A green working medium for medium and low temperature heat power conversion and a preparation method and application thereof

Abstract

The application discloses a kind of low-temperature heat conversion green working medium and its preparation method and application, and green working medium includes the following mass percentage components: 25%~90% alcohol, 1%~5% alcohol amine, 1%~5% aromatic compound, the rest is water;Alcohol includes at least three kinds of methanol, ethanol, isopropanol, ethylene glycol, n-propanol and n-butanol.The working medium of the application is coupled with physical phase change, endothermic chemical reaction, and the heat sink can reach more than 6MJ / kg, which can be used for the absorption of aerodynamic heat of high-speed aircraft with a speed higher than 5 Mach, has the advantages of low cost and strong cooling capacity, and is suitable for the thermal protection system of high heat flux density and long-time aerodynamic heating components.In addition, high-temperature and high-pressure small molecule gas is generated for work, effectively enhancing the maneuverability of high-speed aircraft.

Description

Technical Field

[0001] The present invention relates to the technical field of high-speed aircraft, and more specifically, to a medium- and low-temperature heat-to-power conversion green working fluid, a preparation method thereof, and an application thereof. Background Art

[0002] High-speed aircraft, with their rapid response, quick strike, and easy penetration, have become a crucial tool in transforming future warfare and combat modes, and a key element in international strategic competition. When high-speed aircraft fly at high speeds, shock wave compression, viscous friction, and other factors cause the temperature of their outer walls and surrounding areas to rise rapidly. To ensure that internal components operate within the permitted temperature range and maintain their aerodynamic shape, effective structural thermal protection design is essential.

[0003] Thermal protection technologies can be broadly categorized into passive and active. Passive thermal protection, which utilizes thermal insulation or phase transitions of ablative materials to absorb heat, is the most widely used aerodynamic heat management measure and has been employed in numerous high-speed aircraft, such as the US X-30 and X-47. While this type of thermal protection technology has a relatively simple structure, its fabrication process is complex and costly. During high-speed flight, the material of an ablative thermal protection system gradually ablates as the temperature rises, potentially altering the overall aerodynamic shape and leading to accidents. Furthermore, due to the poor heat absorption capacity of passive thermal protection systems, the required material thickness and weight are large in long-duration applications, significantly compressing the aircraft's payload. In contrast, active thermal protection utilizes a coolant to remove or block heat from the structure through various cooling methods. Compared to passive thermal protection, active thermal protection offers advantages such as high cooling capacity, the ability to withstand prolonged heating from high-density heat fluxes, and closed-loop temperature control. Active thermal protection technologies are primarily categorized into two types: transpiration cooling and convection cooling. Transpiration cooling typically uses water as a coolant. This method, inspired by the way organisms dissipate heat through perspiration, utilizes the latent heat of vaporization to absorb heat and form a thermal barrier. However, this system has poor reliability. Convection cooling is commonly used in aerospace vehicles and aircraft, typically using a circulating liquid hydrocarbon fuel as a coolant. The fuel's physical heat capacity as it heats up removes heat from the surface of the structure. However, due to fuel coking limitations, this heat absorption mode is only suitable for supersonic flight at speeds below Mach 5.

[0004] In light of these challenges, experimental and theoretical research has revealed that using an alcohol-water mixture as the cooling fluid in an active thermal protection system can absorb significant amounts of aerodynamic heat through a physical vaporization reaction. In particular, when a suitable catalyst is present in the system, the alcohol and water can undergo a highly endothermic reforming reaction. For example, the room-temperature enthalpy change of methanol's direct decomposition reaction (Equation 1) is 90.3 kJ / mol (or 2.8 MJ / kg), while that of ethanol reaches 256.8 kJ / mol (or 4.0 MJ / kg). This demonstrates that the alcohol-water reforming reaction has a strong endothermic capacity, and its endothermic properties are closely related to the composition of the alcohol and water. Existing research has found that the optimal chemical reaction conditions vary significantly when the alcohol type is changed. For example, for methanol steam reforming (Nature Catalysis, 2022, 5, 99), the operating temperature is primarily between 180-300°C; whereas for ethanol-water reforming catalysts (Renewable and Sustainable Energy Reviews, 2023, 175, 113-184), the reaction temperature is generally between 350-600°C due to the high stability of the C-C bond. For heat-to-work conversion systems, to broaden their effective operating temperature range, the required alcohol-water working fluid is often a multi-component composite system. For example, low-carbon alcohol-water reforming in the working fluid promotes the absorption of low-temperature aerodynamic heat, while high-carbon alcohol-water reforming increases the total heat absorption capacity of the endothermic working fluid. However, due to the significant differences in catalyst and reaction conditions required by different alcohol components, the mixture often undergoes a highly exothermic methanation side reaction (Equation 3) during the reaction, significantly reducing the system's heat absorption performance. When excess water is added to the reaction system, the methanation reaction can be effectively inhibited, but the excess water does not directly participate in the endothermic reforming reaction.

