A combustion chamber kit for a liquid propellant laser microthruster

Abstract

The application relates to the field of aerospace technology and discloses a combustion chamber set of a liquid working medium laser microthruster, which comprises a lens seat assembly (1), a back-shaped support frame (2), a window sheet (3) and a micro-flow channel base plate (4) which are sequentially connected; the micro-flow channel base plate (4) comprises a supply pipeline and a flow guide groove; the back-shaped support frame (2) is in a back-shaped structure and is provided with a laser window on the upper portion; the lens seat assembly (1) is provided with a lens; the window sheet (3) is attached to the micro-flow channel base plate (4) and forms a combustion chamber (5); liquid working medium enters the combustion chamber (5) through the supply pipeline; laser light is sequentially converged to the combustion chamber (5) through the lens and the window sheet (3), ablates the liquid working medium, realizes pulse laser ablation, and the liquid working medium which is not completely ablated and laser ablation products flow out through the flow guide groove, so that the combustion chamber (5) is prevented from being blocked and the laser ablation effect is affected.

Description

Technical Field

[0001] This invention relates to the field of aerospace technology, and more specifically to a combustion chamber kit for a liquid working fluid laser micro-thruster. Background Technology

[0002] In recent years, laser micro-thrusters have attracted widespread attention due to their advantages such as small mass, small size, low power consumption, small impulse bit, wide adjustable thrust range, and controllability. Currently, domestic and international laser micro-thrusters are mainly based on the integrated use of solid working fluids. However, solid working fluid laser micro-thrusters suffer from low working fluid mass utilization, resulting in poor thruster performance. Liquid working fluid laser micro-thrusters, based on the synergistic enhancement of chemical energy coupling between laser and liquid working fluid, hold promise for solving these problems. However, the development of liquid working fluid laser micro-thrusters is limited by challenges such as spaceborne laser technology, high-performance working fluid selection and development technology, laser optical path design, and integrated micro-thruster design. To date, there is no mature integrated technology for liquid working fluid laser micro-thrusters, and the development technology for prototype liquid working fluid laser micro-thrusters is still immature.

[0003] The combustion chamber module is a crucial component of the liquid working fluid laser micro-thruster and serves as its power source. Compared to traditional combustion chambers, the miniature combustion chamber of the micro-thruster exhibits the following characteristics: difficulty in matching laser parameters, easily leading to combustion chamber damage; small combustion chamber size, easily causing blockage in the liquid working fluid supply pipeline, making it difficult for the laser and liquid working fluid to work in tandem, adversely affecting combustion stability; large surface area and volume ratio, resulting in increased heat transfer loss, easily causing combustion chamber flameout; and difficult combustion chamber manufacturing and bonding processes, leading to high temperature and high pressure generated by laser ablation of the liquid working fluid, which cannot be directionally transmitted, thus affecting the thruster's propulsion performance.

[0004] Therefore, based on the research experience and technology of laser ablation of liquid working fluid ablation performance, it is urgent to propose new combustion chamber kits and design schemes to enable liquid working fluid laser micro-thrusters that meet higher performance requirements. Summary of the Invention

[0005] To address the aforementioned problems, the purpose of this invention is to provide a combustion chamber kit for a liquid working fluid laser micro-thruster, solving the problems of difficult integration and poor propulsion performance of existing liquid working fluid laser micro-thrusters limited by a 1U volume.

[0006] This invention provides a combustion chamber kit for a liquid working fluid laser micro-thruster, comprising: a lens mount assembly, a U-shaped support frame, a window, and a microchannel substrate connected in sequence;

[0007] The microchannel substrate includes: a supply pipeline and a flow guide; the U-shaped support frame has a U-shaped structure and a laser window is provided on it; the lens mount assembly is equipped with a lens; the window and the microchannel substrate are attached to each other to form a combustion chamber;

[0008] The liquid working medium enters the combustion chamber through the supply pipeline. The laser beam is focused into the combustion chamber through the lens and the window in sequence, ablating the liquid working medium to achieve pulsed laser ablation. The incompletely ablated liquid working medium and laser ablation products flow out through the guide groove to prevent blockage of the combustion chamber and affect the laser ablation effect.

[0009] In one possible implementation, the side of the window that connects to the U-shaped support frame is coated with a film to enhance the energy transmitted by the laser.

[0010] In one possible implementation, the supply pipeline is a rectangular anti-backflow pipeline, used to prevent the laser ablation liquid from flowing back, so that the laser ablation products are sprayed in a directional manner, thereby generating the required thrust.

[0011] In one possible implementation, the lens mount assembly has a boss for limiting the U-shaped support frame.

