CN104897530B - A kind of spray atomization measurement of full field device and method based on photon temporal filtering technique - Google Patents

Abstract

Measurement of full field device and method is atomized the invention discloses a kind of spray based on photon temporal filtering technique, and described device is made up of femto-second laser, beam splitter, the polarizer, variable rectangular diaphragm, beam-expanding system, target injection device, the first convex lens, light kerr medium, analyzer, the second convex lens, transmitance and its variable attenuator, ICOMS cameras, half-wave plate, light path delayer, the first speculum, the second speculum, optical beam dump, sequential control system and the computer of spatial distribution structure.Trajectory photon is chosen imaging by the present invention using optical kerr effect, and then obtains field pattern of clearly spraying；Using variable rectangular diaphragm and beam-expanding system, it is the variable rectangular light spot of length-width ratio by beam shaping, effectively covers whole spray fields；Using the variable attenuator of transmitance and its spatial distribution structure, so as to get the trajectory photon number density up to the near field region of ICMOS cameras and other regions is suitable, so as to obtain clearly spray field full field image simultaneously.

Description

An injection atomization full-field measurement device and method based on photon time-domain filtering technology

technical field

The invention belongs to the field of laser measurement, and relates to a full-field measurement device and method for injection atomization of an engine injector based on photon time-domain filtering technology.

Background technique

Liquid fuel (hydrocarbon) has the advantages of easy storage, portability, high density, high calorific value per unit volume, and practical application. It is widely used in ramjet engines, turbine engines, detonation engines, rocket engines, and automobile engines. The injection and atomization process of engine liquid fuel plays a key role in the entire engine working process, and has a very significant impact on engine combustion efficiency, ignition performance and combustion stability. In addition, the design technology of modern engines mainly uses computational fluid dynamics (CFD), but due to the complexity of the combustion process and the lack of experimental data, the CFD model has many shortcomings, one of which is that it is difficult to accurately simulate the liquid fuel atomization process , which in turn affects the accuracy of the simulation of the entire combustion process.

The injection atomization process can be roughly divided into the near field area, the secondary atomization area and the evaporation area, as shown in Figure 1. The liquid breakage and primary atomization of the fuel in the near-field area, where the droplet size is large and the density is high, will cause very serious absorption and scattering of photons in this area, so conventional optical measurement methods cannot obtain the near-field area. information. At present, for the near-field region, the imaging measurement method based on ballistic photon time-gated technology (photon time-domain filtering technology) is a very promising measurement method. Here it needs to be explained: when the laser beam passes through the flow field, due to the different scattering times, it can be roughly divided into three categories. field information. The second is the snake photon, which generally undergoes 1 to 4 scatterings when passing through the flow field, and they exit along the direction of the incident photon, but their divergence angle is larger than that of the ballistic photon. There is also a kind of photon called diffuse photon, which undergoes more than 5 scatterings when passing through the flow field, and its outgoing direction has nothing to do with the incident direction. It exits at a divergence angle of 4π, does not carry flow field information, and belongs to noise. When the incident light passes through the flow field, ballistic photons are at the forefront in terms of time sequence, followed by snake photons, and finally diffuse photons. Ballistic photons carrying flow field information can be selected by using their time characteristics.

The droplet size and density in the secondary atomization area (sparse atomization area) and evaporation area are small, and conventional optical measurement methods, such as shadow method, PLIF, Mie scattering technology and laser phase Doppler particle analysis technology, etc., can for measurements in these two regions.

Since the near-field optical transmittance is about 10 ^-2 10 ^-5 , the number density of ballistic photons is much smaller than that of diffuse photons. The optical transmittance of the secondary atomization area is greater than 0.1, and the optical transmittance of the evaporation area is greater than 0.8, and the ballistic photons are the main ones. Due to the above reasons, the current fogging measurement faces two difficulties. First, for the near-field area, the optical transmittance difference between the center and the edge of the spray area is about 10 ² to 10 ⁵ times, so it is difficult to obtain a clear near-field area at the same time during measurement. The overall structure diagram of . Second, due to the large difference in optical transmittance between the near-field area and other areas, the same measurement method cannot be used. At present, different measurement methods are used to measure separately. Due to the drastic process, there is no correlation between the flow field structure in the near-field region and other regions measured by different means. Based on the above problems, the current atomization measurement methods cannot obtain the full-field transient structure of the injection atomization process at the same time, and cannot reflect the real injection atomization process.