[0005] (Equations 1 and 2) also lead to a decrease in the heat absorption of the working fluid to a certain extent. Therefore, suppressing the methanation reaction while maintaining the high heat sink characteristics of the working fluid is the key to the new heat-absorbing working fluid.

[0006] Summary of the Invention

[0007] The present invention aims to overcome the aforementioned shortcomings of the prior art by providing a low-temperature, heat-to-work conversion green working fluid, its preparation method, and its application. This working fluid absorbs heat through coupled physical (sensible and latent) and chemical reactions, improving its heat sink and thermal protection performance. This overcomes the problems of low heat sink and carbon accumulation in existing active thermal protection technologies. Furthermore, the generated small molecule gases (such as hydrogen and carbon monoxide) can be used to perform external work. Therefore, this green working fluid not only improves the system's heat absorption capacity but also converts aerodynamic heat into chemical energy, realizing waste heat utilization. This can reduce the thickness of an aircraft's thermal insulation layer, increase the system's payload, and improve aircraft maneuverability.

[0008] To achieve the above object, the technical solution of the present invention is as follows:

[0009] A green working fluid for medium- and low-temperature heat-to-work conversion comprises the following components in percentage by mass: 25% to 90% of alcohol, 1% to 5% of alcoholamine, 1% to 5% of aromatic compounds, and the remainder being water; the alcohol comprises at least three of methanol, ethanol, isopropanol, ethylene glycol, n-propanol, and n-butanol.

[0010] Preferably, the alcohol is methanol, ethanol and isopropanol; the mass of the methanol accounts for 10% to 40% of the total mass of the green working fluid for heat and power conversion, the mass of the ethanol accounts for 10% to 30% of the total mass of the green working fluid for heat and power conversion, and the mass of the isopropanol accounts for 5% to 20% of the total mass of the green working fluid for heat and power conversion.

[0011] Preferably, the medium- and low-temperature heat-to-power conversion green working fluid includes the following components in percentage by mass: 20% to 40% methanol, 15% to 30% ethanol, 5% to 10% isopropanol, 1% to 3% alcohol amine, 2% to 5% aromatic compounds, and the rest is water.

[0012] Optionally, the alcoholamine includes one or more of diethanolamine, triethanolamine and isopropanolamine; preferably, the alcoholamine is isopropanolamine.

[0013] Optionally, the aromatic compound includes one or more of phenol, benzyl alcohol, naphthol and p-hydroxytoluene; preferably, the aromatic compound is benzyl alcohol.

[0014] The present invention also discloses a method for preparing the above-mentioned medium- and low-temperature heat-to-work conversion green working fluid, comprising the following steps: mixing alcohol, alcoholamine and water, adding an aromatic compound, stirring at 50°C to 65°C until dissolved, and cooling to room temperature to obtain the medium- and low-temperature heat-to-work conversion green working fluid.

[0015] The present invention also discloses a medium-low temperature heat-to-power conversion green working fluid as described above, or an application of the medium-low temperature heat-to-power conversion green working fluid prepared by the above preparation method in a high-speed aircraft heat-to-power conversion system; the application includes: subjecting the medium-low temperature heat-to-power conversion green working fluid to a chemical endothermic reaction under the action of high-temperature aerodynamic heat and a catalyst to produce high-temperature and high-pressure gas small molecules.

[0016] Optionally, the temperature of the chemical endothermic reaction is 250°C to 600°C; preferably, the temperature of the chemical endothermic reaction is 300°C to 500°C.

[0017] Optionally, the catalyst is a Zr-modified Pd / Al2O3 catalyst, wherein the mass content of Pd in ​​the catalyst is 5% to 15%, and the mass content of Zr in the catalyst is 1% to 10%.

