Gas-liquid two-phase ramjet engine with liquefied gas as gas source

Abstract

The invention belongs to the technical field of underwater propulsion systems, and discloses a gas-liquid two-phase ramjet engine taking liquefied gas as a gas source, which comprises a liquid inlet channel, a mixing and vaporizing chamber and an exhaust nozzle which are coaxially arranged from left to right. The two-phase ramjet engine adopts liquefied gas as a gas source, and has the advantages that the storage density of the liquefied gas is far greater than that of compressed gas, and the liquefied gas is stored as fuel, so that the space utilization efficiency can be effectively improved. The mixing and vaporizing chamber of the two-phase ramjet engine is provided with the groove, water flow forms vortex when flowing through the groove, and the water body and the liquefied gas are mixed more uniformly. The two-phase ramjet engine is provided with the exhaust nozzle straight pipe section which can stretch out and draw back in the mounting cavity of the mixing and vaporizing chamber. In the exhaust nozzle of the two-phase ramjet engine, the convergent-divergent pipe for changing the sectional area of the outlet is arranged, so that the engine adapts to different working conditions.

Description

Technical Field

[0001] The present invention belongs to the technical field of underwater propulsion systems, and relates to a gas-liquid two-phase ramjet engine that can use liquefied gas as a gas source. Background Art

[0002] A conventional gas-liquid two-phase ramjet engine includes a liquid inlet passage, a mixing chamber, and a tail nozzle, and serves surface ships, using compressed gas as "fuel". When a ship sails on the water surface, environmental water enters the engine directly without a booster device such as a pump. The water entering the engine enters the mixing chamber after decelerating and pressurizing through the liquid inlet passage. A high-pressure environment is formed in the mixing chamber only by the ram effect of the water flow; compressed gas is injected into the mixing chamber to achieve gas-liquid two-phase mixing, and the initial acceleration of the water body is completed; subsequently, the gas-liquid two-phase flow enters the tail nozzle, and the bubbles expand and do work on the water body under the action of the favorable pressure gradient, further accelerating the water body, so that the speed of the water body at the engine outlet is greater than its speed at the inlet, thereby generating thrust.

[0003] Gas-liquid two-phase ramjet engines have excellent sound insulation performance and good concealment, and are suitable as propulsion devices for high-speed cruising underwater vehicles. However, conventional gas-liquid two-phase ramjet engines use compressed gas as a gas source. Due to the low storage density of the gas and the large influence of environmental pressure on gas expansion work, the use of compressed gas as a gas source for gas-liquid two-phase ramjet engines is limited for the propulsion of underwater vehicles. Using liquefied gas with a higher storage density than compressed gas as a gas source can significantly improve the space utilization efficiency, and the advantage of propelling an underwater vehicle is more obvious.

[0004] However, for a gas-liquid two-phase ramjet engine using liquefied gas as a gas source, there are still two problems to be solved: (1) How to effectively mix the liquefied gas entering the engine with the water body is crucial, which not only relates to the efficient boiling and gasification of the liquefied gas, but also involves the effective dispersion of the gas after the liquefied gas is gasified in the water body. These will all affect the energy transfer between the liquefied gas and the water body (after the liquefied gas is gasified, it is manifested as the energy transfer between the gas and the water body). The better the mixing degree, the higher the energy transfer efficiency. (2) The speed of sound in the gas-liquid two-phase flow is significantly lower than that in the single-liquid or single-gas flow. Therefore, the gas-liquid two-phase fluid in the engine tail nozzle is more likely to reach choking; choking will affect the energy conversion efficiency and propulsion efficiency of the engine. As a high-speed cruising underwater vehicle, choking of the gas-liquid two-phase ramjet engine is inevitable. It is very important to optimize the engine structure so that the ramjet engine under choking flow has the best working performance. Summary of the Invention

[0005] The object of the present invention is to provide a gas-liquid two-phase ramjet engine applicable to an underwater vehicle, which can strengthen the dispersion of gas in water and improve the engine performance under choked flow. It has the characteristics of simple structure, high efficiency and high reliability, and can well solve the problems of environmental sensitivity of the gas-liquid two-phase ramjet engine and performance degradation under choked flow.