Contents of the invention

The purpose of the present invention is to provide a spray atomization full-field measurement device and method based on photon time-domain filtering technology, which is realized by using ballistic photon time gating technology, attenuation technology with variable transmittance and transmittance spatial distribution structure Injection atomization full-field measurement, used to obtain the engine injection atomization full-field transient structure.

The purpose of the present invention is achieved through the following technical solutions:

A spray atomization full-field measurement device based on photon time-domain filtering technology, including a femtosecond laser, a beam splitter, a polarizer, a variable rectangular diaphragm, a beam expander system, a target injector, a first convex lens, Optical Kerr medium, analyzer, second convex lens, attenuator with variable transmittance and its spatial distribution structure, ICOMS camera, half-wave plate, optical path delay device, first mirror, second mirror, light beam Collector, timing control system, computer, timing control system controls femtosecond laser and ICOMS camera, computer controls ICMOS camera to collect and store image data and controls optical path delay device, femtosecond laser output by femtosecond laser is divided into two parts by beam splitter The beams are used as the imaging beam and the gated beam respectively. The gated beam passes through the half-wave plate, the optical path delayer, the first mirror, the second mirror and the optical Kerr medium in turn, and finally reaches the beam collector, and the imaging beam passes through the starting beam in turn. Polarizer, variable rectangular aperture, beam expander, target injector, first convex lens, optical Kerr medium, analyzer, second convex lens, attenuator with variable transmittance and its spatial distribution structure, and finally Reach the ICOMS camera.

The method for obtaining the full-field image information of the injection atomization flow field by using the above-mentioned device is realized by the following steps:

Step 1: using a femtosecond laser to output 800nm femtosecond laser.

Step 2: Use a beam splitter to split the femtosecond laser into two beams at a ratio of 1:1, which are respectively used as an imaging beam and a gating beam. The imaging beam is used for spray field imaging, and the gating beam is used to trigger the optical Kerr gate.

Step 3: The gated beam passes through the half-wave plate, the optical path delayer, the first reflector, the second reflector and the optical Kerr medium in sequence, and finally reaches the beam collector.

Step 4: (1) The variable rectangular aperture and the beam expander system shape the imaging beam into a rectangular spot with a variable aspect ratio, effectively covering the entire spray field of the target injector; (2) The imaging beam passes through the target injector spray field, forming ballistic photons and noises (snake photons and diffuse photons) carrying spray field information; (3) Optical Kerr gate is formed by polarizer, analyzer and optical Kerr medium to realize the imaging beam Time-domain filtering, to filter out diffuse photons and snake photons; (4) Apply an attenuator with variable transmittance and spatial distribution structure to homogenize the full-field ballistic photons, so that the near-field area and other areas of the ICMOS camera reach The number density of ballistic photons is equivalent; (5) ICOMS camera is used to receive ballistic photons to form a clear full-field image of the spray field.

Step 5: Use the timing control system to simultaneously control the femtosecond laser and the ICOMS camera to ensure that when the imaging beam reaches the ICMOS camera, the camera is in a working state. When the imaging beam ends, the camera stops receiving data immediately.

Step 6: Use the computer to control the ICMOS camera to collect and store image data; at the same time, use the computer to control the optical path delayer to realize time-domain filtering of the imaging beam.

The present invention has the following advantages:

1. Using the optical Kerr effect as a time-domain filtering technology, the ballistic photons are selected for imaging, and then a clear spray field structure map is obtained.

2. Using the variable rectangular aperture and beam expander system, the beam is shaped into a rectangular spot with a variable aspect ratio, effectively covering the entire spray field.

3. Apply the attenuator with variable transmittance and its spatial distribution structure, so that the number density of ballistic photons reaching the near-field area of the ICMOS camera and other areas is equivalent, so as to obtain clear images of the spray field at the same time, solving the problem that cannot be achieved at the same time The problem of obtaining the whole field information of the spray field.

Description of drawings

Fig. 1 is a schematic diagram of the structure of the injection atomization field of the mutual impact injector;

Fig. 2 is a schematic diagram of an injection atomization full-field measurement device based on photon time-domain filtering technology;

Fig. 3 is a schematic diagram of a variable rectangular aperture;

Figure 4 is an attenuator with variable transmittance and its spatial distribution structure;

In the figure, 1. femtosecond laser; 2. beam splitter; 3. polarizer; 4. variable rectangular aperture; 5. beam expander system; 6. target injector; 7. first convex lens; 8. Optical Kerr medium; 9. Analyzer; 10. Second convex lens; 11. Attenuator with variable transmittance and its spatial distribution structure; 12. ICOMS camera; 13. Half-wave plate; 14. Optical path delayer ; 15, the first mirror; 16, the second mirror; 17, the beam collector; 18, the timing control system; 19 computer.

