Pollutant spatial distribution and blow-off and tempering limit measurement method based on flat flame burner

Abstract

The invention provides a pollutant spatial distribution and blow-off and tempering limit measurement method based on a flat flame burner, and relates to the technical field of combustion experiment measurement. According to the method, on the basis of a flat-flame burner, a quartz cover is arranged above the flat-flame burner to form a locally-closed space, and a long-strip-shaped measuring window is formed in the side face; an X-Y plane movable precision probe structure is arranged on the outer side of the window, so that the tip of the sampling probe can extend into a region adjacent to the flame at any coordinate point in the window plane; a camera is arranged on the outer side of the quartz cover, and a camera pixel coordinate probe physical coordinate conversion relation is established through calibration; controlling the probe to move point by point according to a preset scanning path, synchronously collecting pollutant concentration and flame images, and obtaining a pollutant two-dimensional or three-dimensional distribution field under a given working condition; parameters such as gas flow and air-fuel ratio are adjusted, the blow-off / tempering limit is approached and crossed, scanning is repeated at key nodes, and pollutant distribution characteristics in different combustion stability states are obtained.

Description

Technical Field

[0001] This invention relates to the field of combustion experimental measurement technology, and more specifically, to a method for measuring the spatial distribution of pollutants and the flameout and flashback limits of a flat flame burner. Background Technology

[0002] Flat-flame burners, such as McKenna-type flat-flame burners, have become a core platform for basic combustion research due to their stable flame morphology and controllable boundary conditions. They are widely used in research on key topics such as the ignition characteristics of novel gases, stable combustion laws, and flameout / flashback limits. In the research and application of gas-fired equipment such as gas-fired wall-hung boilers and industrial burners, flameout and flashback are typical combustion instability phenomena. They not only lead to a significant decrease in equipment thermal efficiency and an increase in pollutant emission concentrations, but may also cause equipment damage or even safety accidents. Therefore, accurately obtaining the flameout / flashback limits of gases under different operating conditions is of great significance for ensuring safe equipment operation and optimizing combustion performance.

[0003] However, existing experimental measurement methods based on flat flame burners still have many shortcomings. Traditional measurements, which involve placing sampling probes at the flue or hood outlet, can only obtain the overall average concentration of pollutants in the exhaust gas. They cannot distinguish the differences in pollutant production in different areas of the flame, such as the core combustion zone and the edge diffusion zone, and are difficult to reveal the spatial distribution pattern of pollutants. Fixed-point sampling information is incomplete. A few studies have adopted the method of placing a small number of sampling points at fixed heights and fixed radii. Although they can obtain local pollutant concentration data, the number of sampling points is limited and their distribution is irregular. They cannot reconstruct a complete two-dimensional or three-dimensional pollutant field and cannot fully reflect the flame combustion state. The sampling accuracy of manually moving the sampling probe to scan around the flame is greatly affected by human operation and experience judgment, resulting in large repeated positioning errors. Furthermore, it is difficult to accurately correspond the sampling position with the flame image coordinates, making it impossible to establish a correlation between combustion mode and pollutant concentration. Conventional experiments are mostly conducted in open environments, where flames are easily affected by airflow disturbances such as personnel movement and ventilation system airflow, leading to significant randomness and uncertainty in determining the flameout / temper limit. While some studies have incorporated quartz covers or cavities outside the flat-flame burner, the shape and position of the side openings often rely on empirical design, failing to establish a systematic approach compatible with precise planar sampling and unified imaging coordinates, thus failing to balance flame stability and measurement accuracy. Therefore, this paper proposes a method for measuring the spatial distribution of contaminants and the flameout / temper limit based on a flat-flame burner. Summary of the Invention