[0006] The technical solution of the present invention:

[0007] A gas-liquid two-phase ramjet engine using liquefied gas as the gas source, including a liquid inlet passage, a mixing and vaporization chamber, and a tail nozzle arranged coaxially from left to right; the liquid inlet passage is a circular tube that gradually expands from outside to inside. The end with a small cross-sectional area of the liquid inlet passage is the inlet, and the gradually expanding circular tube decelerates and pressurizes the incoming water flow; a liquefied gas inlet hole is arranged between the liquid inlet passage and the mixing and vaporization chamber for introducing liquefied gas; the mixing and vaporization chamber is a stepped circular cavity, and the cross-sectional areas of the inlet and outlet of the mixing and vaporization chamber are equal to the cross-sectional area of the outlet of the liquid inlet passage. A groove is arranged at the front end inlet of the mixing and vaporization chamber to generate a vortex of the water flow to promote the mixing of water and liquefied gas; the tail nozzle is a variable-area nozzle with a straight pipe section at the front end, including a straight pipe section, a contraction section, a throat section, and an expansion section from left to right in sequence. The cross-sectional area of the inlet of the contraction section is consistent with the cross-sectional area of the outlet of the liquid inlet passage; the straight pipe section is inserted into the cavity wall of the mixing and vaporization chamber, and by adjusting the length of the straight pipe section in the cavity wall of the mixing and vaporization chamber, the mixing and vaporization chamber is extended by the straight pipe section, thereby controlling the boiling ratio of the liquefied gas before the inlet of the contraction section, and finally forming a working fluid with a specified gas holdup and liquefied gas content at the inlet of the contraction section, so as to reduce the influence of choking to obtain the maximum thrust; the tail nozzle is used to accelerate the working fluid formed in the mixing and vaporization chamber, and adjust the engine working state by controlling the engine outlet area, enhancing the adaptability of the engine in different environments.

[0008] Preferably, the liquefied gas should be a gas that is easy to obtain, has good economy, low pollution and is insoluble in water, such as liquefied nitrogen, liquefied helium, and R134a, etc.

[0009] Preferably, the liquid inlet passage is a gradually expanding circular tube, and the expansion half angle is set between 1° and 60°.

[0010] Preferably, the liquefied gas inlet hole is a circular hole, and the liquefied gas inlet holes are uniformly arranged circumferentially between the liquid inlet passage and the mixing and vaporization chamber.

[0011] Preferably, the number of the liquefied gas inlet holes is 1 to 16, the hole diameter is 0.8 to 3 mm, and the included angle θ between the center line direction of the liquefied gas inlet hole and the engine axis direction is 10° to 90°.

[0012] Preferably, the liquefied gas boils and vaporizes after contacting the water body, and the gas content of the mixed fluid at the tail nozzle outlet should be between 0.1% and 75%.

[0013] Preferably, the cross-sectional area of ​​the mixing and vaporization chamber inlet, the cross-sectional area of ​​the mixing and vaporization chamber outlet, the cross-sectional area of ​​the mixing and vaporization chamber non-groove portion, and the cross-sectional area of ​​the tail nozzle contraction section inlet are the same as the cross-sectional area of ​​the liquid inlet outlet, and are set to 3 to 8 times the cross-sectional area of ​​the liquid inlet inlet.

[0014] Preferably, the mixing and gasification chamber is provided with a groove, the depth of the groove is set to 0.2 to 0.7 times the inner diameter of the mixing and gasification chamber inlet, and the length is set to 0.2 to 1 times the inner diameter of the mixing and gasification chamber inlet.

[0015] Preferably, there is an installation cavity in the cavity wall of the mixing and vaporization chamber, in which a spring is fixed, one end of the spring is fixedly connected to the inner wall surface of the mixing and vaporization chamber, and the other end is connected to the straight pipe section of the tail nozzle; a slide groove is formed between the cavity wall of the mixing and vaporization chamber and the straight pipe section of the tail nozzle, the slider slides in the slide groove, and the cavity wall of the mixing and vaporization chamber and the straight pipe section of the tail nozzle are positioned by the slider and the slide groove; a sealing ring is provided near the outlet of the mixing and vaporization chamber; the stiffness coefficient of the spring is determined according to the change in length of the mixing and vaporization chamber after the straight pipe section is extended and the navigation speed, and the length of the mixing and vaporization chamber after the straight pipe section is extended is determined according to the navigation speed and the boiling rate of the liquefied gas.

[0016] Preferably, the installation cavities are evenly arranged along the circumferential direction in the wall of the mixing and vaporization chamber, and 2 to 8 are set; 2 to 8 springs are set in the installation cavity; sliders are evenly arranged along the circumferential direction on the outer wall of the straight pipe section of the tail nozzle, and 1 to 16 are set; the slide grooves are evenly arranged along the circumferential direction on the wall of the mixing and vaporization chamber, and the number is consistent with the sliders; the slider can only slide along the axis direction of the engine in the slide groove, and a fixing pin is set at the end of the slide groove to prevent the slider from slipping out.