[0018] Specifically, the medium- and low-temperature heat-to-work conversion green working fluid of the present invention can rapidly vaporize and absorb heat at 250°C to 600°C, and undergo a strongly endothermic chemical endothermic reaction under the action of a catalyst, such as a decomposition reaction of methanol (Equation 1) and a reforming reaction of polyols such as ethanol / alcoholamines (Equation 2). Aromatic compounds can react with excess water to produce high-temperature and high-pressure gas small molecules (hydrogen, carbon monoxide, etc.), inhibiting methane production and improving working fluid heat sink. It is particularly suitable for aerodynamic heat absorption of high-speed aircraft. In addition, by performing external work on the small gas molecules, the aircraft's attitude and speed can be controlled, realizing the heat-to-work conversion process from "harmful aerodynamic heat" to "useful work", thereby ensuring long-term stable flight of high-speed aircraft.

[0019] The implementation of the present invention will have the following beneficial effects:

[0020] 1. Compared with traditional passive insulation methods, the green working fluid for medium and low temperature heat-to-work conversion provided by the present invention belongs to active thermal protection technology, which has the advantages of strong cooling capacity, ability to withstand long-term heating with high-density heat flow, and realization of closed-loop temperature control.

[0021] 2. The present invention has rationally improved the composition and concentration of the green working fluid for medium and low temperature heat-to-work conversion through multiple experiments. By coupling physical phase change and chemical reaction to absorb heat, its heat sink can reach more than 6MJ / kg, which can be used for aerodynamic heat absorption of high-speed aircraft with speeds higher than Mach 5.

[0022] 3. Compared with single hydrocarbon fuels (such as aviation kerosene, methanol) or water endothermic working fluids, the green working fluid for medium and low temperature heat conversion of the present invention has low cost, high endothermic performance, is not prone to carbon deposition during chemical reactions, has strong system stability, and can achieve efficient thermal dynamic heat absorption over a wide temperature range; compared with hydrocarbon fuels and water two-phase endothermic working fluids, the working fluids of the present invention are mixed solutions of a uniform single phase, are easier to store, have a simple system, and are easy to control chemical reactions.

[0023] 4. Compared with the active thermal insulation method of water sweating, the green working fluid for medium- and low-temperature heat-to-work conversion provided by the present invention can not only utilize the physical heat absorption of the working fluid, but also enhance heat absorption through chemical reactions. The theoretical maximum heat absorption capacity of the system is more than doubled (>6.5MJ / kg) compared to the heat absorption of water sweating (~3MJ / kg), which can further enhance the system's heat absorption performance and generate thrust to do work. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 1 is a comparison chart of the heat absorption capacity of methanol and the heat absorption performance of water in Example 1 of the present invention.

[0025] Figure 2 This is a comparison chart of the heat absorption performance of ethanol steam reforming and water in Example 2 of the present invention.

[0026] Figure 3 This is a comparison chart of the heat absorption performance of isopropyl alcohol steam reforming and water in Example 3 of the present invention.

[0027] Figure 4 3 is a comparison chart of heat sink values ​​of the heat-to-work conversion working fluids of Example 1 of the present invention and Comparative Example 1 at different temperatures. DETAILED DESCRIPTION

[0028] The present invention will be further described below with reference to specific examples, but the present invention is not limited thereto in any way.

[0029] The heat sink of the working fluid is evaluated by the current heating reaction, and the heat sink of the endothermic process is calculated using the energy conservation method.

[0030] Q sink =Q in -Q loss (Equation 2)

[0031] ΔH sink =Q sink / m feed (Equation 3)

[0032] Q sink is the heat absorption power of the working medium (kW), Q in is the input power (kW) on the reactor during steady-state operation, Q loss is the heat dissipation power of the reactor and electrodes (kW), ΔH sink is the total heat sink generated by the heat absorbing medium (MJ·kg -1 ), m feed is the feed mass rate of the endothermic working fluid (g·s -1 ).

[0033] Example 1

[0034] Calculate the maximum theoretical heat sink of methanol, where the initial temperature of methanol is room temperature (25°C) and the heat absorbed by its complete decomposition into H2 and CO (Equation 2) at different temperatures is as follows: Figure 1 shown.

[0035] CH3OH(l,25℃)→CO(g,T)+2H2(g,T) (Equation 1)

[0036] Example 2

[0037] Calculate the maximum theoretical heat sink of an ethanol / water solution with a molar ratio of ethanol to water of 1:1 and an initial temperature of room temperature (25°C) for its complete decomposition into H2 and CO (Equation 2) at different temperatures. Figure 2 shown.

[0038] C2H6O(l,25℃)+H2O(l,25℃)→2CO(g,T)+4H2(g,T) (Equation 2)

[0039] Example 3

[0040] Calculate the maximum theoretical heat sink of an isopropanol / water solution, where the molar ratio of isopropanol to water is 1:2 and the initial temperature is room temperature (25°C). The heat absorbed by the solution at different temperatures for complete decomposition into H2 and CO (Equation 3) is as follows: Figure 3 shown.