[0012] In one possible implementation, a sealing membrane is provided between the window and the microchannel substrate to seal the supply pipeline and the aperture, filter out stray light at the ablation location, and prevent stray light from damaging the combustion chamber.

[0013] In one possible implementation, the center points of the lens, the window, and the combustion chamber are on the same straight line.

[0014] In one possible implementation, the microfluidic substrate further includes a nozzle connected to the supply line for spraying a liquid working fluid; the nozzle is a cylindrical nozzle along the laser incident direction.

[0015] In one possible implementation, the laser window of the U-shaped support frame includes a rectangular opening and chamfered holes for the window panels at the four corners of the rectangular opening, the chamfered holes being used to prevent damage to the window panels.

[0016] In one possible implementation, the laser window and the window panel are matched.

[0017] In one possible implementation, the combustion chamber assembly works in conjunction with the laser module, working fluid storage and supply system module, and power control module in the liquid working fluid laser micro-thruster.

[0018] The power control module is used to control the working fluid storage and supply system module, and the laser module and combustion chamber kit work together.

[0019] The working fluid storage and supply system module is used to supply liquid working fluid to the combustion chamber kit;

[0020] The laser module is used to ablate the liquid working fluid in the combustion chamber assembly;

[0021] The combustion chamber assembly is used to provide space for laser ablation and to generate directional thrust.

[0022] The combustion chamber kit for a liquid working fluid laser micro-thruster provided by this invention adopts a miniaturized kit design for the laser micro-thruster combustion chamber module, which is beneficial for the comprehensive integration of the laser micro-thruster; it uses a liquid energetic working fluid as the combustion medium and a stable micro-flow supply method to improve the propulsion performance of the laser micro-thruster combustion chamber module; at the same time, the combustion chamber configuration, laser focusing system, laser window and supply pipeline are designed synchronously to stabilize the combustion chamber performance; and it adopts a micron-scale cylindrical combustion cavity to reduce ablation mass and directional thrust output, improve the specific impulse of the laser micro-thruster, and thus enhance the propulsion performance of the micro-thruster. Attached Figure Description

[0023] Figure 1 This is an overall structural diagram of the combustion chamber kit provided in an embodiment of the present invention;

[0024] Figure 2 A schematic diagram of the installation of the combustion chamber kit provided in an embodiment of the present invention;

[0025] Figure 3(a) is a schematic diagram of the front structure of the microchannel substrate provided in an embodiment of the present invention;

[0026] Figure 3(b) is a schematic diagram of the back structure of the microchannel substrate provided in an embodiment of the present invention;

[0027] Figure 4 This is a schematic diagram of the structure of the spiral support frame provided in an embodiment of the present invention;

[0028] Figure 5(a) is a front view of the lens mount provided in an embodiment of the present invention;

[0029] Figure 5(b) is a schematic diagram of the back structure of the lens mount provided in an embodiment of the present invention;

[0030] Figure 5(c) is a side view of the lens mount provided in an embodiment of the present invention;

[0031] Figure 6 This is a schematic diagram illustrating the ablation principle of the liquid working fluid provided in an embodiment of the present invention. Detailed Implementation

[0032] The embodiments of the present invention will be further described in detail below with reference to the accompanying drawings and examples. The following detailed description of the embodiments and the accompanying drawings are used to illustrate the principles of the present invention by way of example, but should not be used to limit the scope of the present invention. That is, the present invention is not limited to the described preferred embodiments, and the scope of the present invention is defined by the claims.

[0033] In the description of this invention, it should be noted that, unless otherwise stated, "a plurality of" means two or more; the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance; those skilled in the art can understand the specific meaning of the above terms in this invention as appropriate.

[0034] The purpose of this invention is to solve the problems of difficult integration and poor propulsion performance of existing liquid working fluid-based laser micro-thrusters. Figure 1 This is an overall structural diagram of the combustion chamber kit provided in an embodiment of the present invention. Figure 2 This is an installation diagram of the combustion chamber kit provided in an embodiment of the present invention, in conjunction with... Figure 1 and Figure 2 The combustion chamber kit of the liquid working fluid laser micro-thruster of the present invention includes: a lens mount assembly 1, a U-shaped support frame 2, a window 3 and a microchannel substrate 4 connected in sequence; the combustion chamber kit provided by the present invention can be used for the integrated integration of liquid working fluid laser micro-thrusters, and has the function of generating directional thrust by laser ablation of liquid working fluid, and can provide support for the integration of micro-thruster combustion chamber modules and the design of micro-thruster optical paths.

