Optical diagnostic system for plume contamination

Abstract

The invention discloses a plume pollution optical diagnosis system, which relates to the technical field of liquid engine plume liquid phase pollution detection, and comprises a double-frame camera group, a high-speed camera group, a laser illumination system and a sealing protection device, the double-frame camera group comprises two double-frame cameras which are arranged on the top of the vacuum simulation cabin up and down and are respectively used for particle image velocity measurement of a near field and a far field of a plume core jet flow area; according to the invention, through a non-contact optical diagnosis technology, the problems of flow field interference and insufficient dynamic observation of contact measurement are solved by carrying out partition measurement on the characteristics of droplets in different areas of plume; by adopting the layout that double-frame cameras are arranged up and down and a high-speed camera is combined with a reflector and a high-power lens, fine capture in the liquid film breaking process is realized; multi-technology combination is utilized to acquire droplet parameters in real time and construct a distribution model, the process from droplet generation to transportation is comprehensively covered, and an efficient and accurate non-contact diagnosis scheme is provided for plume pollution research.

Description

Technical Field

[0001] The present invention relates to the technical field of liquid engine plume liquid-phase pollution detection, and specifically to an optical diagnostic system for plume pollution. Background Art

[0002] During the operation of a liquid engine, its unsteady characteristics cause the combustion to be in a chemically non-equilibrium state during startup and shutdown, resulting in incomplete combustion of the propellant and the generation of some intermediate products. A part of the droplets cannot be completely evaporated and are ejected from the engine under the action of aerodynamic force, forming liquid-phase pollutants in the plume.

[0003] Previously, most studies on plume liquid-phase pollution used contact measurement methods. However, contact measurement methods have a large interference on the flow field itself, which may affect the distribution and formation process of droplets. In addition, contact measurement usually cannot obtain the particle size information of droplets in real time, but collects droplets and analyzes them after the experiment, resulting in certain errors in the measurement results and affecting the accuracy and reliability of the experiment. The lack of dynamic observation of this process also makes the research in this area lack a detailed understanding of the formation mechanism and breakup process of the near-wall liquid film. There is an urgent need for a technical solution that can achieve non-contact and real-time accurate measurement.

[0004] In view of this, an optical diagnostic system for plume pollution is provided to overcome the above problems. Summary of the Invention

[0005] The purpose of the present invention is to provide an optical diagnostic system for plume pollution to solve the problems raised in the above background art.

[0006] To solve the above technical problems, the optical diagnostic system for plume pollution provided by the present invention includes:

[0007] Dual-frame camera group: Two dual-frame cameras are arranged vertically on the top of the vacuum simulation chamber, and are respectively used for particle image velocimetry measurement in the near field and far field of the plume core jet area. The fields of view of the dual-frame cameras cover the high-speed movement area of droplets inside and after the nozzle exit.

[0008] High-speed camera group: The first high-speed camera is equipped with a high-power lens and focuses on the area of 0-20 mm from the lip of the nozzle exit through a reflector for dynamic observation of the liquid film breakup process. The second high-speed camera is installed on the side wall of the vacuum chamber, and its field of view covers the peripheral area of the plume for particle tracking velocimetry measurement of large-particle-size and low-speed droplets.

[0009] Laser illumination system: It includes a dual-cavity pulsed laser and a semiconductor continuous laser. The dual-cavity pulsed laser forms a sheet of light to illuminate the droplets in the core area, and the continuous laser forms a uniform sheet of light to illuminate the droplets in the nozzle expansion section, lateral area, and peripheral area.

[0010] Sealing protection device: Both the dual-frame camera and the high-speed camera are encapsulated in a sealed protective cover. The tail end of the protective cover is connected to the vacuum chamber flange through a corrugated pipe, which is used for the camera cable to lead out and seal.

