Electrically controlled thrust-regulating capillary ion liquid electrospray thruster

Abstract

The application discloses a capillary type ion liquid electric spray thruster with electrically controlled thrust, and belongs to the technical field of micro-nano satellite micro propulsion. The application comprises a propellant tank, an upper shell, a constant force spring, a limiting plate, a capillary and an extraction electrode. The inner and outer walls of the capillary are covered with a dielectric layer with a micron level thickness, and the inner wall is covered with a hydrophobic layer with a nanometer level thickness. The extraction electrode is fixed through an insulating screw; and the upper shell is fixed with the propellant tank. The application is based on the principle of electric wetting, uses an electric field to control the active supply of ion liquid and simultaneously adjusts the thrust size of the thruster. The application can not only save complicated fluid control components such as high-precision pumps, valves and pipelines, but also can couple the supply process and the emission process of the ion liquid, simplify the operation process of the thruster system and facilitate the miniaturization of the thruster system. The application is suitable for resistance compensation, position keeping and attitude control of low-power micro-nano satellites.

Description

Technical Field

[0001] The invention relates to a capillary ionic liquid electrospray thruster with electrically controlled thrust adjustment, belonging to the technical field of micro-nano satellite micro-propulsion. Background Art

[0002] Low cost, short development cycle, and flexible launch are the main advantages of micro-nanosatellites. Currently, micro-nanosatellites have been widely applied in fields such as communications, remote sensing, Earth observation, and space experimentation, and hold great promise. Due to the limitations of total power, mass, and size, micro-nanosatellites' propulsion systems must possess low power consumption, light weight, compact size, long lifespan, and precise thrust. The ionic liquid electrospray thruster (ILET), with its compact size, light weight, high specific impulse, and high thrust precision, meets these requirements and is an ideal propulsion system for micro-nanosatellites. However, its use of a liquid propellant places high demands on flow control. Traditional capillary ILETs often rely on high-precision pumps and valves controlled by differential pressure to supply the propellant. However, these systems are complex, bulky, and technically challenging, hindering the miniaturization and integration of the thruster. Summary of the Invention

[0003] In order to simplify the supply process of a capillary ionic liquid electrospray thruster and reduce the volume of the capillary ionic liquid electrospray thruster, the main purpose of the present invention is to provide a capillary ionic liquid electrospray thruster with electronically controlled thrust adjustment. The thruster is based on the principle of electrowetting and uses an electric field to change the wettability between the ionic liquid and the capillary emitter, controlling the flow of the ionic liquid in the capillary channel to achieve active supply of propellant. The present invention not only eliminates complex fluid control components such as high-precision pumps, valves, and pipelines, but also couples the ionic liquid supply process and the launch process, simplifying the operation process of the thruster system and facilitating the miniaturization of the thruster system.

[0004] The purpose of the present invention is achieved through the following technical solutions.

[0005] The invention discloses a capillary ionic liquid electrospray thruster with electrically controlled thrust adjustment, comprising a propellant tank, an upper shell, a constant force spring, a limit plate, a capillary, and an extraction electrode.

[0006] The inner and outer walls of the capillary are covered with a micrometer-thick dielectric layer, while the inner wall is covered with a nanometer-thick hydrophobic layer. The capillary and the upper shell are fixed to the corresponding holes in the upper shell using an interference fit. The extraction electrode is fixed with an insulating screw and maintained at a predetermined distance from the capillary through a groove in the upper shell. The upper shell is fixed to the propellant tank. One end of the constant force spring is fixed to the groove at the bottom of the propellant tank, and the other end is fixed to the limit plate. In the initial state, the propellant tank is filled with ionic liquid. Due to the influence of the hydrophobic layer, the ionic liquid cannot enter the capillary tube under the microgravity of space. Subsequently, an alternating positive and negative square wave voltage is applied between the ionic liquid and the capillary tube, changing the wettability of the ionic liquid with the capillary tube and controlling the flow of ionic liquid into the capillary tube, thus achieving active supply of ionic liquid. At the same time, the ionic liquid delivered to the end of the capillary tube forms a Taylor cone under the action of the high electric field to emit charged particles, achieving coupled supply and emission of ionic liquid.

