A hydrogen power system whole-process design method and system for hybrid-electric aircraft

Abstract

This application discloses a full-process design method and system for hydrogen power systems of hybrid aircraft, belonging to the field of aviation hydrogen power technology. The method includes: establishing a polarization characteristic model of a proton exchange membrane fuel cell, obtaining the power characteristics of a single fuel cell unit, determining the overall parameters of the fuel cell module and obtaining the hydrogen consumption based on the aircraft's power requirements; iteratively designing a liquid hydrogen storage tank based on the hydrogen consumption and using effective mass hydrogen storage density as the optimization index, outputting the total mass of the storage tank; embedding the overall parameters of the fuel cell module and the design results of the liquid hydrogen storage tank into the aircraft's overall size design iterative process, replacing the initial guessed value with the total mass of the storage tank to calculate the aircraft's maximum takeoff mass; repeating the above steps until the maximum takeoff mass converges, and outputting the design scheme. This invention realizes the coupled iterative design of the hydrogen power system and the overall aircraft parameters, improving design accuracy and overall aircraft performance.

Description

Technical Field

[0001] This application relates to the field of aviation hydrogen power technology, specifically to a whole-process design method and system for hydrogen power systems for hybrid aircraft. Background Technology

[0002] Traditional fuel-powered aircraft have high carbon emissions and energy consumption, while pure electric aircraft are limited by the energy density bottleneck of batteries, making it difficult to achieve practical long-endurance operation. Hybrid-electric aircraft, which use fuel and batteries as energy storage, can combine the advantages of both traditional fuel-powered and all-electric aircraft, playing an important transitional role in the process of carbon peaking and carbon neutrality. However, developing sustainable aviation technologies and exploring alternative energy sources beyond fossil fuels has become one of the important tasks for the aviation industry to achieve its carbon reduction goals. Research shows that hydrogen fuel has an energy density of approximately 120 MJ / kg, three times that of standard aviation kerosene. The use of hydrogen energy in aviation can not only achieve zero carbon dioxide emissions but also significantly reduce emissions of other pollutants, possessing significant technological and environmental advantages and representing an important direction for the future development of aviation propulsion technology.

[0003] Chinese patent application CN122113446A discloses a design method for the insulation jacket of a liquid hydrogen storage tank, which only optimizes the thickness of the insulation jacket but does not involve the parametric design of the tank's geometry or its adaptation to the fuselage space. Chinese patent application CN119489931A discloses a distributed liquid hydrogen fuel cell aircraft layout scheme, which only focuses on the overall physical layout of the aircraft and lacks detailed modeling and system design methods for the internal structure of the storage tank. Existing technologies mostly remain at the level of modification design, feasibility studies, and market research for pre-defined configurations, lacking a comprehensive and detailed system design for the entire hybrid electric propulsion aircraft. Specific design methods are generally based on simplified estimation models, failing to fully conduct detailed modeling of the hydrogen fuel cell power system, lacking correlation and impact analysis with the initial overall design of the aircraft, and failing to effectively consider the detailed design of the cryogenic liquid hydrogen storage tank within the entire flight mission profile. Furthermore, existing technologies lack analysis and organization of the working logic of the hydrogen-electric power system and do not tightly couple the design of the liquid hydrogen storage tank with the integrated parametric design of the hybrid electric propulsion aircraft, resulting in low design accuracy, conservative schemes, and limited overall aircraft performance.

[0004] Therefore, there is an urgent need to propose a whole-process design method and system for hydrogen power systems of hybrid aircraft. Summary of the Invention

[0005] This application addresses the technical problems in existing technologies, such as reliance on simplified estimations in hydrogen fuel cell power systems, insufficient consideration of multi-physics coupling effects in liquid hydrogen storage tank design, and low design accuracy and limited overall aircraft performance due to the disconnect between hydrogen fuel cell power systems and overall aircraft size design. It provides a full-process design method and system for hydrogen power systems for hybrid aircraft.

[0006] To achieve the above objectives, this application adopts the following technical solution: Firstly, this application provides a complete design method for a hydrogen propulsion system for hybrid aircraft, including the following steps: S1. Establish a polarization characteristic model of the proton exchange membrane fuel cell to obtain the power characteristics of a single fuel cell unit; based on the aircraft power requirements and the power characteristics of the single fuel cell unit, determine the overall parameters of the fuel cell module, perform performance modeling on the fuel cell module, and obtain the hydrogen consumption of the fuel cell module. S2, Based on the hydrogen consumption, the liquid hydrogen storage tank is iteratively designed with the effective mass hydrogen storage density as the optimization index to obtain the design result of the liquid hydrogen storage tank and output the total mass of the liquid hydrogen storage tank. S3, embed the overall parameters of the fuel cell module and the design results of the liquid hydrogen storage tank into the overall aircraft size design iteration process, replace the initial guess value with the total mass of the liquid hydrogen storage tank, and calculate the maximum takeoff mass of the aircraft; S4. Repeat steps S1 to S3 and determine the change in the maximum takeoff mass of the aircraft after each iteration. Stop iterating when the change is no greater than the convergence tolerance and output the design scheme.

[0007] Furthermore, in step S1, a polarization characteristic model of the proton exchange membrane fuel cell is established to obtain the power characteristics of a single fuel cell unit, including: A polarization curve model is established based on the relationship between the output voltage of a single fuel cell unit and the thermodynamic electromotive force, activation loss voltage, ohmic loss voltage, and concentration loss voltage to obtain the relationship between the output voltage and current density of a single fuel cell unit; the power characteristics of a single fuel cell unit are determined based on the relationship between the output voltage and current density.

[0008] Further, in step S1, based on the aircraft's power requirements and the power characteristics of the individual fuel cell unit, the overall parameters of the fuel cell module are determined, and the performance of the fuel cell module is modeled to obtain the hydrogen consumption of the fuel cell module, including: Based on the aircraft's power requirements and the power characteristics of the individual fuel cell unit, the number of parallel stacks in the fuel cell module, the number of basic units connected in series in each stack, and the effective area of ​​the proton exchange membrane in a single fuel cell unit are determined to obtain the overall parameters of the fuel cell module. Based on the number of parallel stacks, the number of series basic units, and the effective area of ​​the proton exchange membrane, calculate the total number of basic fuel cells required for the fuel cell module. The output power and hydrogen consumption of the fuel cell module are calculated based on the total number of basic fuel cells to obtain the hydrogen consumption of the fuel cell module.

