An underwater gas-liquid two-phase ramjet engine based on phase change and its working method

Abstract

The present invention belongs to the field of engines, and specifically relates to an underwater gas-liquid two-phase ramjet engine based on phase change and a working method thereof, wherein the underwater gas-liquid two-phase ramjet engine based on phase change includes a liquid nitrogen injector and a diffuser chamber and a spray chamber connected in sequence; the spray chamber is a tapered structure, and one end of the inlet of the spray chamber is connected to the diffuser chamber, and the inlet cross-sectional area of ​​the spray chamber is smaller than the cross-sectional area of ​​the diffuser chamber; a water inlet is provided in the diffuser chamber; the liquid nitrogen injector is used to inject liquid nitrogen into the spray chamber, and the mass ratio of water entering the water inlet to the liquid nitrogen injected by the liquid nitrogen injector is in the range of 1000-300000. The underwater gas-liquid two-phase ramjet engine based on phase change of the present invention is a thrust drive mode based on phase change, and has the characteristics of high specific impulse, low energy consumption, cost saving and environmental protection.

Description

Technical Field

[0001] The invention belongs to the field of engines, and in particular relates to an underwater gas-liquid two-phase ramjet engine based on phase change and a working method thereof. Background Art

[0002] There are many types of engines currently used for underwater propulsion of underwater vehicles, but they also have many disadvantages, such as propeller propulsion, low speed and short range; pump pressure water jet propulsion, complex blade system, causing additional resistance; metal / water reaction ramjet propulsion, low propulsion efficiency; expensive fuel and product pollution; bubble afterburner water jet propulsion, difficulty in keeping the body watertight and weak acceleration ability; nuclear reaction propulsion, radiation, exhaust pollution and other problems. That is, traditional underwater engines have problems such as low specific impulse, high price and environmental pollution. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide an underwater gas-liquid two-phase ramjet engine based on phase change and having high specific impulse, low energy consumption, cost saving and environmental protection characteristics and a working method thereof.

[0004] The present invention provides an underwater gas-liquid two-phase ramjet engine based on phase change, comprising a liquid nitrogen injector and a diffuser cavity and a spray cavity connected in sequence;

[0005] The liquid nitrogen injector comprises a liquid nitrogen supply pipe and a liquid nitrogen storage tank, one end of the liquid nitrogen supply pipe is connected to the liquid nitrogen storage tank, and the other end extends into the spray chamber;

[0006] The spray chamber is a tapered structure, the inlet of the spray chamber is a large cross-section end, the outlet is a small cross-section end, and one end of the inlet of the spray chamber is connected to the pressure diffuser chamber, and the inlet cross-sectional area of ​​the spray chamber is smaller than the cross-sectional area of ​​the pressure diffuser chamber;

[0007] A water inlet is provided in the pressure diffuser cavity;

[0008] The liquid nitrogen injector is used to inject liquid nitrogen into the spray chamber, and the mass ratio of the water entering the water inlet to the liquid nitrogen injected by the liquid nitrogen injector is in the range of 1000-300000.

[0009] In one of the embodiments, a rectifying chamber is further provided between the pressure diffuser chamber and the spray chamber;

[0010] The cross-sectional area of ​​the rectifying cavity is smaller than the cross-sectional area of ​​the pressure diffuser cavity, and larger than the inlet cross-sectional area of ​​the spray cavity.

[0011] In one of the embodiments, the liquid nitrogen injector includes a liquid nitrogen supply pipe, and the liquid nitrogen supply pipe extends from the end surface of the diffuser chamber through the diffuser chamber and the rectifying chamber in sequence into the injection chamber.

[0012] In one embodiment, the cross-sections of the pressure diffuser cavity, the rectifying cavity, the spray cavity and the outlet of the liquid nitrogen supply pipe are all circular;

[0013] The ratio of the diameter of the pressure diffusion chamber to the diameter of the outlet of the liquid nitrogen supply pipe is 50:1-100:1.

[0014] In one of the embodiments, the ratio of the diameter of the diffuser chamber to the diameter of the spray chamber inlet is 2:1-3:1.

[0015] In one embodiment, the diffusion chamber is a component formed by the outward expansion and rotation of a two-dimensional axial profile.

