on the large flow inerting branch; A controller is used to collect data fed back by various sensors and control the inlet pressure regulating valve, the medium flow cut-off valve and the large flow cut-off valve.

3. The aircraft fuel tank inerting system flow restriction hole matching test method according to claim 2, characterized in that: After the aircraft fuel tank inerting system is started on the ground, the air separation unit is preheated, and after the preheating is completed, the system enters the medium flow mode; During the aircraft climbing and cruising phases, the aircraft fuel tank inerting system enters a low-flow mode; During the aircraft's descent phase, the aircraft fuel tank inerting system enters high-flow mode; In low-flow mode, the aircraft fuel tank is inerted via the low-flow inerting branch; In the medium flow mode, the medium flow cut-off valve is opened to inert the aircraft fuel tank via the low flow inerting branch and the medium flow inerting branch; In the high flow mode, the high flow cut-off valve is opened, and the aircraft fuel tank is inerted through the low flow inerting branch and the high flow inerting branch.

4. The aircraft fuel tank inerting system flow restriction hole matching test method according to claim 3, characterized in that: The first qualification criterion for the low flow mode is that the oxygen concentration of the nitrogen-rich gas in the low flow mode is between O1±0.3%, where O1 is the oxygen concentration corresponding to the low flow mode.

5. The aircraft fuel tank inerting system flow restriction orifice matching test method according to claim 4, characterized in that: The second qualification criterion for the medium flow mode is that the oxygen concentration of the nitrogen-rich gas in the medium flow mode is between O2±0.3%, where O2 is the oxygen concentration corresponding to the medium flow mode.

6. The aircraft fuel tank inerting system flow restriction orifice matching test method according to claim 5, characterized in that: The third qualification criterion for the large flow mode is: the nitrogen-rich gas flow rate in the large flow mode is in the descending stage of the aircraft fuel tank inerting system design section, and the pressure of the fuel tank relative to the atmospheric environment is P min kPa~(P min +2) kPa, where P min The minimum negative pressure designed for aircraft fuel tank inerting systems.

7. The aircraft fuel tank inerting system flow restriction orifice matching test method according to claim 6, characterized in that: The matching process of small flow limiting holes is as follows: S1. Determine the initial dimensions of the three flow restriction holes and install the aircraft fuel tank inerting system; S2. Start the aircraft fuel tank inerting system and introduce high-temperature gas into the aircraft fuel tank inerting system through the gas source to preheat the air separation unit; S3. After the air separation unit is fully preheated, the aircraft fuel tank inerting system enters the medium flow mode; S4. Adjust the air separation unit inlet pressure to a second pressure, where the second pressure is the bleed air pressure after the ground auxiliary power unit (APU) is started; S5. After the inlet pressure stabilizes, record the nitrogen-rich gas flow rate and oxygen concentration at the outlet of the air separation unit in the medium flow mode; S6. Set the wheel load to air and the aircraft fuel tank inerting system to low flow mode; S7, adjusting the air separation unit inlet pressure to a first pressure, where the first pressure is the minimum bleed air pressure when the aircraft is cruising at high altitude; S8. After the inlet pressure stabilizes, record the nitrogen-rich gas flow rate and oxygen concentration at the outlet of the air separation unit in the low-flow mode; S9. Compare the oxygen concentration of the nitrogen-rich gas in the low flow mode with the first qualification criterion. If the first qualification criterion is not met, perform the following steps: S9.

1. Turn off the aircraft fuel tank inerting system; S9.

2. Adjust the low-flow restrictor orifice size and reinstall the aircraft fuel tank inerting system; S9.

3. Adjust the size of the medium flow restrictor orifice and reinstall the aircraft fuel tank inerting system. Return to step S2. Repeat steps S2-S9 until the first qualification criterion is met and the small flow limiting hole matching is completed.

8. The aircraft fuel tank inerting system flow restriction orifice matching test method according to claim 7, characterized in that: In step S9.2, the process of adjusting the size of the low flow limiting hole specifically includes: S9.2.

1. If the oxygen concentration of the nitrogen-rich gas in the low-flow mode is higher than O1 + 0.3%, reduce the size of the low-flow restrictor orifice; S9.2.2 If the oxygen concentration of the nitrogen-rich gas in the low-flow mode is lower than O1-0.3%, increase the size of the low-flow restrictor orifice.

9. The aircraft fuel tank inerting system flow restriction orifice matching test method according to claim 8, characterized in that: In step S9.3, the process of adjusting the size of the medium flow limiting hole specifically includes: S9.3.