[0017] Preferably, the tail nozzle is a convergent-divergent nozzle with a straight pipe section, including a straight pipe section, a contraction section, a throat section and an expansion section, wherein the straight pipe section is a straight pipe section with a length set at 10 to 30 cm, a contraction half angle of the contraction section is 5° to 45°, an expansion half angle of the expansion section is 1° to 60°, and a cross-sectional area of ​​the throat section is set to 1 to 2 times the cross-sectional area of ​​the liquid inlet entrance.

[0018] Preferably, the outlet surface of the expansion section of the tail nozzle is adjustable, including a plurality of connected conical segments, a connecting flexible material, an outlet flexible material and a damping rod. When the navigation speed increases, the pressure in the expansion section increases, so that the conical segments are subjected to an outward expansion force. When the force is large enough, the damping rod is overcome, and finally the cross-sectional area of ​​the outlet can be changed between 2 and 4 times the cross-sectional area of ​​the inlet of the liquid inlet.

[0019] Preferably, 4 to 32 conical segments are provided; the two flexible materials should be made of waterproof and arbitrarily bendable and foldable materials, such as coated canvas, rubber cloth, nylon cloth, etc. The number of connecting flexible materials connecting the conical segments in pairs is the same as the number of conical segments; one end of the outlet flexible material is connected to the conical segment or the connecting flexible material, and the other end is connected to the end of the wall surface of the divergent section of the tail nozzle, and the number is set to the sum of the number of conical segments and the number of connecting flexible materials; one end of the damping rod is connected to the wall surface of the divergent section of the tail nozzle, and the other end is connected to the conical segment, and the number is the same as the number of conical segments.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] (1) This two-phase ramjet engine uses liquefied gas as the gas source. The advantage is that the storage density of liquefied gas is much greater than that of compressed gas. Using liquefied gas as "fuel" storage can effectively improve the space utilization efficiency; in addition, the work done by liquefied gas during the boiling and expansion process is less sensitive to pressure changes compared to the work done by gas expansion, and the work done is more stable, and the advantage is more obvious when sailing underwater. Moreover, during the boiling and expansion process of liquefied gas, there is not only the expansion work of gas, but also the boiling work of liquefied gas. Therefore, at the same mass, the work done by liquefied gas is significantly higher than that of compressed gas, which can provide higher kinetic energy for the water flow, and then make the water flow spray out at a higher speed at the outlet, thereby providing greater thrust for the engine.

[0022] (2) The mixing and gasification chamber of this two-phase ramjet engine is provided with grooves. When the water flow passes through the grooves, vortices are formed, and the mixing of the water body and the liquefied gas is more uniform. Uniform mixing can, on the one hand, increase the contact area between the liquefied gas and the water, promoting the efficient boiling of the liquefied gas; on the other hand, it promotes the uniform dispersion of the gas obtained by the boiling and gasification of the liquefied gas in the water body. These will all affect the energy transfer between the liquefied gas and the water body (after the liquefied gas is gasified, it is the energy transfer between the gas and the water body). The better the mixing degree, the higher the energy transfer efficiency, and the higher the energy transfer efficiency, the faster the water flow speed at the outlet of the engine.

[0023] (3) This two-phase ramjet engine is provided with a straight pipe section of the tail nozzle that can be telescoped in the installation cavity of the mixing and gasification chamber. The speed of sound in the gas-liquid two-phase flow is significantly reduced compared to that in the single liquid phase or single gas phase flow. Therefore, it is easier for the gas-liquid two-phase fluid in the engine tail nozzle to reach choking, and choking will affect the energy conversion efficiency and propulsion efficiency of the engine. When using liquefied gas, since it takes time for the liquefied gas to boil and gasify to generate gas, the liquefied gas can be made to boil and expand to do work in the area with higher energy conversion efficiency, increasing the useful work of the liquefied gas, thereby increasing the thrust. Therefore, the present invention designs a straight pipe section of the tail nozzle that can be telescoped within the cavity wall of the mixing and gasification chamber to control the complete boiling position of the liquefied gas to increase the thrust.

[0024] (4) In the nozzle of this two-phase ramjet engine, a convergent-divergent nozzle that changes the exit cross-sectional area is provided to enable the engine to adapt to different operating conditions. When the flow inside the engine is transonic, the operating state of the engine at choking needs to be considered when designing the engine model. If the exit area of the engine is small at this time, the gas is discharged at an exit pressure higher than the ambient pressure, resulting in incomplete expansion of the gas inside the nozzle, and further expansion will occur outside the nozzle exit, and the thrust and specific impulse do not reach the maximum value; while once the exit area is large, the exit pressure is lower than the ambient pressure. This causes the fluid to expand too violently inside the nozzle, and flow separation may occur, and the fluid completely detaches from the nozzle wall, generating unstable and asymmetric forces. This may damage the nozzle and lead to serious engine failures, so it needs to be avoided. Only when the pressure at the exit is equal to the ambient pressure, the engine is in the ideal state of complete expansion, and the thrust and specific impulse of the engine are the largest at this time. Therefore, if the thrust of the engine is to be at a large value, the exit area cannot always be a fixed value, but should not deviate too much from the exit area required for complete expansion as much as possible to obtain a large thrust. Description of the Drawings