[0011] Further, in the dual-frame camera group, the upper dual-frame camera lens faces downward, and the field of view covers the near-field area within the nozzle and 0 - 1 m after the outlet. The lower dual-frame camera lens faces downward, and the field of view covers the far-field diffusion area of 1 - 3 m. The shooting focal planes of the two cameras and the pulsed laser sheet light plane coincide with the nozzle central cross-section.

[0012] Further, the optical axis of the first high-speed camera is deflected by 90° through a 45° mirror and focused on the area of 0 - 20 mm at the nozzle lip. The magnification of the high-power lens is ≥10×, and the spatial resolution is ≤1 μm / pixel. It cooperates with a frame rate of more than 10 4 fps to complete the dynamic capture of the liquid film breakup process.

[0013] Further, the included angle between the optical axis of the second high-speed camera and the nozzle axis is 15° - 45°. The field of view covers the droplets in the peripheral area, and the movement trajectory of a single droplet is tracked through continuous imaging at more than 500 fps.

[0014] Further, the double-cavity pulsed laser is a Nd:YAG laser with a wavelength of 532 nm, a single-pulse energy of 100 - 200 mJ, and an adjustable range of pulse interval Δt of 1 - 100 μs. It is used to emit two laser pulses within an extremely short time interval to capture the scattered light of high-speed droplets.

[0015] Further, the semiconductor continuous laser has a wavelength of 650 nm and a power of ≥30 W. It forms a uniform sheet light through a collimating lens to illuminate the droplets in the nozzle expansion section and the peripheral area, and is used to provide a stable light source for low-speed droplet tracking.

[0016] Further, the sealed protective cover is made of aluminum alloy, and an anti-reflection coating is provided on the inner wall. The inner diameter of the corrugated pipe is ≥50 mm, allowing the camera power supply line and data line to pass through and maintaining the air pressure isolation inside and outside the vacuum chamber.

[0017] Further, it also includes a synchronous control device and a graphics workstation. The synchronous control device triggers the dual-frame camera to collect images at a frequency of more than 10 kHz, calculates the droplet velocity vector field by combining the cross-correlation algorithm, inversely calculates the droplet diameter using the Mie scattering theory, extracts the droplet edge and tracks the trajectory through the watershed algorithm, and constructs a three-dimensional spatio-temporal distribution model of plume contamination.

[0018] Compared with the prior art, the beneficial effects of the present invention are:

[0019] 1. Non-contact measurement eliminates the flow field interference and improves the measurement accuracy:

[0020] A non-contact optical diagnosis method that combines a double-frame camera group (PIV technology) and a high-speed camera group (PTV technology). The camera system is encapsulated in a sealed protective cover, and optical observation of droplets is achieved through laser illumination, avoiding interference with the flow field by contact devices such as probes.

[0021] For example, the measured velocity measurement accuracy of droplets in the core area reaches ±2%, and the particle size inversion error < 5%. The original motion state of droplets in the flow field is truly restored, solving the problems of droplet distribution and motion trajectory distortion caused by contact measurement, and ensuring the reliability of experimental data.

[0022] 2. Zonal diagnosis and joint measurement cover the entire physical process, filling the gap in dynamic observation:

[0023] The double-frame cameras are arranged vertically, covering the near field (0 - 1 m) and far field (1 - 3 m) of the plume core area respectively. The velocity field and particle size distribution of high-speed droplets (velocity 30 - 1500 m / s, particle size 10 - 500 μm) are measured through PIV technology.

[0024] High-speed camera 1 is equipped with a high-power lens with a magnification of ≥10× (spatial resolution ≤ 1 μm / pixel) and a reflector. It focuses on the area of 0 - 20 mm at the lip of the nozzle (liquid film thickness 50 - 300 μm), and captures the liquid film breakup process at a frame rate of 10 4 fps.

[0025] High-speed camera 2 observes large-particle-size low-speed droplets (particle size 1 - 4 mm, velocity < 50 m / s) in the peripheral area (1.5 - 3 m), and tracks the motion trajectory through PTV technology.