[0007] By controlling the applied square wave voltage, the liquid supply mass flow rate and thrust are controlled. Since the ionic liquid is only affected by surface tension and viscous resistance when flowing in the capillary, the liquid flow rate can be approximated to a uniform velocity once the flow stabilizes. For charged particles, the equivalent conversion of electrical energy into particle kinetic energy is achieved, and the thrust is calculated using the following formula:

[0008]

[0009] Where n is the number of capillaries, ρ is the density of the ionic liquid, γ is the surface tension coefficient of the ionic liquid, μ is the dynamic viscosity of the ionic liquid, r is the radius of the capillary wall, θ0 is the initial contact angle between the ionic liquid and the hydrophobic dielectric layer, ε0 is the vacuum dielectric constant, and ε r is the dielectric constant of the dielectric layer material, d is the thickness of the dielectric layer, U is the amplitude of the loaded square wave voltage, q is the charge of the emitted charged particles, is the average mass of the emitted charged particles.

[0010] Preferably, the dielectric layer material covering the capillary surface includes silicon dioxide and parylene; and the hydrophobic layer material is a fluorine-containing polymer.

[0011] Preferably, there is at least one corresponding hole between the capillary tube and the upper shell.

[0012] Preferably, the insulating material is required to have a high dielectric constant; the hydrophobic layer material is required to have a low surface free energy.

[0013] Preferably, the elastic force provided by the constant force spring only needs to overcome the viscous resistance of the ionic liquid flowing in the propellant tank and the friction resistance encountered by the limit plate movement, so that the limit plate moves with the ionic liquid to prevent the ionic liquid in the propellant tank from being in a floating state.

[0014] The present invention discloses an operating method for a capillary ionic liquid electrospray thruster with electrically controlled thrust adjustment. In a space environment, the ionic liquid in the propellant tank is primarily affected by surface tension. Initially, the ionic liquid and the capillary are in a non-wetting state and cannot enter the capillary channel under capillary action. When operation is required, the ionic liquid is connected to a positive and negative alternating square wave voltage with a 50% duty cycle. The capillary and the extractor are grounded, causing electrowetting on the inner wall of the capillary. This reduces the surface free energy of the inner wall of the capillary, causing the ionic liquid and the capillary to become wetted. Under capillary action, the ionic liquid in the propellant tank flows along the capillary channel to the end. Simultaneously, a high electric field is formed between the end of the capillary and the extractor. Under the action of the high electric field, the ionic liquid at the end of the capillary forms a Taylor cone, emitting charged particles. The charged particles are accelerated in the electric field and ejected from the holes in the extractor to generate thrust, thus coupling the ionic liquid supply and emission processes. As the ionic liquid flows out of the propellant tank, the stopper plate slowly moves under the action of the constant force spring, ensuring that the ionic liquid is always in contact with the capillary, thereby ensuring continuous and stable operation of the thruster. When the thrust level needs to be changed, simply change the amplitude of the applied square wave voltage to achieve active and efficient propellant supply, thereby actively and precisely adjusting the thrust.

[0015] Beneficial effects

[0016] 1. The capillary ionic liquid electrospray thruster with electronically controlled thrust adjustment disclosed in the present invention is based on the principle of electrowetting and uses an electric field to change the wettability between the ionic liquid and the capillary emitter to achieve active, efficient and precise flow control of the thruster.

[0017] 2. Conventional capillary ionic liquid electrospray thrusters often use extremely high-precision pumps and valves, controlling the supply of ionic liquid via a pressure differential method. This results in a complex structure and hinders miniaturization of the thruster. The capillary ionic liquid electrospray thruster with electronically controlled thrust control controls the supply via a voltage applied between the capillary and the ionic liquid, eliminating the need for complex pumps, pipes, and valves. This significantly reduces the size and weight of the thruster, facilitating miniaturization of the thruster system.

[0018] 3. Conventional capillary ionic liquid electrospray thrusters control the liquid supply and launch processes separately, making operation complex. The capillary ionic liquid electrospray thruster with electronically controlled thrust adjustment disclosed in the present invention couples the ionic liquid supply and launch processes, simplifying the thruster's operation and improving the efficiency of active propellant supply. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a cross-sectional view of a capillary ionic liquid electrospray thruster with electronically controlled thrust adjustment according to the present invention;

[0020] Figure 2 Schematic diagram of the upper shell;

[0021] Figure 3 Schematic diagram of the capillary covered with dielectric layer and hydrophobic layer.