Detailed ways

The technical solution of the present invention will be further described below in conjunction with the accompanying drawings, but it is not limited thereto. Any modification or equivalent replacement of the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention should be covered by the present invention. within the scope of protection.

Specific Embodiment 1: As shown in Fig. 2, Fig. 3 and Fig. 4, the injection atomization full-field measurement device based on photon time-domain filtering technology provided by this embodiment consists of a femtosecond laser 1, a beam splitter 2, a polarizer Device 3, variable rectangular diaphragm 4, beam expander system 5, target injector 6, first convex lens 7, optical Kerr medium 8, analyzer 9, second convex lens 10, transmittance and its spatial distribution structure Variable attenuator 11, ICOMS camera 12, half-wave plate 13, optical path delayer 14, first mirror 15, second mirror 16, beam collector 17, timing control system 18 and computer 19 constitute.

The femtosecond laser output by the femtosecond laser 1 is divided into two beams by the beam splitter 2, which are respectively used as the imaging beam and the gating beam, and the gating beam passes through the half-wave plate 13, the optical path delayer 14, the first reflector 15, The second mirror 16 and the optical Kerr medium 8 finally reach the beam collector 17, and the imaging beam passes through the polarizer 3, the variable rectangular diaphragm 4, the beam expander system 5, the target injector 6, the first convex lens 7, Optical Kerr medium 8 , analyzer 9 , second convex lens 10 , attenuator 11 with variable transmittance and its spatial distribution structure, and finally reaches ICOMS camera 12 .

In order to ensure that the ICMOS camera can effectively obtain the image of the spray field and effectively reduce background noise interference, the present invention uses a timing control system 18 to control the femtosecond laser 1 and the ICOMS camera 12 to ensure that when the imaging beam reaches the ICMOS camera 12, the camera 12 is in a working state. When the imaging beam ends, the camera 12 stops receiving data immediately. The computer 19 controls the ICMOS camera 12 to collect and store image data and controls the optical path delayer 14 .

In this embodiment, the output laser energy of the femtosecond laser 1 is 0.5-2 mJ, the repetition frequency is 0.1-10 kHz, the center wavelength of the output laser is 800 nm, the pulse width is 40-100 fs, and the output laser is linearly polarized light.

In this embodiment, the ICOMS camera 12 is an image-enhanced CMOS camera with a frame frequency of 0.1-10 kHz, a resolution greater than 256×256, and an acquisition gate width less than 20 ns.

In this embodiment, in order to effectively utilize the energy of the imaging beam and ensure uniform energy distribution of the imaging beam, a variable rectangular diaphragm 4 is designed. As shown in Figure 3, the variable rectangular aperture is composed of four high-strength black thin iron sheets (1mm in thickness, 30mm in length, and 10mm in width), two in the horizontal direction and two in the vertical direction. The central axis can move independently and freely, so that the length and width of the clear hole can be independently and freely adjusted. The length and width range is 1-10mm, and the aspect ratio range is 1-10.

In this embodiment, the beam expansion ratio of the beam expander system 5 is 1-10.

In this embodiment, the target injector 6 may be an injector or a simulated injector of various engines such as a ramjet engine, a turbine engine, a detonation engine, a rocket engine, and an automobile engine.

In this embodiment, the polarizer 3 is perpendicular to the polarizing direction of the analyzer 9 .

In this embodiment, the attenuator 11 with variable transmittance and its spatial distribution structure is designed, which can make the different regions with a large difference in photon number density (difference 10-10 ⁵ times) uniform within the same observation range, The number density of ballistic photons reaching the near-field area of the ICMOS camera 12 is equal to that of other areas, so that a clear full-field image of the spray field can be obtained at the same time. As shown in Figure 4, the attenuator 11 with variable transmittance and its spatial distribution structure is composed of multiple groups of attenuators with different transmittances. Areas A, B, C, and D are different in terms of transmittance and area according to different measurement targets. The area is variable. In the actual application process, the shape, area and transmittance of different areas should be measured first, and then the specific parameters should be designed. Generally speaking, in the near-field area (B), the transmittance is greater than 0.9, the attenuation sheet is trapezoidal, the length of the upper base is 1-5mm, the length of the lower base is 1-10mm, and the height is 1-20mm; outside the spray field Area (A), with a transmittance of 10 ^-2 to 10 ^-5 , is composed of two equal-area trapezoidal attenuation sheets, the length of the upper base is 22-25mm, the length of the lower base is 1-25mm, and the height is 50mm; In the secondary atomization area (C), the transmittance is 10 ^-1 ~ 10 ^-4 , the attenuation plate is trapezoidal, the length of the upper base is 1-10mm, the length of the lower base is 1-30mm, and the height is 1-20mm; Evaporation zone (D), the transmittance is 1.2 times that of zone A, the attenuation plate is trapezoidal, the length of the upper base is 1-30mm, the length of the lower base is 1-50mm, and the height is 1-40mm.