[0026] Realize the full-process dynamic observation from liquid film breakup (initial droplet generation) to high-speed transport in the core area and low-speed diffusion in the peripheral area. For example, reverse-moving droplets (velocity -10 m / s, particle size 2 mm) are observed in the peripheral area, directly verifying the mechanism of the reverse action of the plume on droplets after liquid film breakup, filling the gap in the observation of the process of "liquid film formation → breakup → droplet transport" in the existing technology, and providing key data for studying the plume pollution generation mechanism.

[0027] 3. High-precision imaging solves the problem of observing subtle changes in the liquid film:

[0028] High-speed camera 1 is equipped with a high-power lens with a magnification of ≥10× (spatial resolution ≤ 1 μm / pixel). The optical path is deflected by a 45° reflector, and the field of view is focused on the tiny area of 0 - 20 mm at the lip of the nozzle exit, and the liquid film dynamics are captured in combination with high-frequency imaging (above 10 4 fps).

[0029] Break through the problem of insufficient resolution caused by the liquid film thickness of only dozens to hundreds of micrometers in traditional cameras, clearly record the complete process of the liquid film from fluctuation (0.1 ms period) to breaking into initial droplets (particle size 50 - 200 μm, initial velocity 10 - 30 m / s), provide direct image evidence for analyzing the liquid film breaking mechanism (such as Rayleigh - Taylor instability), and solve the technical bottleneck of "blurred observation" in the formation and breaking process of the near - wall liquid film.

[0030] 4. Optimize the optical layout and light source design to improve the system synergy and measurement efficiency:

[0031] The dual - frame cameras are arranged vertically, and the high - speed cameras are placed on both sides and deflect the light path through mirrors, so that the overlapping area of the fields of view of the four cameras is ≥10% and there is no spatial interference, ensuring synchronous acquisition of multiple devices (time synchronization error < 1 μs);

[0032] The dual - cavity pulsed laser (532 nm) provides transient sheet light (pulse interval 1 - 100 μs) for high - speed droplet imaging in the core area, and the semiconductor continuous laser (650 nm) provides stable sheet light to illuminate the liquid film and low - speed droplets in the peripheral area.

[0033] The pulsed laser meets the requirements for transient capture of high - speed droplets (for example, a droplet with a speed of 500 m / s has a displacement < 10 pixels within Δt = 2 μs), and the continuous laser supports high - frequency tracking of low - speed droplets (frame rate above 500 fps). The targeted application of these two types of light sources improves the speed measurement accuracy in the core area to ±2% and the particle size measurement error in the peripheral area < 3%. At the same time, the camera focal plane coincides with the laser sheet light plane at the center section (yz plane) of the nozzle, ensuring that the spatio - temporal consistency error of the data < 0.5%, and realizing the synergy and efficiency of multi - region diagnosis.

[0034] 5. Replace post - experiment analysis with real - time dynamic measurement to improve the real - time performance and reliability of data:

[0035] The dual - frame cameras trigger to acquire dual - frame images at a frequency of 10 kHz, and the high - speed cameras continuously image at a frame rate above 500 fps. Combine cross - correlation algorithm, watershed algorithm, etc. to process droplet displacement, edge features and motion trajectories in real - time, and construct a three - dimensional spatio - temporal distribution model.

[0036] The real - time acquisition delay of parameters such as droplet particle size, velocity, and trajectory is < 50 μs. Compared with traditional post - experiment analysis (which takes more than 24 hours and has an error > 10%), the real - time performance of the data is improved by 100%, and the measurement error is reduced by more than 60%, providing an immediate and accurate experimental basis for the dynamic characteristic research of engine plume pollution.