[0004] The purpose of this invention is to address the problems identified in the existing background technology. To achieve the above-mentioned objective, this invention provides the following technical solution: a method for measuring the spatial distribution of pollutants and the flameout / temper limit in a flat-flame burner, comprising the following steps: Step 1: Construct a measuring device, which includes a flat flame burner, a quartz shroud and its opening structure, an XY plane movable precision probe structure, a camera and optical system, and a gas supply and control system; wherein the flat flame burner is a McKenna type with an outlet diameter of 50-100mm and a power adjustment range of 2-15kW. Step 2: Perform coordinate calibration: Place a 100mm×100mm standard coordinate plate with an accuracy of 0.01mm at the side opening of the quartz cover, control the probe tip to move sequentially to at least 10 evenly distributed feature points, record the physical coordinates and corresponding pixel coordinates, establish the transformation equation through polynomial fitting, and the calibration error is ≤0.15mm. Step 3: Set combustion conditions: Determine the gas type, including natural gas, hydrogen-blended natural gas, ammonia, blending ratio of hydrogen 0-50% / ammonia 0-30%, air-fuel ratio of 0.8-1.5, burner power of 2-15kW, start the burner and stabilize for 12-18 minutes; Step 4, Spatial distribution measurement of pollutants: Using a grid scanning path with a step size of 3-8 mm, the probe is controlled to stay at each sampling point for 35-55 seconds, and the pollutant concentration and flame image are recorded simultaneously. A two-dimensional distribution cloud map is drawn using Kriging interpolation. Step 5, Flameout / Temperature Limit Measurement: Adjust the operating parameters by 3%-5% each time, stabilize for 6-9 minutes, and then measure; when the flame fluctuation amplitude of the critical operating condition is >5mm, repeat the scan until flameout / temper occurs, repeat the measurement 4-6 times and take the average value; Step 6, Post-experiment processing: After shutting down the system, let it cool for 30-45 minutes, clean the probe and quartz cover, analyze the data using Origin software, and output a report on the correlation between operating conditions, concentration, and images.

[0005] As a preferred technical solution of the present invention, the quartz cover in step 1 is a cylindrical structure made of high-transmittance quartz glass, with an inner diameter 60-90mm larger than the maximum diameter of the flat flame and a height of 200-300mm; the bottom is sealed by a high-temperature resistant silicone rubber ring with a thickness of 5-8mm and a sealing width of 12-18mm; a long strip opening is opened on the side wall 60-140mm away from the burner outlet, with the length of the major axis being 1.3-1.4 times the diameter of the flat flame, the height of the minor axis being 25-45mm, and the radius of the rounded corners at both ends being 6-9mm; a detachable metal baffle with a width of 8-25mm is provided on the outside, and the baffle material is 304 stainless steel.

[0006] As a preferred technical solution of the present invention, the XY plane movable precision probe structure in step 1 includes two sets of linear guides with a stroke of 80-150mm, which are driven by ball screws and have a positioning accuracy of 0.02-0.04mm. The driving method is a stepper motor with a step angle of 1.8° and a reduction ratio of 1:10, which, together with a microstepping driver, achieves a minimum displacement of 0.005mm. The sampling probe is made of 310S stainless steel tube with an inner diameter of 0.6-0.9mm, an outer diameter of 1.2-1.8mm, a tip angle of 45°±2°, and an insertion depth of 5-45mm into the quartz cover.

[0007] As a preferred technical solution of the present invention, the camera and optical system in step 1 are selected from industrial CCD cameras with a resolution of 2048×1536 or higher, equipped with a 25-50mm fixed focal length lens, an aperture of f / 5.6-f / 7.1, and a shutter speed of 1 / 120s-1 / 800s; the distance between the camera and the quartz cover is 600-900mm, and the height difference between the center of the lens and the center of the flat flame is ≤3mm; equipped with a ring light source with a power of 30-50W, an illumination angle of 40°-50°, and a color temperature of 5500-6500K.

[0008] As a preferred technical solution of the present invention, the gas supply and control system in step 1 includes: a fuel gas mass flow controller with a range of 0-15 L / min and an accuracy of ±0.3%FS; an air mass flow controller with a range of 0-150 L / min and an accuracy of ±0.3%FS; a pressure stabilizing valve to control inlet pressure fluctuation ≤±0.08 kPa; a cooling water pump with a flow rate of 10-20 L / min to control the burner base temperature ≤75℃; and a nitrogen protective gas flow rate of 5-15 L / min, which is axially introduced from the top of the quartz cover.

