A solid rocket engine combustion particle wide diameter remote in-situ measurement system

Abstract

This invention discloses a wide-range in-situ measurement system for solid rocket motor combustion particles, comprising: a first beam-splitting prism for splitting an incident converging beam into two paths, the first path being an upward-reflected upper beam at 90°, and the second path being a relay beam transmitted to the right; a second beam-splitting prism for splitting the relay beam into two paths, the first path being a central beam transmitted to the right, and the second path being a downward-reflected lower beam at 90°; a first reflecting prism and a second reflecting prism, the first reflecting prism being used to deflect the upper beam from the first beam-splitting prism by 90° into a first beam propagating horizontally to the right, and the second reflecting prism being used to deflect the lower beam from the second beam-splitting prism by 90° into a second beam propagating horizontally to the right; this invention enables wide-range (1-1000 μm) real-time and synchronous visual measurement of the particle size of solid rocket motor condensation combustion products.

Description

Technical Field

[0001] This invention belongs to the field of optical measurement, and in particular relates to a long-distance in-situ measurement system for wide-diameter combustion particles in solid rocket engines. Background Technology

[0002] Solid rocket engines often employ aluminum-containing composite propellants. The addition of aluminum not only effectively improves the engine's energy characteristics but also significantly suppresses combustion instability. The combustion of aluminum-containing composite propellants generates condensed combustion products (mainly alumina particles). The particle size distribution and dynamic evolution characteristics of these condensed combustion particles determine their behavior within the combustion chamber, making them key factors in controlling engine energy performance and combustion instability. From an energy performance perspective, the particle size of condensed combustion particles directly determines the level of two-phase flow losses: excessively large particles cannot fully expand and perform work with the combustion gas flow, leading to severe two-phase flow losses and reducing the engine's specific impulse. Simultaneously, particle size significantly affects the erosion and deposition behavior of the nozzle inner wall, thus impacting engine efficiency and structural lifespan. From a combustion stability perspective, particles of different sizes have a dual effect on the combustion chamber's acoustic field, exhibiting both acoustic damping and acoustic gain. The particle size distribution of condensed combustion particles is a core factor in inducing or suppressing combustion instability. Therefore, accurately measuring the wide-range particle size distribution of condensed combustion products in the combustion field is of significant guiding importance for propellant formulation optimization and engine design.

[0003] Currently, the traditional method for measuring the particle size of condensed phase particles in solid rocket motors mainly relies on particle collection. This involves collecting condensed combustion products at the engine nozzle exit or plume, and then obtaining particle size distribution data through sieving and particle size analyzers. While this method can cover a wide particle size range of 1-1000 μm, it does not capture the condensed combustion products within the combustion chamber. After exiting the combustion chamber, particles undergo secondary combustion, collision agglomeration, and fragmentation within the nozzle and at the nozzle exit, significantly altering their particle size distribution and failing to accurately reflect the particle size distribution within the combustion chamber. Furthermore, this method only obtains the average particle size result throughout the entire experimental process and cannot capture the dynamic evolution of particle size in real time. Existing visualization measurement technologies can achieve online measurement of condensed-phase combustion particles, but they suffer from several core problems and cannot be adapted to the extreme test scenarios of solid rocket motors. Current high-speed microscopic imaging and other technologies rely on high-speed cameras to capture particles, but the resolution limitations of high-speed cameras prevent them from simultaneously covering a wide particle size range of 1-1000 μm. Measurements can only be performed through multiple independent engine ignition tests, using imaging systems with different magnifications to measure particles in corresponding size ranges—for example, using a 1-2x low-magnification system to measure large particles of 200-1000 μm, a 3-5x medium-magnification system to measure medium-sized particles of 100-200 μm, and a 5-10x high-magnification system to measure small particles of 1-100 μm. However, data from different particle size ranges obtained in different tests cannot be correlated and compared under the same temporal and spatial reference. Industrial-grade ultra-large format high-resolution cameras can simultaneously achieve a wide field of view and high resolution, but they cannot achieve high sampling rates and therefore cannot capture the transient state of condensed-phase particles moving at high speeds of hundreds of meters per second within the combustion chamber.

[0004] To address the asynchronous nature of multiple measurements, existing technologies have attempted to utilize beam splitting techniques to construct multi-path imaging systems, aiming for synchronous measurements across a wide particle size range. However, this approach is limited by the extremely short focusing distance at high magnifications, making it difficult to incorporate multiple beam splitters within a confined physical space. Imaging systems with different magnifications exhibit significant differences in their working focal lengths and conjugate distances, hindering the synchronous coupling and common field-of-view alignment of multiple optical paths. Furthermore, existing optical measurement methods face a contradiction: high-temperature environments require long-distance setups, while high-magnification macro measurements necessitate close-range focusing. Solid rocket motor combustion chambers operate at temperatures exceeding 3000K, and intense thermal radiation can cause irreversible thermal damage to closely positioned optical components. Conversely, the extremely short working focal lengths of high-magnification macro systems prevent clear imaging from locations far from the high-temperature combustion chamber, further limiting the adaptability of existing online measurement technologies. Summary of the Invention

[0005] The purpose of this invention is to provide a wide-range, in-situ measurement system for combustion particles in solid rocket engines, in order to solve the problem of the difficulty in achieving wide-range, synchronous, and real-time measurement of condensed combustion products in solid rocket engines.

[0006] This invention employs the following technical solution: a long-distance in-situ measurement system for wide particle size of solid rocket motor combustion particles, comprising: The first beam splitter prism has its incident surface facing the observation window of the solid rocket engine combustion chamber. An optical converging structure is also provided between the combustion chamber and the first beam splitter prism. The optical converging structure is used to image the combustion particles in the combustion chamber through the observation window and to accurately converge parallel scattered light from different angles on the object side to the image-side focal point on the image-side focal plane. The first beam splitter prism is located on the converging light path between the optical converging structure and the image-side focal point. The first beam splitter prism is used to split the incident converging beam into two paths: the first path is an upward beam reflected at 90°, and the second path is a relay beam transmitted to the right. The second beam splitter is positioned in the output light path of the first beam splitter. The incident surface of the second beam splitter faces the transmission and output surface of the first beam splitter. The second beam splitter is used to split the relay beam into two paths: the first path is the main beam transmitted to the right, and the second path is the lower beam reflected 90° downwards. The first reflecting prism and the second reflecting prism have their incident surfaces facing the upper exit surface of the first beam splitter. The first reflecting prism is used to fold the upper beam from the first beam splitter by 90° into a first beam that propagates horizontally to the right. The second reflecting prism has its incident surfaces facing the lower exit surface of the second beam splitter. The second reflecting prism is used to fold the lower beam from the second beam splitter by 90° into a second beam that propagates horizontally to the right. Among them, the central main beam, the first beam, and the second beam all carry holographic information of the burning particles and are incident on the corresponding macro lenses, which then image and capture the beams carrying the holographic information.