[0037] Through non-contact zonal diagnosis, high-precision observation of the liquid film, non-interfering optical layout, and targeted light source design, the present invention systematically solves the core problems in the prior art such as contact interference, insufficient real-time performance, and incomplete observation, achieving "real-time, accurate, and comprehensive" measurement of the entire process of plume contamination from generation to transport, providing key technical support for the research on the mechanism of liquid rocket engine plume contamination and the development of control technologies. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 is a top view of the optical diagnosis system for plume contamination of the present invention;

[0039] Figure 2 is a front view of the optical diagnosis system for plume contamination of the present invention;

[0040] Figure 3 is a schematic diagram of the field of view of the optical diagnosis system for plume contamination of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0041] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0042] Please refer to Figures 1 - 3 , the present invention provides a technical solution:

[0043] Refer to Figures 1 - 3 shown, an embodiment of the optical diagnosis system for plume contamination:

[0044] I. Application Scenario:

[0045] This embodiment is applied to the experimental study on the plume contamination characteristics of a certain type of liquid rocket engine. The experimental environment is a vacuum simulation chamber (the internal vacuum degree is maintained below 1×10-3 Pa), and the chamber size is 3m×3m×4m. The object to be measured is a certain bipropellant liquid rocket engine, the nozzle exit diameter is 50mm, and the experimental condition is the process from engine startup to shutdown (the total duration is 120s). The focus is on observing the droplet distribution in the core jet region (0-0.5m from the nozzle exit), the diffusion region (0.5-1.5m), and the peripheral region (1.5-3m) of the plume, and simultaneously dynamically recording the liquid film breakup process at the nozzle exit (in the range of 0-20mm from the nozzle lip).

[0046] II. Implementation Steps:

[0047] (I) System Hardware Installation and Calibration (24 hours before the experiment):

[0048] Camera system layout:

[0049] Two double-frame cameras (double-frame camera 1 and double-frame camera 2) are arranged vertically (z-axis) above and below the top of the vacuum chamber, with a spacing of 0.3 m. The lens of double-frame camera 1 faces downward, and its field of view covers the area within the nozzle and 0 - 1 m behind the outlet, for PIV measurement of high-speed droplets (speed 30 - 1500 m / s, particle size 10 - 500 μm) in the core area; the lens of double-frame camera 2 faces downward, and its field of view covers the 1 - 3 m far-field area, for PIV measurement of tiny droplets (particle size 1 - 2 μm) in the diffusion area.

[0050] A high-speed camera 1 (equipped with a 100 mm focal length high-power lens) is installed on the left side wall of the vacuum chamber. The optical axis of the lens points horizontally (x-axis) towards the nozzle outlet. The optical path is deflected by 90° through a 45° mirror (installed on the right side of the nozzle, 50 mm from the outlet), so that the field of view is focused on the 0 - 20 mm area of the nozzle lip (liquid film thickness 50 - 300 μm) to achieve dynamic observation of the liquid film breaking process.

[0051] A high-speed camera 2 is installed on the right side wall of the vacuum chamber. The angle between the optical axis of the lens and the x-axis is 30°. The field of view covers the peripheral area (1.5 - 3 m) for PTV measurement of large-particle-size and low-speed droplets (particle size 1 - 4 mm, speed < 50 m / s).

[0052] All cameras are encapsulated in a sealed protective cover (made of aluminum alloy, with an anti-reflective coating on the inner wall). The end of the protective cover is connected to the chamber flange through a bellows with an inner diameter of 80 mm to ensure the normal operation of the cameras in a vacuum environment. At the same time, the cables (power cable, data cable) are led out of the chamber through the bellows to the external synchronous control equipment.

[0053] The double-frame cameras are arranged vertically above and below to cover the near-field and far-field core areas. High-speed camera 1 uses a mirror to achieve high-precision imaging of the tiny liquid film area, avoiding the problem of insufficient resolution caused by the small liquid film thickness (only dozens to hundreds of micrometers) of traditional cameras; high-speed camera 2 and the double-frame cameras are placed on both sides. Through the design of overlapping fields of view (overlapping area ≥ 10%), spatial interference is eliminated to ensure the coordinated operation of multiple cameras.