[0009] Furthermore, in step S2, the specific process of iteratively designing the liquid hydrogen storage tank based on the hydrogen consumption and using the effective mass hydrogen storage density as the optimization index to obtain the design result of the liquid hydrogen storage tank includes: The volume of the liquid hydrogen storage tank is determined based on the hydrogen consumption. Based on the tank volume, the liquid hydrogen storage tank is designed with parametric geometry to obtain the geometric parameters of the tank. The tank wall structure is designed based on the geometric parameters of the storage tank to obtain the tank wall thickness; Thermodynamic design is performed based on the geometric parameters and wall thickness of the storage tank to obtain the heat flux density; Based on the heat flux density, the pressure fluctuation and emission loss inside the tank are assessed to obtain data on the mass of hydrogen lost in emission and the change in pressure inside the tank. Based on the geometric parameters of the storage tank, the tank wall thickness, the heat flux density, the mass of hydrogen lost in emissions, and the pressure change data inside the tank, iterative optimization is performed using the effective mass hydrogen storage density as the optimization index to obtain the design result of the liquid hydrogen storage tank.

[0010] Furthermore, in step S2, the specific process of determining the tank volume of the liquid hydrogen storage tank based on the hydrogen consumption includes: The exhaust pressure and filling pressure of the liquid hydrogen storage tank, as well as the volume fraction of gaseous hydrogen in the tank, are set, and the average density of hydrogen is determined based on the exhaust pressure. The tank volume is determined based on the ratio of the total mass of hydrogen required for the entire flight mission to the average density of hydrogen, wherein the total mass of hydrogen required for the entire flight mission includes the mass of hydrogen lost due to emissions.

[0011] Furthermore, the process of parametrically designing the geometric shape of the liquid hydrogen storage tank based on its volume, and obtaining the geometric shape parameters of the tank, specifically includes: The shape of the liquid hydrogen storage tank is characterized by three dimensionless parameters, wherein the first dimensionless parameter determines the elliptical shape of the cross-section of the tank shell, the second dimensionless parameter determines the basic shape of the tank head, and the third dimensionless parameter represents the ratio of the shell length to the total length of the tank. Given the volume of the storage tank, the values ​​of the three dimensionless parameters are obtained by solving the storage tank volume equation, thereby obtaining the geometric parameters of the storage tank.

[0012] Furthermore, the process of designing the tank wall structure based on the geometric parameters of the storage tank to obtain the tank wall thickness specifically includes: Based on the geometric parameters of the storage tank, the relationship between the circumferential average stress of the tank wall and the internal overpressure of the elliptical cylindrical geometry is determined. The minimum required tank wall thickness is determined by iterative solution using the ultimate stress, safety factor and burst pressure.

[0013] Furthermore, the process of obtaining the heat flux density through thermodynamic design based on the geometric parameters and wall thickness of the storage tank specifically includes: An insulation layer is installed on the outer surface of the tank wall, and the insulation layer includes a hood layer, a steam barrier layer, and an open-cell foam layer. The total thermal resistance is determined based on the geometric parameters of the storage tank and the tank wall thickness. The heat flux density entering the liquid hydrogen storage tank from the outside is calculated based on the sum of the total thermal resistances using a one-dimensional steady-state thermal equation, thus obtaining the heat flux density.

[0014] Furthermore, the process of assessing the pressure fluctuations and emission losses within the tank based on the heat flux density, and obtaining data on the mass of hydrogen emitted as a loss and the changes in pressure within the tank, specifically includes: Based on the first law of thermodynamics and the law of conservation of mass, a pressure change rate evaluation model is established according to the heat flux density. Based on the pressure change rate assessment model, the tank pressure change data over time is determined to obtain the tank pressure change data. When the tank pressure is greater than the exhaust pressure, hydrogen is discharged through the pressure reducing valve to maintain the tank pressure at the maximum allowable value, and the mass flow rate of the discharged hydrogen is evaluated according to the pressure change rate evaluation model to obtain the mass of hydrogen lost in the discharge. When the tank pressure is lower than the filling pressure, the heater is started to evaporate liquid hydrogen to maintain the hydrogen demand, and the required additional heat power and number of heaters are calculated according to the pressure change rate evaluation model.

[0015] Secondly, this application provides a complete design system for hydrogen power systems in hybrid aircraft, including: The fuel cell modeling unit is used to establish a polarization characteristic model of a proton exchange membrane fuel cell and obtain the power characteristics of a single fuel cell unit; based on the aircraft power requirements and the power characteristics of the single fuel cell unit, the overall parameters of the fuel cell module are determined, and the performance of the fuel cell module is modeled to obtain the hydrogen consumption of the fuel cell module. The storage tank design unit is used to iteratively design the liquid hydrogen storage tank based on the hydrogen consumption and with the effective mass hydrogen storage density as the optimization index, to obtain the design result of the liquid hydrogen storage tank and output the total mass of the liquid hydrogen storage tank. The overall size calculation unit is used to embed the overall parameters of the fuel cell module and the design results of the liquid hydrogen storage tank into the overall size design iteration process of the aircraft, and to replace the initial guess value with the total mass of the liquid hydrogen storage tank to calculate the maximum takeoff mass of the aircraft. The iterative control unit is used to repeatedly call the fuel cell modeling unit, the tank design unit, and the overall size calculation unit, and to determine the change in the maximum takeoff mass of the aircraft after each iteration. The iteration stops when the change is no greater than the convergence tolerance, and the design scheme is output.