[0016] In one of the embodiments, the expansion angle between the axis of the water inlet and the axis of the pressure diffuser chamber is 10°-50°.

[0017] In one embodiment, a plurality of water inlets are equidistantly arranged along the inner wall of the diffuser chamber;

[0018] The ratio of the diameter of the water inlet to the diameter of the outlet of the liquid nitrogen supply pipe is between 10:1 and 100:1.

[0019] In one of the embodiments, the spray chamber outlet convergence angle is 2°-6°.

[0020] The present invention also provides a working method of the above-mentioned underwater gas-liquid two-phase ramjet engine based on phase change, comprising the following steps:

[0021] Water flows into the diffusion chamber from the water inlet 4, decelerates and increases pressure, and then flows into the spray chamber to increase speed and reduce pressure. The liquid nitrogen injector injects liquid nitrogen into the spray chamber. The liquid nitrogen and water are mixed at the downstream of the outlet of the liquid nitrogen supply pipe of the liquid nitrogen injector in the spray chamber. During the mixing process, the liquid nitrogen absorbs heat, expands and boils to produce nitrogen and form nitrogen bubbles. The nitrogen bubbles absorb heat and expand continuously to the ambient temperature, and do work on the water, so that the water is continuously accelerated and ejected at the outlet of the spray chamber to generate thrust.

[0022] The beneficial effect of the present invention is that the underwater gas-liquid two-phase ramjet engine based on phase change provided by the present invention, through the mixing of low-temperature liquid nitrogen and water in the engine, the liquid nitrogen absorbs the heat of the water and expands and boils rapidly to produce nitrogen, forming nitrogen bubbles, and the nitrogen bubbles absorb heat to the ambient temperature and continuously expand to do work on the water, so that the water is continuously accelerated in the nozzle and ejected from the nozzle cavity outlet to generate thrust.

[0023] That is, the underwater gas-liquid two-phase ramjet engine based on phase change of the present invention is a thrust drive mode based on phase change, and has the following effects: first, high specific impulse, the theoretical specific impulse can reach 800-1000s, and the experimental specific impulse can reach 687s, which can increase the specific impulse by about 50% compared with the metal / water ramjet engine scheme; second, the working fluid required by the present invention is only liquid nitrogen, and water is taken from the environment. The price of raw materials required for 1 kilometer is 0.11 yuan, and the emission product is nitrogen, which is much more economical and environmentally friendly than other types of engines; third, compared with a simple water jet thrust engine, the present engine uses the phase change work generated by the endothermic expansion of liquid nitrogen to generate additional thrust; fourth, the present engine has no rotating parts and intermediate transmission links, and is not restricted by the bubble phenomenon.

[0024] In addition, by providing a structural design of interconnected pressure diffuser chamber and spray chamber, the pressure diffuser chamber can decelerate and pressurize the water to ensure that the water flow entering the spray chamber has sufficient pressure. The pressure diffuser chamber can also rectify the water to a certain extent to avoid excessive bubbles and vortices in the water flowing into the spray chamber, thereby ensuring full contact between the liquid nitrogen and the water flowing with accelerated speed and reduced pressure, improving the mixing effect, ensuring the utilization rate of the liquid nitrogen, and allowing the liquid nitrogen to fully absorb heat and do work on the water before flowing out of the outlet of the spray chamber. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Attached Figure 1 It is a structural schematic diagram of the present invention;

[0026] Attached Figure 2 It is a front cross-sectional view of the present invention;

[0027] Attached Figure 3 This is a thermodynamic cycle diagram of liquid nitrogen-water mixing during theoretical analysis in the present invention;

[0028] Attached Figure 4 It is the curve of the change of specific impulse with water flow in the theoretical analysis of the present invention;

[0029] Attached Figure 5 This is the curve of the change of specific impulse with water flow in the experiment of the present invention.