[0025] Figure 1 It is a sectional view of a two-phase ramjet engine using liquefied gas as the gas source;

[0026] Figure 2 It is a front view of a two-phase ramjet engine using liquefied gas as the gas source;

[0027] Figure 3 It is for Figure 1 The sectional view of the mixing and vaporization chamber at A-A in

[0028] Figure 4 It is for Figure 1 The sectional view of the mixing and vaporization chamber at B-B in

[0029] Figure 5 It is a schematic diagram of the slider connection between the mixing and vaporization chamber and the straight pipe section of the nozzle;

[0030] Figure 6 It is a sectional view when the exit area of the nozzle is the smallest;

[0031] Figure 7 It is a side view when the exit area of the nozzle is the smallest;

[0032] Figure 8 It is a sectional view after the exit area of the nozzle becomes larger;

[0033] Figure 9 It is a side view after the exit area of the nozzle becomes larger;

[0034] In the figure: 1 liquid inlet channel, 2 liquefied gas inlet hole, 3 mixing and gasification chamber, 301 groove, 302 spring, 303 spring installation hole, 304 installation cavity, 305 chute, 306 sealing ring, 307 fixing pin, 4 tail nozzle, 401 straight pipe section, 402 contraction section, 403 throat section, 404 expansion section, 405 slider, 406 conical section, 407 connecting flexible material, 408 outlet flexible material, 409 damping rod. Detailed implementation manners

[0035] The following further describes the detailed implementation manners of the present invention in combination with the accompanying drawings and technical solutions.

[0036] Please refer to Figures 1 to 9 , a specific embodiment of a two-phase ramjet engine using liquefied gas as the gas source:

[0037] A two-phase ramjet engine with liquefied gas as a gas source includes a liquid inlet 1, a liquefied gas inlet hole 2, a mixing and gasification chamber 3, and a tail nozzle 4. The liquid inlet 1, the mixing and gasification chamber 3, and the tail nozzle 4 are coaxial and arranged from left to right in sequence, and the parts can be connected by welding or flanges. The liquid inlet 1 is a gradually expanding circular tube, and the water flow enters from the entrance of the liquid inlet 1 from left to right, and is decelerated and pressurized under the action of the gradually expanding circular tube. The liquefied gas inlet hole 2 is evenly arranged in an annular direction between the liquid inlet 1 and the mixing and gasification chamber 3. The liquefied gas can be liquefied nitrogen. The liquefied gas can be connected to the liquefied gas inlet hole 2 through a cryogenic pump or a self-pressurization system to introduce liquefied gas into the engine. The mixing and gasification chamber 3 is a stepped circular cavity, including a groove 301, a spring 302, a spring mounting hole 303, a mounting cavity 304, a slide groove 305, a sealing ring 306, and a sealing ring 307. The groove 301 is arranged at the pipe wall of the entrance of the mixing and gasification chamber 3, and the water flowing through the groove 301 will form a vortex in the groove 301. The liquefied gas introduced by the liquefied gas inlet hole 2 will contact the water forming the vortex, mix evenly and initially boil and gasify to form a working fluid. The spring 302 is fixed in the installation cavity 304 in the wall of the mixing and gasification chamber 3, one end of the spring 302 is fixedly connected to the inner wall surface of the mixing and gasification chamber 3, and the other end is connected to the tail nozzle straight pipe section 401, the tail nozzle straight pipe section 401 is positioned with the slide 305 through the slider 405, the sealing ring 306 is sealed, and the sealing ring 307 is set at the end of the slide 305 to prevent the slider 405 from sliding out of the slide 305. The water flow impacts the tail nozzle 4 to generate a tensile force, which acts on the spring 302. After the spring 302 is stretched, a force in the opposite direction is generated to balance the tensile force. As a result, the tail nozzle straight pipe section 401 is displaced relative to the mixing and vaporization chamber 3 so that the mixing and vaporization chamber 4 is extended by the straight pipe section 401, changing the distance from the fluid flow to the inlet of the tail nozzle contraction section 402, thereby changing the boiling ratio of the liquefied gas, and finally forming a working fluid with a specified gas holdup and liquefied gas holdup at the inlet of the tail nozzle contraction section 402 to flow into the tail nozzle expansion section 402. The tail nozzle 4 is a convergent-convergent pipe with a straight pipe section, including a straight pipe section 401, a contraction section 402, a throat section 403, an expansion section 404, a slider 405, a conical segment 406, a connecting flexible material 407, an outlet flexible material 408, and a damping rod 409. There are multiple conical segments 406 connected inside the expansion section 404, and two conical segments 406 are connected by connecting flexible materials 407 to change the expansion angle of the conical segments 406; wherein one end of the outlet flexible material 408 is connected to the conical segment 406 or the connecting flexible material 407, and the other end is connected to the end of the wall of the tail nozzle expansion section 404. One end of the damping rod 409 is connected to the wall of the tail nozzle expansion section 404, and the other end is connected to the conical segment 404. When the pressure of the tail nozzle expansion section 404 rises, the conical segment 406 is affected by the internal and external pressure difference, which pushes the conical segment 406 to expand, thereby changing the outlet area.