[0022] Among them: 1-propellant tank, 2-upper shell, 3-constant force spring, 4-limiting plate, 5-capillary, 6-extraction pole. DETAILED DESCRIPTION

[0023] In order to better illustrate the purpose and advantages of the present invention, the invention is further described below with reference to the accompanying drawings and examples.

[0024] Example 1:

[0025] like Figure 1 As shown, the present embodiment discloses a capillary ionic liquid electrospray thruster with electrically controlled thrust adjustment, comprising a liquid storage tank 1, an upper shell 2, a constant force spring 3, a limit plate 4, a capillary 5, and an extraction electrode 6.

[0026] The propellant tank 1 is made of polyetheretherketone, 20 mm long, 20 mm wide, 10 mm high, and 2 mm thick. A circular groove is provided at the bottom for fixing the constant force spring 3, 2 mm in diameter and 1 mm deep.

[0027] The upper shell 2 is made of polyetheretherketone (PEEK), measuring 20 mm long, 20 mm wide, and 6 mm high. It has 100 evenly distributed holes (1 mm in diameter) in the center to accommodate the capillaries 5. A 1 mm deep groove is provided at the top to control the distance between the capillaries 5 and the extraction electrode 6.

[0028] Capillary tube 5 is made of stainless steel, 5 mm long, with an outer diameter of 0.8 mm and an inner diameter of 0.6 mm. To prevent high voltage from breaking down the dielectric layer, the inner and outer walls of capillary tube 5 are coated with 400 μm of N-type parylene, a material with a high dielectric constant. The inner wall is additionally coated with 500 nm of a fluoropolymer with low surface free energy, resulting in excellent dielectric and hydrophobic properties. One hundred treated capillaries 5 are placed in the holes of upper housing 2.

[0029] The ionic liquid is 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI-BF4), and its contact angle with the inner wall of the capillary 6 is 100° in the initial state.

[0030] The limit plate 4 is made of polyetheretherketone, 16mm long, 16mm wide and 1mm high. The bottom is connected to the constant force spring 3. It is surrounded by a silicone pad to prevent liquid from passing between it and the inner wall of the propellant tank 1.

[0031] This embodiment discloses an electronically controlled capillary ionic liquid electrospray thruster operating method as follows: In a space environment, the ionic liquid in the propellant tank 1 is primarily affected by surface tension during its static state. Initially, the ionic liquid in the propellant tank 1 is in a non-wetting state with the inner wall of the capillary 5, preventing it from entering the capillary 5 due to capillary action. When operation is required, the ionic liquid is connected to a 4000V square wave voltage with a duty cycle of 50% and alternating positive and negative amplitudes. The capillary 5 and the extractor 6 are grounded, causing electrowetting of the inner wall of the capillary 5. This reduces the surface free energy of the inner wall of the capillary 5, causing the ionic liquid and the capillary 5 to become wetted. Under capillary action, the ionic liquid in the propellant tank 1 flows along the capillary channel to the end. Simultaneously, a high electric field is formed between the end of the capillary 5 and the extractor 6. Under the action of the high electric field, the ionic liquid at the end of the capillary 5 forms a Taylor cone, subsequently emitting charged particles. These charged particles are accelerated in the electric field and ejected from the holes in the extractor 6, generating thrust. As the ionic liquid flows out of the propellant tank 1, the limit plate 4 slowly moves under the action of the constant-force spring 3, ensuring that the ionic liquid is always in contact with the capillary 5, thereby maintaining the thruster's stable operation. To increase or decrease the thrust, the applied voltage amplitude can be increased or decreased, while ensuring that the dielectric layer does not break down, thereby varying the thruster's mass flow rate and accelerating electric field.