In this embodiment, the first convex lens 7 and the second convex lens 10 form a beam reduction system, and the beam reduction ratio is 0.1-1.

In this embodiment, the optical path delayer 14 is used to adjust the delay of the imaging beam and the gating beam, the adjustment range is 1-1000 picoseconds, and the adjustment accuracy is 0.1 picosecond.

Embodiment 2: In this embodiment, the device described in Embodiment 1 can simultaneously acquire the transient full-field image of the spray field, which is realized by the following steps:

Step 1: using a femtosecond laser to output 800nm femtosecond laser.

Step 2: Use a beam splitter to split the femtosecond laser into two beams at a ratio of 1:1, which are respectively used as an imaging beam and a gating beam. The imaging beam is used for spray field imaging, and the gating beam is used to trigger the optical Kerr gate.

Step 3: The gated light beam sequentially passes through the half-wave plate 13 , the optical path delayer 14 , the first mirror 15 , the second mirror 16 and the optical Kerr medium 8 , and finally reaches the beam collector 17 . The half-wave plate 13 is used to change the deflection direction of the gated beam to ensure that the deflected direction of the gated beam and the imaging beam is at an angle of 45°; the optical path delayer 14 is used to adjust the delay of the imaging beam and the gated beam; the gate The control beam passes through the optical Kerr medium 8 to induce a time gate with a duration of about 1-2 picoseconds, and the imaging beam can pass through and reach the ICOMS camera 12 only during this time, thereby realizing the time gating of the ballistic photons in the imaging beam.

Step 4: The imaging beam passes through the polarizer 3, the variable rectangular diaphragm 4, the beam expander system 5, the target injector 6, the convex lens 7, the optical Kerr medium 8, the analyzer 9, the first convex lens 10, the transparent The attenuator 11 with variable pass rate and its spatial distribution structure; finally reaches the ICOMS camera 12 . First, the variable rectangular diaphragm 4 and the beam expander system 5 shape the beam into a rectangular spot with a variable aspect ratio, effectively covering the entire spray field of the target injector 6 . Then, the imaging beam passes through the spray field of the target injector 6 to form ballistic photons and noises (snake photons and diffuse photons) carrying spray field information. Then, an optical Kerr gate is formed by the polarizer 3 , the analyzer 9 and the optical Kerr medium 8 to realize time-domain filtering of the imaging beam and filter out diffuse photons and snake photons. Then, the attenuator 11 with variable transmittance and its spatial distribution structure is used to homogenize the ballistic photons in the whole field, so that the number density of the ballistic photons reaching the near field area of the ICMOS camera 12 is equivalent to that in other areas. Finally, the ICOMS camera 12 is used to receive the ballistic photons to form a clear full-field image of the spray field.

Step 5: Use the timing control system 18 to simultaneously control the femtosecond laser 1 and the ICOMS camera 12 to ensure that when the imaging beam reaches the ICMOS camera 12, the camera 12 is in a working state, and when the imaging beam ends, the camera 12 immediately stops receiving data.

Step 6: Using the computer 19 to control the ICMOS camera 12 to collect and store image data; at the same time, using the computer 19 to control the optical path delayer 14 to realize time-domain filtering of the imaging beam.