[0038] Further, the liquefied gas is selected as liquid nitrogen.

[0039] Further, the liquid inlet channel 1 is a gradually expanding circular tube, the inlet of the liquid inlet channel 1 has a radius of 30 mm, and the expansion half angle is set to 6°.

[0040] Further, the liquid nitrogen inlet holes 2 are circular holes, and the liquefied gas inlet holes 2 are circumferentially and uniformly arranged between the liquid inlet channel 1 and the mixing and gasification chamber 3.

[0041] Further, the number of the liquefied gas inlet holes is 4, the hole diameter is 2 mm, and the included angle θ between the central line direction of the liquefied gas inlet hole and the engine axis direction is 80°. Liquid nitrogen can be introduced into the engine mixing and gasification chamber 3 through a cryogenic pump or a self-pressurizing system and connected to the liquefied gas inlet hole 2.

[0042] Further, after the liquid nitrogen forms a mixed fluid with water, the gas holdup of the mixed fluid at the outlet of the tail nozzle 5 should be about 55%, that is, the ratio of the mass flow rate of liquid nitrogen to the mass flow rate of water is 0.2%.

[0043] Further, the cross-sectional area of the inlet of the mixing and gasification chamber 3, the cross-sectional area of the outlet of the mixing and gasification chamber 3, the cross-sectional area of the non-groove 301 of the mixing and gasification chamber 3, the cross-sectional area of the inlet of the tail nozzle contraction section 402 are the same as the cross-sectional area of the outlet of the liquid inlet channel 1, and are set to be 3 to 8 times the cross-sectional area of the inlet of the liquid inlet channel 1.

[0044] Further, the mixing and gasification chamber 3 is provided with a groove 301, the groove 301 is arranged on the wall surface of the inlet of the mixing and gasification chamber 3, the depth of the groove 301 is 0.5 times the diameter of the mixing and gasification chamber 1, and the length is 0.8 times the diameter of the mixing and gasification chamber 1.

[0045] Further, there is an installation cavity 304 inside the cavity wall of the mixing and gasification chamber 3, in which a spring 302 is fixed. One end of the spring 302 is fixedly connected to the inner wall surface, and the other end is connected to the straight pipe section 401 of the tail nozzle; a sliding groove 305 is formed between the cavity wall of the mixing and gasification chamber 3 and the straight pipe section 401 of the tail nozzle, and a slider 405 slides in the sliding groove 305. The cavity wall of the mixing and gasification chamber 3 and the straight pipe section 401 of the tail nozzle are positioned through the slider 405 and the sliding groove 305; the outlet of the mixing and gasification chamber 3 is sealed by a sealing ring 306. The length of the non-groove 301 of the mixing and gasification chamber 3 is set to 30 cm, and the length of the straight pipe section 401 of the tail nozzle is set to 20 cm.

[0046] Further, the installation cavities 304 are uniformly arranged circumferentially within the cavity wall of the mixing and gasification chamber 3, with 4 provided; 4 springs are provided within the installation cavities; 4 spring mounting holes 303 are provided at the corresponding positions of the cavity wall of the mixing and gasification chamber 3 and the springs; 4 sliders 405 are uniformly arranged circumferentially on the outer wall of the straight pipe section 401 of the tail nozzle; the number of the chutes 305 uniformly arranged circumferentially on the cavity wall of the mixing and gasification chamber is the same as that of the sliders 405; the sliders 405 can only slide along the engine axis direction within the chutes 305, and fixing pins 307 are provided at the ends of the chutes to prevent the sliders 405 from sliding out.