[0007] The beneficial effects of this invention are: This invention enables real-time, synchronous visualization measurement of the particle size of solid rocket motor condensation combustion products over a wide range (1-1000 μm). This invention enables in-situ, non-contact measurement of condensed particles in the combustion flow field, eliminating the need for nozzle outlet sampling and avoiding measurement distortion caused by changes in particle state. The acquired particle size data perfectly matches the actual high-temperature and high-pressure conditions inside the combustion chamber. A single transient test can simultaneously capture particle data across the entire particle size range of 1μm to 1000μm, solving the problem of traditional techniques where multiple test data cannot be correlated spatiotemporally. This significantly reduces test costs and improves the integrity and continuity of particle size distribution data. This invention decouples the measurement distance from the back-end magnification. The front-end optical converging structure only performs angle and position transformations and does not participate in the magnification. This ensures a safe protection distance between the optical elements and the high-temperature combustion chamber, while also allowing for flexible magnification adjustment via the back-end macro lens to achieve clear imaging of small particles. This solves the inherent contradiction between high-temperature long-distance arrangement and macro close-range focusing in existing technologies, and significantly improves the system's adaptability to extreme engine operating conditions. This invention predefines unique, non-overlapping statistical particle size intervals for three lenses and executes rigid screening rules to ensure that each particle belongs to only one statistical interval, thus eliminating the problem of duplicate counting in multi-magnification statistics. Combined with a normalized number density that matches the interval, it eliminates statistical bias caused by differences in the field of view area of ​​different branches, ultimately achieving seamless stitching across the entire particle size range of 1μm to 1000μm, forming a continuous and complete particle size distribution result. Attached Figure Description

[0008] Figure 1 This is a schematic diagram of the architecture of the present invention; Figure 2 This is a partial structural schematic diagram of the present invention; Figure 3 The image shows grainy particles captured at a certain moment by three macro lenses used in this embodiment. Figure 4 The following is a graph showing the probability density and cumulative frequency of the number of combustion particles in the example. Figure 5 The graph shows the volume probability density and volume cumulative frequency results of combustion particles in the example.

[0009] Among them: 10, first beam splitter prism; 11, second beam splitter prism; 12, combustion chamber; 13, optical converging structure; 14, first reflecting prism; 15, second reflecting prism; 16, first macro lens; 17, second macro lens; 18, third macro lens; 19, first high-speed camera; 20, second high-speed camera; 21, third high-speed camera; 22, light shield; 23, laser emitter; 24, observation window. Detailed Implementation

[0010] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0011] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "multiple" means two or more. The term "orientation" in this invention refers to the orientation of the device or element according to the invention. Figure 1 Description of the state's progression.

[0012] This invention discloses a long-distance in-situ measurement system for wide-diameter combustion particles in solid rocket engines, such as... Figure 1 and Figure 2 As shown, it includes: a first beam splitter prism 10, a second beam splitter prism 11, a first reflecting prism 14, and a second reflecting prism 15.

[0013] The incident surface of the first beam splitter prism 10 is positioned directly opposite the observation window 24 of the solid rocket motor combustion chamber 12. An optical converging structure 13 is also provided between the combustion chamber 12 and the first beam splitter prism 10. The optical converging structure 13 is used to image the combustion particles in the combustion chamber 12 through the observation window 24 and to accurately converge parallel scattered light from different angles on the object side to the image-side focal point on the image-side focal plane. The first beam splitter prism 10 is located on the converging light path between the optical converging structure 13 and the image-side focal point. The first beam splitter prism 10 is used to split the incident converging beam into two paths: the first path is an upward beam reflected at 90°, and the second path is a relay beam transmitted to the right.

[0014] The second beam splitter 11 is disposed in the output light path of the first beam splitter 10; the incident surface of the second beam splitter 11 is directly opposite the transmission and output surface of the first beam splitter 10. The second beam splitter 11 is used to split the relay beam into two paths, the first path being the main beam transmitted to the right and the second path being the lower beam reflected 90° downward.

[0015] The first reflecting prism 14 and the second reflecting prism 15 have their incident surfaces facing the upper exit surface of the first beam splitter prism 10. The first reflecting prism 14 is used to refract the upper beam from the first beam splitter prism 10 by 90° into a first beam that propagates horizontally to the right. The incident surface of the second reflecting prism 15 faces the lower exit surface of the second beam splitter prism 11. The second reflecting prism 15 is used to refract the lower beam from the second beam splitter prism 11 by 90° into a second beam that propagates horizontally to the right. The central main beam, the first beam, and the second beam all carry holographic information of the burning particles and are respectively incident on the corresponding macro lens, which then images the beams carrying the holographic information.

[0016] The present invention also includes a laser emitter 23, which is located on the left side of the combustion chamber 12. The laser emitter 23 is used to emit a laser beam at the observation window 24 of the combustion chamber 12, so that the laser beam passes through the observation window 24 and enters the optical converging structure 13.

[0017] The laser emitter is used to output a parallel laser beam with excellent collimation as the incident light source. The laser emitter is preferably a high-power laser. The center wavelength of the output laser of the single-longitudinal-mode high-power laser is 532nm in the visible light band. The maximum output power can be continuously adjusted within the range of 50W. The output laser has excellent collimation, with a coherence length ≥5m, which is not less than the axial length of the combustion chamber measurement area. It can completely record the holographic information of all condensed particles on the laser propagation path. The diameter of the high-power parallel laser spot is 40mm.

[0018] The present invention also includes a light shield 22, which is located between the optical converging structure 13 and the combustion chamber 12. The light shield 22 is used to shield and suppress stray light, reflected light and ambient light from the combustion chamber 12 to prevent interference light from entering the imaging optical path.

[0019] The light shield 22 is a high-temperature resistant light shield that eliminates stray light. It is made of stainless steel and has a black high-temperature matte paint coating on the inner wall. It has a diameter of 50mm and its overall length can be replaced according to the experimental scenario. The distance between the front end of the light shield 22 and the observation window 24 can be flexibly adjusted according to the thermal radiation safety threshold to form a high-temperature safety protection distance. At the same time, it suppresses stray light from flames and the environment from entering the subsequent optical path and improves the imaging signal-to-noise ratio.

[0020] A 532nm narrowband limiter is also provided between the light shield 22 and the optical converging structure 13. The half-width of the narrowband limiter is ≤10 nm and the peak transmittance is ≥90%. It is used to filter out the broadband stray light of the engine flame and only allow the 532 nm measurement laser to pass through, further improving the contrast and signal-to-noise ratio of the holographic interferogram.