[0030] In the figure, 1-diffuser chamber; 2-rectifier chamber; 3-spray chamber; 4-water inlet; 5-liquid nitrogen supply pipe. DETAILED DESCRIPTION

[0031] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0033] In addition, in the present invention, descriptions such as "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" or "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0034] In the present invention, unless otherwise clearly specified and limited, the terms "connection", "fixation", etc. should be understood in a broad sense. For example, "fixation" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, an electrical connection, a physical connection, or a wireless communication connection; it can be a direct connection, or an indirect connection through an intermediate medium, or it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0035] In addition, the technical solutions between the various embodiments of the present invention can be combined with each other, but it must be based on the fact that ordinary technicians in the field can implement it. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0036] As attached Figure 1 -Attached Figure 5 As shown, the present invention provides an underwater gas-liquid two-phase ramjet engine based on phase change, comprising a liquid nitrogen injector and a diffuser chamber 1 and a spray chamber 3 connected in sequence;

[0037] The liquid nitrogen injector comprises a liquid nitrogen supply pipe 5 and a liquid nitrogen storage tank, one end of the liquid nitrogen supply pipe 5 is connected to the liquid nitrogen storage tank, and the other end extends into the spray chamber 3;

[0038] The spray chamber 3 is a tapered structure, the inlet of the spray chamber 3 is a large cross-section end, and the outlet is a small cross-section end, that is, the cross-sectional area of ​​the spray chamber 3 gradually decreases from the inlet to the outlet, and one end of the inlet of the spray chamber 3 is connected to the pressure diffuser chamber 1, and the inlet cross-sectional area of ​​the spray chamber 3 is smaller than the cross-sectional area of ​​the pressure diffuser chamber 1;

[0039] The pressure diffuser chamber 1 is provided with a water inlet 4, which is used to inject water into the pressure diffuser chamber 1. The water flows to the spray chamber 3 after being decelerated and pressurized in the pressure diffuser chamber 1.

[0040] The liquid nitrogen injector is used to inject liquid nitrogen into the spray chamber 3, so that the water flowing in the spray chamber 3 with the increased speed and reduced pressure is fully mixed with the liquid nitrogen, so that the low-temperature liquid nitrogen absorbs the heat in the water, expands rapidly, boils, generates nitrogen, and forms nitrogen bubbles. The nitrogen bubbles absorb heat to the ambient temperature (water temperature) and continuously expand to do work on the water. The spray chamber 3 with a tapered structure reduces the increased speed of the water flow, so that the water is continuously accelerated in the spray chamber 3 and ejected from the outlet of the spray chamber 3 to generate thrust. The mass ratio of the water entering the water inlet 4 to the liquid nitrogen injected by the liquid nitrogen injector is in the range of 1000-300000, that is, the minimum ratio of water to liquid nitrogen is 1000:1, and the maximum ratio of water to liquid nitrogen is 300000:1.

[0041] The underwater gas-liquid two-phase ramjet engine based on phase change provided by the present invention mixes low-temperature liquid nitrogen and water in the engine, and the liquid nitrogen absorbs the heat of the water to rapidly expand and boil to generate nitrogen, forming nitrogen bubbles. The nitrogen bubbles absorb heat to the ambient temperature and continuously expand to do work on the water, so that the water is continuously accelerated in the nozzle and ejected from the outlet of the spray chamber 3 to generate thrust.

[0042] The underwater gas-liquid two-phase ramjet engine based on phase change of the present invention is a thrust drive mode based on phase change, and has the following effects: first, high specific impulse, the theoretical specific impulse can reach 800-1000s, the experimental specific impulse can reach 687s, compared with the metal / water ramjet engine solution, the specific impulse can be increased by about 50%; second, the working fluid required by the present invention is only liquid nitrogen, and water is taken from the environment. The price of raw materials required for 1 kilometer is 0.11 yuan, and the emission product is nitrogen, which is far more economical and environmentally friendly than other types of engines; third, compared with a simple water jet thrust engine, the present engine uses the phase change work generated by the endothermic expansion of liquid nitrogen to generate additional thrust; fourth, the present engine has no rotating parts and intermediate transmission links, and is not restricted by the bubble phenomenon.

[0043] In addition, by providing a structural design of the diffuser chamber 1 and the spray chamber 3 that are interconnected, the diffuser chamber 1 can decelerate and pressurize the water to ensure that the water flow entering the spray chamber 3 has sufficient pressure. The diffuser chamber 1 can also rectify the water to a certain extent to avoid excessive bubbles and vortices in the water flowing into the spray chamber 3, thereby ensuring full contact between the liquid nitrogen and the water flowing with increased speed and reduced pressure, improving the mixing effect, fully vaporizing the liquid nitrogen, and increasing the vaporization work to improve the thrust gain.