[0016] Compared with the prior art, this application has the following beneficial effects: This application provides a full-process design method for hydrogen power systems in hybrid aircraft. By establishing a polarization characteristic model of a proton exchange membrane fuel cell (PEMFC) to obtain the power characteristics of a single fuel cell unit, and determining the overall parameters and hydrogen consumption of the fuel cell module based on the aircraft's power requirements, it achieves systematic and accurate modeling from a single cell unit to a module, effectively overcoming the technical shortcomings of existing technologies that rely on simplified estimations and coarse component characteristic characterization. Based on this, the liquid hydrogen storage tank is iteratively designed using the effective mass hydrogen storage density as an optimization index according to the hydrogen consumption, outputting the total mass of the storage tank, thus realizing a shift from coarse estimation to refined design in tank design. The transformation involves further embedding the overall parameters of the fuel cell module and the design results of the liquid hydrogen storage tank into the overall aircraft size design iteration process. The initial guessed value is replaced by the total mass of the storage tank to calculate the maximum takeoff mass of the aircraft, and the above steps are repeated until the maximum takeoff mass converges. This creates a closed loop of bidirectional coupling and iteration among the fuel cell module design, liquid hydrogen storage tank design, and overall aircraft size design. This effectively overcomes the technical defects in the prior art where the hydrogen fuel cell power system and the overall aircraft size design are isolated from each other and the impact of power parameters on the overall aircraft design indicators cannot be quantified. This provides a reliable design tool for the accurate evaluation of overall aircraft performance.

[0017] Specifically, in fuel cell modeling, a polarization curve model incorporating thermodynamic electromotive force, activation loss voltage, ohmic loss voltage, and concentration loss voltage is established to obtain the relationship between the output voltage and current density of a single fuel cell unit and its power characteristics. Based on this, overall parameters such as the number of parallel stacks, the number of series basic units, and the effective area of ​​the proton exchange membrane of the fuel cell module are determined, significantly improving the accuracy of the calculation of the fuel cell module's output power and hydrogen consumption. Furthermore, by modeling the power demand of the air compressor and determining the auxiliary system power consumption based on the adiabatic compression equation and atmospheric pressure and temperature under given flight conditions, the efficiency calculation of the fuel cell module is made more closely aligned with actual flight conditions, further improving the accuracy of hydrogen consumption calculations across the entire flight mission profile. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a flowchart illustrating a complete design method for a hydrogen power system for hybrid aircraft, provided as an embodiment of this application.

[0020] Figure 2 This is a schematic diagram illustrating the relationship between the average density of liquid hydrogen and the exhaust pressure, provided for an embodiment of this application.

[0021] Figure 3 This is a schematic diagram illustrating the effect of filling pressure and venting pressure on the liquid volume fraction in the storage tank, provided for embodiments of this application.

[0022] Figure 4 This is a schematic diagram illustrating the relationship between energy derivative, average density of liquid hydrogen, and tank pressure, provided for embodiments of this application.

[0023] Figure 5 This is a schematic diagram illustrating the design process of a liquid hydrogen storage tank provided in an embodiment of this application. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0025] See Figure 1 This application provides a complete design method for a hydrogen propulsion system for hybrid aircraft, including the following steps: S1. Establish a polarization characteristic model of the proton exchange membrane fuel cell to obtain the power characteristics of a single fuel cell unit; based on the aircraft power requirements and the power characteristics of the single fuel cell unit, determine the overall parameters of the fuel cell module, perform performance modeling on the fuel cell module, and obtain the hydrogen consumption of the fuel cell module. In aerospace applications, fuel cells must balance requirements such as safety, efficiency, specific power, and lightweight design. Proton exchange membrane fuel cells (PEMFCs) offer a combination of advantages, including high efficiency, low operating temperature, and high specific power, making them suitable for aerospace propulsion scenarios. Therefore, this application is based on a PEMFC model.

[0026] In step S1, a polarization characteristic model of the proton exchange membrane fuel cell is first established to obtain the power characteristics of a single fuel cell unit. This polarization characteristic model, based on the internal physical properties of the fuel cell, correlates the current density and output voltage of the basic fuel cell unit. The output voltage of a single fuel cell unit is composed of the thermodynamic electromotive force minus three types of irreversible voltage losses: activation loss voltage, ohmic loss voltage, and concentration loss voltage. Their functional relationship is as follows: (1) in, This represents the thermodynamic electromotive force on the anode side of a basic fuel cell unit; , , These represent the irreversible voltage losses inside the fuel cell, corresponding to the activation loss voltage, ohmic loss voltage, and concentration loss voltage, respectively, and i represents the current density.

[0027] The thermodynamic electromotive force is described by the Nernst equation: (2) and: (3) (4) In the formula, The gas constant ( = 8.314 J / (mol·K) The operating temperature of the fuel cell is 333 K. Faraday constant ( = 96485 C / mol). The activity is hydrogen (considering 100% relative humidity and 80°C conditions). The operating pressure for the fuel cell is 2.5 bar. This represents the mole fraction of hydrogen gas (considering 100% relative humidity and 80°C). It is a reference constant. and These represent the reference pressure and reference temperature, respectively.

[0028] The activation loss voltage It can be represented as: (5) In the formula, is the charge transfer coefficient (taken as 0.8). For the exchange current density (taken as 1.2 × 10⁻⁶), -4 A / cm²).

[0029] Ohmic loss voltage Determined by the resistivity characteristics of the proton exchange membrane: (6) In the formula, The thickness of the proton exchange membrane is 0.0125 cm. The membrane conductivity is taken as 0.1 S / cm.

[0030] Concentration loss voltage Determined by the mass transfer limitation of reactants at high current densities: (7) and: (8) (9) in, Indicates the gas activity of oxygen. Indicates the limiting current density. This represents the mole fraction of oxygen in the air (its value is 0.209). It is the diffusion coefficient of the gas diffusion layer. Indicates the thickness of the gas diffusion layer (its value is...) Therefore, the power polarization curve of a basic fuel cell unit can be expressed as: (10) The polarization curve model described above allows us to obtain the output voltage and power of a single fuel cell unit under different current densities, i.e., the power characteristics of a single fuel cell unit. This polarization curve model, based on the internal electrochemical mechanism of the fuel cell, accurately reflects the performance of the fuel cell under actual operating conditions.