[0047] Further, for the mixing and gasification chamber 3 and the straight pipe section 401 of the tail nozzle, the depth of insertion of the straight pipe section 401 of the tail nozzle into the cavity wall of the mixing and gasification chamber 3 is changed by the pulling force of the spring 302 and the impact force of the water flow on the engine tail nozzle 4, so that the mixing and gasification chamber 4 is extended by the straight pipe section 401, and further the distance from the fluid to the divergent section 402 of the tail nozzle is changed, according to Equation (1):

[0048]

[0049] where, L b is the length of the mixing and gasification chamber 4 extended by the straight pipe section 401; u is the fluid velocity within the mixing and gasification chamber 4 and the straight pipe section 401; t is the time; t b is the sum of the residence times of the fluid in the two parts of the mixing and gasification chamber 4 and the straight pipe section 401, and can be calculated by Equation (2)

[0050]

[0051] where, m g is the mass of the vaporized liquid nitrogen within the mixing and gasification chamber 4 and the straight pipe section 401; M is the mass flow rate of the introduced liquid nitrogen; h fb is the heat transfer coefficient of film boiling (which can be approximately considered as 577 W / (m 2 ·K)); ΔT l is the temperature difference between water and liquid nitrogen; ρ l is the density of liquid nitrogen; d p0 is the initial diameter of the liquid nitrogen droplets formed; L is the latent heat of vaporization of liquid nitrogen. d p0 can be estimated according to the liquid nitrogen introduction velocity and the diameter of the liquefied gas introduction hole 2:

[0052] When Bo J ≤π 2

[0053]

[0054] When Bo J >π 2

[0055]

[0056] Among them, Bo J is the jet Bond number, d J ′ is the effective diameter of the jet, ρ w is the density of water; β is the constant 0.3; We J is the jet Weber number, Lp J is the jet Weber Reynolds number, g is the acceleration due to gravity; u J is the nitrogen liquid injection velocity; σ l is the surface tension of nitrogen liquid; Re J is the jet Reynolds number, μ l is the viscosity of nitrogen liquid.

[0057] m g is determined according to the gas holdup α0 required at the inlet of the tail nozzle contraction section 402 when choking occurs at the engine navigation speed:

[0058]

[0059] Among them, u in is the navigation speed of the underwater vehicle; P0 is the pressure at the inlet of the tail nozzle contraction section 402 when choking occurs at this navigation speed; α0 is the gas holdup required at the inlet of the tail nozzle contraction section 402 when choking occurs at this navigation speed; R g is the gas constant; T g is the temperature of nitrogen; A in is the inlet area of the engine liquid inlet channel 1. The gas holdup α0 at the inlet of the tail nozzle contraction section 402 and the pressure P0 at the inlet of the tail nozzle contraction section 402 when choking occurs at this navigation speed can be calculated according to equations (6), (7) and (8)

[0060]

[0061] Among them, α th is the gas holdup of the tail nozzle throat section 403 when choking occurs at this navigation speed; A th is the cross-sectional area of the tail nozzle throat section 403; A0 is the inlet area of the tail nozzle contraction section 402; P a is the ambient pressure; By solving the above implicit equations by the bisection method, the gas holdup α0 at the inlet of the tail nozzle contraction section 402 and the pressure P0 at the inlet of the tail nozzle contraction section 402 when choking occurs at this navigation speed can be obtained.

[0062] Furthermore, the spring 302 should be installed through the spring installation hole 303, and the stiffness coefficient of the spring 302 should satisfy formula (9):

[0063]

[0064] Wherein, k is the stiffness coefficient of the spring 302; L0 is the length of the mixing and vaporization chamber 4.

[0065] Furthermore, the tail nozzle 4 is a convergent-divergent nozzle with a straight pipe section, including a straight pipe section 401, a contraction section 402, a throat section 403 and an expansion section 404, wherein the straight pipe section 401 is a straight pipe section, the contraction half angle of the contraction section 402 is 20°, the cross-sectional area of ​​the throat section 403 is set to 1.44 times the inlet area of ​​the liquid inlet channel 1, the expansion half angle of the expansion section 404 varies between 10° and 20° to change the outlet area, and the outlet of the expansion section 404 varies between 2 and 3 times the inlet area of ​​the liquid inlet channel 1.

[0066] Furthermore, the outlet surface of the expansion section 404 of the tail nozzle is adjustable, and includes a plurality of connected conical segments 406, a connecting flexible material 407, an outlet flexible material 408, and a damping rod 409. When the navigation speed increases, the pressure of the expansion section 404 of the tail nozzle increases, so that the conical segments 406 are subjected to an outward expansion force, and when the force is large enough, the damping rod 409 is overcome, and finally the cross-sectional area of ​​the outlet can be changed between 2 and 3 times the cross-sectional area of ​​the inlet of the liquid inlet 1.

[0067] Furthermore, the conical segments 406 are provided in eight pieces, and the connecting flexible material 407 and the outlet flexible material 408 are made of coated canvas. The connecting flexible material 407 connecting the conical segments 406 is provided in eight pieces; the outlet flexible material 408 is connected to the conical segment 406 or the connecting flexible material 407 at one end, and connected to the end of the wall of the tail nozzle expansion section 404 at one end, and is provided in 16 pieces; the damping rod 409 is connected to the wall of the tail nozzle expansion section 404 at one end, and connected to the conical segment 406 at one end, and the number is the same as the number of the conical segments 406.

