System and method for measuring volume fraction of soot in flame on basis of single-pixel imaging

Abstract

Provided in the present disclosure are a system and method for measuring the volume fraction of soot in a flame on the basis of single-pixel imaging. The system comprises: an LED collimating light source; a spatial light modulator, which modulates a light signal generated by the LED collimating light source; a burner, which is configured for producing a flame; an imaging unit, which focuses and projects an image light beam; an optical screen, which images and reflects the image light beam that has passed through the position where the flame is located; a single-pixel detector, which is configured for respectively receiving a first luminous intensity detection signal and a second luminous intensity detection signal in the presence and absence of the flame; and a computer, which is configured for performing Fourier transform on the first luminous intensity detection signal and the second luminous intensity detection signal so as to respectively obtain a first Fourier transform spectrum and a second Fourier transform spectrum, performing two-dimensional inverse discrete Fourier transform on the first Fourier transform spectrum and the second Fourier transform spectrum to respectively obtain a first image and a second image, calculating the transmissivity on the basis of the luminous intensities of the first and second images according to RDG-PFA theory, then using a deconvolution method to obtain a local light extinction coefficient, and calculating the local volume fraction of soot.

Description

System and method for measuring soot volume fraction in flames based on single-pixel imaging Technical Field

[0001] The present disclosure relates to the field of soot volume fraction measurement, and in particular to a system and method for measuring the soot volume fraction in a flame based on single-pixel imaging. Background Art

[0002] Soot is one of the main sources of pollution generated by the combustion of hydrocarbon fuels. Unlike other gaseous pollutants, soot is a solid particle. Research has shown that soot not only increases combustion losses and heat radiation losses, reducing the useful work of many combustion devices, but also absorbs radiation in the air, causing a warming effect and contributing to global warming. Furthermore, fine soot particles can accumulate in the lungs and cause respiratory problems. The uneven distribution of the diesel engine mixture results in relatively high local fuel-air equivalence. Once the combustion temperature enters the soot-generating temperature range, soot particles will be produced during the in-cylinder combustion process.

[0003] Optical diagnostic methods for soot fall into two main categories. One is based on external light sources such as lasers, including light extinction (LE), laser-induced incandescence (LII), and light scattering (LS). The other is based on flame emission spectroscopy. This technique uses the flame's emission spectrum to detect groups, soot temperature, and volume fraction, and includes two-color, computed tomography (CT), and spectral soot emission (SSE). The extinction method is one of the most widely used methods for measuring soot volume fraction. According to the Lambert-Beer law, the soot volume fraction in a flame is related to the amount of light absorbed and scattered by the soot. Based on this, the cumulative soot volume fraction along the flame optical path can be measured, and the local soot volume fraction can be further obtained through deconvolution. Currently, the extinction method using conventional industrial cameras or CCD cameras can also achieve two-dimensional imaging, but the sensor size is generally large.

[0004] Optical measurement has certain limitations. For example, when measuring internal parameters in confined spaces such as engines, it is difficult to achieve good measurements due to the extreme restrictions on the optical path arrangement. Since endoscopic technology can break through the optical path limitations of traditional optical measurement technology in confined spaces, it is currently gaining more and more favor among scholars in the field of engine measurement. Research results show that endoscopic optical measurement technology is an effective means of measuring internal parameters in confined spaces of engines. It can provide ways and methods for measuring various parameters and has great development potential. It can greatly reduce the optical path requirements when measuring various parameters, and there is no need to simplify the object to be measured or open windows over a large area. The original structure of the test piece can be modified as little as possible or not at all, realizing non-contact, transient, and full-field parameter measurements under real conditions. However, due to the poor integration of endoscopic technology with existing optical measurement technology, the diversity and complexity of problems in different practical applications are different. Therefore, this field urgently needs to propose a new measurement method that addresses the limitations of the endoscopic measurement structure, which can achieve accurate measurement of the soot volume fraction, with a simple optical path, small detection size, low cost, and higher measurement accuracy. In the future, it can be coupled into the endoscopic system to measure the soot volume fraction in the real engine.