[0041] C3H8O(l,25℃)+2H2O(l,25℃)→3CO(g,T)+6H2(g,T) (Equation 3)

[0042] The calculation results show that the methanol decomposition reaction is relatively active. At around 200°C, its theoretical maximum heat sink can exceed the physical heat absorption of water. For ethanol and isopropanol, the theoretical maximum heat sinks are equivalent to the physical heat absorption of water at around 250°C and 300°C, respectively. In addition, for the three alcohols, the theoretical maximum heat sinks increase linearly with temperature after 450°C, indicating that their theoretical conversion rates all reach 100%. However, from the maximum heat sink values, it can be seen that the maximum heat sink value increases significantly with the increase in the number of carbon atoms. At 500°C, the methanol decomposition heat sink is 5.4MJ / kg, the ethanol / water maximum heat sink is 6.6MJ / kg, and the isopropanol / water maximum heat sink is 7.0MJ / kg. This shows that in order to make the endothermic working fluid exhibit a larger heat sink in a wider temperature range, its formula needs to be optimized.

[0043] Example 4

[0044] The green working fluid for medium- and low-temperature heat-to-power conversion in this embodiment includes the following components in percentage by mass: 30% methanol, 20% ethanol, 10% isopropanol, 5% phenol, 1% triethanolamine, and the remainder is water.

[0045] The preparation method of the working fluid of this embodiment comprises the following steps: mixing methanol, ethanol, isopropanol, triethanolamine and water, adding phenol, stirring at 50° C. until dissolved, and cooling to room temperature to obtain the working fluid.

[0046] Example 5

[0047] The green working fluid for medium- and low-temperature heat-to-power conversion in this embodiment includes the following components in percentage by mass: 30% methanol, 20% ethanol, 10% isopropanol, 5% phenol, 5% triethanolamine, and the remainder is water.

[0048] The medium- and low-temperature heat-to-work conversion green working fluid of this embodiment was prepared according to the preparation method of Example 4.

[0049] Example 6

[0050] The green working fluid for medium- and low-temperature heat-to-power conversion in this embodiment includes the following components in percentage by mass: 20% methanol, 10% ethanol, 20% isopropanol, 5% phenol, 5% triethanolamine, and the remainder is water.

[0051] The medium- and low-temperature heat-to-work conversion green working fluid of this embodiment was prepared according to the preparation method of Example 4.

[0052] Example 7

[0053] The green working fluid for medium- and low-temperature heat-to-power conversion in this embodiment includes the following components in percentage by mass: 60% methanol, 5% ethanol, 5% isopropanol, 5% benzyl alcohol, 5% triethanolamine, and the remainder is water.

[0054] The medium- and low-temperature heat-to-work conversion green working fluid of this embodiment was prepared according to the preparation method of Example 4.

[0055] Example 8

[0056] The only difference between this embodiment and embodiment 4 is that ethanol is replaced by ethylene glycol.

[0057] Example 9

[0058] The only difference between this embodiment and embodiment 4 is that isopropyl alcohol is replaced by n-propyl alcohol.

[0059] Example 10

[0060] The only difference between this embodiment and embodiment 4 is that isopropyl alcohol is replaced by n-butanol.

[0061] Comparative Example 1

[0062] The working fluid in this comparative example is only water.

[0063] Comparative Example 2

[0064] The working fluid of this comparative example contains only methanol.

[0065] Comparative Example 3

[0066] The working fluid of this comparative example is an aqueous solution containing methanol, and the molar ratio of methanol to water is 1:0.5.

[0067] Comparative Example 4

[0068] The working fluid of this comparative example is an aqueous solution containing ethanol, and the molar ratio of ethanol to water is 1:1.

[0069] Comparative Example 5

[0070] The working fluid of this comparative example is an aqueous solution containing ethanol, and the molar ratio of ethanol to water is 1:2.

[0071] Comparative Example 6

[0072] The working fluid of this comparative example is an aqueous solution containing ethylene glycol, and the molar ratio of ethylene glycol to water is 1:1.

[0073] Comparative Example 7

[0074] The working fluid of this comparative example is an aqueous solution containing isopropyl alcohol, and the molar ratio of isopropyl alcohol to water is 1:3.