[0044] In one embodiment, a rectifying chamber 2 is further provided between the pressure diffuser chamber 1 and the spray chamber 3;

[0045] The cross-sectional area of ​​the rectifying cavity 2 is smaller than the cross-sectional area of ​​the diffusion cavity 1 , and larger than the inlet cross-sectional area of ​​the injection cavity 3 .

[0046] By setting up the rectifying chamber 2, a transition can be formed between the diffuser chamber 1 and the spray chamber 3. The water in the diffuser chamber 1 is accelerated and decompressed to a certain extent in the process of flowing into the rectifying chamber 2, and the water flow is turned from the relative turbulence in the diffuser chamber 1 to a stable state, further reducing the bubbles and vortices of the water in the spray chamber 3.

[0047] In one embodiment, the liquid nitrogen injector includes a liquid nitrogen supply pipe 5 and a liquid nitrogen storage tank, one end of the liquid nitrogen supply pipe 5 is connected to the liquid nitrogen storage tank, and the other end of the liquid nitrogen supply pipe 5 extends from the end face of the pressure diffuser chamber 1 through the pressure diffuser chamber 1 and the rectifying chamber 2 in sequence into the spray chamber 3. In this embodiment, the outlet direction of the liquid nitrogen supply pipe 5 is in the same direction as the outlet direction of the spray chamber 3, so that the liquid nitrogen can flow out along the direction of the water flow, thereby avoiding the flow resistance, circumference and bubbles caused by the liquid nitrogen to the water flow. Preferably, the liquid nitrogen supply pipe 5 adopts a vacuum tube with a double-layer vacuum structure to avoid the water flow in the pressure diffuser chamber 1 and the rectifying chamber 2 from heating the liquid nitrogen and wasting its working performance.

[0048] In one embodiment, the cross-sections of the pressure diffuser chamber 1, the rectifying chamber 2, the spray chamber 3 and the outlet of the liquid nitrogen supply pipe 5 are all circular. This arrangement is convenient for production and processing, and can also ensure structural strength and avoid stress concentration, and can also ensure the uniformity of water flow.

[0049] The ratio of the diameter of the diffusion chamber 1 to the outlet diameter of the liquid nitrogen supply pipe 5 is 50:1-100:1. If it is greater than this ratio, bubbles or swirls will be generated in the water flow entering the diffusion chamber, resulting in capacity loss; if it is less than this ratio, the amount of liquid nitrogen is too large to be completely vaporized after mixing, and the energy utilization rate is not high.

[0050] In one of the embodiments, the ratio of the diameter of the diffuser chamber 1 to the inlet diameter of the spray chamber 3 is 2:1-3:1. If it is not within this range, the flow of the entire engine will be blocked, and backflow will form at some locations, resulting in reduced thrust.

[0051] In one of the embodiments, the diffusion chamber 1 is a component formed by the outward expansion and rotation of a two-dimensional axial profile, and is of a gradually expanding type in two-dimensional scale, so that the incoming water can expand and increase pressure rapidly over a short distance.

[0052] In one of the embodiments, the expansion angle (included angle) between the axis of the water inlet 4 and the axis of the diffuser chamber 1 is 10°-50°, that is, the water inlet 4 is inclined toward the outlet side of the spray chamber 3. Such an arrangement can prevent the water flow flowing in from the water inlet 4 from directly hitting the inner wall of the diffuser chamber 1 to generate excessive bubbles and vortex flow.

[0053] In one embodiment, a plurality of water inlets 4 are equidistantly arranged along the inner wall of the pressure diffuser chamber 1, thereby ensuring the overall water inlet amount, water inlet speed and water inlet pressure into the pressure diffuser chamber 1 on the basis of reducing the water inlet amount, water inlet speed and water inlet pressure of a single water inlet 4, and reducing bubbles and circumferential flow of water flowing in from the water inlet 4 on this basis. In an embodiment in which the expansion angle (included angle) between the axis of the water inlet 4 and the axis of the pressure diffuser chamber 1 is 10°-50°, direct vertical collision of water flows from multiple water inlets 4 can be further avoided;

[0054] The ratio of the diameter of the water inlet 4 to the diameter of the outlet of the liquid nitrogen supply pipe 5 is between 10:1 and 100:1, so as to meet the ratio requirement of liquid nitrogen to water.