[0021] The optical converging structure 13 includes a cemented doublet achromatic positive lens and an aspherical positive lens arranged sequentially along the optical path. The cemented doublet achromatic positive lens and the aspherical positive lens are arranged inside the mounting tube, which is arranged in a left-right direction, with the left end opening facing the observation window 24.

[0022] Through precise design of lens focal length ratio and axial spacing, an effective focal length of 400mm is achieved. Operating in infinity focusing mode, it only completes the optical path conversion from parallel scattered light from the 12 particles in the combustion chamber to the converging light, and does not participate in the system's magnification. The image-side focal spot of the converged beam in the optical converging structure 13 is located at the right end of the mounting tube, 150mm from the right end of the mounting tube.

[0023] The double-cemented achromatic positive lens is made by cementing two pieces of optical glass together. It has a light-transmitting aperture of 50mm, a total thickness of 12mm at the center of the lens, and an effective focal length of 800mm for a single group. As a primary converging element, it undertakes the core functions of basic optical power distribution, axial chromatic aberration correction, and primary spherical aberration suppression. It can convert incident parallel scattered light into regular weakly converging spherical waves, while eliminating the imaging blur caused by dispersion and ensuring the wavefront integrity of the scattered light from the particles.

[0024] A limiting ring is installed inside the mounting tube, located between the double-cemented achromatic positive lens and the aspherical positive lens. The limiting ring is coaxial with the mounting tube and is made of aluminum alloy with an anodized matte finish on the inner wall. The diameter of the central hole of the limiting ring is 50mm and the axial thickness is 5mm. It limits the effective light transmission diameter, locks the numerical aperture and beam divergence characteristics, eliminates invalid diffraction light and stray light at the lens edge, and improves the contrast of holographic interference fringes.

[0025] The aspherical positive lens is made of molded optical glass with a light-transmitting aperture of 50mm, a lens center thickness of 10mm, and an effective focal length of 600mm per group. As a precise focusing element, it undertakes the core functions of high-order spherical aberration correction, image-side principal point position control, and precise beam convergence.

[0026] Based on the optical imaging principle of a double-lens group, the total effective focal length of the two coaxially arranged lenses is determined by the focal length of each lens group and the distance between the principal surfaces. The cemented doublet achromatic positive lens has a focal length of 800mm, the aspherical lens has a focal length of 600mm, and the distance between the cemented doublet achromatic positive lens and the aspherical positive lens is 200mm. After optical simulation and thick lens calibration, the total effective focal length is precisely locked to 400mm.

[0027] This invention employs a beam splitting mechanism in the converging optical path in front of the image-side focal spot of the optical converging structure. Only the parallel scattered light from the object-side particles is converted into a converging spherical wave. The focal spot is located at the spatial spectral convergence surface of the object-side particle field. If beam splitting were performed behind the focal spot, the beam would diverge rapidly after passing the focal point, and the excessive distance would cause the spot size to exceed the size of the subsequent macro lens. By placing a beam-splitting prism in the converging optical path in front of the focal spot, and considering the 150mm gap between the focal spot and the mounting cylinder, it is convenient to install the beam-splitting prism and reflecting prism, eliminating the need for separate focusing and mounting space. This significantly reduces the mounting space and avoids the installation interference problems caused by the extremely small working distance of high-magnification macro lenses. This avoids thermal damage, nonlinear optical effects, and film ablation caused by focusing high-power lasers inside the beam splitter and reflecting prisms. If the beam is split at or behind the focal spot, the extremely high energy density at the focal point will directly affect the beam splitter and reflecting prisms, which can easily damage them. In the converging optical path in front of the focal spot, the beam energy is always in a dispersed state, and the energy density of the light-transmitting surfaces of the beam splitter and reflecting prisms is low, thus ensuring the stability and service life of the system under high-power laser irradiation conditions.

[0028] The core function of the optical converging structure 13 is to perform angle and position transformations, precisely converging parallel scattered light from different angles in the object side to the image-side focal point F on its image-side focal plane, forming a spatial spectrum distribution corresponding to the object-side particle field near the focal plane. In this process, the optical converging structure 13 does not participate in magnification; it only realizes the coordinate transformation from parallel light to converged light. The outgoing beam from the optical converging structure 13 converges to the image-side focal point F, which is located in air without an optical medium, avoiding thermal damage and nonlinear optical effects caused by focusing high-power laser light inside the optical elements. The aperture range of the optical converging structure 13 is F2.8~F16, with a full field-of-view distortion ≤0.03%.

[0029] Preferably, the first beam splitter prism 10 is a 532 nm unpolarized cubic beam splitter prism with a light-transmitting aperture of 46 mm. All light-transmitting surfaces are coated with a 532 nm anti-reflection film. The incident surface faces the exit light port of the optical converging structure 13. The beam splitting ratio is 25% upward reflection and 75% rightward transmission. It is used to split the incident converging beam into two paths. The first path is an upward beam reflected at 25°, and the second path is a relay beam transmitted to the right. Both beams maintain the same converging characteristics as the incident light.

[0030] Preferably, the second beam splitter prism 11 is a non-polarizing cubic beam splitter prism with its incident surface facing the transmission and exit surface of the first beam splitter prism 10. The splitting ratio is 10% transmission to the right and 90% reflection downwards. It is used to split the relay beam into two paths: the first path is the main beam that is transmitted to the right, and the second path is the lower beam that is reflected downwards at 90°. Both beams maintain the same converging characteristics as the incident light, and the final converging endpoint is the image-side focal point F.

[0031] Preferably, the first reflecting prism 14 and the second reflecting prism 15 are both right-angle reflecting prisms made of K9 material, with a 532 nm enhanced high-reflection coating on the reflecting surface. The first reflecting prism 14 is arranged on the upper exit surface of the first beam splitter prism 10 and is used to fold the upward propagating upper beam by 90° into a beam propagating horizontally to the right. The second reflecting prism 15 is arranged on the lower exit surface of the second beam splitter prism 11 and is used to fold the downward propagating lower beam by 90° into a beam propagating horizontally to the right.

[0032] The beam splitting ratio of the two beam splitters is precisely matched with the total magnification of the corresponding branches. The image plane illuminance of the industrial lens is inversely proportional to the square of the magnification. Therefore, the beam splitting ratio is directly proportional to the square of the magnification, which compensates for the square-order attenuation of image plane illuminance caused by different magnifications. This ensures that the image brightness of the three imaging systems is similar under the same exposure time and the same gain parameters, providing imaging quality that meets the standard requirements for subsequent data processing.