[0075] Comparative Example 8

[0076] The working fluid of this comparative example is an aqueous solution containing n-propanol, and the molar ratio of n-propanol to water is 1:3.

[0077] Comparative Example 9

[0078] The working fluid of this comparative example is an aqueous solution containing n-butanol, and the molar ratio of n-butanol to water is 1:4.

[0079] Comparative Example 10

[0080] The working fluid of this comparative example is an ethanol / water / phenol mixed solution, the molar ratio of ethanol to water is 1:2, and phenol accounts for 5% of the total mass of the solution.

[0081] Comparative Example 11

[0082] The working fluid of this comparative example is an ethanol / water / triethanolamine mixed solution, the molar ratio of ethanol to water is 1:2, and triethanolamine accounts for 5% of the total mass of the solution.

[0083] Comparative Example 12

[0084] The working fluid of this comparative example is a methanol / ethanol / water / phenol mixed solution, the molar ratio of methanol to water is 1:1, the molar ratio of ethanol to water is 1:2, and benzyl alcohol accounts for 5% of the total mass of the solution.

[0085] Comparative Example 13

[0086] The working fluid of this comparative example is an isopropanol / ethanol / water / phenol mixed solution, the molar ratio of isopropanol to water is 1:5, the molar ratio of ethanol to water is 1:5, and benzyl alcohol accounts for 5% of the total mass of the solution.

[0087] Comparative Example 14

[0088] The working fluid of this comparative example is an isopropanol / methanol / water / phenol mixed solution, the molar ratio of isopropanol to water is 1:3, the molar ratio of methanol to water is 1:1, and benzyl alcohol accounts for 5% of the total mass of the solution.

[0089] Comparative Example 15

[0090] The working fluid of this comparative example is a methanol / ethanol / water / triethanolamine mixed solution, the molar ratio of methanol to water is 1:1, the molar ratio of ethanol to water is 1:2, and triethanolamine accounts for 5% of the total mass of the solution.

[0091] Comparative Example 16

[0092] The working fluid of this comparative example is an isopropanol / ethanol / water / triethanolamine mixed solution, the molar ratio of isopropanol to water is 1:5, the molar ratio of ethanol to water is 1:5, and triethanolamine accounts for 5% of the total mass of the solution.

[0093] Comparative Example 17

[0094] The working fluid of this comparative example is an isopropanol / methanol / water / triethanolamine mixed solution, the molar ratio of isopropanol to water is 1:3, the molar ratio of methanol to water is 1:1, the molar ratio of ethanol to water is 1:2, and triethanolamine accounts for 5% of the total mass of the solution.

[0095] Comparative Example 18

[0096] The working fluid of this comparative example is an isopropanol / methanol / ethanol / water / phenol mixed solution, the molar ratio of isopropanol to water is 1:5, the molar ratio of methanol to water is 3:5, the molar ratio of ethanol to water is 1:5, and benzyl alcohol accounts for 5% of the total mass of the solution.

[0097] Comparative Example 19

[0098] The working fluid of this comparative example is a mixed solution of isopropanol / methanol / ethanol / water / triethanolamine, the molar ratio of isopropanol to water is 1:5, the molar ratio of methanol to water is 3:5, the molar ratio of ethanol to water is 1:5, and triethanolamine accounts for 5% of the total mass of the solution.

[0099] Comparative Example 20

[0100] The working fluid of this comparative example is a mixed solution of isopropanol / water / methanol / ethanol, with the molar ratio of isopropanol to water being 1:5, the molar ratio of methanol to water being 3:5, and the molar ratio of ethanol to water being 1:5.

[0101] Test Case

[0102] The heat absorption of the endothermic working fluid was measured for Examples 4-10 and Comparative Examples 1-20. The test process included: the initial temperature of the solution was set to 25°C, the flow rate was set to 30 g / min, and the working fluid was subjected to a chemical endothermic reaction under the action of high-temperature aerodynamic heat and 10 g of Zr-Pd / Al2O3 catalyst. The reaction temperature was controlled by adjusting the heating power and was set to 300°C, 450°C and 600°C, respectively. The reaction pressure was set to 1.0 MPa. The heat absorption of the endothermic working fluid was measured, and the results are shown in Table 1.

[0103] The heat absorption of the endothermic working fluid was measured for Example 5 and Comparative Example 1. The test process included: the initial temperature of the solution was set to 25°C, the flow rate was set to 30g / min, and the working fluid was subjected to a chemical endothermic reaction under high-temperature aerodynamic heat and 10g of Zr-Pd / Al2O3 catalyst. The reaction temperature was controlled by adjusting the heating power and was set to 300°C, 350°C, 400°C, 450°C, 500°C, 600°C, 700°C and 800°C, respectively. The reaction pressure was set to 1.0MPa. The heat absorption of the endothermic working fluid was measured. The results are as follows: Figure 4 shown.