[0035] The microfluidic substrate 4 includes: a supply pipeline and a guide channel; a U-shaped support frame 2 with a U-shaped structure and a laser window on it; a lens mount assembly 1 with a lens installed; and a combustion chamber 5 formed by the window plate 3 and the microfluidic substrate 4 being attached together.

[0036] Figure 6 This is a schematic diagram of the ablation principle of the liquid working fluid provided in the embodiments of the present invention, combined with... Figure 6 The liquid working medium enters the combustion chamber 5 through the supply pipeline. The laser beam is focused into the combustion chamber 5 through the lens and window 3 in sequence, ablation the liquid working medium, and realizes pulsed laser ablation. The liquid working medium that is not completely ablated and the laser ablation products flow out through the guide groove to prevent blockage of the combustion chamber 5 and affect the laser ablation effect.

[0037] Specifically, Figure 3 is a schematic diagram of the microfluidic substrate provided in an embodiment of the present invention. Referring to Figure 3, the microfluidic substrate 4 includes an M3 mounting hole 41, a liquid working fluid injection hole 42, a combustion chamber nozzle 43, a guide groove 44, a limiting boss 45, a supply pipe 46, an anti-backflow supply pipe 47, and a flow channel substrate 48. The liquid working fluid flows into the microfluidic substrate 4 through the injection hole, then enters the micro anti-backflow pipe 50-100μm, and flows into the combustion chamber 5 and the nozzle position. The combustion chamber 5 has a cylindrical shape, with a diameter designed to range from 50-1000μm and a length designed to range from 0-2000μm. The flow rate of the liquid working fluid can be adjusted by the length and shape of the micro anti-backflow pipe. The flow rate of the liquid working fluid is designed to be 2-800 μg / s. The flow rate of the liquid working fluid flowing into the combustion chamber 5 corresponds to the frequency of the pulsed laser ablation, ensuring a fixed amount of working fluid for each laser ablation. A fixed quantity of liquid working fluid is ignited by a high-power-density laser, with the peak power density of the laser designed to be 10⁹-10⁻⁶. 11 W / cm 2 This plasma is then generated inside the combustion chamber 5 and ejected outwards, producing the required thrust. Incompletely ablated liquid working fluid and laser ablation products can flow out through the guide channel to prevent blockage of the combustion chamber 5 and ensure effective laser ablation. The microchannel substrate 4 integrates the liquid supply pipeline, combustion chamber 5, limiting boss, M3 fixing threaded hole, and guide channel. The limiting boss and M3 fixing threaded hole are used to install the combustion chamber assembly.

[0038] Specifically, Figure 4 This is a schematic diagram of the structure of the spiral support frame provided in an embodiment of the present invention, combined with... Figure 4 The U-shaped support frame 2 includes a laser window, a chamfered hole 21 for the window plate, a U-shaped fixing hole 22 for the window plate, a kit mounting hole 23, and a window support frame substrate 24. The laser window component forms a constrained combustion chamber 5 by tightly fitting the laser window and the microchannel substrate 4. The window plate 3 is sealed to the microchannel substrate 4 by a sealing film. External pressure is applied to tightly adhere the window plate 3 to the microchannel substrate 4. The window plate 3 is limited by the U-shaped fixing hole. The thickness of the window plate 3 is designed to be 2mm, and the length and width are both 15mm. The material is designed to be fused silica. The window plate 3 is coated on the laser incident side to enhance the energy of laser transmission. The other side is not designed with an anti-reflection film because repeated laser ablation may damage the anti-reflection film. Effective laser ablation is achieved by optimizing the selection of the sealing film material and the size and position of the sealing film aperture. Under this design, the liquid working fluid enters the combustion chamber through the microchannel. The combustion chamber and the nozzle are along the laser incident direction. The laser passes through the light-transmitting window and ablates the liquid working fluid reaching the combustion chamber 5 and the nozzle position, performing pulsed laser ablation. The U-shaped support bracket 2 has a kit fixing through hole, internal rounded corners, and a square fixing hole for the laser window.

[0039] The microchannel substrate features microchannel shapes including rectangular, semicircular, polygonal, and straight lines. Microchannel supply methods include continuous, pulsed, and intermittent liquid supply. Microfluidic flow control methods include valved and valveless liquid flow control. The microchannel diameter ranges from 0-1 mm. Microchannel cross-sectional shapes include rectangular, square, semicircular, and circular cross-sectional shapes. The combustion chamber 5 nozzle configuration includes direct injection, expanding injection, contracting injection, and combined injection nozzles. The micro-combustion chamber 5 diameter ranges from 0-1 mm. The micro-combustion chamber 5 length ranges from 0-5 mm. The micro-combustion chamber 5 material includes aluminum alloy, titanium alloy, nickel-based alloy, tungsten-based alloy, rhodium-based alloy, and stainless steel. The combustion chamber 5 sealing method can be integral bonding or extrusion.