[0055] In one of the embodiments, the outlet convergence angle of the spray chamber 3 is 2°-6°. If the angle is smaller than this range, the gas-liquid two-phase flow expansion acceleration is insufficient. If the angle is larger than this range, congestion occurs in the flow, and a part of the gas-liquid two-phase flow does not generate thrust.

[0056] The present invention also provides a working method of the above-mentioned underwater gas-liquid two-phase ramjet engine based on phase change, comprising the following steps:

[0057] Water flows into the diffusion chamber 1 from the water inlet 4, decelerates and increases pressure, and then flows into the spray chamber 3 to increase speed and reduce pressure. The liquid nitrogen injector injects liquid nitrogen into the spray chamber 3. The liquid nitrogen and water are mixed at the downstream of the outlet of the liquid nitrogen supply pipe 5 of the liquid nitrogen injector in the spray chamber 3. During the mixing process, the liquid nitrogen absorbs heat, expands and boils to produce nitrogen and form nitrogen bubbles. The nitrogen bubbles absorb heat and continue to expand and do work on the water during the process of reaching the ambient temperature, so that the water is continuously accelerated and ejected at the outlet of the spray chamber 3 to generate thrust.

[0058] In this embodiment, the underwater gas-liquid two-phase ramjet engine based on phase change is theoretically analyzed. The ambient pressure and temperature (water pressure and temperature) are 101325Pa and 300K respectively. By analyzing the thermodynamic cycle of the entire physical process, such as Figure 3 As shown, liquid nitrogen is sprayed out from the liquid nitrogen storage tank and injected into the engine, and water is injected into the diffuser chamber 1 from the side wall of the diffuser chamber 1 (AB section throttling expansion); since liquid nitrogen is a low-temperature liquid and water is at room temperature, the liquid nitrogen mixed with water will absorb heat from the water and boil rapidly (BC section) until it is completely vaporized and converted into nitrogen; nitrogen is stored in the form of bubbles in the water, and the temperature of the newly vaporized nitrogen is relatively low and enters the surrounding environment and then absorbs heat to the ambient temperature (CD section); the water flow entrains the bubble flow and flows out along the spray chamber 3, accelerating the decompression, the liquid nitrogen bubbles expand and burst, and the high-pressure nitrogen does work on the water, playing a driving role (DE section); at this time, the outlet velocity of the spray chamber 3 is greater than the incoming flow velocity, thereby generating thrust.

[0059] At this time, the area enclosed by ABCD (attached Figure 3The area enclosed by the double-dotted line in the middle is the work done externally. The theoretical specific impulse is equal to the work divided by the liquid nitrogen flow rate. The theoretical specific impulse is as follows: Figure 4 As shown, when the liquid nitrogen flow rate is 0.001kg / s, the maximum theoretical specific impulse is about 800s-1000s, which is far higher than the specific impulse of solid rocket engines and is expected to become the energy source for the engine.

[0060] When the underwater gas-liquid two-phase ramjet engine based on phase change is experimentally tested and verified in this embodiment, the thrust before and after adding liquid nitrogen is tested by a six-component balance, and the liquid nitrogen flow rate is measured by a platform scale, and the experimental specific impulse can be obtained, such as Figure 5 The experimental specific impulse of this embodiment is about 600s, which is still superior in terms of power compared with solid rocket engines (specific impulse of about 400s) and metal / water ramjet engines (specific impulse of 250s-450s).

[0061] The above is only an embodiment and does not limit the present invention in any way. Any person skilled in the art can use the above disclosed technical contents to make many possible changes, modifications or modifications to the technical solutions of the present invention into equivalent embodiments of equivalent changes without departing from the scope of the technical solutions of the present invention. Therefore, any simple modification, equivalent changes and modifications made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall fall within the scope of protection of the technical solutions of the present invention.