[0005] Summary of the Invention

[0006] To address the above problems, the present disclosure provides a system and method for measuring the soot volume fraction in a flame based on single-pixel imaging, so as to achieve coupling into an endoscopy system to measure the soot volume fraction in a real engine.

[0007] As one aspect of the present disclosure, a system for measuring the volume fraction of soot in a flame based on single-pixel imaging is provided, comprising:

[0008] LED collimated light source, suitable for providing LED collimated uniform light signal;

[0009] A spatial light modulator is used to modulate the LED collimated uniform light signal to obtain an image beam with a Fourier basis pattern;

[0010] a burner, suitable for producing a flame;

[0011] An imaging unit is adapted to focus an image beam and project the focused image beam, wherein the focused image beam passes through a flame. In the presence of a flame, the imaging unit is adapted to project a Fourier basis pattern onto the flame, and soot in the flame absorbs the focused image beam to obtain an absorption beam carrying soot information.

[0012] A light screen, which images and reflects the image light beam passing through the flame;

[0013] a single-pixel detector, wherein when a flame is present, the single-pixel detector detects the absorption beam reflected by the light screen to obtain a first detection light intensity signal, and when a flame is absent, the single-pixel detector detects the image beam reflected by the light screen to obtain a second detection light intensity signal; and

[0014] The computer is adapted to perform Fourier transform on the first detection light intensity signal to obtain a first Fourier transform spectrum, perform Fourier transform on the second light intensity to obtain a second Fourier transform spectrum, and obtain the volume fraction of carbon soot in the flame according to the first Fourier transform spectrum and the second Fourier transform spectrum.

[0015] According to an embodiment of the present disclosure, obtaining the volume fraction of soot in the flame according to the first Fourier transform spectrum and the second Fourier transform spectrum includes:

[0016] A first image with flames is obtained according to the first Fourier transform spectrum, and a second image without flames is obtained according to the second Fourier transform spectrum;

[0017] respectively acquiring the light intensity of the first image and the light intensity of the second image; and

[0018] Based on the extinction method, the volume fraction of soot in the flame is obtained according to the light intensity of the first image and the light intensity of the second image.

[0019] According to an embodiment of the present disclosure, based on the extinction method, the volume fraction of soot in the flame is obtained according to the light intensity of the first image and the light intensity of the second image, including:

[0020] Obtaining transmittance of the modulated light signal to the flame according to the light intensity of the first image and the light intensity of the second image;

[0021] Performing deconvolution processing on the transmittance to obtain the extinction coefficient of the soot to the modulated light signal; and

[0022] The volume fraction of soot is obtained according to the extinction coefficient.

[0023] According to an embodiment of the present disclosure, the light intensity distribution of the image formed on the light screen is expressed as follows: P(x, y; f x ,f y )=a+b·cos(2πf x x+2πf y y+Φ)

[0024] The image formed on the screen is represented by discrete pixels, and the size is a matrix of M×N pixels, where M and N are positive integers, x and y represent the coordinates of the pixel points of the image formed on the screen, x represents the coordinate of the pixel point in the first direction, and y represents the coordinate of the pixel point in the second direction, the first direction and the second direction are perpendicular, x takes an integer between 0 and M-1, and y takes an integer between 0 and N-1, and f xIndicates the frequency of the pixel in the first direction, f y Indicates the frequency of the pixel in the second direction, f x 、f y The normalized frequency is expressed as Where α is an integer between 0 and M-1, β is an integer between 0 and N-1, P(x, y; f x ,f y ) represents the light intensity of the pixel, a represents the average light intensity of all pixels in the image, b is the contrast of the image, a and b are positive numbers, and Φ represents the initial phase of the pixel.

[0025] According to an embodiment of the present disclosure, the Fourier transform spectrum is expressed as follows:

[0026] Among them, D fp (f x ,f y ) represents the Fourier transform spectrum, each group (f x , f y ) frequency corresponds to Q equal-step initial phases.

[0027] According to an embodiment of the present disclosure,

[0028] The measurement system also includes:

[0029] Neutral density filters are used to reduce the amount of light entering and avoid overexposure.