[0031] After obtaining the power characteristics of a single fuel cell unit, the overall parameters of the fuel cell module are determined based on the aircraft's power requirements and the power characteristics of that single fuel cell unit. Specifically, the overall parameters include the number of parallel stacks in the fuel cell module, the number of basic units connected in series in each stack, and the effective area of ​​the proton exchange membrane in a single fuel cell unit. In aviation applications, fuel cell modules typically consist of multiple basic fuel cell units connected in series to form a single stack, and then multiple stacks are connected in parallel to form a module.

[0032] In one embodiment of this application, the overall parameters of the fuel cell module are determined based on the aircraft power requirements and the power characteristics of the individual fuel cell unit, and the performance of the fuel cell module is modeled to obtain the hydrogen consumption of the fuel cell module. The specific process is as follows.

[0033] The output current and output voltage of the fuel cell module are expressed as follows: (11) In the formula, This represents the effective area of ​​the proton exchange membrane in a basic fuel cell. For the number of parallel fuel cells, The number of basic units connected in series in each fuel cell stack.

[0034] The total number of basic fuel cells required for a fuel cell module can be calculated as follows: (12) Based on the aircraft's power requirements and the power characteristics of a single fuel cell unit, the required number of parallel stacks for the fuel cell module, the number of basic units connected in series in each stack, and the effective area of ​​the proton exchange membrane in a single fuel cell unit are determined to obtain the overall parameters of the fuel cell module.

[0035] In a more specific embodiment provided in this application, the output power of the fuel cell module is: (13) The efficiency of the fuel cell module is: (14) Furthermore, the molar flow rate of hydrogen entering the anode channel of the fuel cell is determined by equation (15), and the mass flow rate of hydrogen consumed by the fuel cell is determined by equation (16): (15) (16) in, Indicates the power required by the auxiliary system. This refers to the mass flow rate of hydrogen consumed by the fuel cell. This represents the energy density of hydrogen, and its value is... , This indicates the molar flow rate of hydrogen entering the anode channel, expressed in mol / s. It is the excess coefficient of hydrogen relative to the stoichiometric ratio, with a value of 1.05. This represents the molar mass of hydrogen gas, and its value is... .

[0036] The auxiliary system includes an air compressor. This is based on the adiabatic compression equation and takes into account the air compressor efficiency. The unit compression work of an air compressor The assessment is as follows: (17) In the formula, The compression ratio is... It is the specific heat capacity of air at constant pressure, and its value is... The specific heat ratio of air. and These represent the atmospheric pressure and temperature under given flight conditions.

[0037] The power requirement for the air compressor is: (18) The required air mass flow rate is: (19) The molar flow rate of air is: (20) in, It is air mass flow rate. Indicates the molar flow rate of air. It is the excess coefficient of air relative to the stoichiometric ratio, with a value of 1.7. The molar mass of air is expressed as a value of kg / mol.

[0038] S2, Based on the hydrogen consumption, the liquid hydrogen storage tank is iteratively designed with the effective mass hydrogen storage density as the optimization index to obtain the design result of the liquid hydrogen storage tank and output the total mass of the liquid hydrogen storage tank. For liquid hydrogen hybrid aircraft, the liquid hydrogen storage tank is one of the most critical components in the power system architecture. Its specific installation location, usable volume, structural layout, and thermodynamic characteristics closely affect its performance and structural quality, and have a significant impact on the overall flight performance and design analysis of the aircraft. In this step S2, based on the hydrogen consumption obtained in step S1, a refined iterative design of the liquid hydrogen storage tank is carried out.

[0039] In a more specific embodiment provided in this application, the specific process of iteratively designing the liquid hydrogen storage tank based on the hydrogen consumption and using the effective mass hydrogen storage density as the optimization index in step S2, to obtain the design result of the liquid hydrogen storage tank, includes: See Figure 3 The volume of the liquid hydrogen storage tank is determined based on the hydrogen consumption. When determining the tank volume, it is necessary to set the venting pressure, filling pressure, and gaseous hydrogen volume fraction parameters of the liquid hydrogen storage tank. The venting pressure is the maximum allowable pressure of the tank; when the internal pressure reaches this value, the system needs to be able to vent to maintain or reduce the internal pressure level. The filling pressure is the minimum allowable pressure of the tank, which should be maintained at a relatively low level to prevent excessive pressure rise when the venting valve is blocked. It should also be slightly higher than the ambient pressure to prevent air from entering the tank, and sufficient volume space should be ensured within the tank to accommodate the predetermined proportion of gaseous hydrogen. In this embodiment, the gaseous hydrogen volume fraction parameter is set as follows: .

[0040] The average hydrogen density is determined based on the exhaust pressure. Higher exhaust pressures not only increase the tank wall thickness, thus increasing the tank mass, but also decrease the average hydrogen density and increase the tank volume. In this embodiment, the exhaust pressure is selected as [value missing]. bar, the average density of hydrogen can be determined according to Figure 2 The relationship between the average density of liquid hydrogen and the exhaust pressure is determined by interpolation.

[0041] The tank volume is determined based on the ratio of the total mass of hydrogen required for the entire flight mission to the average density of hydrogen, wherein the total mass of hydrogen required for the entire flight mission includes the mass of hydrogen lost due to emissions. Tank Volume Determined by equation (21): (twenty one) In the formula, The total mass of hydrogen required for the entire flight mission (including the mass of hydrogen lost due to emissions). This represents the average density of hydrogen gas.

[0042] Based on the tank volume, the liquid hydrogen storage tank is designed with parametric geometry to obtain the geometric parameters of the tank. In a more specific embodiment provided in this application, the geometry of the storage tank needs to be adapted as closely as possible to the internal structural shape of the fuselage to make more rational use of its internal space. This application installs the liquid hydrogen storage tank inside the fuselage to avoid additional aerodynamic drag caused by external installation and to free the tank design from external aerodynamic constraints. Specifically, an ellipsoidal geometry is adopted, whose geometric characteristics and mathematical description provide a more flexible design for installation adaptability.