[0054] Laser illumination system debugging:

[0055] Pulsed laser system: A double-cavity Nd:YAG laser (wavelength 532 nm, single-pulse energy 200 mJ, adjustable range of pulse interval Δt 1 - 100 μs) is used. A sheet of light with a thickness of 1 mm is formed through a cylindrical lens group. The plane of the sheet of light coincides with the central section (yz plane) of the nozzle to illuminate the droplets within the field of view of the double-frame cameras. For high-speed droplets in the core area (such as speed 500 m / s), set Δt = 2 μs to ensure that the droplet displacement in the two frames of images < 10 pixels (camera resolution 2048×2048, pixel size 7 μm).

[0056] Continuous laser system: A semiconductor continuous laser (wavelength 650 nm, power 50 W) is used. Through a collimating lens, a uniform sheet of light is formed to illuminate the expansion section of the nozzle (from 100 mm to the outlet of the nozzle), the lateral region (±50 mm along the x-axis), and the droplets in the peripheral area, providing a stable light source for the PTV measurement of the high-speed camera 2, and simultaneously meeting the illumination requirements of the high-speed camera 1 for the liquid film.

[0057] The pulsed laser cooperates with the double-frame camera to achieve transient imaging of high-speed droplets (time resolution up to 1 μs), solving the problem that traditional contact measurements cannot obtain particle size and velocity in real time; the continuous laser provides stable illumination, meeting the trajectory tracking of low-speed droplets in the periphery (frame rate 1000 fps), and avoiding errors caused by post-experiment analysis.

[0058] (II) Experimental data acquisition (during engine operation):

[0059] Measurement of droplets in the core area and diffusion area (double-frame cameras 1 and 2):

[0060] From 0 to 30 s (start-up stage) after engine ignition, the double-frame camera is triggered at a frequency of 10 kHz, and two images with an interval of Δt = 5 μs are acquired each time it is triggered. The droplet displacement is calculated through the cross-correlation algorithm to obtain the velocity vector field (accuracy ±2%), and at the same time, using the Mie scattering theory, the particle size is inversed according to the gray value of the droplet image (error < 5%).

[0061] Non-contact measurement avoids probe interference with the flow field and obtains the distribution of droplet particle size (10 - 500 μm) and velocity (30 - 1500 m / s) in real time, providing dynamic data for analyzing droplet generation under combustion non-equilibrium conditions.

[0062] Tracking of droplets in the peripheral area (high-speed camera 2):

[0063] During the stable operation stage of the engine (30 - 90 s), the high-speed camera 2 continuously shoots at a frame rate of 500 fps. The droplet edges are extracted through an image processing algorithm (such as the watershed algorithm), and the movement trajectories of individual droplets for more than 100 frames are tracked. The velocity (accuracy ±1 m / s) and particle size (converted through the number of pixel points, error < 3%) are calculated. Reverse-moving droplets (velocity -10 m / s, particle size 2 mm) are observed in the peripheral area, verifying the phenomenon that droplets are affected by the reverse action of the plume after liquid film breakup.

[0064] High-frequency continuous imaging realizes the trajectory tracking of large-particle-size and low-speed droplets, solving the problem that traditional contact measurements cannot dynamically observe the movement trajectories of droplets, and providing key parameters for the plume pollution diffusion model.

[0065] Observation of the liquid film breakup process (high-speed camera 1):

[0066] 10 s (110 - 120 s) before engine shutdown, the high-speed camera 1 captures images at a frame rate of 10 4 fps, and cooperates with a high-magnification lens (magnification 10×, spatial resolution 1 μm / pixel) to capture the breakup process of the liquid film on the nozzle lip (thickness 100 μm). The complete process of the liquid film from fluctuation (0.1 ms period) to breakup into initial droplets (particle size 50 - 200 μm) is recorded, and the initial velocity (10 - 30 m / s) and distribution angle (±15°) of the droplets are obtained.

[0067] High-time (100 μs) and spatial-resolution (1 μm / pixel) imaging solves the problem that conventional cameras cannot capture the subtle changes of the liquid film, providing direct evidence for revealing the liquid film breakup mechanism (such as Rayleigh - Taylor instability).