[0030] According to an embodiment of the present disclosure, the distances between the spatial light modulator, the light screen, the burner, and the LED collimated light source are configured so that the image of the modulated light signal passing through the flame position on the light screen is clearest.

[0031] According to an embodiment of the present disclosure, the center of the imaging unit, the center of the spatial light modulator, and the center of the flame are at the same height.

[0032] According to an embodiment of the present disclosure, the flame is a laminar flame or a swirl flame, and the LED collimated uniform light signal is white light or monochromatic light.

[0033] According to an embodiment of the present disclosure, as a second aspect of the present disclosure, a method for measuring the volume fraction of soot in a flame is further provided. The method is implemented using the above-mentioned system, and the method includes:

[0034] Using LED collimated light source to provide LED collimated uniform light signal;

[0035] The spatial light modulator is used to modulate the LED collimated uniform light signal to obtain an image beam with a Fourier basis pattern;

[0036] Using a burner to generate flame;

[0037] An imaging unit is used to focus an image beam, and the focused image beam is projected so that the focused image beam passes through the location of the flame. In the presence of a flame, a Fourier basis pattern is projected onto the flame using the imaging unit so that soot in the flame absorbs the focused image beam, thereby obtaining an absorption beam carrying soot information.

[0038] Using a light screen, an image beam passing through the flame position is imaged and reflected;

[0039] In the presence of a flame, the absorption light beam is detected using a single-pixel detector to obtain a first detection light intensity signal; in the absence of a flame, the image light beam reflected by the light screen is detected using the single-pixel detector to obtain a second detection light intensity signal; and

[0040] A computer is used to perform Fourier transform on the first detection light intensity signal to obtain a first Fourier transform spectrum, and a computer is used to perform Fourier transform on the second detection light intensity signal to obtain a second Fourier transform spectrum. The volume fraction of carbon soot in the flame is obtained based on the first Fourier transform spectrum and the second Fourier transform spectrum.

[0041] According to the embodiments of the present disclosure, a single-pixel detector is used to detect the reflected image light beam in the presence of a flame (with flame and light source) and the reflected image light beam in the absence of a flame (with no flame and light source), respectively, thereby realizing the detection of the volume fraction of carbon soot in the flame. Compared with the existing extinction method (using conventional industrial cameras or CCD cameras), the device size is much smaller, and it has the prospect of being integrated into an endoscope system in the future. It can be used to test and measure the carbon soot volume fraction of actual power units with limited shooting windows, such as aircraft engines, internal combustion engines, ramjet engines, etc.

[0042] According to the embodiments of the present disclosure, the measurement method provided by the embodiments of the present disclosure requires taking two fewer sets of pictures with flame but no light source and pictures without flame and no light source than the existing extinction method. Data processing is simpler, the calculation process is simplified to a certain extent, and memory storage costs and time are saved. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] FIG1 shows a schematic diagram of a system for measuring the volume fraction of soot in a flame based on single-pixel imaging according to an embodiment of the present disclosure;

[0044] FIG2 shows a top view of a system for measuring the volume fraction of soot in a flame based on single-pixel imaging according to an embodiment of the present disclosure.

[0045] Description of Reference Numerals

[0046] 1-LED collimated light source; 2-spatial light modulator; 3-burner; 4-imaging unit;

[0047] 5-light screen; 6-single pixel detector; 7-computer; 8-neutral density filter; 9-power switch. DETAILED DESCRIPTION

[0048] During the implementation of this disclosure, it was discovered that single-pixel imaging, a novel computational imaging technique, utilizes spatial light modulation to acquire spatial information about an object using only a single-pixel detector without spatial resolution. Combining single-pixel imaging with the extinction method to measure the soot volume fraction in flames differs from traditional extinction methods in its optical principles and path, and it also features a smaller detector size. Future integration into endoscopic systems holds great potential for testing actual power plants, such as aircraft engines, internal combustion engines, and ramjets, with limited imaging windows.

[0049] FIG1 shows a schematic diagram of a system for measuring the volume fraction of soot in a flame based on single-pixel imaging according to an embodiment of the present disclosure.