[0009] As a preferred technical solution of the present invention, in the coordinate calibration process of step 2, the feature points are selected according to the principle of 4 points on the edge + 4 points in the center + 2 points on the diagonal, and the distance between adjacent feature points is 20-30mm; image processing is performed using Matlab software, and the probe tip is identified by a sub-pixel positioning algorithm.

[0010] As a preferred technical solution of the present invention, the criteria for determining stable combustion in step 3 are: the flame center position shift ≤2mm within 5 consecutive minutes, and the pollutant concentration fluctuation ≤5%; the air-fuel ratio adjustment adopts the linkage adjustment of the mass flow controller to ensure that the fuel gas and air flow change synchronously.

[0011] As a preferred technical solution of the present invention, in step 4, the starting coordinates of the grid scanning path are -40mm, -40mm, and the ending coordinates are 40mm, 40mm. The step size is selected according to the accuracy requirements: 3-5mm for high-precision measurement and 6-8mm for fast measurement; the sampling probe moving speed is 5-10mm / s, and the concentration data is collected 3 times at each sampling point, and the average value is taken as the final result; the flame image shooting frequency is 1-3 frames / second, and the image with a time difference of ≤0.5 seconds from the concentration data acquisition time is selected for association.

[0012] As a preferred technical solution of the present invention, the criteria for determining flameout in step 5 are: the flame completely detaches from the burner surface for ≥3 seconds and cannot recover on its own; the criteria for determining flashback are: the flame retracts into the burner and the burner outlet temperature rises sharply by ≥50℃ / s; during extreme measurements, the initial adjustment range is 5%, and the adjustment range is 3% when approaching the critical value; the inner wall of the probe needs to be cleaned before each repeated measurement to avoid residual gas affecting the data.

[0013] As a preferred technical solution of the present invention, the post-experiment processing in step 6 further includes: analyzing the flame image using ImageJ software, calculating the flame area error ≤2% and the average brightness error ≤3%; plotting the air-fuel ratio-pollutant concentration curve using Origin software, and determining the limit value using linear interpolation; the data report should include a device parameter table, calibration error analysis, and a relative standard deviation of repeatability verification results ≤3%, and include a pollutant distribution cloud map and flame image under typical operating conditions.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. Excellent flame stabilization and high measurement repeatability: Through the partial closed design of the quartz cover and the bottom sealing structure, external airflow interference is effectively isolated, and the stability of the flat flame shape is improved by more than 40%. At the same time, the airflow inside the cover can be controlled by adjusting the opening baffle, avoiding the measurement error caused by flame shaking in the traditional open environment. The repeatability error of flameout / tempering limit measurement is reduced to within ±2%.

[0015] 2. High sampling accuracy and complete spatial distribution: The XY plane movable precision probe structure achieves precise positioning with a resolution of 0.1mm, solving the problem of operational errors caused by manual probe movement; combined with the grid scanning path, it can obtain complete data on the distribution of pollutants in the flame cross section. Compared with fixed point sampling, the information coverage is improved by more than 80%, which can more accurately reveal the spatial pattern of pollutant generation.

[0016] 3. Unified coordinates and strong data correlation: Through pixel-physical coordinate calibration, a one-to-one correspondence between the physical position of the sampling probe and the coordinates of the flame image is achieved for the first time. A three-dimensional correlation database of combustion mode, pollutant concentration and spatial location is established, providing direct evidence for analyzing the pollutant generation mechanism in different areas of the flame, such as high temperature zone and low temperature zone.

[0017] 4. Wide adaptability and easy operation: The device can be adapted to various gas types such as natural gas, hydrogen-blended gas, and ammonia. The core equipment such as the flat flame burner and gas analyzer are all standard models and do not require customization. The measurement process can be automated through programming, such as stepper motor drive and automatic data recording, reducing the intensity of manual operation and making it suitable for batch operation experiments. Attached Figure Description

[0018] Figure 1 A flowchart of the method steps provided by the present invention; Figure 2 A data block diagram provided for this invention; Figure 3 This is a data block diagram of the tempering and de-flammation determination criteria provided by the present invention; Figure 4 This is a data processing flowchart provided for the present invention. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention.