[0033] The dimensions of the first beam splitter 10 and the second beam splitter 11 are both 46mm × 46mm. The first beam splitter 10 and the second beam splitter 11 are both installed inside the first sleeve, and the first beam splitter 10 and the second beam splitter 11 are 10mm apart. The left end opening of the first sleeve is used for laser entry, and the right end opening is used for the light path after passing through the second beam splitter 11. The right end opening of the first sleeve is connected to the left end opening of the second sleeve. The right end of the second sleeve is equipped with a second macro lens 17. The length of the second sleeve is preferably 90mm.

[0034] A first reflecting prism 14 is positioned 50 mm after the first beam splitter prism 10, reflecting the upward beam. Both the first beam splitter prism 10 and the first reflecting prism 14 are installed inside a third sleeve. The third sleeve is positioned vertically, with its upper opening facing right and aligned with the emission direction of the first reflecting prism 14. The upper opening of the third sleeve is connected to the left opening of the fourth sleeve. A first macro lens 16 is installed at the right opening of the fourth sleeve. Preferably, the length of the fourth sleeve is 160 mm.

[0035] A second reflecting prism 15 is set 50mm after the reflection path of the second beam splitter prism 11. Both the second beam splitter prism 11 and the second reflecting prism 15 are installed inside the fifth sleeve. The fifth sleeve is set vertically, with the lower end opening facing to the right and in the direction of the second reflecting prism 15's emission. The lower end opening of the fifth sleeve is connected to the left end opening of the sixth sleeve. A third macro lens 18 is installed at the right end opening of the sixth sleeve. The length of the sixth sleeve is preferably 170mm.

[0036] The central main beam is used by the second macro lens 17 and the third high-speed camera 21 to image the burning particles, while the second high-speed camera 20 and the third high-speed camera 21 simultaneously acquire data.

[0037] The first beam is used by the first macro lens 16 and the third high-speed camera 21 to image the burning particles, while the first high-speed camera 19 and the third high-speed camera 21 simultaneously acquire data.

[0038] The second beam is used by the third macro lens 18 and the third high-speed camera 21 to image the burning particles, while the third high-speed camera 21 performs synchronous acquisition.

[0039] The magnification of the first macro lens 16, the third high-speed camera 21, the second macro lens 17, the third high-speed camera 21, the third macro lens 18, and the third high-speed camera 21 are all different.

[0040] Each fixed-magnification macro lens and high-speed camera are arranged sequentially along the propagation direction, corresponding to the upper, middle, and lower beam paths, respectively. The principal optical axes are parallel to each other and are all in the same vertical plane with the principal optical axis of the optical converging structure 13. All lenses are uniformly focused on the image-side focal spot F, achieving strict coincidence of the object-side field of view centers of the three optical paths and a unified object-side spatial coordinate reference. The total magnification is determined separately by the fixed-magnification macro lens of the corresponding branch at the rear end, and the object-side pixel size is the magnification of the rear macro lens multiplied by the pixel size of the high-speed camera.

[0041] The macro lenses all use lenses with different magnifications, and their focusing distance is constant at a certain magnification. The working magnification of the three sets of macro lenses is determined based on the sampling theorem and the particle robust recognition engineering rules: Where M is the magnification setting for the macro lens, and p is the pixel size of the high-speed camera. This refers to the minimum particle diameter that needs to be measured for the corresponding branch.

[0042] The object-side pixel size must be less than or equal to 1 / 3 of the smallest particle diameter to ensure that a single particle covers at least 3×3 pixel areas on the imaging surface. This satisfies the resolution requirement of the Nyquist sampling theorem and can resist the effects of image noise and edge blurring, enabling accurate calculation of particle contour, centroid, and equivalent particle size.

[0043] For the first beam, a macro lens with 3x magnification is connected, and its focusing distance is constant at 16cm; for the middle main beam, a macro lens with 10x magnification is connected, and its focusing distance is constant at 5cm; for the second beam, a macro lens with 1x magnification is connected, and its focusing distance is constant at 23cm.

[0044] All macro cameras used were CMOS high-speed cameras with a full-frame sampling rate greater than 2000fps. High-speed cameras with different pixel sizes were matched to branches with different magnifications. For the 3x magnification branch, the high-speed camera pixel size was 10μm with a resolution of 1600*960, and the pixel size after the magnification optical path was 3.3μm, which meets the measurement particle size range of 10-100μm. For the 10x magnification branch, the high-speed camera pixel size was 3μm with a resolution of 2560*1600, and the pixel size after the magnification optical path was 0.3μm, which meets the measurement particle size range of 1-10μm. For the 1x magnification branch, the high-speed camera pixel size was 20μm with a resolution of 1280*800, and the pixel size after the magnification optical path was 20μm, which meets the measurement particle size range of 100-1000μm.

[0045] Therefore, this invention can solve the problems of misalignment of spatiotemporal references in multiple lenses, repeated counting of the same particle, distribution distortion caused by overlapping particle size ranges, and inability to stitch together wide-range measurement data in existing multi-magnification holographic particle size measurement technologies.

[0046] To strictly comply with the requirements of GB / T 19077-2024 "Particle Size Analysis - Laser Diffraction Method" and ultimately output synchronous measurement results with a wide particle size range of 1μm to 1000μm, the specific implementation method is as follows: 1. Spatiotemporal integrated joint calibration of multi-magnification synchronous holographic system Synchronous calibration image acquisition: A high-precision transmissive checkerboard calibration plate calibrated by the National Institute of Metrology is placed in the measurement area of ​​combustion chamber 12. The plane of the calibration plate is strictly perpendicular to the main optical axis, the grid spacing of the calibration plate is 0.1mm, the accuracy is ±0.5μm, and it covers the entire aperture of the laser light transmission. The laser emitter 23 is turned on to emit a high-power parallel laser. The calibration plate images are synchronously acquired through three sets of high-speed cameras with the same trigger pulse. Each channel acquires no less than 20 sets of synchronous images at the same calibration plate position to eliminate the random error of single image calibration.

[0047] Based on the synchronously acquired calibration board image, the pixel-level corner coordinates of the chessboard grid are extracted. Combined with the known physical grid spacing of the calibration board, the actual object-side field of view size of each path is calculated, and then the actual shooting area Si of the camera at the corresponding magnification is obtained (i=1,2,3, corresponding to the three magnification branches of 10x, 3x, and 1x respectively), ensuring that the field of view area measurement error is ≤1%.

[0048] Based on the actual physical distance between adjacent corner points of the calibration board and the corresponding pixel distance on the image, the actual object-space pixel size for each path is calculated. The core formula is: In the formula: Let be the object-side pixel size of the i-th path, in μm; This represents the actual physical distance between adjacent corner points of the calibration board, in μm. The pixel distance between adjacent corner points on the image; ensuring that the relative error of pixel size calibration is ≤0.5%.