Claims (2)

1. A spray atomization full-field measurement device based on photon time-domain filtering technology, characterized in that the device consists of a femtosecond laser, a beam splitter, a polarizer, a variable rectangular diaphragm, a beam expander system, and a target Injector, first convex lens, optical Kerr medium, analyzer, second convex lens, attenuator with variable transmittance and its spatial distribution structure, ICOMS camera, half-wave plate, optical path delayer, first reflector Mirror, second reflector, beam collector, timing control system and computer. The timing control system controls the femtosecond laser and ICOMS camera. The computer controls the ICMOS camera to collect and store image data and control the optical path delay device. The femtosecond laser output femtosecond The second laser beam is divided into two beams by the beam splitter, which are respectively used as the imaging beam and the gate beam. The gate beam passes through the half-wave plate, the optical path delayer, the first mirror, the second mirror and the optical Kerr medium in turn, and finally reaches the The beam collector, the imaging beam passes through the polarizer, the variable rectangular diaphragm, the beam expander system, the target injector, the first convex lens, the optical Kerr medium, the analyzer, the second convex lens, the transmittance and its space Attenuators with variable distribution structures finally reach the ICOMS camera; the beam expansion rate of the beam expander system is 1 to 10; the first convex lens and the second convex lens form a beam reduction system, and the beam reduction rate is 0.1 to 1; The femtosecond laser output laser energy is 05~2mJ, the repetition frequency is 0.1~10kHz, the output laser center wavelength is 800nm, the pulse width is 40~100fs, and the output laser is linearly polarized light; the ICOMS camera is an image-enhanced CMOS Camera with a frame frequency of 0.1~10kHz, a resolution greater than 256×256, and an acquisition gate width less than 20ns; the variable rectangular aperture is composed of four black thin iron plates, two in the horizontal direction and two in the vertical direction, and each iron plate can Move independently and freely along the central axis of the diaphragm, the range of length and width is 1-10mm, and the range of aspect ratio is 1-10; the target injector is an injector of various engines or a simulated injector; the The polarizer is perpendicular to the polarizing direction of the analyzer; the optical path delayer is used to adjust the delay of the imaging beam and the gating beam, the adjustment range is 1-1000 picoseconds, and the adjustment accuracy is 0.1 picosecond; the transmission The attenuator with variable rate and spatial distribution structure is composed of multiple groups of attenuators with different transmittances. In the near-field area B, the transmittance is greater than 0.9. The length of the bottom side is 1~10mm, and the height is 1~20mm; In the area A outside the spray field, the transmittance is 10-2~10-5, which is composed of two equal-area trapezoidal attenuation sheets, and the length of the upper bottom side is 22 -25mm, the length of the lower bottom is 1~25mm, and the height is 50mm; in the secondary atomization zone C, the transmittance is 10-1~10-4, the attenuation sheet is trapezoidal, and the length of the upper bottom is 1~10mm, The length of the lower base is 1~30mm, and the height is 1~20mm; in the evaporation area D, the transmittance is 1.2 times that of the area A, the attenuation sheet is trapezoidal, the length of the upper base is 1~30mm, and the length of the lower base is 1 ~50mm, height 1~40mm. 2. a method for obtaining the full-field image information of the spray atomization flow field by utilizing the spray spray atomization full-field measurement device based on the photon time-domain filtering technology described in claim 1, is characterized in that said method is realized by the following steps: Step 1: Use femtosecond laser to output 800nm femtosecond laser; Step 2: Use a beam splitter to divide the femtosecond laser into two beams at a ratio of 1:1, which are used as imaging beams and gating beams respectively. The imaging beam is used for spray field imaging, and the gating beam is used to trigger the optical Kerr gate; Step 3: The gated beam passes through the half-wave plate, the optical path delayer, the first reflector, the second reflector and the optical Kerr medium in sequence, and finally reaches the beam collector; Step 4: (1) The variable rectangular aperture and the beam expander system shape the imaging beam into a rectangular spot with a variable aspect ratio, effectively covering the entire spray field of the target injector; (2) The imaging beam passes through the target injector (3) The optical Kerr gate is formed by the polarizer, the analyzer and the optical Kerr medium, which realizes the time-domain filtering of the imaging beam and converts the diffused photons and snake photon filtering; (4) apply the attenuator with variable transmittance and its spatial distribution structure to homogenize the ballistic photons in the whole field, so that the number density of ballistic photons reaching the near-field area of the ICMOS camera is equivalent to that of other areas; ( 5) Use the ICOMS camera to receive ballistic photons to form a clear full-field image of the spray field; Step 5: Use the timing control system to simultaneously control the femtosecond laser and the ICOMS camera to ensure that when the imaging beam reaches the ICMOS camera, the camera is in a working state. When the imaging beam ends, the camera stops receiving data immediately; Step 6: Use the computer to control the ICMOS camera to collect and store image data; at the same time, use the computer to control the optical path delayer to realize time-domain filtering of the imaging beam.