[0020] Therefore, the following detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely illustrates some embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention. It should be noted that, in the absence of conflict, the embodiments and features and technical solutions in the embodiments of the present invention can be combined with each other. It should be noted that similar reference numerals and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0021] Example 1: A method for measuring the spatial distribution of pollutants and the flameout and flashback limits based on a flat flame burner, comprising the following steps: Step 1: Constructing a measuring device, which includes a flat flame burner, a quartz shroud and its opening structure, an XY plane movable precision probe structure, a camera and optical system, and a gas supply and control system; wherein the flat flame burner is a McKenna type, with an outlet diameter of 50-100mm and a power adjustment range of 2-15kW; Step 2: Perform coordinate calibration: Place a 100mm×100mm standard coordinate plate with an accuracy of 0.01mm at the side opening of the quartz cover, control the probe tip to move sequentially to at least 10 evenly distributed feature points, record the physical coordinates and corresponding pixel coordinates, establish the transformation equation through polynomial fitting, and the calibration error is ≤0.15mm. Step 3: Set combustion conditions: Determine the gas type, including natural gas, hydrogen-blended natural gas, ammonia, blending ratio of hydrogen 0-50% / ammonia 0-30%, air-fuel ratio of 0.8-1.5, burner power of 2-15kW, start the burner and stabilize for 12-18 minutes; Step 4, Spatial distribution measurement of pollutants: Using a grid scanning path with a step size of 3-8 mm, the probe is controlled to stay at each sampling point for 35-55 seconds, and the pollutant concentration and flame image are recorded simultaneously. A two-dimensional distribution cloud map is drawn using Kriging interpolation. Step 5, Flameout / Temperature Limit Measurement: Adjust the operating parameters by 3%-5% each time, stabilize for 6-9 minutes, and then measure; when the flame fluctuation amplitude of the critical operating condition is >5mm, repeat the scan until flameout / temper occurs, repeat the measurement 4-6 times and take the average value; Step 6, Post-experiment processing: After shutting down the system, let it cool for 30-45 minutes, clean the probe and quartz cover, analyze the data using Origin software, and output a report on the correlation between operating conditions, concentration, and images.

[0022] The quartz cover mentioned in step 1 is a cylindrical structure made of high-transmittance quartz glass, with an inner diameter 60-90mm larger than the maximum diameter of the flat flame and a height of 200-300mm. The bottom is sealed with a high-temperature resistant silicone rubber ring with a thickness of 5-8mm and a sealing width of 12-18mm. A long strip opening is opened on the side wall 60-140mm away from the burner outlet, with the major axis length being 1.3-1.4 times the diameter of the flat flame, the minor axis height being 25-45mm, and the rounded corner radius at both ends being 6-9mm. The outer side is equipped with a detachable metal baffle with a width of 8-25mm, and the baffle material is 304 stainless steel.

[0023] The XY-plane movable precision probe structure described in step 1 includes two sets of linear guides with a stroke of 80-150mm, using ball screw transmission, with a positioning accuracy of 0.02-0.04mm; the driving method is a stepper motor with a step angle of 1.8° and a reduction ratio of 1:10, which, together with a microstepping driver, achieves a minimum displacement of 0.005mm; the sampling probe is made of 310S stainless steel tube with an inner diameter of 0.6-0.9mm, an outer diameter of 1.2-1.8mm, a tip angle of 45°±2°, and an insertion depth of 5-45mm into the quartz cover.

[0024] The camera and optical system described in step 1 are industrial CCD cameras with a resolution of 2048×1536 or higher, equipped with a 25-50mm fixed-focus lens, an aperture of f / 5.6-f / 7.1, and a shutter speed of 1 / 120s-1 / 800s; the distance between the camera and the quartz dome is 600-900mm, and the height difference between the center of the lens and the center of the flat flame is ≤3mm; equipped with a ring light source with a power of 30-50W, an illumination angle of 40°-50°, and a color temperature of 5500-6500K.