[0040] Specifically, Figure 5 is a schematic diagram of the lens mount provided in an embodiment of the present invention. Referring to Figure 5, the lens mount assembly 1 includes a lens mount substrate 11, a laser emission port 12, a laser window fixing hole 13, a kit fixing hole 14, a kit fixing hole 15, a laser window position adjustment hole 16, a lens mounting hole 17, a fixing hole 18 for the kit and the thrust prototype, and an optical lens 19 connected by a screw ring. As an important part of the combustion chamber design, the lens mount assembly 1 shapes the beam with the parallel light emitted from the laser, focusing it to a designated working position, thereby achieving effective ablation of the liquid working fluid. To achieve laser-generated plasma, resulting in photoexplosion and combustion, the relative positions of the lens mount optical assembly and the head of the combustion chamber 5 are often related. In this embodiment, the laser ablation position is adjusted by selecting lenses with different optical parameters, laser window thickness, and the thickness of the laser window fixing component and the U-shaped support frame 2. This positioning method is simple and reliable.

[0041] Because lens 19 is a hemispherical converging lens, the size of the ablation spot can be adjusted by adjusting the thickness of the spiral support 2. The size of the ablation spot is similar to the diameter of the combustion chamber 5. This arrangement ensures performance and the simplicity and effectiveness of the combustion chamber assembly structure. The lens 19 in the lens mount can be a spherical lens, an aspherical lens, or a lens group, etc.

[0042] Specifically, the lens mount is mainly used to fix different types of lenses. By changing the lens, the convergence point of the parallel light emitted from the laser can be adjusted, thereby adjusting the size of the ablation spot in the combustion chamber. Four M3 through holes along the laser incident direction on the lens mount are used for fixing and installing the assembly. Four M2 threaded holes are used to fix the laser window 3 to the microchannel substrate 4, ensuring a tight fit between the window 3 and the supply channel. Two M2 through holes perpendicular to the laser incident direction are used to connect to the laser micro-thruster bridge plate, achieving the fixing and installation of the combustion chamber assembly. The boss is used for limiting the U-shaped support frame 2. The lens mount has a boss, assembly fixing through holes, laser window position adjustment holes, fixing threaded holes for connecting to the thruster, and an aluminum alloy substrate.

[0043] In one possible implementation, the supply pipeline is a rectangular anti-backflow pipeline to prevent the backflow of laser ablation liquid, ensuring the directional spraying of laser ablation products and thus generating the required thrust. The pipeline's length and diameter are designed to effectively increase the flow resistance of the liquid supply, enabling continuous supply at a low flow rate. The guide channel allows incompletely ablated liquid to flow out, preventing liquid accumulation at the combustion chamber nozzle and thus affecting the thrust generated by ablation.

[0044] In one possible implementation, the microfluidic substrate 4 also includes a nozzle 6 connected to a supply line for spraying a liquid working fluid; the nozzle 6 is a cylindrical nozzle along the laser incident direction.

[0045] In one possible implementation, the lens mount assembly 1 has a boss for limiting the U-shaped support frame 2.

[0046] In one possible implementation, the side of the window 3 that connects to the U-shaped support frame 2 is coated with a film to enhance the energy of laser transmission.

[0047] In one possible implementation, the laser window of the U-shaped support frame 2 includes a rectangular opening and chamfered holes 21 at the four corners of the rectangular opening. The chamfered holes 21 are used to prevent damage to the window 3.

[0048] In one possible implementation, the laser window and window plate 3 are matched. The laser window portion is a square laser window with high transmittance and high damage threshold. The material of the laser window, used for high energy density laser transmission and combustion chamber confinement sealing film, can be PVC film, PET film, PE film, etc. The material of window plate 3 can be pure quartz, fused silica, zinc sulfide, magnesium fluoride, diamond, etc.

[0049] In one possible implementation, the center points of lens 19, window 3, and combustion chamber 5 are on the same straight line.

[0050] In one possible implementation, a sealing film clamp is disposed between the window 3 and the microchannel substrate 4 to seal the supply pipeline and the aperture, filtering out stray light from the ablation location and preventing stray light from damaging the combustion chamber 5. The sealing film has a PVC film with a circular aperture.

[0051] In one possible implementation, the combustion chamber assembly can be secured using methods such as threaded tightening or integral welding. The working fluid used in the combustion chamber assembly can be HAN-based, ADN-based, methylimidazolium-based, GAP-based, low-melting-point liquid metals, magnetorheological fluids, or nitrate solutions. The pulsed laser ignition method used in the combustion chamber assembly can be single-point, continuous, or intermittent laser ablation modes.