[0043] With three dimensionless parameters , and The shape of the liquid hydrogen storage tank is characterized by this. The first dimensionless parameter... The elliptical shape that determines the cross-section of the tank shell; the second dimensionless parameter Determine the basic shape of the tank head—if Then the head is hemispherical; the third dimensionless parameter Indicates shell length Total length of storage tank The ratio, when When this is the case, it indicates a spherical storage tank, and the shell length will be 0. When... When, corresponding to This will cause the system to become unreliable. If not... or With an absolute definition, the shape of a storage tank has countless solutions. Therefore, this paper will... The range is set to .

[0044] Given the tank volume, the values ​​of the three dimensionless parameters are obtained by solving the tank volume equation, as shown in equations (22) and (23): (twenty two) (twenty three) Obtain the geometric parameters of the storage tank. This parameterization method allows the tank shape to be flexibly configured according to the internal cavity space of a specific aircraft model, maximizing space utilization.

[0045] In a more specific embodiment provided in this application, the tank wall structure is designed according to the geometric parameters of the storage tank to obtain the tank wall thickness; The tank wall material is made of aluminum alloy 2219, with a density of [missing information]. This material has comprehensive advantages in terms of lightweight, hydrogen permeability resistance, and low-temperature mechanical properties.

[0046] Thermodynamic design is performed based on the geometric parameters and wall thickness of the storage tank to obtain the heat flux density; In a more specific embodiment provided in this application, the average circumferential stress of the tank wall with an elliptical cylindrical geometry is derived from the internal overpressure as Equation (24): (twenty four) in, The ultimate stress, For safety, a value of 1.75 is used. The burst pressure is set to twice the release pressure. For Young's modulus, Let be the tank wall thickness. The minimum required wall thickness can be obtained by iteratively solving equation (24).

[0047] In a more specific embodiment provided in this application, the pressure fluctuation and emission loss inside the tank are assessed based on the heat flux density to obtain data on the mass of hydrogen emitted as a loss and the change in pressure inside the tank. In thermodynamic design, an insulation layer is installed on the outer surface of the tank wall. This insulation layer includes a hood layer, a vapor barrier layer, and an open-cell foam layer. In this embodiment, a polymer foam (such as Rohacell foam) is used as the insulation material, which offers combined advantages in safety and lightweight design. This structural system includes a surface density... Shielding layer, surface density The MAAMF vapor barrier layer and the open-cell foam layer (OCF layer) with a density of about 31-51 kg / m³.

[0048] The total thermal resistance is determined based on the geometric parameters of the storage tank and the tank wall thickness: Based on the one-dimensional steady-state thermal equation, the heat flux density entering the liquid hydrogen storage tank from the outside is calculated using the sum of the total thermal resistances as a benchmark, as shown in equation (25): (25) in, Indicates the internal temperature of the storage tank. This represents the total thermal resistance from the external environment. This represents the total thermal resistance of the foam layer. This indicates the thermal resistance of the tank wall.

[0049] The specific expression is: (26) and: (27) in, The radius of the storage tank, including the thickness of the insulation layer (i.e., the radial distance from the inner point of the tank wall to the outer surface of the insulation layer). The outer radius of the tank wall, including the wall thickness (i.e., the radial distance from the inner point of the tank wall to the outer surface of the tank wall). Given the inner radius of the tank wall, take the two semi-axes of the elliptic head. and The average value (i.e., the radial distance from the inner point of the tank wall to the inner wall surface). The total external heat transfer coefficient is . For external forced convection heat transfer coefficient, The external equivalent radiative heat transfer coefficient. For Nusselt numbers, For Prandtl numbers, Let Reynolds number be 1. The thermal conductivity of air. , and These are the Stefan-Boltzmann constant, the emissivity of the outermost protective layer, and the temperature, respectively.

[0050] For the foam layer, the thermal conductivity of the foam depends on its temperature, and the temperature within the foam layer changes significantly during heat transfer. The entire foam layer is divided into... layer( n =5 10) The thermal resistance of each foam layer is given by the radial one-dimensional thermal conduction formula, as shown in equation (29): (28) and: (29) in, For the first Thermal resistance of the foam layer To get from the inside of the tank wall to the first The radial distance of the foam layers, To get from the inside of the tank wall to the first The radial distance of the foam layers, For the first Thermal conductivity of the foam layer (as it changes with temperature). The length of the tank shell, Number the foam layer ( ).

[0051] Furthermore, the thermal conductivity of each layer of foam changes with temperature, and the thermal conductivity of the tank wall material also varies. and thermal resistance It can be regarded as a constant, as shown in equation (30): (30) After determining the expressions for each component of the total thermal resistance, and considering the above factors, a set of linear temperature-heat flux equations determined by the series relationship of thermal resistance can be established. Since there is a nonlinear relationship between the heat transfer coefficient and temperature within the foam layer, it is necessary to iteratively solve the following set of equations to determine the temperature value of each layer, and thus determine the final heat flux and obtain the heat flux density: (31) In one embodiment of this application, the pressure fluctuation and emission loss inside the tank are assessed based on the heat flux density to obtain data on the emission loss of hydrogen mass and the change in pressure inside the tank. The specific process is as follows.

[0052] See Figure 4 During aircraft flight, the internal pressure of the storage tank may change due to heat transfer or hydrogen emission. Based on the first law of thermodynamics and the law of conservation of mass, a pressure change rate assessment model is established based on the stated heat flux density: (32) Furthermore, the total thermal power entering the storage tank is determined by the following formula, and the total mass flow rate of hydrogen discharged from the tank is determined by the following formula: (33) (34) in, The rate of change of pressure, This represents the total mass flow rate of hydrogen discharged from the tank. This represents the mass flow rate of hydrogen lost due to the release. The latent heat of vaporization of liquid hydrogen at 20 K. It is the mass fraction of steam. and These are the densities of gaseous hydrogen and liquid hydrogen inside the tank, respectively. The energy derivative depends on the density and pressure of the hydrogen gas inside the container; it decreases as density increases and increases as pressure increases. Its value can be obtained through... Figure 4 The relationship between the energy derivative, the average density of liquid hydrogen, and the tank pressure is determined by interpolation.