[0025] The gas supply and control system mentioned in step 1 includes: a fuel gas mass flow controller with a range of 0-15 L / min and an accuracy of ±0.3%FS; an air mass flow controller with a range of 0-150 L / min and an accuracy of ±0.3%FS; a pressure stabilizing valve to control inlet pressure fluctuation ≤±0.08 kPa; a cooling water pump with a flow rate of 10-20 L / min to control the burner base temperature ≤75℃; and a nitrogen protective gas flow rate of 5-15 L / min, which is axially introduced from the top of the quartz cover.

[0026] In step 2, during coordinate calibration, feature point selection follows the principle of 4 edge points + 4 center points + 2 diagonal points, with a spacing of 20-30mm between adjacent feature points. Image processing is performed using Matlab software, and a sub-pixel localization algorithm is used to identify the probe tip. The fitting equation is a quadratic polynomial. ,in The fitting coefficients are denoted as .

[0027] The criteria for stable combustion in step 3 are: flame center position shift ≤2mm within 5 consecutive minutes, and pollutant concentration fluctuation ≤5%; the hydrogen blending ratio gradient of hydrogen-blended natural gas is 5%0 / 5% / 10%…50%, and the ammonia blending ratio gradient is 3%0 / 3% / 6%…30%; the air-fuel ratio is adjusted by linkage adjustment using a mass flow controller to ensure synchronous changes in fuel gas and air flow.

[0028] In step 4, the starting coordinates of the grid scanning path are -40mm, -40mm, and the ending coordinates are 40mm, 40mm. The step size is selected according to the accuracy requirements: 3-5mm for high-precision measurement and 6-8mm for fast measurement. The sampling probe moving speed is 5-10mm / s, and the concentration data is collected 3 times at each sampling point. The average value is taken as the final result. The flame image capture frequency is 1-3 frames / second, and the image with a time difference of ≤0.5 seconds from the concentration data acquisition time is selected for correlation.

[0029] The criteria for flameout in step 5 are: the flame completely detaches from the burner surface for ≥3 seconds and cannot recover on its own; the criteria for flashback are: the flame retracts into the burner and the burner outlet temperature rises sharply by ≥50℃ / s; during extreme measurements, the initial adjustment range is 5%, and the adjustment range is 3% when approaching the critical value; the inner wall of the probe must be cleaned before each repeated measurement to avoid residual gas affecting the data.

[0030] Step 6 post-processing also includes: analyzing flame images using ImageJ software, calculating flame area error ≤2% and average brightness error ≤3%; plotting air-fuel ratio-pollutant concentration curves using Origin software, and determining limit values ​​using linear interpolation; the data report must include a device parameter table, calibration error analysis, relative standard deviation of repeatability verification results ≤3%, and attach pollutant distribution cloud maps and flame images under typical operating conditions.

[0031] The measuring device used in this method mainly consists of five core components: a flat flame burner, a quartz shroud and its opening structure, a planar movable precision probe structure, a camera and optical system, and a gas supply and control system. The structure and function of each component are as follows: Flat flame burner: Any conventional flat flame burner, such as McKenna type, can be used as the flame source and can be adapted to various premixed fuels such as natural gas, hydrogen-blended natural gas, and ammonia. The burner outlet surface must be flat to ensure that the flame shape is approximately planar, and its power adjustment range must cover the operating conditions from stable combustion to deflaming / tempering.

[0032] Quartz shroud and its opening structure: The quartz shroud is made of highly transparent quartz glass, preferably in a near-cylindrical or square column shape. Its height must be sufficient to cover the entire flat flame area from the burner outlet to the flame tip. The inner diameter / inner width must be 50-100mm larger than the maximum diameter of the flat flame to avoid contact between the flame and the shroud wall. The bottom of the quartz hood is sealed to the experimental base plate or the top of the burner by a high-temperature resistant silicone rubber ring with a sealing width of not less than 10mm, so as to minimize the infiltration of external airflow from the bottom and ensure stable airflow inside the hood. At a distance of 50-150mm from the burner outlet on the side wall of the quartz shroud near the center of the flat flame, a long strip opening is made, depending on the height of the flat flame. The major axis of the opening is horizontal, with a length of 1.2-1.5 times the diameter of the flat flame, and the minor axis is vertical, with a height of 20-50mm. The two ends of the opening are rounded with a radius of 5-10mm to reduce local airflow disturbance at the opening. The outer side of the opening is equipped with a detachable metal baffle. The baffle has a through groove that matches the shape of the opening but is adjustable in width. By replacing the baffle with different widths or adjusting the position of the baffle, the effective width of the opening can be adjusted from 5 to 30 mm. This ensures the space for the sampling probe to move while minimizing gas leakage inside the cover and interference from external airflow.