[0049] Based on three calibration board images acquired simultaneously at the same time, the pixel coordinates of the same chessboard corner point in the three images are extracted. Using the 1x branch coordinate system as the unified object space reference coordinate system for the entire system, the spatial transformation matrices Ti (including rotation and translation matrices) of the 10x and 3x branches relative to the reference coordinate system are solved to complete the joint registration of multi-path spatial coordinates, ensuring that the reprojection error of the coordinate registration between the three paths is ≤0.3 pixels, and achieving complete unification of the spatial reference of the entire system.

[0050] 2. Holographic image preprocessing, full-field reconstruction and intelligent particle recognition Holographic image standardization preprocessing: The acquired raw holographic images are sequentially subjected to adaptive noise reduction and non-uniform background correction preprocessing to eliminate lens traces, stray light from the combustion flow field and environmental noise interference. Different filter kernel parameters are adapted to the image signal-to-noise ratio characteristics of 10x, 3x and 1x branches to maximize the improvement of holographic image signal-to-noise ratio and particle target recognition.

[0051] 3D Full-Field Numerical Reconstruction Adapted to Multiple Magnification Characteristics: Based on scalar diffraction theory, the Fresnel transform method is used to perform 3D full-field numerical reconstruction on the preprocessed holographic image. Different axial reconstruction step sizes are set for the particle size range and axial positioning accuracy requirements corresponding to different magnification branches: 10 μm for the 10x branch (fine particle detection, 1–10 μm), 20 μm for the 3x branch (medium particle detection, 10–100 μm), and 50 μm for the 1x branch (coarse particle detection, 100–1000 μm). All three branches complete the full flow field reconstruction within a unified 0–100 mm axial range, achieving digital focusing of the burning aluminum particles across the entire flow field, balancing the axial positioning accuracy of fine particles with overall reconstruction efficiency.

[0052] Depth of field expansion and intelligent particle recognition: The reconstructed multi-depth slice images are subjected to depth of field expansion and image fusion processing, projecting clearly focused particles in different depth planes into the same image, while simultaneously preserving the three-dimensional spatial coordinate information of the particles; a pre-trained intelligent target detection model based on the YOLO deep learning framework is adopted, and the anchor frame size and detection threshold are optimized for the particle imaging characteristics of three different magnifications, respectively, to perform end-to-end detection on the fused particle image, automatically identifying aluminum combustion particles in complex backgrounds and extracting particle contour, centroid coordinates and basic particle size information.

[0053] Initial screening and particle size calculation of particle data: The particle data output by the model is standardized and preprocessed to remove static noise, dynamic noise and irregularly shaped invalid particles in sequence to obtain an initial effective particle dataset; Combined with the calibrated object-space pixel size, the equivalent spherical particle size of each particle is calculated by the equivalent circle method. At the same time, the three-dimensional coordinates of all particles are uniformly transformed to the reference coordinate system of the whole system through the calibrated spatial transformation matrix, and the equivalent particle size and three-dimensional spatial position of each particle in the unified coordinate system are output.

[0054] 3. Two-dimensional, non-repetitive rigid screening based on a unified spatiotemporal benchmark Based on the pre-defined non-overlapping statistical particle size intervals uniquely assigned to the three lenses, a rigid screening rule is applied to the particle detection results of each lens to establish an interval determination matrix Ω: ; In the formula: The unique range for the 10x magnification branch: This branch has the highest optical resolution and the best imaging linearity for fine particles of 1~10μm, and is the only statistical branch in this range; The only assigned interval for the 3x magnification branch: This branch balances resolution and field of view, and has the best imaging linearity for particles in the 10~100μm range. It is the only statistical branch in this interval. The unique assigned interval for the 1x magnification branch: This branch has the largest field of view and depth of field, and the best imaging linearity for coarse particles in the range of 100~1000μm. It is the only statistical branch in this interval.

[0055] First screening dimension: Spatial uniqueness pre-screening Based on the unified object-space reference coordinate system established by calibration, for the three initial particle data collected synchronously at the same time, the determination and pre-assignment of duplicate particles in physical space are first completed, so as to avoid the same particle being counted repeatedly by multiple branches from the source: After holographic reconstruction, the initial set of three-dimensional coordinates of the particles in the i-th path is:

[0056] Where N i,total The initial total number of particles identified by the i-th path; all particle coordinates have been transformed to a unified object-space reference coordinate system. Establish a particle spatial overlap determination model: For any two particles p (from path i) and q (from path j, j ≠ i) originating from different branches, calculate the three-dimensional spatial distance ΔDpq between their centroids and the relative deviation of their equivalent particle sizes. : in, Let p be the particle size. Let q be the particle size; Spatial uniqueness determination rule: when ΔD pq ≤2×min(d p ,d q And Δd pq If the count is ≤5%, particles p and q are determined to be the same physical particle, triggering a duplicate count warning; if the above conditions are not met, they are determined to be different physical particles, and the process proceeds to the next screening stage.

[0057] Duplicate particle pre-assignment rule: For duplicate data identified as the same physical particle, priority is given to the optimal linear response interval. High magnification accuracy priority principle for pre-assignment: Particle data from the branch whose equivalent particle size falls into the designated interval is retained, and duplicate data from other branches are removed; if the particle size is within the critical range of the interval, data from the branch with higher magnification is retained. Higher magnification provides higher accuracy in particle imaging and particle size calculation, avoiding the erroneous removal of valid particles.

[0058] Second dimension: Rigid screening for unique particle size range attribution For non-repeating particles that have undergone spatial uniqueness pre-screening, a rigid screening rule for unique assignment is applied, and a particle interval membership determination function is established to ensure that each particle belongs to only one statistical interval, with no overlap, no conflict, and no breakpoints. In the formula: For the first Particles for the first Membership degree of road intervals.

[0059] 1) When At that time, it was determined that the particle uniquely belonged to the first... The section of the road will be retained; 2) When When the particle is in the critical range, it is determined to be a particle in the critical range. 3) When When a particle is found to be invalid across intervals, it is removed.

[0060] Effective particle set generation and verification: After the above two-dimensional screening, the final effective particle set of the three branches is obtained: 1) Effective particle set of the 10x magnification branch The effective particle count is 10 times the number of particles in the branch, and all particle sizes fall into the range. The intervals must be distinct and not cross-interval. 2) Effective particle set of the 3x magnification branch The effective particle count is 3 times the total number of particles in the branch, and all particle sizes fall into the range. The intervals must be distinct and not cross-interval. 3) Effective particle set of the 1x magnification branch The effective number of particles in the branch is 1, and all particle sizes fall into the range. The intervals are non-repeating and do not cross intervals.