[0032] The above specific description further illustrates the purpose, technical solutions and beneficial effects of the invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A capillary ionic liquid electrospray thruster with electronically controlled thrust adjustment, characterized in that: It includes a propellant tank, an upper shell, a constant force spring, a limit plate, a capillary tube, and an extraction electrode; The inner and outer walls of the capillary are covered with a dielectric layer of micron-scale thickness, and the inner wall is covered with a hydrophobic layer of nanometer-scale thickness. The capillary and the upper shell are fixed in the corresponding holes of the upper shell by interference fit; the extraction electrode is fixed by an insulating screw and maintains a predetermined distance from the capillary through the groove of the upper shell; the upper shell is fixed to the propellant tank; one end of the constant force spring is fixed to the groove at the bottom of the propellant tank, and the other end is fixed to the limit plate; in the initial state, the ionic liquid fills the propellant tank. Due to the influence of the hydrophobic layer, the ionic liquid cannot enter the capillary under the microgravity of space. An alternating positive and negative square wave voltage is loaded between the ionic liquid and the capillary to change the wettability of the ionic liquid and the capillary, control the flow of the ionic liquid into the capillary, and realize the active supply of the ionic liquid; at the same time, the ionic liquid transported to the end of the capillary forms a Taylor cone to emit charged particles under the action of a high electric field, thereby realizing the coupling of ionic liquid supply and emission; By controlling the applied square wave voltage, the liquid supply mass flow rate and thrust are controlled. Since the ionic liquid is only affected by surface tension and viscous resistance when flowing in the capillary, the liquid flow rate can be approximately uniform when the flow stabilizes. For charged particles, the electrical energy is equivalent to being fully converted into particle kinetic energy, and the thrust is calculated using the following formula: Where n is the number of capillaries, ρ is the density of the ionic liquid, γ is the surface tension coefficient of the ionic liquid, μ is the dynamic viscosity of the ionic liquid, r is the radius of the capillary wall, θ0 is the initial contact angle between the ionic liquid and the hydrophobic dielectric layer, ε0 is the vacuum dielectric constant, and ε r is the dielectric constant of the dielectric layer material, d is the thickness of the dielectric layer, U is the amplitude of the loaded square wave voltage, q is the charge of the emitted charged particles, is the average mass of the emitted charged particles.

2. The capillary ionic liquid electrospray thruster with electrically controlled thrust adjustment according to claim 1, characterized in that: The dielectric layer material covering the capillary surface includes silicon dioxide and parylene; the hydrophobic layer material is a fluorine-containing polymer.

3. The capillary ionic liquid electrospray thruster with electronically controlled thrust adjustment according to claim 1, characterized in that: There is at least one corresponding hole between the capillary tube and the upper shell.

4. The capillary ionic liquid electrospray thruster with electronically controlled thrust adjustment according to claim 1, characterized in that: The insulating material is required to have a high dielectric constant; the hydrophobic layer material is required to have a low surface free energy.

5. The capillary ionic liquid electrospray thruster with electronically controlled thrust adjustment according to claim 1, characterized in that: The elastic force provided by the constant force spring only needs to overcome the viscous resistance of the ionic liquid flowing in the propellant tank and the friction resistance encountered by the limit plate, so that the limit plate moves with the ionic liquid to prevent the ionic liquid in the propellant tank from being in a floating state.

6. The capillary ionic liquid electrospray thruster with electronically controlled thrust adjustment according to claim 1, characterized in that: In the space environment, the ionic liquid in the propellant tank is mainly affected by surface tension. In the initial state, the ionic liquid and the capillary are in a non-wetting state and cannot enter the capillary tube under the capillary action. When it needs to work, the ionic liquid is connected to a positive and negative alternating square wave voltage with a duty cycle of 50%, and the capillary and the extraction electrode are grounded, so that the inner wall of the capillary tube undergoes electrowetting, the surface free energy of the inner wall of the capillary tube is reduced, and the ionic liquid and the capillary tube become in a wetting state. Under the capillary action, the ionic liquid in the propellant tank flows along the capillary tube to the end. At the same time, the end of the capillary tube A high electric field is formed between the capillary and the extraction electrode. Under the action of the high electric field, the ionic liquid at the end of the capillary forms a Taylor cone, emitting charged particles. The charged particles are accelerated in the electric field and ejected from the holes of the extraction electrode to generate thrust, forming a coupling of the ionic liquid supply and emission process; as the ionic liquid flows out of the propellant tank, the limit plate moves slowly under the action of the constant force spring, so that the ionic liquid is always in contact with the capillary, so that the thruster continues to work stably; when the thrust size needs to be changed, it is only necessary to change the amplitude of the loaded square wave voltage to achieve active and efficient supply of propellant, and then actively and accurately adjust the thrust.

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