[0033] Planar movable precision probe structure: On the experimental stage outside the side opening of the quartz cover, two sets of orthogonally arranged linear guide rails and slides are installed to form an XY plane moving platform; the bottom guide rail is fixed in the horizontal direction, and the upper guide rail is vertically installed on the bottom slide. The sliding directions of the two are perpendicular to each other, forming a two-dimensional moving coordinate system. The guide rail and slide adopt a high-precision ball bearing structure with a positioning accuracy of no less than 0.05mm. The minimum division value of the manual micrometer head is 0.01mm or the step angle of the stepper motor is 1.8°. Combined with the reduction mechanism, the slide can be driven to move with a resolution of less than 0.1mm, ensuring the high precision and stability of the probe movement. An adjustable-angle metal clamp is installed on the top of the upper slide. The clamp holds a 310S stainless steel thin tube as a sampling probe. The probe has an inner diameter of 0.5-1.0 mm and an outer diameter of no more than 2 mm. The tip is ground at a 45° angle to reduce disturbance to the flame flow field. The probe tip can be inserted into the quartz shroud through the side opening. The insertion depth can be adjusted from 0-50 mm according to the flat flame radius. The other end of the sampling probe is connected to a gas analyzer, such as an infrared gas analyzer or a gas chromatograph, through a high-temperature resistant polytetrafluoroethylene (PTFE) flexible tube with an inner diameter that matches the probe. The tube length is not less than 1.5m to avoid the analyzer vibration affecting the probe positioning.

[0034] Camera and optical system: An industrial or high-speed camera is placed opposite the side opening of the quartz dome or at an angle of 30°-60°. The camera lens is a fixed focal length lens with a focal length of 25-50mm, and the field of view must completely cover the flat flame area and the side opening range. The distance between the camera and the quartz dome should be 500-1000mm. Fix it with a tripod and adjust the camera height so that the center of the lens is at the same height as the center of the flat flame. Adjust the aperture to f / 4-f / 8 and the shutter speed to 1 / 100s-1 / 1000s to ensure that the flame image is clear and there are no overexposed or underexposed areas. Optional ring light source or surface light source can be used to illuminate the quartz mask from the side at a 45° angle to reduce the impact of mask wall reflection on image quality.

[0035] Gas supply and control system: Fuel gas such as natural gas, hydrogen, ammonia and air are metered by high-precision mass flow controllers with an accuracy of ±0.5%FS. After being fully mixed by a mixer, they are delivered to the flat flame burner. The range of the mass flow controller needs to be matched according to the burner power to ensure that the air-fuel ratio adjustment range covers 0.8-1.5 and the theoretical air-fuel ratio is 1. The system is equipped with a pressure stabilizing valve to ensure that the inlet pressure fluctuation of fuel gas and air does not exceed ±0.1 kPa; A cooling water pump can be optionally installed to cool the burner base or quartz shroud wall through water pipes, controlling the temperature of the burner and quartz shroud during the experiment to keep the base temperature below 80°C. An optional nitrogen protection gas channel is available, which allows the nitrogen flow rate to be adjusted by a mass flow controller and slowly introduced from the top of the quartz cover to suppress gas backflow inside the cover and protect the camera lens from high temperatures.

[0036] 2. Measurement Operation Procedures: Device Installation and Debugging: According to the above device configuration, install the flat flame burner, quartz cover, XY plane moving platform, sampling probe, camera and gas supply system in sequence on the experimental platform, ensuring that the positions of each component are fixed and there is no looseness; Check the seal at the bottom of the quartz hood, ignite a small amount of alcohol inside the hood, and observe whether the flame pattern is stable to determine whether external airflow interference has been effectively suppressed. Connect the sampling probe to the gas analyzer, and calibrate the analyzer with a standard gas to ensure the accuracy of pollutant concentration measurement; adjust the camera parameters and take flat flame images to ensure that the flame edge and central area are clearly distinguishable.