[0050] As shown in FIG1 , a measurement system for measuring the soot volume fraction in a flame based on single-pixel imaging includes an LED collimated light source 1 , a spatial light modulator 2 , a burner 3 , an imaging unit 4 , a light screen 5 , a single-pixel detector 6 , and a computer 7 .

[0051] An LED collimated light source 1 is configured to provide a collimated, uniform LED light signal. A spatial light modulator 2 is configured to modulate the collimated, uniform LED light signal to produce an image beam with a Fourier basis pattern. A burner 3 is configured to generate a flame. An imaging unit 4 is configured to focus the image beam and project the focused image beam. The focused image beam passes through the location of the flame. In the presence of a flame, the imaging unit 4 projects the Fourier basis pattern onto the flame. Soot in the flame absorbs the focused image beam, producing an absorption beam carrying soot information. A light screen 5 images and reflects the image beam that passes through the location of the flame. A single-pixel detector 6 is configured to detect the reflected image beam after it is reflected by the light screen 5 to produce a detection light intensity signal. In the presence of a flame, the single-pixel detector 6 detects the absorption beam reflected by the light screen 5 to produce a first detection light intensity signal. In the absence of a flame, the single-pixel detector 6 detects the image beam reflected by the light screen 5 to produce a second detection light intensity signal. Computer 7 is adapted to perform Fourier transform on the first detection light intensity signal to obtain a first Fourier transform spectrum, perform Fourier transform on the second detection light intensity signal to obtain a second Fourier transform spectrum, and obtain the volume fraction of soot in the flame based on the first Fourier transform spectrum and the second Fourier transform spectrum.

[0052] According to the embodiments of the present disclosure, a single-pixel detector 6 is used to detect the reflected image light beam in the presence of a flame (with flame and light source) and the reflected image light beam in the absence of a flame (with no flame and light source), thereby realizing the detection of the volume fraction of carbon soot in the flame. Compared with the existing extinction method (using conventional industrial cameras or CCD cameras), the device size is much smaller and has the prospect of being integrated into an endoscope system in the future. It can be used to test and measure the carbon soot volume fraction of actual power units such as aircraft engines, internal combustion engines, ramjet engines, etc. with limited shooting windows.

[0053] According to the embodiments of the present disclosure, the measurement method provided by the embodiments of the present disclosure requires taking two fewer sets of pictures with flame but no light source and pictures without flame and no light source than the existing extinction method. Data processing is simpler, the calculation process is simplified to a certain extent, and memory storage costs and time are saved.

[0054] 1-2 , the single-pixel detector 6 can perform measurements within a position range of ±90°.

[0055] According to an embodiment of the present disclosure, the image formed on the light screen 5 is an image formed by the image light beam with flames on the light screen or an image formed by the image light beam without flames on the light screen 5 .

[0056] The light intensity distribution of the image formed on the screen 5 is expressed as follows: P(x, y; f x ,f y )=a+b·cos(2πf x x+2πf y y+Φ) (1)

[0057] Wherein, x and y represent the coordinates of the pixel points of the image formed on the light screen 5, x represents the coordinates of the pixel points in the first direction, y represents the coordinates of the pixel points in the second direction, and f x Indicates the frequency of the pixel in the first direction, the first direction and the second direction are perpendicular, f y Indicates the frequency of the pixel in the second direction, P(x,y;f x ,f y ) represents the light intensity of the pixel, a represents the average light intensity of all pixels in the image, b is the contrast of the image, a and b are positive numbers, Φ represents the initial phase of the pixel, in the presence or absence of flame, f x The value is different when there is flame or no flame. y The values ​​are different when there is a flame or when there is no flame.

[0058] According to an embodiment of the present disclosure, each group (f x , f y) frequencies correspond to at least three different initial phase φ values, and these cosine distribution light fields (image light beams with Fourier basis patterns) of different frequencies and initial phases are irradiated onto the light screen 5. The light intensity signals from the light screen 5 are sequentially received by the single-pixel detector 6, and the response values ​​of the single-pixel detector 6 (including the first detection light intensity signal or the second detection light intensity signal) are sequentially collected and recorded. The Fourier transform spectrum D of the image formed on the light screen 5 is obtained according to the response values. fp (f x , f y ) is represented as follows:

[0059] Among them, D fp (f x ,f y ) represents the Fourier transform spectrum, each group (f x , f y ) The frequency corresponds to Q initial phases with equal steps, where Q is an integer greater than or equal to 3, and j is an imaginary unit.