[0053] Based on the pressure change rate assessment model, the pressure change data of the storage tank over time is determined, and the pressure change data inside the tank is obtained.

[0054] Specifically, the overall operating logic of the storage tank system is as follows: at each point in time during the task, the evaporation rate of liquid hydrogen in the tank needs to be matched with the consumption rate of gaseous hydrogen to ensure that the pressure inside the tank is maintained at a reasonable and controllable level.

[0055] When the tank pressure exceeds the venting pressure, hydrogen is released through the pressure reducing valve to maintain the tank pressure at the maximum permissible value. In this case, the pressure change rate is set to [value missing] in the time step. The mass flow rate of emitted hydrogen is assessed as follows: (35) Obtain the mass of hydrogen lost due to emissions.

[0056] When the tank pressure is lower than the filling pressure, the heater is activated to evaporate liquid hydrogen to maintain hydrogen demand, and the required additional heat power is calculated based on the pressure change rate assessment model. The required additional heat power is: (36) The total number of heaters required is: (37) in, This represents the maximum additional thermal power required throughout the entire mission. The power supplied to a single heater. This invention uses a cylindrical heater with a power output of 800W and a mass of 0.1 kg.

[0057] In one embodiment of this application, the design result of the liquid hydrogen storage tank is obtained by iterative optimization using effective mass hydrogen storage density as the optimization index.

[0058] Using effective mass hydrogen storage density As a global optimization index characterizing the overall design performance of a storage tank, its definition is as follows: (38) in: (39) (40) in This indicates the mass hydrogen storage density of the liquid hydrogen storage tank. This represents the ratio of hydrogen consumed by the FCM to the total hydrogen storage. This indicates the amount of hydrogen stored that has been lost due to emissions. This indicates the total mass of the liquid hydrogen storage tank, including the mass of the tank walls. Insulation system quality and heater quality . This represents the surface area of ​​the liquid hydrogen storage tank.

[0059] See Figure 5 This application completes the design by constructing a dual-loop iterative architecture. The inner loop is for the convergence of the tank capacity design, and the geometric design, tank wall structure design, thermodynamic design, and assessment of internal pressure fluctuation and emission loss are executed in sequence. The tank capacity is adjusted according to the assessment results, and the process is iterated repeatedly until the design capacity meets the hydrogen requirements of the entire flight mission.

[0060] The external circulation is for global optimization convergence, with effective mass hydrogen storage density. With the objective of maximizing the thermal density, an iterative search for the optimal solution is performed within the feasible region of the insulation layer thickness. A thicker insulation layer results in lower heat loss and less hydrogen emission loss, but also a larger total tank mass, exhibiting a peak value. The globally optimal design parameters are output when the change in effective mass hydrogen storage density between two consecutive iterations is less than the convergence threshold.

[0061] Through the above-mentioned dual-loop iterative optimization, the design result of the liquid hydrogen storage tank is obtained, and the total mass of the liquid hydrogen storage tank is output.

[0062] S3, embed the overall parameters of the fuel cell module and the design results of the liquid hydrogen storage tank into the overall aircraft size design iteration process, replace the initial guess value with the total mass of the liquid hydrogen storage tank, and calculate the maximum takeoff mass of the aircraft; This application, based on the preliminary dimensional design framework of an electric propulsion aircraft, incorporates an improved hydrogen fuel cell system model to achieve the overall dimensional design of a hydrogen-powered hybrid electric propulsion aircraft. The hydrogen fuel cell hybrid electric propulsion system mainly consists of hydrogen fuel, a proton exchange membrane fuel cell, a power management and control device, a battery, an electric motor, and a propeller.

[0063] In step S3, the overall parameters of the fuel cell module obtained in step S1 and the design results of the liquid hydrogen storage tank obtained in step S2 are embedded into the overall aircraft size design iteration process. The initial guess value is replaced by the total mass of the liquid hydrogen storage tank output in step S2, and the maximum takeoff mass of the aircraft is calculated.

[0064] In one embodiment of this application, the overall parameters of the fuel cell module and the design results of the liquid hydrogen storage tank are embedded into the overall aircraft size design iteration process. The initial guess value is replaced with the total mass of the liquid hydrogen storage tank to calculate the maximum takeoff mass of the aircraft. The specific process is as follows: The maximum takeoff mass of the aircraft is determined based on the mass decomposition method. The maximum takeoff mass of the aircraft is expressed as: (41) in, For motor quality, For battery quality, For the quality of fuel cell power generation systems (PGS), hydrogen mass, For the quality of hydrogen storage tanks.

[0065] The mass of the motor is determined by its rated power and specific power: (42) in, and These are the rated power and specific power of the motor, respectively.

[0066] The quality of the battery depends on the energy it needs to store and its maximum output power: (43) In the formula, To store energy in the battery For the specific energy of the battery, The specific power of the battery. These are the battery's maximum state of charge (SOC) and minimum state of charge (SOC). To prevent overcharging and over-discharging and extend battery life, in this embodiment, the maximum SOC is set to 90% and the minimum SOC to 20%.

[0067] The fuel cell power generation system consists of three parts: fuel cell module, air compressor, and thermal management system. (44) The mass of both the fuel cell module and the air compressor is determined by the rated power and specific power. (45) in, and These are the specific power of the fuel cell and the air compressor, respectively.

[0068] The thermal management system includes a water cooling system and cooling fans. The mass of both the water cooling system and the cooling fans is determined by the heat dissipation of the fuel cell module and its own specific power. (46) and, (47) in, and The masses of the water cooling system and the cooling fan are respectively. This indicates the heat dissipation of the FCM; and These are the specific power of the water cooling system and the cooling fan, respectively.

[0069] The hydrogen mass is based on the total energy requirement of the entire flight mission. and the energy stored in the battery Confirmed. The energy provided by hydrogen. for: (48) in These represent the efficiencies of the propeller, motor, and power management control and distribution (PMCD), respectively.