[0068] Working principle: Water flow enters the two-phase ramjet from the inlet of the liquid inlet passage 1 and gradually decelerates and pressurizes under the action of the liquid inlet passage. Then it flows into the mixing and gasification chamber 3. The water flow forms a vortex under the action of the groove 301, enabling the liquefied gas entering the mixing and gasification chamber 3 through the liquefied gas inlet hole 2 to mix with the water flow and promoting the initial dispersion of the gas generated by the initial gasification of the liquefied gas in the mixing and gasification chamber 3, thus forming the working fluid. In order to regulate the gas volume fraction and liquefied gas volume fraction of the working fluid flowing into the divergent section 402 of the nozzle, there is an installation cavity 304 inside the cavity wall of the mixing and gasification chamber 3, in which a spring 302 is fixed. One end of the spring 302 is fixedly connected to the inner wall surface, and the other end is connected to the straight section 401 of the nozzle. By the impact of the water flow on the nozzle 4, a tensile force is generated, and the spring 302 is stretched, causing the straight section 401 of the nozzle to displace relative to the mixing and gasification chamber 3, extending the mixing and gasification chamber 3 by the straight section 401, thereby changing the residence time of the liquefied gas in the mixing and gasification chamber 3 and the straight section 401, and thus changing the boiling amount of the liquefied gas in the mixing and gasification chamber 3, and finally forming a working fluid with a specified gas volume fraction and liquefied gas volume fraction. During choked flow, the thrust is maximum when the pressure at the outlet of the nozzle 4 is equal to the external pressure. As the sailing speed of the engine increases, the pressure at the outlet of the engine nozzle 4 also increases, which will lead to a decrease in the propulsion efficiency. In order to control the pressure at the outlet of the nozzle 4, a conical section 406 is provided in the divergent section 404 of the nozzle 4, and the conical sections 406 are connected to each other in pairs through the connecting flexible material 407. When the sailing speed increases, the pressure in the divergent section 404 of the nozzle rises, the pressure difference force inside and outside the conical section 406 increases, pushing the conical section 406 to expand, increasing the outlet area of the nozzle 4, and thus reducing the outlet pressure of the nozzle 4, and finally improving the propulsion efficiency of the engine.

[0069] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A gas-liquid two-phase ramjet engine with liquefied gas as the gas source, characterized in that, The gas-liquid two-phase ramjet engine includes a liquid inlet passage, a mixing and vaporization chamber, and a tail nozzle arranged coaxially from left to right; the liquid inlet passage is a circular tube that gradually expands from outside to inside, and the end with a smaller cross-sectional area of the liquid inlet passage is the inlet, and the gradually expanding circular tube decelerates and pressurizes the incoming water flow; a liquefied gas inlet hole is arranged between the liquid inlet passage and the mixing and vaporization chamber for introducing liquefied gas; the mixing and vaporization chamber is a stepped circular cavity, and the cross-sectional areas of the inlet and outlet of the mixing and vaporization chamber are equal to the cross-sectional area of the outlet of the liquid inlet passage. A groove is arranged at the front end inlet of the mixing and vaporization chamber to generate a vortex of the water flow to promote the mixing of water and liquefied gas; the tail nozzle is a variable-area nozzle with a straight pipe section at the front end, and successively includes a straight pipe section, a contraction section, a throat section, and an expansion section from left to right. The cross-sectional area of the inlet of the contraction section is consistent with the cross-sectional area of the outlet of the liquid inlet passage; the straight pipe section is inserted into the cavity wall of the mixing and vaporization chamber, and by adjusting the length of the straight pipe section in the cavity wall of the mixing and vaporization chamber, the mixing and vaporization chamber is extended by the straight pipe section, thereby controlling the boiling ratio of the liquefied gas before the inlet of the contraction section, and finally forming a working fluid with a specified gas content rate and liquefied gas content rate at the inlet of the contraction section, so as to reduce the influence of choking to obtain the maximum thrust; the tail nozzle is used to accelerate the working fluid formed in the mixing and vaporization chamber, and adjust the engine working state by controlling the engine outlet area, enhancing the adaptability of the engine in different environments.

2. The gas-liquid two-phase ramjet engine according to claim 1, wherein The liquid inlet passage is a gradually expanding circular tube, and the expansion half-angle is set between 1° and 60°.