[0068] (3) Data processing and analysis (24 hours after the experiment):

[0069] Multi-source data fusion:

[0070] The PIV data (velocity field, particle size distribution) of the double-frame camera, the PTV data (trajectory, particle size) of the high-speed camera, and the liquid film images are imported into self-developed software. Data alignment is achieved through coordinate transformation (based on the pre-calibrated world coordinate system), and a three-dimensional spatio-temporal distribution model of plume contamination is constructed.

[0071] By integrating the measurement data in different regions, the whole process of droplets from generation (liquid film breakup) to transport (movement in the core region and peripheral region) is comprehensively reflected, solving the problem of insufficient research on the formation mechanism of the near-wall liquid film in the existing technology.

[0072] Error calibration and verification:

[0073] Using standard particles (glass beads with a particle size of 100 μm and a speed of 200 m / s) for system calibration, it is verified that the PIV measurement error < 3%, the PTV particle size measurement error < 2%, and the liquid film thickness measurement error < 5%.

[0074] Ensuring data reliability through calibration provides an accurate experimental basis for engine plume contamination prediction.

[0075] III. Summary:

[0076] 1. Joint diagnostic method for zoning characteristics:

[0077] Two double-frame cameras (double-frame camera 1 and 2) are arranged vertically, covering the near field (0 - 1 m) and far field (1 - 3 m) of the plume core region respectively. The PIV technology is used to measure the velocity field and particle size distribution of high-speed droplets (10 - 500 μm, 30 - 1500 m / s);

[0078] Two high-speed cameras are respectively used for PTV tracking of low-speed large-size droplets (1 - 4 mm, < 50 m / s) in the peripheral area (high-speed camera 2) and observation of the liquid film breakup at the nozzle exit (high-speed camera 1 + high-power lens).

[0079] Non-contact in-situ monitoring: Through the combined diagnosis of PIV / PTV, the interference of the contact measurement on the flow field (such as the probe changing the droplet trajectory) is avoided. In the embodiment, the measurement accuracy of the droplet velocity in the core area reaches ±2%, and the inversion error of the particle size is < 5%, truly reflecting the original motion characteristics of the droplets under the non-equilibrium combustion state.

[0080] Full physical process coverage: The zonal diagnosis covers the whole process of droplet generation (liquid film breakup), high-speed transport (core area), and low-speed diffusion (peripheral area). For example, reverse-moving droplets (velocity -10 m / s, particle size 2 mm) are observed in the peripheral area, directly verifying the mechanism of the reverse action of the plume on the droplets after the liquid film breakup, filling the gap in the dynamic observation of the "liquid film breakup → droplet transport" process in the existing technology.

[0081] 2. High-precision measurement of the tiny area of the liquid film:

[0082] High-speed camera 1 is equipped with a 10× high-power lens (spatial resolution 1 μm / pixel). The optical path is deflected by a 45° mirror and focused on the area of 0 - 20 mm at the nozzle lip (liquid film thickness 50 - 300 μm), and the liquid film breakup process is captured at a frame rate of 10 4 fps.

[0083] Breaking through the resolution limit: Due to the liquid film thickness of only dozens to hundreds of micrometers in traditional cameras, the lack of pixel points leads to the loss of details. In this embodiment, through high-power magnification and high-speed imaging, the dynamic process of the liquid film from fluctuation (0.1 ms period) to breakup into initial droplets (particle size 50 - 200 μm, initial velocity 10 - 30 m / s) is clearly recorded, providing direct image evidence for analyzing the liquid film breakup mechanism (such as Rayleigh-Taylor instability), and solving the problem of "blurred observation" of the formation and breakup process of the near-wall liquid film in the existing technology.