[0061] After screening, verification is performed: the total number of effective particles in the three channels N = N_1 + N_2 + N_3, and the deviation from the total number of non-repeating particles after spatial uniqueness pre-screening is ≤0.1%, ensuring that no effective particles are lost and no duplicates are counted, which fully complies with the requirements of GB / T19077-2024.

[0062] Based on multi-magnification normalization of effective measurement volume and full-range result stitching output, this method addresses the issues in existing multi-magnification measurements, such as statistical weight imbalance caused by inconsistencies in field of view and effective measurement volume across different branches, inability to directly stitch data, and problems with particle size discontinuities and cumulative distribution jumps during stitching. It integrates normalization processing, seamless full-range stitching, and result output, based on a unified spatiotemporal benchmark and normalized statistics established in the pre-processing steps. This achieves continuous and smooth stitching across a wide particle size range of 1μm to 1000μm, outputting complete measurement results that conform to national standards. Specific operations are as follows: 1) Unified Effective Measurement Volume Calibration: Based on the unified holographic reconstruction range set in the holographic reconstruction, a unified effective measurement depth L shared by the three channels is defined. The entire holographic reconstruction range is 0~100mm, and L=100mm is taken as the unified effective measurement depth of the entire system. All three channels only count effective particles within this axial depth range to ensure the effective measurement volume V of the three channels. i =S i ×L is based on a completely consistent depth benchmark, eliminating statistical bias caused by differences in measured depth at the source.

[0063] 2) Number Density Normalization Calculation: For each effective particle after screening, calculate the normalized number density for the corresponding particle size range. The core formula is: Where: n i The particle number density is the number of particles in the interval corresponding to the i-th path, in units of particles / m³. 3 N i S represents the total number of effective particles in this interval; i The area of ​​the object's field of view for this branch is defined in meters. 2 L represents the unified effective measurement depth shared by all three channels, in meters (m). According to the requirements of GB / T 19077-2024, the dedicated particle size range of each amplification branch is divided into m continuous sub-intervals with equal logarithmic spacing, and the upper and lower limits of the particle size of the k-th sub-interval are d.k,low d k,high , satisfying d k,high -d k,low =Constant, ensuring uniform distribution within the sub-interval across a wide particle size range, resulting in smooth statistical results without jumps. Calculate the frequency and cumulative distribution of particle counts within this sub-interval: In the formula: For the first Lu Di Frequency of particle count in each sub-interval; For the first The particle size in the path falls at the first The number of effective particles within each sub-interval; This represents the cumulative number distribution.

[0064] 3) Calculate the volume of a single particle and the total volume of particles in the sub-interval: In the formula: This refers to the volume of a single particle. For the first Lu Di Total particle volume of each sub-interval Calculate the frequency distribution and cumulative volume distribution of sub-intervals: In the formula: For the first Lu Di Volume frequency distribution of each sub-interval; This represents the cumulative volume distribution.

[0065] 4) Using the total particle volume across the entire range as a unified benchmark, the volume frequency of each branch is weighted and corrected, breaking away from the conventional method of directly splicing together after normalizing each branch individually. This ensures that the spliced ​​distribution has no breaks, no overlaps, and the sum is equal to the expected value. .

[0066] First, calculate the total volume of particles across the entire measurement range. ,in The total volume of effective particles in the three branches is represented; then, the seamless splicing of the full-range volume frequency distribution is completed according to the order of particle size from smallest to largest. Full-range cumulative volume distribution continuous stitching: Based on the corrected full-range volume frequency distribution, the cumulative volume distribution is calculated sequentially according to particle size from smallest to largest, ensuring that the cumulative distribution ranges from 0 to... Continuous and smooth transition, without jumps or breaks: when At that time, the cumulative volume distribution ; when At that time, the cumulative volume distribution ,in for The cumulative volume distribution value at the endpoint of the interval; when At that time, the cumulative volume distribution ,in for The cumulative volume distribution value at the end of the interval.

[0067] 5) Final measurement result output: Output complete measurement results Measurement results across a wide particle size range include: frequency / cumulative distribution curves for the entire particle size range, volumetric frequency / cumulative distribution curves, characteristic particle sizes of D10 / D50 / D90, Sauter average particle size D32, volume average particle size D43, and other key parameters.

[0068] This invention enables in-situ, non-contact, wide-range synchronous measurement of condensed combustion particles in the combustion chamber 12 of a solid rocket engine, completely solving the problems of traditional measurement methods. It directly measures particles within the combustion chamber 12, avoiding particle size distribution distortion caused by secondary combustion, collision, agglomeration, and breakage within the nozzle. The measurement data perfectly matches the actual high-temperature and high-pressure conditions inside the combustion chamber 12. Through a coaxial spectroscopic multi-magnification synchronous imaging architecture, particle distribution data across the entire particle size range of 1μm to 1000μm can be simultaneously acquired in a single engine ignition test. This eliminates the need for multiple independent tests with different magnification systems, significantly reducing test costs while achieving complete consistency between the temporal and spatial references of the measurement data. The measurement accuracy, data integrity, and spatiotemporal consistency are significantly superior to existing technologies.

[0069] The optical converging structure 13 of this invention only converts the parallel scattered light from the object particles into a converging spherical wave, without participating in the system magnification. This achieves complete decoupling between the long focal length thermal protection distance and the imaging magnification, ensuring a safe protection distance between the optical components and the high-temperature combustion chamber 12 (above 3000K) to avoid irreversible damage caused by strong thermal radiation. Furthermore, it allows for flexible adjustment of the imaging resolution through macro lenses of different magnifications, enabling clear imaging of ultrafine particles. This fundamentally solves the inherent contradiction between high-temperature long-distance arrangement and high-magnification macro close-range focusing in existing technologies. Simultaneously, it innovatively adopts a beam-splitting design with a front-converging optical path, fully utilizing the 150mm gap between the focal spot and the mounting cylinder to install the beam-splitting prism and reflecting prism. This significantly reduces the system volume, avoids installation interference problems caused by the extremely small working distance of the high-magnification macro lens, and avoids thermal damage, nonlinear optical effects, and film ablation problems caused by the high energy density of the laser focus on the beam-splitting components. This significantly improves the system's operational stability and lifespan under high-power laser irradiation conditions.

[0070] This invention establishes a standardized post-processing method for the entire process, achieving distortion-free and seamless stitching of measurement data across a wide particle size range, with measurement results fully compliant with national standards. This invention establishes a unique object-space reference coordinate system for the entire system through a multi-magnification synchronous holographic system spatial integrated joint calibration method, achieving precise registration of spatial coordinates across multiple optical paths and laying a foundation for non-repetitive statistics. By pre-defining exclusive, non-overlapping particle size statistical intervals, combined with spatial uniqueness pre-screening and rigid screening for unique particle size interval assignment, the invention fundamentally eliminates the problems of repeated particle counting and particle size distribution distortion in multi-magnification measurements. Simultaneously, it completes multi-magnification data normalization based on a unified effective measurement volume, using the total particle volume across the entire range as a benchmark for weight correction. This breaks away from the conventional method of directly stitching together data after separate normalization of each branch, achieving continuous, smooth, and seamless stitching of the number and volume distributions across the entire particle size range of 1μm to 1000μm. The final output is a full-range measurement result compliant with the requirements of GB / T 19077-2024 "Particle Size Analysis - Laser Diffraction Method".