[0060] According to an embodiment of the present disclosure, obtaining the volume fraction of soot in the flame according to the first Fourier transform spectrum and the second Fourier transform spectrum includes operations S1 to S3.

[0061] In operation S1 , a first image with flames is obtained according to a first Fourier transform spectrum, and a second image without flames is obtained according to a second Fourier transform spectrum.

[0062] The first image and the second image can be obtained by the following process:

[0063] In formulas (1)-(2), each group (f x , f y ) frequency can also correspond to other initial phases to obtain the Fourier transform spectrum D of the target object image fp (f x , f y ) should be changed accordingly, such as each frequency group corresponds to three initial phases, and the initial phases are The response values ​​of the single pixel detector 6 to the light intensity signal received from the light screen 5 are expressed as: D1(f x , f y )、D2(f x , f y )、D3(f x , f y ), Fourier transform spectrum D fp (f x , f y ) is shown in formula (3): D fp (f x ,f y)=[2D2(f x ,f y )-D1(f x ,f y )-D3(f x ,f y )]+j·[D3(f x ,f y )-D1(f x ,f y )] (3)

[0064] Fourier transform spectrum D fp (f x , f y ) performs a two-dimensional discrete inverse Fourier transform, substitutes the data into formula (4), and reconstructs the first image with flame or the second image without flame I (x, y),

[0065] In operation S2 , light intensities of the first image and the second image are acquired respectively.

[0066] In operation S3 , based on the extinction method, the volume fraction of soot in the flame is obtained according to the light intensity of the first image and the light intensity of the second image.

[0067] According to an embodiment of the present disclosure, operation S3 includes operations S31 to S33.

[0068] In operation S31 , the transmittance of the modulated light signal to the flame is obtained according to the light intensity of the first image and the light intensity of the second image.

[0069] The Matlab program written by the computer is used to process the first image with flame to obtain the light intensity of the first image. L+f (x, y) represents the light intensity of the second image obtained by processing the second image without flame, and the light intensity of the first image is expressed as I L+f (x, y) represents the light intensity of the second image. L (x,y) represents.

[0070] Substituting the above light intensity signal into formula (5) to calculate the transmittance τ λ (x,y),

[0071] In the above formula: τ λ (x,y) is the transmittance, I L+f (x, y) is the light intensity of the first image, I L (x, y) is the light intensity of the second image.

[0072] In operation S32 , a deconvolution process is performed on the transmittance to obtain an extinction coefficient of the soot to the modulated light signal.

[0073] According to formula (5), τ is calculated λ (x, y), and then use formula (6) combined with Tikhonov regularized onion-peeling deconvolution method to calculate the absorption coefficient or extinction coefficient

[0074] K λ (x, y), formula (6) is expressed as follows:

[0075] In the above formula: K λ (x,y) is the absorption coefficient or extinction coefficient.

[0076] In operation S33 , the volume fraction of soot is obtained according to the extinction coefficient.

[0077] According to the RDG–PFA (Rayleigh-Debye-Gans-Polydisperse-Fractal-Aggregate) theory and the soot in the flame is approximately spherical particles with particle sizes within the Rayleigh particle size range, ignoring the scattering effect of particles on light, the volume fraction of soot f is v (x,y) and extinction coefficient K λ The relationship between (x,y) is:

[0078] In the above formula: K λ (x, y) is the absorption coefficient or extinction coefficient, λ is the wavelength, and E(m) is the refractive index function; the volume fraction of soot f is calculated according to formula (7): v (x,y), unit is ppm.

[0079] According to an embodiment of the present disclosure, the measurement system also includes: a neutral density filter (ND filter) 8, which is suitable for reducing the amount of incoming light and avoiding overexposure, so as to make the measurement more accurate. The ND filter can be directly installed on the single-pixel detector, and the overall installation distance needs to be fine-tuned according to the single-pixel imaging clarity.