3. The gas-liquid two-phase ramjet engine according to claim 1, wherein, The liquefied gas inlet holes are circular holes, and the liquefied gas inlet holes are uniformly arranged circumferentially between the liquid inlet passage and the mixing and vaporization chamber; the number of the liquefied gas inlet holes is 1 to 16, the hole diameter is 0.8 to 3 mm, and the included angle θ between the center line direction of the liquefied gas inlet hole and the engine axis direction is 10° to 90°.

4. The gas-liquid two-phase ramjet engine according to claim 1, wherein The liquefied gas boils and vaporizes after contacting the water body, and the gas content rate of the mixed fluid at the outlet of the tail nozzle should be between 0.1% and 75%.

5. The gas-liquid two-phase ramjet engine according to claim 1, characterized in that, The cross-sectional areas of the inlet of the mixing and vaporization chamber, the outlet of the mixing and vaporization chamber, the cross-sectional area of the non-groove part of the mixing and vaporization chamber, and the cross-sectional area of the inlet of the contraction section of the tail nozzle are the same as the cross-sectional area of the outlet of the liquid inlet passage, and are set to be 3 to 8 times the cross-sectional area of the inlet of the liquid inlet passage.

6. The gas-liquid two-phase ramjet engine according to claim 1, characterized in that The mixing and vaporization chamber is provided with a groove, the groove depth is set to be 0.2 to 0.7 times the inner diameter of the inlet of the mixing and vaporization chamber, and the length is set to be 0.2 to 1 times the inner diameter of the inlet of the mixing and vaporization chamber; There is an installation cavity in the cavity wall of the mixing and vaporization chamber, in which a spring is fixed. One end of the spring is fixedly connected to the inner wall surface of the mixing and vaporization chamber, and the other end is connected to the straight pipe section of the tail nozzle; a sliding groove is formed between the cavity wall of the mixing and vaporization chamber and the straight pipe section of the tail nozzle, and the slider slides in the sliding groove. The cavity wall of the mixing and vaporization chamber and the straight pipe section of the tail nozzle are positioned by the slider and the sliding groove; a sealing ring is arranged near the outlet of the mixing and vaporization chamber for sealing; the stiffness coefficient of the spring is determined according to the length change of the mixing and vaporization chamber extended by the straight pipe section and the sailing speed, and the length of the mixing and vaporization chamber extended by the straight pipe section is determined according to the sailing speed and the boiling rate of the liquefied gas.

7. The gas-liquid two-phase ramjet engine according to claim 6, characterized in that, The installation cavities are evenly arranged along the circumferential direction in the wall of the mixing and vaporization chamber, and 2 to 8 are set; 2 to 8 springs are set in the installation cavity; the sliders are evenly arranged along the circumferential direction on the outer wall of the straight pipe section of the tail nozzle, and 1 to 16 are set; the slide grooves are evenly arranged along the circumferential direction on the wall of the mixing and vaporization chamber, and the number is consistent with the sliders; the slider can only slide along the axis direction of the engine in the slide groove, and a fixing pin is set at the end of the slide groove to prevent the slider from sliding out.

8. The gas-liquid two-phase ramjet engine according to claim 1, wherein The tail nozzle is a convergent-divergent nozzle with a straight pipe section, including a straight pipe section, a contraction section, a throat section and an expansion section, wherein the straight pipe section is a straight pipe section, the length of which is set at 10 to 30 cm, the contraction half angle of the contraction section is 5° to 45°, the expansion half angle of the expansion section is 1° to 60°, and the cross-sectional area of ​​the throat section is set to 1 to 2 times the cross-sectional area of ​​the inlet of the liquid inlet; The outlet surface of the expansion section of the tail nozzle is adjustable, including a plurality of connected conical segments, a connecting flexible material, an outlet flexible material and a damping rod; when the navigation speed increases, the pressure in the expansion section increases, causing the conical segments to be subjected to an outward expansion force, and when the force is large enough, it overcomes the damping rod, and ultimately the cross-sectional area of ​​the outlet can be varied between 2 and 4 times the cross-sectional area of ​​the inlet of the liquid inlet.

9. The gas-liquid two-phase ramjet engine according to claim 8, characterized in that, The number of the conical segments is 4 to 32; the flexible material should be a waterproof material that can be bent and folded at will; the number of connecting flexible materials connecting the conical segments in pairs is consistent with the number of conical segments; one end of the outlet flexible material is connected to the conical segment or the connecting flexible material, and the other end is connected to the end of the wall of the tail nozzle expansion section, and the number is set to the sum of the number of conical segments and the connecting flexible material; one end of the damping rod is connected to the wall of the tail nozzle expansion section, and the other end is connected to the conical segment, and the number is the same as the number of conical segments.

10. The gas-liquid two-phase ramjet engine according to claim 1, wherein, The liquefied gas is liquefied nitrogen, liquefied helium and R134a.

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