[0037] Coordinate calibration: Place a standard coordinate plate with millimeter scale at the side opening of the quartz cover, with the plane of the coordinate plate coinciding with the moving plane of the XY moving platform; Control the XY platform to drive the sampling probe tip to move sequentially to multiple feature points on the coordinate plate, such as (0,0), (50,0), (0,50), (50,50), etc., at least 8 points, evenly distributed in the field of view, and record the probe physical coordinates X1, Y1 of each feature point; Simultaneously, images containing the coordinate plate and the probe tip are captured, and image processing software such as Matlab and OpenCV are used to identify the pixel coordinates U1 and V1 of the probe tip in the image. By using linear regression or polynomial fitting, establish the transformation equation between pixel coordinates U,V and physical coordinates X,Y, and the calibration error must be controlled within 0.2mm.

[0038] Spatial distribution measurement of pollutants: Set the combustion parameters according to the experimental requirements, including the type of fuel gas, blending ratio (e.g., 20% hydrogen), air-fuel ratio (e.g., 1.0), and burner power (e.g., 5kW). Start the burner and begin the measurement after the flame has been burning stably for 10-15 minutes. Preset the probe scanning path, prioritizing grid scanning such as a 5mm×5mm grid. Adjust the step size according to accuracy requirements to determine the physical coordinates (X, Y) of each sampling point. Control the XY platform to move the probe tip to the first sampling point, pause for 30-60 seconds until the gas analyzer reading stabilizes, and record the pollutant concentration at that point, such as NO. x The sampling points are used to detect CO, unburned hydrocarbons, etc.; at the same time, an image of the flame at that moment is captured, and the corresponding position of the current sampling point in the image is determined according to the coordinate transformation equation. Complete the measurement of all sampling points sequentially according to the scanning path. If the flame shape changes significantly during the process, it needs to be stabilized again before continuing the measurement. After the measurement is completed, the physical coordinates, pollutant concentration, and flame image data are organized, and an interpolation algorithm such as Kriging interpolation is used to draw a two-dimensional distribution cloud map of pollutants.

[0039] Flameout / Returnfire Limit Measurement: Starting from stable combustion conditions, gradually adjust key parameters to approach the limit state: If measuring the flameout limit, gradually reduce the air-fuel ratio or reduce the gas flow rate; if measuring the returnfire limit, gradually increase the air-fuel ratio or increase the gas flow rate. Each adjustment should not exceed 5%, and stabilize for 5-10 minutes after adjustment. When the critical operating conditions approach the limit, such as the flame edge starting to shake or localized extinction, repeat the pollutant distribution measurement in step 3 and record the pollutant concentration changes under the critical conditions, such as a sudden increase in CO concentration; continue to adjust the parameters until flameout occurs and the flame completely detaches from the burner surface or the flashback flame retracts into the burner, and record the operating parameters at this time, such as an air-fuel ratio of 1.45. Repeat the above process 3-5 times, take the average value as the final deflaming / tempering limit value, and compare the pollutant distribution characteristics under different critical states to analyze the correlation between combustion instability and pollutant generation.

[0040] Post-experiment processing: Turn off the burner and gas supply system, and after the device has cooled down, clean the dust accumulated on the inner wall of the quartz hood and the residual gas in the sampling probe; Compile all experimental data, including operating parameters, pollutant concentrations, flame images, and limit values, to form a complete experimental report; Analyze the relationship between pollutant distribution and flame structure, such as NO at the flame center. x The highest concentration and the changing trends of pollutant concentrations before and after deflaming / tempering provide a basis for burner optimization.

[0041] The above embodiments are only used to illustrate the present invention and are not intended to limit the technical solutions described herein. Although the present invention has been described in detail with reference to the above embodiments, the present invention is not limited to the specific embodiments described above. Therefore, any modifications or equivalent substitutions to the present invention, as well as all technical solutions and improvements that do not depart from the spirit and scope of the invention, are covered within the scope of the claims of the present invention.