[0080] According to an embodiment of the present disclosure, the distances among the spatial light modulator 2 , the light screen 5 , the burner 3 , and the LED collimated light source 1 are configured so that the image of the modulated light signal passing through the flame position on the light screen 5 is clearest.

[0081] According to an embodiment of the present disclosure, the center of the imaging unit 4 , the center of the spatial light modulator 2 , and the center of the flame are at the same height.

[0082] According to an embodiment of the present disclosure, the measurement system further includes a power switch 9 adapted to control the on and off of the LED collimated light source.

[0083] According to an embodiment of the present disclosure, the flame is a laminar flame or a swirl flame. In the case of a laminar flame, burner 3 is a laminar diffusion burner. A laminar diffusion burner contains gas and air. The combustion method adopted by a laminar diffusion burner is layer-by-layer combustion. By controlling the ratio and flow rate of air and fuel, complete combustion of the fuel can be achieved. The flow rate corresponding to the gas-to-air equivalence ratio is set, the gas and air gas paths in the laminar diffusion burner are opened, and the gas is ignited using an igniter to form a laminar flame above the laminar diffusion burner. In the case of a swirl flame, burner 3 is a swirl diffusion burner. A swirl diffusion burner is a fluid dynamics burner with a rotating spiral flow channel that generates centrifugal force through gas rotation. During use, the flow rate corresponding to the gas-to-air equivalence ratio is set, the gas and air gas paths in the swirl diffusion burner are opened, and the gas is ignited using an igniter to form a swirl flame above the swirl burner.

[0084] According to an embodiment of the present disclosure, a method for measuring the volume fraction of soot in a flame is also provided. The method is implemented using the above system and includes:

[0085] Using the LED collimated light source 1 to provide an LED collimated uniform light signal;

[0086] The spatial light modulator 2 is used to modulate the LED collimated uniform light signal to obtain an image beam with a Fourier basis pattern;

[0087] Generating flame using burner 3;

[0088] The image beam is focused by the imaging unit 4, and the focused image beam is projected so that the focused image beam passes through the location of the flame. In the presence of a flame, the Fourier basis pattern is projected onto the flame by the imaging unit 4, so that the soot in the flame absorbs the focused image beam, thereby obtaining an absorption beam carrying soot information.

[0089] The image light beam passing through the flame position is imaged and reflected by the light screen 5;

[0090] In the presence of flame, the absorption light beam is detected by the single-pixel detector 6 to obtain a first detection light intensity signal; in the absence of flame, the image light beam reflected by the light screen 5 is detected by the single-pixel detector 6 to obtain a second detection light intensity signal; and

[0091] The computer 7 performs Fourier transform on the first detection light intensity signal to obtain a first Fourier transform spectrum, and performs Fourier transform on the second detection light intensity signal to obtain a second Fourier transform spectrum, and is suitable for obtaining the volume fraction of carbon soot in the flame based on the first Fourier transform spectrum and the second Fourier transform spectrum.

[0092] The following is a specific example to illustrate the method for measuring the soot volume fraction in a flame using the above-mentioned measurement system.

[0093] Step A: Set the flow rate corresponding to the gas-to-air equivalence ratio, open the gas and air paths in the combustion device (laminar diffusion burner or swirl burner), use the igniter to ignite the gas, and form a laminar flame or swirl flame above the laminar diffusion burner or swirl burner. Turn on the LED collimated light source 1 by the power switch 9. The light beam emitted by the LED collimated light source 1 is modulated by the spatial light modulator 2 and then focused onto the light screen 5 by the imaging unit 4. The reflected image beam reflected by the light screen 5 passes through the ND filter and hits the single-pixel detector 6. The light field intensity detected by the single-pixel detector 6 is collected by the computer 7 and then processed using the optical imaging method of single-pixel imaging. Specifically, using equations (1)-(4), a first image with flame is obtained and recorded in the computer.