[0071] Example The object under test in this embodiment is a windowed solid rocket motor. The combustion chamber 12 of the motor has an inner diameter of Φ200mm. The combustion chamber 12 has symmetrical circular optical observation windows 24 with a diameter of Φ50mm on both sides. The observation windows 24 are made of quartz glass with a thickness of 10mm, providing a coaxial light path for the measurement laser. The motor uses a composite propellant with an aluminum powder mass fraction of 18%. The alumina condensed phase particles generated by combustion cover the entire range of particle size from 1μm to 1000μm.

[0072] Laser emitter 23 employs a 532nm single-longitudinal-mode continuous laser with a maximum output power of 50W, a beam divergence angle ≤0.05mrad, a coherence length ≥5m, and outputs standard plane-wave parallel light with a diameter of 40mm. The laser's mounting position is adjusted so that the principal axis of the output parallel light perfectly coincides with the central axis of the optical observation windows 24 on both sides of the engine, ensuring the parallel light is perpendicularly incident on the optical observation windows 24. The continuous output power of laser emitter 23 is 30W; the exposure time of the three high-speed cameras is uniformly set to 10μs.

[0073] Along the laser emission direction, a light shield 22, a 532nm narrowband filter, and an optical converging structure 13 are sequentially installed on the light-emitting side of the engine's optical observation window 24. The whole structure is an integrated package without any adjustable moving mechanism and works in infinity focusing mode throughout.

[0074] The light shield 22 is made of stainless steel in one piece, with the inner wall coated with black high-temperature matte paint. The light transmission diameter is 50mm and the overall length is 500mm. The distance between the end face of the light shield 22 and the observation window 24 is fixed at 10m, forming a high-temperature safety protection distance, while suppressing flame and ambient stray light from entering the subsequent optical path; it meets the thermal radiation safety protection distance under extreme working conditions, while preventing ambient stray light from affecting the laser propagation in the path; The narrowband filter has a half-width of 5nm and a peak transmittance of 92%, ensuring that the laser is perpendicularly incident on the light-containing surface of the beam limiter, allowing the 532nm laser to enter the subsequent optical path, while eliminating stray flame light and ambient scattered light from entering the subsequent optical path. The double-cemented achromatic positive lens has a light-transmitting aperture of 50mm, an effective focal length of 800mm per group, a central hole diameter of 50mm in the limiting ring, and an axial thickness of 5mm. The aspherical positive lens has a light-transmitting aperture of 50mm and an effective focal length of 600mm per group. There is a 150mm gap between the focal spot and the mounting cylinder.

[0075] Both the first beam splitter prism 10 and the second beam splitter prism 11 are non-polarizing cubic beam splitters.

[0076] The first beam-splitting prism 10 is positioned at the right exit of the optical converging structure 13, and the second beam-splitting prism 11 is positioned close to the exit surface of the first beam-splitting prism 10. Both prisms have a light-transmitting aperture of 46mm×46mm, and both light-transmitting surfaces are coated with a 532nm anti-reflection film. The beam splitting ratio of the first beam-splitting prism 10 is 25% upward reflection and 75% rightward transmission, while the beam splitting ratio of the second beam-splitting prism 11 is 90% downward reflection and 10% rightward transmission. The beam splitting ratio is proportional to the square of the magnification of the corresponding branch, compensating for the square-order attenuation of image illuminance at high magnification, and ensuring that the brightness deviation of the three imaging systems is ≤2% under the same exposure and the same gain.

[0077] Three sets of fixed-magnification macro lenses and high-speed cameras are arranged sequentially along the propagation direction to correspond to the upper, middle and lower beam paths, respectively. They are rigidly connected to the prism exit flange of the corresponding optical path through a custom-length aluminum alloy rigid sleeve. The sleeve length is precisely matched to the focusing distance of the corresponding macro lens. There are no adjustable moving structures, and the vibration resistance meets the requirements of the engine test bench environment.

[0078] Upper beam (first beam splitter prism 10 reflection beam path): equipped with a 3x fixed magnification macro lens, with a constant focusing distance of 27cm, and a global shutter CMOS high-speed camera with a pixel size of 10μm, a resolution of 1600*960, a full-frame sampling rate of 2000fps, and an object-side pixel size of 3.3μm after magnification, corresponding to the particle measurement range of 10~100μm; The central main beam (second beam splitter prism 11 transmission path): equipped with a 10x fixed magnification macro lens, with a constant focusing distance of 5cm, and a global shutter CMOS high-speed camera with a pixel size of 3μm, a resolution of 2560*1600, a full-frame sampling rate of 2200fps, and an object-side pixel size of 0.3μm after magnification, corresponding to the measurement range of fine particles from 1 to 10μm; The lower beam (reflection path of the second beam splitter prism 11): equipped with a 1x fixed magnification macro lens, with a constant focusing distance of 16cm, and a global shutter CMOS high-speed camera with a pixel size of 20μm, a resolution of 1280*800, a full-frame sampling rate of 2500fps, and an object-side pixel size of 20μm after magnification, corresponding to a coarse grain measurement range of 100~1000μm.

[0079] An 8-channel high-precision synchronous signal generator is used, and its synchronous output is electrically connected to the external trigger interfaces of three high-speed cameras through coaxial cables to achieve strict time synchronization of the three imaging systems. At the same time, the synchronous port of the signal generator is linked with the timing port of the engine ignition control system to achieve strict timing synchronization between camera acquisition and engine ignition.

[0080] First screening dimension: Spatial uniqueness pre-screening For any two particles from different branches, if the three-dimensional spatial distance between their centroids is ≤2 × the minimum particle size and the relative deviation of their equivalent particle size is ≤5%, they are determined to be the same physical particle. They are pre-assigned according to the principle of prioritizing the optimal linear response range and prioritizing high magnification accuracy, and duplicate data from other branches are eliminated. If the determination conditions are not met, they are determined to be different physical particles and proceed to the next screening stage.