[0052] In one possible implementation, the combustion chamber kit works in conjunction with the laser module, working fluid storage and supply system module, and power control module in the liquid working fluid laser micro-thruster.

[0053] The power control module is used to control the working fluid storage and supply system module, the laser module, and the combustion chamber kit to work together.

[0054] The working fluid supply system module is used to supply liquid working fluid to the combustion chamber kit;

[0055] The laser module is used to ablate the liquid working fluid in the combustion chamber kit;

[0056] The combustion chamber kit is used to provide space for laser ablation and to generate directional thrust.

[0057] The above describes the structure of the combustion chamber kit. The following describes the design methodology of the combustion chamber kit, including:

[0058] Step 1: Overall Design of Combustion Chamber Kit

[0059] The micro thruster mainly consists of a laser module, a working propellant storage and supply system module, a power control module, and a combustion chamber structure.

[0060] The total volume of the micro-thruster is 1U (10cm×10cm×10cm), of which the laser is designed to be 0.15U, the working fluid storage and supply system module is designed to be 0.5U, the power control module is designed to be 0.2U, the combustion chamber is located in front of the laser outlet, and for ease of installation and integration, its volume is designed to be less than 0.03U (length×width×height=15mm×40mm×50mm), and the volume of other structural components is designed to be 0.12U.

[0061] The combustion chamber assembly is secured to the thruster base plate via two through holes connected to threaded holes. The laser ablation mode is designed as a transmission mode, and the working fluid is required to be an energetic liquid propellant with excellent flowability. The laser operating frequency is designed to be 1-100Hz, the working fluid supply flow rate is designed to be 2μg / s-800μg / s, the inlet pressure is designed to be greater than 0.2MPa, and the outlet pressure is designed to be less than 0.1MPa. The combustion chamber nozzle 6 adopts a cylindrical nozzle design along the laser incident direction.

[0062] The combustion kit has outer dimensions of 15mm × 40mm × 50mm. The lens mount has outer dimensions of 9mm × 40mm × 50mm. To ensure laser energy reaches the combustion chamber through the aperture and lens without energy loss, the laser aperture is 4mm, the divergence angle is approximately 7mrad, the internal lens mounting hole diameter is 9mm, and the exit aperture after passing through the optical lens is 7mm. The lens is a high-power-density hemispherical lens with a focal length f = 11mm and NA = 0.18. The size of the circular laser spot focused into the combustion chamber through the lens mount is designed to be 90% of the reference cross-sectional area of ​​combustion chamber 5; that is, when the spot area is 500μm, the cross-sectional area of ​​combustion chamber 5 is approximately 450μm.

[0063] The overall outer dimensions of the laser window and fixture are 3mm × 40mm × 40mm. The laser window is made of fused silica material with a high power threshold and high transmittance at 1064nm, and its outer dimensions are 2mm × 15mm × 15mm. In this example, the laser window transmittance is designed to be 99%, and the laser window breakdown threshold is greater than 10. 9 W / cm 2 The overall outer dimensions of the microchannel and nozzle substrate are 3mm×40mm×40mm. A liquid working fluid injection hole with a diameter of 1mm is provided. A rectangular microchannel supply pipeline is provided, which is connected to the combustion chamber 5 and the nozzle. The nozzle is externally connected to a guide groove. The lens seat assembly 1, the laser window assembly, and the microchannel and nozzle substrate assembly are reinforced and connected by a fixing component to form a combustion chamber kit.

[0064] Because this type of combustion chamber is a subsystem of a space micro-thruster, the focus is on miniaturization, high specific impulse, high total impulse and high stability. Therefore, while ensuring high power density and wide frequency range of the laser, it is also necessary to ensure micro-flow supply and micro-combustion chamber 5 and nozzle design to ensure that the main combustion zone of the combustion chamber is plasma formed by laser ablation of liquid working fluid.

[0065] Step 2: Determine the basic selection of the combustion chamber kit.

[0066] Energetic liquid working fluid is a high-quality working fluid selected for the combustion chamber of laser micro-thruster. It has the characteristics of high laser energy deposition efficiency, high calorific value, and short ignition delay time. When used in the combustion chamber, it mainly adopts pulsed laser ablation mode and adopts a single-channel DC combustion chamber. In order to reduce the influence of pressure backflow during laser ablation, the air participating in the combustion is mainly introduced through anti-backflow micro-pipeline. In order to increase the service life of the combustion chamber (5), the laser emission direction is consistent with the plasma plume jet direction generated by laser ablation in the combustion chamber 5.