[0094] Step B: Keep the LED collimated light source 1 turned on, extinguish the flame on the laminar diffusion burner or the swirl burner, and at this time, the light path setting remains unchanged. Use equations (1)-(4) to obtain a second image without flame.

[0095] Step C: First, the Matlab program written by the computer 7 is used to process the first image with flames to obtain the light intensity signal of the first image with flames. L+f (x, y) represents that the second image of the flame is processed by the Matlab program written by computer 7 to obtain the light intensity signal of the second image without flame, and then the transmittance τ is obtained by using formula (5) λ (x,y),

[0096] Step D: τ calculated according to formula (5) λ (x, y), and then use formula (6) combined with Tikhonov regularized onion-peeling deconvolution method to calculate the absorption coefficient or extinction coefficient K λ (x,y). According to the volume fraction of soot f v (x,y) and extinction coefficient K λ (x, y) relationship, that is, the volume fraction of soot f is calculated by formula (7) v (x,y).

[0097] The system for measuring the volume fraction of soot in flames based on single-pixel imaging provided in an embodiment of the present disclosure can be integrated into an endoscope system to enable testing of actual power units such as aircraft engines, internal combustion engines, and ramjets with limited shooting windows.

[0098] The system for measuring the volume fraction of soot in flames based on single-pixel imaging provided by the embodiments of the present disclosure is much smaller in size than the detection equipment for measuring soot concentration using the traditional extinction method. In the future, it will be further developed and integrated into an endoscope system to test actual power units such as aircraft engines, internal combustion engines, and ramjets with limited shooting windows.

[0099] According to the measurement system for measuring the soot volume fraction based on single-pixel imaging provided by the embodiment of the present disclosure, compared with the previous measurement system for measuring the soot volume fraction using the extinction method, two sets of pictures with flame but no light source and pictures without flame and no light source are not required. Data processing is simpler, the calculation process is simplified to a certain extent, and memory storage costs and time are saved.

[0100] According to the measurement system for measuring soot volume fraction based on single-pixel imaging provided by the embodiment of the present disclosure, the measurement optical path consisting of the neutral density filter 8, the LED collimated light source 1, and the power switch 9 used is extremely easy to establish.

[0101] The soot volume fraction measurement system based on single-pixel imaging provided by the embodiments of the present disclosure is simple to operate. It only requires processing the light intensity signals of images with flames and light sources and images without flames and light sources via a computer 7. Furthermore, single-pixel imaging can eliminate the influence of flame self-luminescence, making the measurement more accurate.

[0102] The specific embodiments of the present disclosure described above do not limit the scope of protection of the present disclosure. Any other corresponding changes and modifications made based on the technical concept of the present disclosure should be included in the scope of protection of the claims of the present disclosure.

Claims

1. A system for measuring the volume fraction of soot in a flame based on single-pixel imaging, comprising: LED collimated light source, suitable for providing LED collimated uniform light signal; A spatial light modulator, adapted to modulate the LED collimated uniform light signal to obtain an image light beam with a Fourier basis pattern; a burner, suitable for producing a flame; An imaging unit, adapted to focus the image beam and to project the focused image beam, wherein the focused image beam passes through the position where the flame is located, and in the presence of the flame, the imaging unit is adapted to project the Fourier basis pattern onto the flame, and the soot in the flame absorbs the focused image beam to obtain an absorption beam carrying the soot information; A light screen for imaging and reflecting an image light beam passing through the position where the flame is located; a single-pixel detector, wherein when the flame exists, the single-pixel detector detects the absorption light beam reflected by the light screen to obtain a first detection light intensity signal, and when the flame does not exist, the single-pixel detector detects the image light beam reflected by the light screen to obtain a second detection light intensity signal; as well as A computer is suitable for performing Fourier transform on the first detection light intensity signal to obtain a first Fourier transform spectrum, performing Fourier transform on the second detection light intensity signal to obtain a second Fourier transform spectrum, and being suitable for obtaining the volume fraction of carbon soot in the flame based on the first Fourier transform spectrum and the second Fourier transform spectrum.