[0084] 3. Non-interfering spatial arrangement and optical system design:

[0085] Camera layout: The double-frame cameras are arranged vertically (spacing 0.3 m). High-speed camera 1 is installed on the right side of the nozzle through a mirror (optical axis deflected by 90°), and high-speed camera 2 is located on the left side. The overlapping area of the fields of view of the four cameras

[0086] ≥10%, and the sealed protective cover is connected through a bellows to avoid spatial interference;

[0087] Laser illumination: A dual - cavity pulsed laser (532 nm) forms a sheet - light illumination core area (Δt = 2 μs), and a continuous laser (650 nm) illuminates the liquid film and the peripheral area. The sheet - light planes of the two types of light sources and the camera focal plane coincide with the nozzle central cross - section (yz plane).

[0088] Improved system coordination: A reasonable spatial arrangement enables the compact installation of the dual - frame camera and the high - speed camera in the vacuum chamber, avoiding the interference of the protective cover. At the same time, it ensures that the laser sheet - light and the camera focal plane are strictly coincident, realizing synchronous acquisition of multiple devices (time - synchronization error < 1 μs). For example, PIV measurement in the core area and observation of liquid - film breakup can be carried out simultaneously, and the spatio - temporal consistency error of the data is < 0.5%, ensuring the comprehensiveness of the experimental results.

[0089] Optimized illumination efficiency: The pulsed laser meets the requirements of high - speed droplet transient imaging (e.g., a droplet with a speed of 500 m / s has a displacement < 10 pixels within Δt = 2 μs), and the continuous laser provides a stable light source for tracking the trajectories of low - speed droplets (frame rate 500 fps). The targeted application of the two types of light sources improves the measurement accuracy of droplets in different regions: the speed measurement accuracy in the core area is ±2%, and the particle - size measurement error in the peripheral area is < 3%, solving the problem in the prior art that "a single light source cannot take into account droplets with different speeds / sizes".

[0090] 4. Core improvements compared with the prior art:

[0091] Non - contact measurement replaces contact interference:

[0092] The prior art relies on probes to collect droplets, resulting in flow - field distortion and inability to perform real - time measurement. In this embodiment, in - situ observation is realized in the vacuum chamber through optical diagnostic techniques, and the reduction degree of droplet distribution and movement trajectory is increased by 100%, providing reliable data for the study of the true characteristics of engine plume pollution.

[0093] Dynamic real - time measurement replaces post - experiment analysis:

[0094] The 10 kHz trigger frequency of the dual - frame camera and the 10 4 fps frame rate of the high - speed camera enable real - time acquisition of droplet particle size, speed, and trajectory (delay < 50 μs). Compared with the traditional method (post - experiment analysis takes more than 24 hours and the error is > 10%), the real - time performance of the data is improved by 100%, and the measurement error is reduced by more than 60%.

[0095] Full - area coverage replaces local observation:

[0096] Partition diagnosis and multi-camera collaboration expand the measurement range from the core area to the peripheral area and the liquid film generation area, covering all-scale droplets with a particle size of 1 μm - 4 mm and a velocity of 1 - 1500 m / s, solving the defects of the existing technology of "only being able to observe a single area and lacking the initial conditions of liquid film breakup", and providing key parameters for establishing a full-chain model of plume pollution generation - transport.

[0097] Through the engineering implementation of the technical key protection scheme in this embodiment, a non-contact diagnosis system covering the entire physical process of plume pollution is constructed. Through partition diagnosis (combined PIV / PTV), high-precision observation of the liquid film, non-interference layout, and targeted light source design, problems such as contact interference, insufficient real-time performance, and incomplete observation in the existing technology are effectively solved, improving the measurement accuracy of droplet particle size to within ±3% and the velocity measurement error < 2%, and for the first time realizing the dynamic capture of the liquid film breakup process (thickness 50 - 300 μm, breakup time < 0.1 ms). This system provides "real-time, accurate, and comprehensive" experimental technical means for the research on the mechanism of liquid engine plume pollution, promoting the development of engine pollution control technology.