[0067] Step 3: Determine the optical path design parameters for the combustion chamber assembly;

[0068] Based on the laser parameters, lens parameters, and nozzle configuration parameters required for the combustion chamber, the laser ablation spot size d, ablation position f, Rayleigh interval F, and energy distribution of the Gaussian spot can be calculated.

[0069]

[0070] In the formula, λ is the incident laser wavelength, D is the laser output aperture, and NA is the numerical aperture of the lens (NA = sin(D / 2f)). According to formula (1), when the laser output aperture is 4 mm, the focal length is 13 mm, and the laser wavelength is 1064 nm, the laser spot size at the focal point is approximately d = 43.43 μm. When the laser output aperture is fixed, the laser spot size can be adjusted according to the focal length of the lens and the distance from the lens. The spot size at the laser focal point is the minimum ablation cross-section of the lens.

[0071]

[0072] According to equation (2), when the laser emission aperture is 4 mm, the focal length is 13 mm, and the laser wavelength is 1064 nm, the Rayleigh interval (focal length) of the laser at the focal point is l = 28.63 μm. When the laser emission aperture is fixed, the focal length at the laser focal point can be adjusted according to the focal length of the lens. The focal length at the laser focal point is designed to be comparable to the absorption depth of the laser.

[0073] I r =I0exp(-8r 2 / d 2 (3)

[0074] In the formula, I0 is the laser energy at the center of the laser spot, I r Let I be the laser energy at different positions from the center of the laser spot, and r be the laser spot radius. According to equation (3), when the laser performs ablation with a Gaussian beam, the laser energy at different positions can be designed according to equation 3. When the laser aperture is 4 mm, the laser spot radius is 0.25 mm, and the laser energy is 40 mJ, the laser energy I at a position 0.25 mm from the center of the laser spot is... r=5.4mJ, indicating that the laser energy decays rapidly from the center outwards. The Gaussian distribution of the laser energy determines the ablation effect; a good ablation effect is achieved only when the laser energy reaches the breakdown threshold of the liquid working medium in the main central region of the laser spot. Therefore, the energy distribution of the laser spot determines the design of the laser ablation spot size.

[0075] Step 4: Determine the design parameters of the U-shaped support frame 2 for the combustion chamber assembly;

[0076] The main function of the combustion chamber spiral support frame 2 is to fix the laser window and, in conjunction with the lens, adjust the size of the laser ablation spot. The thickness of the combustion chamber spiral support frame 2 is designed according to the actual size of the ablation spot. The main method used is to adjust the spot size at the ablation position by adjusting the thickness of the spiral support frame.

[0077]

[0078] In the formula, x is the distance from the ablation spot to the lens exit, d is the spot size, and r is the spot radius. When the focal length of the lens is 13mm and the designed ablation spot is 500μm, the distance from the ablation spot to the lens exit is 11.37mm, the thickness of the U-shaped support frame 2 is designed to be 11.37-9=2.37mm, and its overall external dimensions are 2.37mm×40mm×40mm.

[0079] Step 5: Determine the sealing pressure design parameters for the combustion chamber assembly;

[0080] The combustion chamber assembly design employs four screws to secure the laser window to the microchannel and nozzle substrate, thereby achieving a seal between the microchannel and combustion chamber 5. During the laser ablation of the liquid working fluid, the working fluid supply pressure exceeds 0.2 MPa. A short-term high pressure, typically designed to be 10 MPa, is generated at the connection between combustion chamber 5 and the laser window during laser loading. A sealing pressure exceeding 10 MPa is necessary to ensure that the liquid working fluid does not leak out at the sealing interface during laser ablation.

[0081]

[0082] In the formula, L is the side length of the square laser window, F1, F2, F3, and F4 are the pressures exerted by the four screws on the laser window, and P is the sealing pressure. When the diameter of the combustion chamber 5 is 0.5 mm and the designed sealing pressure is greater than 10 MPa, the screw clamping force is approximately 1.96 N. If the clamping forces F1, F2, F3, and F4 of the four screws are the same, the clamping force of a single screw is approximately 0.5 N. The structural parameters of the screws can be designed based on the screw clamping force.

[0083] Step 6: Determine the laser window design parameters for the combustion chamber kit;

[0084] The design of the laser window must consider the laser's damage threshold. When the laser power density exceeds the laser window's damage threshold, the laser window is severely damaged and cannot transfer laser energy to the working fluid. Therefore, when a laser ablates a liquid working fluid under high repetition rate conditions, the laser's peak power density should be less than the laser window's damage threshold.