1. If the oxygen concentration of the nitrogen-rich gas in the medium flow mode is between O2 ± 0.3%, if the small flow rate limiting orifice size is reduced, the medium flow rate limiting orifice size shall be increased; if the small flow rate limiting orifice size is increased, the medium flow rate limiting orifice size shall be decreased; S9.3.2 If the oxygen concentration of the nitrogen-rich gas in the medium flow mode is higher than O2 + 0.3%, if the small flow rate limiting orifice size is reduced, the medium flow rate limiting orifice size shall be reduced or kept unchanged; if the small flow rate limiting orifice size is increased, the medium flow rate limiting orifice size shall be reduced; S9.3.

3. If the oxygen concentration of the nitrogen-rich gas in the medium flow mode is lower than O2-0.3%, when the small flow rate limiting orifice size is reduced, the medium flow rate limiting orifice size is increased; when the small flow rate limiting orifice size is increased, the medium flow rate limiting orifice size is increased or remains unchanged.

10. The aircraft fuel tank inerting system flow restriction orifice matching test method according to claim 9, characterized in that: The matching process of the medium flow restrictor hole is as follows: S10: Compare the oxygen concentration of the nitrogen-rich gas in the medium flow mode with the second qualification criterion. If the second qualification criterion is not met, perform the following steps: S10.

1. Turn off the aircraft fuel tank inerting system; S10.

2. Adjust the size of the medium flow restrictor orifice and reinstall the aircraft fuel tank inerting system; S10.

3. Start the aircraft fuel tank inerting system and introduce high-temperature gas into the aircraft fuel tank inerting system through the gas source to preheat the air separation unit; S10.

4. After the air separation unit is fully preheated, the aircraft fuel tank inerting system enters the medium flow mode; S10.

5. Adjust the air separation unit inlet pressure to the second pressure; S10.

6. After the inlet pressure stabilizes, record the nitrogen-rich gas flow rate and oxygen concentration at the outlet of the air separation unit in the medium flow mode, and return to step S10. Repeat step S10 until the second qualification criterion is met, and the medium flow limiting hole matching is completed.

11. The aircraft fuel tank inerting system flow restriction orifice matching test method according to claim 10, characterized in that: In step S10.2, the process of adjusting the size of the medium flow limiting hole specifically includes: S10.2.

1. If the oxygen concentration of the nitrogen-rich gas in the medium flow mode is higher than O2 + 0.3%, reduce the size of the medium flow restrictor orifice; S10.2.

2. If the oxygen concentration of the nitrogen-rich gas in the medium flow mode is lower than O2-0.3%, increase the size of the medium flow restrictor orifice.

12. The aircraft fuel tank inerting system flow restriction orifice matching test method according to claim 11, characterized in that: The matching process of large flow restrictor holes is as follows: S11. Set the wheel load to air and simulate the aircraft climbing and descending according to the designed profile; S12. Before the aircraft descends, adjust the air separation unit inlet pressure to a third pressure, where the third pressure is the average bleed air pressure during the aircraft's descent phase; S13, during the descent phase, the aircraft fuel tank inerting system enters high-flow mode; S14. After the inlet pressure stabilizes, record the minimum pressure of the fuel tank in the high-flow mode, as well as the nitrogen-rich gas flow rate and oxygen concentration at the outlet of the air separation unit; S15. Compare the minimum pressure of the fuel tank in the high flow mode with the third qualification criterion. If the third qualification criterion is not met, perform the following steps: S15.

1. Turn off the aircraft fuel tank inerting system; S15.

2. Adjust the size of the high-flow restrictor orifice and reinstall the aircraft fuel tank inerting system; S15.

3. Start the aircraft fuel tank inerting system and introduce high-temperature or room-temperature gas into the aircraft fuel tank inerting system through the gas source to preheat the air separation unit; S15.

4. After the air separation unit is fully preheated, return to step S11; Repeat steps S11-S15 until the third qualification criterion is met, and then proceed to step S16; S16: Determine whether the gas introduced by the gas source to the aircraft fuel tank inerting system in the high flow mode is high temperature gas. If so, proceed to step S17; if not, perform the following steps: S16.

1. Turn off the aircraft fuel tank inerting system; S16.

2. Start the aircraft fuel tank inerting system and introduce high-temperature or room-temperature gas into the aircraft fuel tank inerting system through the gas source to preheat the air separation unit; S16.

3. After the air separation unit is fully preheated, return to step S11; S17. Turn off the aircraft fuel tank inerting system and complete the matching of the large flow limiting orifice.

13. The aircraft fuel tank inerting system flow restriction orifice matching test method according to claim 12, characterized in that: In step S15.2, the process of adjusting the large flow limiting hole size specifically includes: S15.2.

1. If the minimum pressure of the fuel tank in the high flow mode during the descent phase is less than P min kPa, increase the size of the large flow restrictor hole; S15.2.2 If the minimum pressure of the fuel tank in the high flow mode during the descent phase is greater than (P min +2) kPa, reduce the size of the large flow restrictor hole.

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