Claims

1. Plume pollution optical diagnosis system, characterized in that, Comprising: Dual-frame camera group: Two dual-frame cameras are arranged vertically at the top of the vacuum simulation chamber, respectively used for particle image velocimetry measurement in the near field and far field of the plume core jet region. The fields of view of the dual-frame cameras cover the high-speed movement region of droplets inside the nozzle and after the outlet. High-speed camera group: The first high-speed camera is equipped with a high-power lens and focuses on the 0 - 20 mm region of the nozzle outlet lip through a mirror, used for dynamic observation of the liquid film breaking process; the second high-speed camera is installed on the side wall of the vacuum chamber, and its field of view covers the peripheral region of the plume, used for particle tracking velocimetry measurement of large-diameter low-speed droplets. Laser illumination system: Comprising a dual-cavity pulsed laser and a semiconductor continuous laser. The dual-cavity pulsed laser forms a sheet of light to illuminate the droplets in the core region, and the continuous laser forms a uniform sheet of light to illuminate the droplets in the nozzle expansion section, lateral region, and peripheral region. Sealing and protection device: The dual-frame cameras and high-speed cameras are both encapsulated in a sealed protective cover. The tail end of the protective cover is connected to the flange of the vacuum chamber through a bellows, used for leading out the camera cables and sealing.

2. The plume contamination optical diagnosis system according to claim 1, wherein: In the dual-frame camera group, the upper dual-frame camera has its lens facing downwards, and its field of view covers the 0 - 1 m near field region inside the nozzle and after the outlet; the lower dual-frame camera has its lens facing downwards, and its field of view covers the 1 - 3 m far field diffusion region. The shooting focal planes of the two cameras coincide with the pulsed laser sheet of light plane on the central cross-section of the nozzle.

3. The plume contamination optical diagnostic system according to claim 1, characterized in that: The optical axis of the first high-speed camera is deflected by 90° through a 45° mirror and focused on the 0-20 mm area of the nozzle lip. The magnification of the high-power lens is ≥10×, and the spatial resolution is ≤1 μm / pixel. It completes the dynamic capture of the liquid film breakup process at a frame rate of 10 4 fps or above.

4. The plume contamination optical diagnostic system according to claim 1, wherein: The optical axis of the second high-speed camera forms an angle of 15° - 45° with the nozzle axis, and its field of view covers the droplets in the peripheral region. The movement trajectories of individual droplets are tracked through continuous imaging at a rate of more than 500 fps.

5. The plume contamination optical diagnosis system according to claim 1, characterized in that: The dual-cavity pulsed laser is a Nd:YAG laser, with a wavelength of 532 nm, a single-pulse energy of 100 - 200 mJ, and an adjustable pulse interval Δt in the range of 1 - 100 μs, used to emit two laser pulses within an extremely short time interval to capture the scattered light of high-speed droplets.

6. The plume contamination optical diagnosis system according to claim 1, characterized in that: The semiconductor continuous laser has a wavelength of 650 nm and a power of ≥30 W. It forms a uniform sheet of light through a collimating lens to illuminate the droplets in the nozzle expansion section and peripheral region, used to provide a stable light source for low-speed droplet tracking.

7. The plume contamination optical diagnostic system according to claim 1, characterized in that: The sealed protective cover is made of aluminum alloy, with an anti-reflection coating on the inner wall. The inner diameter of the bellows is ≥50 mm, allowing the camera power supply wires and data lines to pass through and maintaining air pressure isolation inside and outside the vacuum chamber.

8. The plume contamination optical diagnostic system according to claim 1, characterized in that: It also includes a synchronous control device and a graphics workstation. The synchronous control device triggers the dual-frame cameras to collect images at a frequency of more than 10 kHz, calculates the droplet velocity vector field by combining the cross-correlation algorithm, inversely calculates the droplet diameter using the Mie scattering theory, extracts the droplet edges and tracks the trajectories through the watershed algorithm, and constructs a three-dimensional spatio-temporal distribution model of plume contamination.

Images