[0085]

[0086] In the formula, J is the peak power density of the laser, E is the laser energy, τ is the laser pulse width, and d is the ablation spot size. When the laser energy is 40 mJ, the laser pulse width is 10 ns, and the ablation spot size is 500 μm, the peak power density of the laser should be less than 2.04 × 10⁻⁶. 9 W / cm 2 Similarly, the threshold for plasma generation by laser ablation of the same liquid working fluid should also be less than 2.04 × 10⁻⁶. 9 W / cm 2 Only in this way can a good ablation effect be guaranteed.

[0087] Besides the damage threshold of the laser window, its transmittance is another crucial indicator, significantly influencing the transfer of laser energy to the liquid working medium. Therefore, the design of the laser window must consider the incident wavelength of the laser, the material of the laser window, and minimizing the laser energy reflected and scattered through the window. According to Beer-Lambert's law:

[0088]

[0089] In the formula, T is the transmittance, I is the energy of the laser passing through the window, I0 is the initial energy of the laser, k is the absorption coefficient of the laser window, and x is the thickness of the laser window. This design uses high-purity fused silica material with a low absorption coefficient. The thickness of the laser window is 2 mm, and its absorption coefficient at 1064 nm is 0.0005 cm⁻¹. -1 Therefore, the transmittance of laser light through the quartz window is 99.99%.

[0090] Step 7: Determine the design parameters of the microchannels and nozzle substrate of the combustion chamber kit;

[0091] The substrate of the microchannels and nozzles mainly features a liquid working fluid supply microchannel, a combustion chamber nozzle, and a fixing assembly for the combustion chamber assembly. The supply microchannel utilizes single or multiple sets of rectangular anti-backflow channels to design flow resistance, thereby achieving the liquid working fluid mass flow rate design for coordinated laser operation. For a microchannel of length L, its flow resistance can be calculated using the following formula:

[0092]

[0093] In the formula, Q is the volumetric flow rate, b is the width of the microchannel, a is the depth of the microchannel, ΔP is the pressure difference between the inlet and outlet of the microchannel, μ is the viscosity of the liquid working fluid, and L is the viscosity of the liquid working fluid. This design employs a single-unit rectangular anti-backflow design. The width of the microchannel is 100 μm, the total length of the microchannel is 11 mm, the viscosity of the liquid working fluid is 1.01 × 10³ Pa·s, and when the pressure difference between the inlet and outlet of the microchannel is 0.3 MPa, the corresponding volumetric flow rate is 13.3 nL / s. Considering the density of the liquid working fluid is 1.37 g / cm³,... 3 This corresponds to a mass flow rate of 9.7 μg / s. Therefore, the structural parameters and supply pressure of the microchannel can be adjusted to obtain the required liquid working fluid supply mass flow rate.

[0094] The nozzle in combustion chamber 5 is a key component for generating the thrust required by laser ablation of the liquid working medium. As considered in the laser spot design, the laser spot size should be close to the nozzle diameter. Therefore, the diameter of the nozzle in combustion chamber 5 is designed to be 0.5 mm. The laser ablation of the liquid working medium in combustion chamber 5 generates high-temperature, high-pressure plasma and gas-liquid two-phase ablation products. The nanosecond laser loading process is extremely fast; temperature and pressure reach their optimal values ​​in a short time and then rapidly decay. Therefore, a straight nozzle configuration (6) is adopted. The length of nozzle 6 should not be too long, mainly because an excessively long nozzle 6 would cause the plume to be lost inside combustion chamber 5. A nozzle that is too short would increase the splash angle of the laser ablation products, thus affecting the required directional thrust. According to simulation results, when the length-to-diameter ratio of the straight nozzle is 2-3, laser ablation has better propulsion performance. Based on these reasons, the ablation spot size is 0.5 mm, and the length of the combustion chamber nozzle is designed to be 1.5 mm.

[0095] Step 8: Determine the combustion chamber ignition method.

[0096] The liquid working fluid in the combustion chamber is ablated using a pulsed laser ablation mode, which is mainly attributed to the following characteristics of the pulsed laser ablation mode:

[0097] (1) Pulse ablation mode is the main working mode of static experiments under laboratory conditions;

[0098] (2) The pulsed ablation mode laser has high energy utilization and better propulsion performance;

[0099] (3) The time gap between laser pulses is beneficial for heat dissipation of the laser;

[0100] (4) The average power of the pulse ablation mode will decrease, which can effectively reduce the power consumption of the micro-thruster.