2. The measurement system according to claim 1, wherein: Obtaining the volume fraction of soot in the flame according to the first Fourier transform spectrum and the second Fourier transform spectrum includes: Obtain a first image with the flame according to the first Fourier transform spectrum, and obtain a second image without the flame according to the second Fourier transform spectrum; respectively acquiring the light intensity of the first image and the light intensity of the second image; and Based on the extinction method, the volume fraction of the soot in the flame is obtained according to the light intensity of the first image and the light intensity of the second image.

3. The measurement system according to claim 1, wherein: Based on the extinction method, the volume fraction of carbon smoke in the flame is obtained according to the light intensity of the first image and the light intensity of the second image, including: Obtaining transmittance of the modulated light signal to the flame according to the light intensity of the first image and the light intensity of the second image; Performing a deconvolution process on the transmittance to obtain an extinction coefficient of the soot to the modulated light signal; and The volume fraction of the soot is obtained according to the extinction coefficient.

4. The measurement system according to claim 1, wherein: The light intensity distribution of the image formed on the light screen is expressed as follows: P(x, y; f x ,f y )=a+b·cos(2πf x x+2πf y y+Φ) The image formed on the light screen is represented by discretized pixels, and the size is a matrix of M×N pixels, M and N are positive integers, x and y represent the coordinates of the pixel points of the image formed on the light screen, x represents the coordinate of the pixel point in the first direction, y represents the coordinate of the pixel point in the second direction, the first direction and the second direction are perpendicular, x takes an integer between 0 and M-1, y takes an integer between 0 and N-1, and f x Represents the frequency of the pixel in the first direction, f y Represents the frequency of the pixel in the second direction, f x 、f y The normalized frequency is expressed as Where α is an integer between 0 and M-1, β is an integer between 0 and N-1, P(x, y; f x ,f y ) represents the light intensity of the pixel, a represents the average light intensity of all pixels in the image, b is the contrast of the image, a and b are positive numbers, and Φ represents the initial phase of the pixel.

5. The measurement system according to claim 1, wherein: The Fourier transform spectrum is expressed as follows: Among them, D fp (f x ,f y ) represents the Fourier transform spectrum, each group (f x , f y ) The frequency corresponds to Q initial phases with equal steps, and j is an imaginary unit.

6. The measurement system according to claim 1, wherein: The measuring system further comprises: Neutral density filters are used to reduce the amount of light entering and avoid overexposure.

7. The measurement system according to claim 1, wherein: The distances among the spatial light modulator, the light screen, the burner, and the LED collimated light source are configured so that the image of the modulated light signal passing through the position of the flame is clearest on the light screen.

8. The measurement system according to claim 4, wherein: The center of the imaging unit, the center of the spatial light modulator and the center of the flame are at the same height.

9. The measurement system according to claim 1, wherein: The flame is a laminar flame or a swirl flame; The LED collimated uniform light signal is white light or monochromatic light.

10. A method for measuring the volume fraction of soot in a flame, implemented using the system according to any one of claims 1 to 9, wherein the method include:. Using LED collimated light source to provide LED collimated uniform light signal; Using a spatial light modulator to modulate the LED collimated uniform light signal to obtain an image light beam with a Fourier basis pattern; Using a burner to generate flame; The image beam is focused by using an imaging unit, and the focused image beam is projected so that the focused image beam passes through the position where the flame is located, wherein, in the presence of the flame, the Fourier basis pattern is projected onto the flame by using the imaging unit so that the soot in the flame absorbs the focused image beam, thereby obtaining an absorption beam carrying the soot information; Using a light screen, imaging and reflecting an image light beam passing through the location of the flame; In the presence of the flame, the absorption light beam is detected by using a single pixel detector to obtain a first detection light intensity signal, and in the absence of the flame, the image light beam reflected by the light screen is detected by using the single pixel detector to obtain a second detection light intensity signal; and The first detection light intensity signal is Fourier transformed by a computer to obtain a first Fourier transform spectrum, the second detection light intensity signal is Fourier transformed to obtain a second Fourier transform spectrum, and the volume fraction of carbon soot in the flame is obtained according to the first Fourier transform spectrum and the second Fourier transform spectrum.

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