Claims

1. An underwater gas-liquid two-phase ramjet engine based on phase change, characterized in that: It comprises a liquid nitrogen injector and a diffusion chamber (1) and a spray chamber (3) which are connected in sequence; The liquid nitrogen injector comprises a liquid nitrogen supply pipe (5) and a liquid nitrogen storage tank, one end of the liquid nitrogen supply pipe (5) is connected to the liquid nitrogen storage tank, and the other end extends into the spray chamber (3); The spray chamber (3) is of a tapered structure, the inlet of the spray chamber (3) is a large-section end, the outlet is a small-section end, and one end of the inlet of the spray chamber (3) is connected to the pressure diffuser chamber (1), and the inlet cross-sectional area of ​​the spray chamber (3) is smaller than the cross-sectional area of ​​the pressure diffuser chamber (1); A water inlet (4) is provided in the pressure diffuser chamber (1); The liquid nitrogen injector is used to inject liquid nitrogen into the spray chamber (3), and the mass ratio of water entering the water inlet (4) to the liquid nitrogen injected by the liquid nitrogen injector is in the range of 1000-300000; A rectifying chamber (2) is further provided between the pressure diffuser chamber (1) and the spray chamber (3); The liquid nitrogen injector comprises a liquid nitrogen supply pipe (5), wherein the liquid nitrogen supply pipe (5) extends from the end surface of the pressure diffuser chamber (1) through the pressure diffuser chamber (1) and the rectifying chamber (2) in sequence and then extends into the injection chamber (3).

2. The underwater gas-liquid two-phase ramjet engine based on phase change as claimed in claim 1, characterized in that: The cross-sectional area of ​​the rectifying cavity (2) is smaller than the cross-sectional area of ​​the pressure diffuser cavity (1), and larger than the inlet cross-sectional area of ​​the spray cavity (3).

3. The underwater gas-liquid two-phase ramjet engine based on phase change as claimed in claim 1, characterized in that: The cross-sections of the pressure diffuser chamber (1), the rectifying chamber (2), the spray chamber (3) and the outlet of the liquid nitrogen supply pipe (5) are all circular; The ratio of the diameter of the pressure diffusion chamber (1) to the outlet diameter of the liquid nitrogen supply pipe (5) is 50:1-100:

1.

4. The underwater gas-liquid two-phase ramjet engine based on phase change according to any one of claims 1 to 3, characterized in that: The ratio of the diameter of the diffusion chamber (1) to the inlet diameter of the spray chamber (3) is 2:1-3:

1.

5. The underwater gas-liquid two-phase ramjet engine based on phase change according to any one of claims 1 to 3, characterized in that: The pressure diffuser cavity (1) is a component formed by the outward expansion and rotation of a two-dimensional axial profile.

6. The underwater gas-liquid two-phase ramjet engine based on phase change as claimed in claim 5, characterized in that: The expansion angle between the axis of the water inlet (4) and the axis of the pressure diffusion chamber (1) is 10°-50°.

7. The underwater gas-liquid two-phase ramjet engine based on phase change as claimed in claim 5, characterized in that: A plurality of water inlets (4) are arranged at equal intervals along the inner wall of the pressure diffuser chamber (1); The ratio of the diameter of the water inlet (4) to the diameter of the outlet of the liquid nitrogen supply pipe (5) is between 10:1 and 100:

1.

8. The underwater gas-liquid two-phase ramjet engine based on phase change according to any one of claims 1-3, 6, and 7, characterized in that: The outlet convergence angle of the spray chamber (3) is 2°-6°.

9. A method for operating an underwater gas-liquid two-phase ramjet engine based on phase change according to any one of claims 1 to 8, characterized in that: The steps include: Water flows from the water inlet (4) into the diffuser chamber (1) and decelerates and increases pressure, and then flows into the spray chamber (3) and increases speed and decreases pressure. The liquid nitrogen injector injects liquid nitrogen into the spray chamber (3). The liquid nitrogen and water are mixed at the downstream of the outlet of the liquid nitrogen supply pipe (5) of the liquid nitrogen injector in the spray chamber (3). During the mixing process, the liquid nitrogen absorbs heat, expands and boils to generate nitrogen and form nitrogen bubbles. The nitrogen bubbles absorb heat to the ambient temperature and continuously expand and do work on the water, so that the water is continuously accelerated and ejected at the outlet of the spray chamber (3), thereby generating thrust.

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