[0101] When ablates a liquid working medium with a laser, a continuous micro-flow supply mode is adopted, and the laser frequency is matched with the liquid working medium flow rate for coordinated operation. Therefore, the laser operating frequency is designed as follows:

[0102]

[0103] In the formula, f is the laser operating frequency, V is the volume of the liquid working medium in the combustion chamber 5, Q is the volumetric flow rate of the liquid working medium, d is the diameter of the combustion chamber 5, and L is the thickness of the liquid working medium (20 μm). When the diameter of the combustion chamber 5 is 500 μm, the thickness of the liquid working medium layer is [missing value], and the volumetric flow rate of the working medium is 10 nL / s, the laser operating frequency is designed to be 2.5 Hz. However, in actual use, the ionization rate of the liquid working medium is not high, and some working medium remains on the inner wall of the combustion chamber 5. Therefore, a higher laser frequency is needed to ablate the liquid working medium adhering to the inner wall of the nozzle 6, thereby achieving effective utilization of the working medium.

[0104] This invention employs a miniaturized kit design for the combustion chamber assembly of a laser micro-thruster, which facilitates the comprehensive integration of laser micro-thrusters and provides a solution for the design of miniaturized, high-performance laser micro-thrusters. Using a liquid energetic working medium as the combustion medium and a stable micro-flow supply further improves the propulsion performance of the laser micro-thruster combustion chamber module. Simultaneous design of the combustion chamber configuration, laser focusing system, laser window, and supply pipeline stabilizes the combustion chamber performance. The micron-scale cylindrical combustion cavity 5 helps reduce ablation mass and directional thrust output, increasing the specific impulse of the laser micro-thruster and thus enhancing its propulsion performance. This invention standardizes the design process for the combustion chamber of a miniature laser micro-thruster using a liquid energetic working medium and, based on this design process, designs a combustion chamber kit structure with stable performance that meets design requirements. Detailed design of the laser optical path, laser window, and liquid working medium supply pipeline assembly effectively solves the problems of poor propulsion performance in the comprehensive design of miniaturized laser micro-thrusters.

[0105] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A combustion chamber kit for a liquid working fluid laser micro-thruster, characterized in that, include: The lens mount assembly (1), the U-shaped support frame (2), the window plate (3), and the microchannel substrate (4) are connected in sequence. The microfluidic substrate (4) includes: a supply pipeline and a guide channel; the U-shaped support frame (2) has a U-shaped structure and a laser window is provided on it; the lens seat assembly (1) is equipped with a lens (19); the window piece (3) is attached to the microfluidic substrate (4) to form a combustion chamber (5). The liquid working medium enters the combustion chamber (5) through the supply pipeline. The laser beam is focused into the combustion chamber (5) through the lens (19) and the window (3) in sequence, ablates the liquid working medium, and realizes pulsed laser ablation. The liquid working medium that is not completely ablated and the laser ablation products flow out through the guide groove to prevent blockage of the combustion chamber (5) and affect the laser ablation effect. The supply pipeline is a rectangular anti-backflow pipeline, which is used to prevent the backflow of laser ablation liquid and to direct the laser ablation products to generate the required thrust.

2. The combustion chamber kit according to claim 1, characterized in that, The side of the window (3) that is connected to the U-shaped support frame (2) is coated with a film to enhance the energy of laser transmission.

3. The combustion chamber kit according to claim 1, characterized in that, The lens mount assembly (1) has a boss for limiting the position of the spiral support frame (2).

4. The combustion chamber kit according to claim 1, characterized in that, A sealing membrane clamp is provided between the window (3) and the microchannel substrate (4) to seal the supply pipeline and the aperture, filter out stray light at the ablation location, and prevent stray light from damaging the combustion chamber (5).

5. The combustion chamber kit according to claim 1, characterized in that, The center points of the lens (19), the window (3), and the combustion chamber (5) are on the same straight line.

6. The combustion chamber kit according to claim 1, characterized in that, The microfluidic substrate (4) also includes a nozzle (6) connected to the supply pipeline for spraying liquid working fluid; the nozzle (6) is a cylindrical nozzle along the laser incident direction.

7. The combustion chamber kit according to claim 1, characterized in that, The laser window of the spiral support frame (2) includes a rectangular opening and chamfered holes (21) on the four corners of the rectangular opening. The chamfered holes (21) are used to prevent damage to the window (3).

8. The combustion chamber kit according to claim 1, characterized in that, The laser window and the window piece (3) are matched.

9. The combustion chamber kit according to claim 1, characterized in that, The combustion chamber kit works in conjunction with the laser module, working fluid storage and supply system module, and power control module in the liquid working fluid laser micro-thruster. The power control module is used to control the working fluid storage and supply system module, and the laser module and combustion chamber kit work together. The working fluid storage and supply system module is used to supply liquid working fluid to the combustion chamber kit; The laser module is used to ablate the liquid working fluid in the combustion chamber assembly; The combustion chamber assembly is used to provide space for laser ablation and to generate directional thrust.

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