[0070] Therefore, the mass of hydrogen is: (49) in, This is the minimum amount of hydrogen.

[0071] The quality of storage tanks can be assessed separately for high-pressure gaseous hydrogen storage tanks and cryogenic liquid hydrogen storage tanks.

[0072] For high-pressure gaseous hydrogen storage tanks, their mass can be determined based on the hydrogen storage density given the tank mass: (50) The mass of the cryogenic liquid hydrogen storage tank is determined by the overall design in step S2, that is, the total mass of the storage tank output by step S2. In this application, the liquid hydrogen storage tank scheme is adopted, so the mass of the storage tank in the overall aircraft size design directly adopts the output result of step S2.

[0073] By substituting the overall parameters of the fuel cell module in step S1 and the total mass of the liquid hydrogen storage tank in step S2 into the overall aircraft size design process, the maximum takeoff mass of the aircraft in the current iteration step is calculated.

[0074] S4. Repeat steps S1 to S3 and determine the change in the maximum takeoff mass of the aircraft after each iteration. Stop iterating when the change is no greater than the convergence tolerance and output the design scheme.

[0075] If the change in the maximum takeoff mass of the aircraft calculated in step S3 is greater than the convergence tolerance compared to the previous iteration, it indicates that the overall size of the aircraft needs to be adjusted, and the power requirements for each flight phase will change accordingly. Therefore, the process returns to step S1 to re-select the fuel cell module and recalculate the hydrogen consumption, thereby driving the synchronous update of the tank design in step S2. If the change in the maximum takeoff mass of the aircraft is not greater than the convergence tolerance, it indicates that the fuel cell module design, liquid hydrogen tank design, and overall aircraft size design have achieved self-consistency, and the iteration terminates.

[0076] The convergence tolerance is a preset allowable error value, which can be set by those skilled in the art according to the design accuracy requirements, for example, it can be set to the maximum takeoff mass of the aircraft. to .

[0077] This application also provides a complete design system for hydrogen propulsion systems in hybrid aircraft, including: The fuel cell modeling unit is used to establish a polarization characteristic model of a proton exchange membrane fuel cell and obtain the power characteristics of a single fuel cell unit; based on the aircraft power requirements and the power characteristics of the single fuel cell unit, the overall parameters of the fuel cell module are determined, and the performance of the fuel cell module is modeled to obtain the hydrogen consumption of the fuel cell module. The storage tank design unit is used to iteratively design the liquid hydrogen storage tank based on the hydrogen consumption and with the effective mass hydrogen storage density as the optimization index, to obtain the design result of the liquid hydrogen storage tank and output the total mass of the liquid hydrogen storage tank. The overall size calculation unit is used to embed the overall parameters of the fuel cell module and the design results of the liquid hydrogen storage tank into the overall size design iteration process of the aircraft, and to replace the initial guess value with the total mass of the liquid hydrogen storage tank to calculate the maximum takeoff mass of the aircraft. The iterative control unit is used to repeatedly call the fuel cell modeling unit, the tank design unit, and the overall size calculation unit, and to determine the change in the maximum takeoff mass of the aircraft after each iteration. The iteration stops when the change is no greater than the convergence tolerance, and the design scheme is output.

[0078] The above-described embodiments are merely preferred embodiments of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various improvements and substitutions without departing from the principles of the present invention, and these improvements and substitutions should also be considered within the scope of protection of the present invention. Therefore, the scope of protection of this invention should be determined by the scope of the claims.

Claims

1. A full-process design method for hydrogen propulsion systems in hybrid aircraft, characterized in that, Includes the following steps: S1. Establish a polarization characteristic model of the proton exchange membrane fuel cell to obtain the power characteristics of a single fuel cell unit; based on the aircraft power requirements and the power characteristics of the single fuel cell unit, determine the overall parameters of the fuel cell module, perform performance modeling on the fuel cell module, and obtain the hydrogen consumption of the fuel cell module. S2, Based on the hydrogen consumption, the liquid hydrogen storage tank is iteratively designed with the effective mass hydrogen storage density as the optimization index to obtain the design result of the liquid hydrogen storage tank and output the total mass of the liquid hydrogen storage tank. S3, embed the overall parameters of the fuel cell module and the design results of the liquid hydrogen storage tank into the overall aircraft size design iteration process, replace the initial guess value with the total mass of the liquid hydrogen storage tank, and calculate the maximum takeoff mass of the aircraft; S4. Repeat steps S1 to S3 and determine the change in the maximum takeoff mass of the aircraft after each iteration. Stop iterating when the change is no greater than the convergence tolerance and output the design scheme.

2. The whole-process design method for hydrogen propulsion systems of hybrid aircraft according to claim 1, characterized in that, In step S1, a polarization characteristic model of a proton exchange membrane fuel cell is established to obtain the power characteristics of a single fuel cell unit, including: A polarization curve model is established based on the relationship between the output voltage of a single fuel cell unit and the thermodynamic electromotive force, activation loss voltage, ohmic loss voltage, and concentration loss voltage to obtain the relationship between the output voltage and current density of a single fuel cell unit; the power characteristics of a single fuel cell unit are determined based on the relationship between the output voltage and current density.

3. The whole-process design method for hydrogen propulsion systems of hybrid aircraft according to claim 2, characterized in that, In step S1, based on the aircraft's power requirements and the power characteristics of the individual fuel cell unit, the overall parameters of the fuel cell module are determined, and the performance of the fuel cell module is modeled to obtain the hydrogen consumption of the fuel cell module, including: Based on the aircraft's power requirements and the power characteristics of the individual fuel cell unit, the number of parallel stacks in the fuel cell module, the number of basic units connected in series in each stack, and the effective area of ​​the proton exchange membrane in a single fuel cell unit are determined to obtain the overall parameters of the fuel cell module. Based on the number of parallel stacks, the number of series basic units, and the effective area of ​​the proton exchange membrane, calculate the total number of basic fuel cells required for the fuel cell module. The output power and hydrogen consumption of the fuel cell module are calculated based on the total number of basic fuel cells to obtain the hydrogen consumption of the fuel cell module.