[0081] Second dimension: Rigid screening for unique particle size range attribution Based on the defined non-overlapping particle size intervals, an interval determination matrix Ω is established, where the unique interval for a 10-fold branch is [1μm, 10μm], the unique interval for a 3-fold branch is (10μm, 100μm], and the unique interval for a 1-fold branch is (100μm, 1000μm]. A particle interval membership determination function is established to ensure that each particle belongs to only one statistical interval. Specifically, critical particles in the [9.8μm, 10.2μm] interval are preferentially assigned to the 10-fold branch, and critical particles in the [98μm, 102μm] interval are preferentially assigned to the 3-fold branch, ensuring that no critical particles are lost or duplicated.

[0082] Valid particle set verification: After dual-dimensional screening, the total number of valid particles in the three channels deviates from the total number of non-repeating particles after spatial uniqueness pre-screening by ≤0.1%, ensuring that no valid particles are lost and no duplicates are counted, which meets the requirements of GB / T 19077-2024.

[0083] Unified effective measurement volume calibration: Define a unified effective measurement depth L=100mm for all three channels. All three channels only count effective particles within this axial depth range to ensure that the effective measurement volume Vi=Si×L of the three channels is based on a completely consistent depth benchmark, thus eliminating statistical deviations caused by differences in measurement depth.

[0084] Normalized statistic calculation: For each effective particle after screening, calculate the normalized number density of the corresponding particle size interval. In accordance with the requirements of GB / T 19077-2024, divide the exclusive particle size interval of each branch into continuous sub-intervals with equal logarithmic intervals, and calculate the particle number frequency, cumulative number distribution, volume frequency distribution and cumulative volume distribution of each sub-interval.

[0085] Seamless splicing across the entire range: Using the total volume of particles across the entire range as a unified benchmark, the volume frequency of each branch is weighted and corrected. Following the order of particle size from small to large, the continuous and smooth splicing of the volume frequency distribution and cumulative volume distribution across the entire range of 1μm to 1000μm is completed, without any breaks, jumps, or overlaps. The cumulative distribution transitions continuously from 0 to 100%.

[0086] Final output: Output complete measurement results for a wide particle size range of 1μm to 1000μm, including key parameters such as the frequency / cumulative distribution curve of the total particle size range, the volume frequency / cumulative distribution curve, the characteristic particle sizes of D10 / D50 / D90, the Sotel average particle size D32, and the volume average particle size D43.

[0087] This embodiment achieves synchronous, in-situ, and high-precision measurement of particles ranging from 1 to 1000 μm, effectively avoiding particle size distortion problems such as secondary combustion and agglomeration caused by traditional nozzle sampling methods, and truly restoring the original distribution state of alumina particles inside the combustion chamber. Images acquired at different magnifications during engine operation are shown below. Figure 3 As shown.

[0088] from Figure 4 and Figure 5 It can be seen that the number distribution is multi-peaked, with obvious peaks near 40μm and 120μm, indicating that small-diameter particles dominate in terms of quantity; the volume distribution is a typical bimodal distribution, with two significant peaks near approximately 220μm and 700μm. Although large-diameter particles account for a low proportion of the total number, they play an important role in the total volume proportion through the volume weight of individual particles.

[0089] Characteristic particle size parameters: D10 is 22.4 μm, D50 is 67.2 μm, D90 is 235.2 μm, Soter average diameter D32 is 40.1 μm, and volume average diameter D43 is 110.1 μm, which fully quantifies the quantity and volume distribution characteristics of solid rocket motor condensation combustion products.

[0090] The above results show that this embodiment can achieve in-situ condensed combustion product particle size measurement over a wide range in solid rocket engines, providing reliable data support for solid rocket propellant formulation optimization and engine combustion performance control.

[0091] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A long-distance in-situ measurement system for wide particle size of solid rocket motor combustion particles, characterized in that, include: The first beam splitter (10) is positioned with its incident surface facing the observation window (24) of the solid rocket engine combustion chamber (12). An optical converging structure (13) is also provided between the combustion chamber (12) and the first beam splitter (10). The optical converging structure (13) is used to image the combustion particles in the combustion chamber (12) through the observation window (24) and to accurately converge parallel scattered light from different angles on the object side to the image focal point on the image focal plane. The first beam splitter (10) is located on the converging light path between the optical converging structure (13) and the image focal point. The first beam splitter (10) is used to split the incident converging beam into two paths. The first path is an upward beam reflected at 90°, and the second path is a relay beam transmitted to the right. The second beam splitter (11) is disposed on the outgoing light path of the first beam splitter (10); the incident surface of the second beam splitter (11) is directly opposite the transmission and exiting surface of the first beam splitter (10); the second beam splitter (11) is used to split the relay beam into two paths, the first path is the middle main beam transmitted to the right, and the second path is the lower beam reflected 90° downward. The first reflecting prism (14) and the second reflecting prism (15) are used to fold the upper beam from the first beam splitter (10) by 90° into a first beam that propagates horizontally to the right. The incident surface of the second reflecting prism (14) is directly opposite the lower exit surface of the second beam splitter (11). The second reflecting prism (15) is used to fold the lower beam from the second beam splitter (11) by 90° into a second beam that propagates horizontally to the right. The central main beam, the first beam, and the second beam all carry holographic information of the burning particles and are incident on the corresponding macro lenses, which then image and capture the beams carrying the holographic information.

2. The long-distance in-situ measurement system for wide particle size of solid rocket motor combustion particles according to claim 1, characterized in that, The optical converging structure (13) includes a cemented doublet achromatic positive lens and an aspherical positive lens arranged sequentially along the optical path. The cemented doublet achromatic positive lens and the aspherical positive lens are arranged inside the mounting tube, which is arranged in a left-right direction and the left end opening is positioned directly opposite the observation window (24).

3. The long-distance in-situ measurement system for wide particle size of solid rocket motor combustion particles according to claim 1, characterized in that, The central main beam is used by the second macro lens (17) to image and capture the burning particles, while the second high-speed camera (20) performs synchronous acquisition. The first beam is used by the first macro lens (16) to image the burning particles, and is simultaneously acquired by the first high-speed camera (19). The second beam is used by the third macro lens (18) to image the burning particles, while the third high-speed camera (21) performs synchronous acquisition. The magnification of the first macro lens (16), the second macro lens (17), and the third macro lens (18) are all different.

4. The long-distance in-situ measurement system for wide particle size of solid rocket motor combustion particles according to claim 1, characterized in that, Also includes: The light shield (22) is located between the optical converging structure (13) and the combustion chamber (12) to shield and suppress stray light, reflected light and ambient light from the combustion chamber (12) and prevent interference light from entering the imaging optical path.

5. The long-distance in-situ measurement system for wide particle size of solid rocket motor combustion particles according to claim 1, characterized in that, Also includes: The laser emitter (23), located on the left side of the combustion chamber (12), is used to emit a laser beam through the observation window (24) of the combustion chamber (12), so that the laser beam passes through the observation window (24) and enters the optical converging structure (13).

Images