[0104] Table 1 Comparison of actual heat absorption of heat absorbing medium in Examples 4-10 and Comparative Examples 1-20

[0105]

[0106]

[0107] Examples 4-10 and Comparative Examples 1-20 demonstrate that varying the cooling fluid composition significantly improves its heat absorption performance. Generally speaking, the lower the number of carbon atoms in the organic alcohol, the better the low-temperature heat absorption performance, but the higher-temperature heat absorption capacity significantly decreases. Relatively speaking, n-propanol has a slightly lower heat absorption capacity than isopropanol, while n-butanol exhibits good heat absorption only above 600°C, far inferior to C1-C3 alcohols at lower temperatures. Adding an appropriate amount of aromatic compounds to the working fluid improves its maximum heat absorption performance, indicating that it promotes the participation of excess water in endothermic chemical reactions. The addition of alcoholamines can further enhance heat absorption capacity by inhibiting the methanation side reaction. For the methanol / ethanol / isopropanol / water / benzyl alcohol / triethanolamine mixed solution, especially when the methanol content is about 30%, the ethanol content is about 20%, the isopropanol content is about 10%, and a small amount of alcoholamine and aromatic compounds are added, its comprehensive heat absorption performance is the best. Above 300 degrees Celsius, the heat sink value (2.99MJ / kg) is higher than that of pure water; at 600℃, the heat sink value reaches nearly 6MJ / kg. As the temperature is further increased, the heat sink of the working fluid increases linearly, indicating that at this temperature, all working fluids are completely converted. It can be seen that this working fluid is particularly suitable for medium and low temperature (<600℃) aerodynamic heat absorption. Above 800℃ ( Figure 4), its maximum heat sink value reaches more than 6.5MJ / kg.

[0108] The above-described embodiments merely represent several implementation methods of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that a person skilled in the art would be able to make various modifications and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A high-speed aircraft heat-to-power conversion system, characterized in that: The medium-low temperature heat-to-work conversion green working fluid undergoes a chemical endothermic reaction under the action of high-temperature aerodynamic heat and a catalyst to produce high-temperature and high-pressure gas small molecules; the medium-low temperature heat-to-work conversion green working fluid includes the following components in percentage by mass: 25%~90% alcohol, 1%~5% alcoholamine, 1%~5% aromatic compound, and the rest is water; The alcohol includes at least three of methanol, ethanol, isopropanol, ethylene glycol, n-propanol and n-butanol; The aromatic compound includes one or more of phenol, benzyl alcohol, naphthol and p-hydroxytoluene.

2. The high-speed aircraft heat-to-work conversion system according to claim 1, characterized in that: The alcohol is methanol, ethanol and isopropanol; The mass of the methanol accounts for 10% to 40% of the total mass of the green working fluid for heat-work conversion, the mass of the ethanol accounts for 10% to 30% of the total mass of the green working fluid for heat-work conversion, and the mass of the isopropanol accounts for 5% to 20% of the total mass of the green working fluid for heat-work conversion.

3. The high-speed aircraft heat-to-work conversion system according to claim 2, characterized in that: The medium and low temperature heat-to-work conversion green working fluid includes the following components in percentage by mass: 20%~40% methanol, 15%~30% ethanol, 5%~10% isopropanol, 1%~3% alcoholamine, 2%~5% aromatic compounds, and the rest is water.

4. The high-speed aircraft heat-to-work conversion system according to claim 1, characterized in that: The alcoholamine includes one or more of diethanolamine, triethanolamine and isopropanolamine.

5. The high-speed aircraft heat-to-work conversion system according to claim 1, characterized in that: The method for preparing the medium- and low-temperature heat-to-work conversion green working fluid comprises the following steps: After mixing alcohol, alcoholamine and water, adding aromatic compound and stirring at 50°C to 65°C until dissolved, cooling to room temperature to obtain the medium- and low-temperature heat-to-work conversion green working fluid.

6. The high-speed aircraft heat-to-power conversion system according to claim 1, characterized in that: The temperature of the chemical endothermic reaction is 250°C to 600°C.

7. The high-speed aircraft heat-to-power conversion system according to claim 6, characterized in that: The temperature of the chemical endothermic reaction is 300°C to 500°C.

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