4. The whole-process design method for hydrogen propulsion systems of hybrid aircraft according to claim 1, characterized in that, In step S2, the specific process of iteratively designing the liquid hydrogen storage tank based on the hydrogen consumption and using the effective mass hydrogen storage density as the optimization index to obtain the design result of the liquid hydrogen storage tank includes: The volume of the liquid hydrogen storage tank is determined based on the hydrogen consumption. Based on the tank volume, the liquid hydrogen storage tank is designed with parametric geometry to obtain the geometric parameters of the tank. The tank wall structure is designed based on the geometric parameters of the storage tank to obtain the tank wall thickness; Thermodynamic design is performed based on the geometric parameters and wall thickness of the storage tank to obtain the heat flux density; Based on the heat flux density, the pressure fluctuation and emission loss inside the tank are assessed to obtain data on the mass of hydrogen lost in emission and the change in pressure inside the tank. Based on the geometric parameters of the storage tank, the tank wall thickness, the heat flux density, the mass of hydrogen lost in emissions, and the pressure change data inside the tank, iterative optimization is performed using the effective mass hydrogen storage density as the optimization index to obtain the design result of the liquid hydrogen storage tank.

5. The whole-process design method for hydrogen propulsion systems of hybrid aircraft according to claim 4, characterized in that, In step S2, the specific process of determining the tank volume of the liquid hydrogen storage tank based on the hydrogen consumption includes: The exhaust pressure and filling pressure of the liquid hydrogen storage tank, as well as the volume fraction of gaseous hydrogen in the tank, are set, and the average density of hydrogen is determined based on the exhaust pressure. The tank volume is determined based on the ratio of the total mass of hydrogen required for the entire flight mission to the average density of hydrogen, wherein the total mass of hydrogen required for the entire flight mission includes the mass of hydrogen lost due to emissions.

6. The whole-process design method for hydrogen propulsion systems of hybrid aircraft according to claim 4, characterized in that, The process of parametrically designing the geometric shape of the liquid hydrogen storage tank based on its volume, and obtaining the geometric shape parameters of the tank, specifically includes: The shape of the liquid hydrogen storage tank is characterized by three dimensionless parameters, wherein the first dimensionless parameter determines the elliptical shape of the cross-section of the tank shell, the second dimensionless parameter determines the basic shape of the tank head, and the third dimensionless parameter represents the ratio of the shell length to the total length of the tank. Given the volume of the storage tank, the values ​​of the three dimensionless parameters are obtained by solving the storage tank volume equation, thereby obtaining the geometric parameters of the storage tank.

7. The whole-process design method for hydrogen propulsion systems of hybrid aircraft according to claim 6, characterized in that, The process of designing the tank wall structure and obtaining the tank wall thickness based on the geometric parameters of the storage tank specifically includes: Based on the geometric parameters of the storage tank, the relationship between the circumferential average stress of the tank wall and the internal overpressure of the elliptical cylindrical geometry is determined. The minimum required tank wall thickness is determined by iterative solution using the ultimate stress, safety factor and burst pressure.

8. The whole-process design method for hydrogen propulsion systems of hybrid aircraft according to claim 1, characterized in that, The process of obtaining the heat flux density through thermodynamic design based on the geometric parameters and wall thickness of the storage tank specifically includes: An insulation layer is installed on the outer surface of the tank wall, and the insulation layer includes a hood layer, a steam barrier layer, and an open-cell foam layer. The total thermal resistance is determined based on the geometric parameters of the storage tank and the tank wall thickness. The heat flux density entering the liquid hydrogen storage tank from the outside is calculated based on the sum of the total thermal resistances using a one-dimensional steady-state thermal equation, thus obtaining the heat flux density.

9. The whole-process design method for hydrogen propulsion systems of hybrid aircraft according to claim 4, characterized in that, The process of assessing tank pressure fluctuations and emission losses based on the heat flux density, and obtaining data on the emission loss hydrogen mass and tank pressure changes, specifically includes: Based on the first law of thermodynamics and the law of conservation of mass, a pressure change rate evaluation model is established according to the heat flux density. Based on the pressure change rate assessment model, the tank pressure change data over time is determined to obtain the tank pressure change data. When the tank pressure is greater than the exhaust pressure, hydrogen is discharged through the pressure reducing valve to maintain the tank pressure at the maximum allowable value, and the mass flow rate of the discharged hydrogen is evaluated according to the pressure change rate evaluation model to obtain the mass of hydrogen lost in the discharge. When the tank pressure is lower than the filling pressure, the heater is started to evaporate liquid hydrogen to maintain the hydrogen demand, and the required additional heat power and number of heaters are calculated according to the pressure change rate evaluation model.

10. A complete design system for hydrogen propulsion systems in hybrid aircraft, characterized in that, include: The fuel cell modeling unit is used to establish a polarization characteristic model of a proton exchange membrane fuel cell and obtain the power characteristics of a single fuel cell unit; based on the aircraft power requirements and the power characteristics of the single fuel cell unit, the overall parameters of the fuel cell module are determined, and the performance of the fuel cell module is modeled to obtain the hydrogen consumption of the fuel cell module. The storage tank design unit is used to iteratively design the liquid hydrogen storage tank based on the hydrogen consumption and with the effective mass hydrogen storage density as the optimization index, to obtain the design result of the liquid hydrogen storage tank and output the total mass of the liquid hydrogen storage tank. The overall size calculation unit is used to embed the overall parameters of the fuel cell module and the design results of the liquid hydrogen storage tank into the overall size design iteration process of the aircraft, and to replace the initial guess value with the total mass of the liquid hydrogen storage tank to calculate the maximum takeoff mass of the aircraft. The iterative control unit is used to repeatedly call the fuel cell modeling unit, the tank design unit, and the overall size calculation unit, and to determine the change in the maximum takeoff mass of the aircraft after each iteration. The iteration stops when the change is no greater than the convergence tolerance, and the design scheme is output.

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