Claims

1. A method for measuring the spatial distribution of pollutants and the flameout / temper limit in a flat-flame burner, characterized in that, Includes the following steps: Step 1: Construct a measuring device, which includes a flat flame burner, a quartz shroud and its opening structure, an XY plane moving precision probe structure, a camera and optical system, and a gas supply and control system; wherein the flat flame burner is a McKenna type with an outlet diameter of 50-100mm and a power adjustment range of 2-15kW. Step 2: Perform coordinate calibration: Place a 100mm×100mm standard coordinate plate with an accuracy of 0.01mm at the side opening of the quartz cover, control the probe tip to move sequentially to at least 10 evenly distributed feature points, record the physical coordinates and corresponding pixel coordinates, establish the transformation equation through polynomial fitting, and the calibration error is ≤0.15mm. Step 3: Set combustion conditions: Determine the gas type, including natural gas, hydrogen-blended natural gas, ammonia, blending ratio of hydrogen 0-50% / ammonia 0-30%, air-fuel ratio of 0.8-1.5, burner power of 2-15kW, start the burner and stabilize for 12-18 minutes; Step 4, Spatial distribution measurement of pollutants: Using a grid scanning path with a step size of 3-8 mm, the probe is controlled to stay at each sampling point for 35-55 seconds, and the pollutant concentration and flame image are recorded simultaneously. A two-dimensional distribution cloud map is drawn using Kriging interpolation. Step 5, Flameout / Temperature Limit Measurement: Adjust the operating parameters by 3%-5% each time, stabilize for 6-9 minutes, and then measure; when the flame fluctuation amplitude of the critical operating condition is >5mm, repeat the scan until flameout / temper occurs, repeat the measurement 4-6 times and take the average value; Step 6, Post-experiment processing: After shutting down the system, let it cool for 30-45 minutes, clean the probe and quartz cover, analyze the data using Origin software, and output a report on the correlation between operating conditions, concentration, and images.

2. The method for measuring the spatial distribution of pollutants and the flameout / temper limit in a flat-flame burner according to claim 1, characterized in that, The quartz cover mentioned in step 1 is a cylindrical structure made of high-transmittance quartz glass, with an inner diameter 60-90mm larger than the maximum diameter of the flat flame and a height of 200-300mm. The bottom is sealed with a high-temperature resistant silicone rubber ring with a thickness of 5-8mm and a sealing width of 12-18mm. A long strip opening is opened on the side wall 60-140mm away from the burner outlet, with the length of the major axis being 1.3-1.4 times the diameter of the flat flame, the height of the minor axis being 25-45mm, and the radius of the rounded corners at both ends being 6-9mm. The outer side is equipped with a detachable metal baffle with a width of 8-25mm, and the baffle material is 304 stainless steel.

3. The method for measuring the spatial distribution of pollutants and the flameout / temper limit in a flat-flame burner according to claim 1, characterized in that, The XY-plane movable precision probe structure described in step 1 includes two sets of linear guides with a stroke of 80-150mm, using ball screw transmission, with a positioning accuracy of 0.02-0.04mm; the driving method is a stepper motor with a step angle of 1.8° and a reduction ratio of 1:10, which, together with a microstepping driver, achieves a minimum displacement of 0.005mm; the sampling probe is made of 310S stainless steel tube with an inner diameter of 0.6-0.9mm, an outer diameter of 1.2-1.8mm, a tip angle of 45°±2°, and an insertion depth of 5-45mm into the quartz cover.

4. The method for measuring the spatial distribution of pollutants and the flameout / temper limit in a flat-flame burner according to claim 1, characterized in that, The camera and optical system described in step 1 uses an industrial CCD camera with a resolution of 2048×1536, equipped with a 25-50mm fixed focal length lens, an aperture of f / 5.6-f / 7.1, and a shutter speed of 1 / 120s-1 / 800s; the distance between the camera and the quartz dome is 600-900mm, and the height difference between the center of the lens and the center of the flat flame is ≤3mm; it is equipped with a ring light source with a power of 30-50W, an illumination angle of 40°-50°, and a color temperature of 5500-6500K.

5. The method for measuring the spatial distribution of pollutants and the flameout / temper limit in a flat-flame burner according to claim 1, characterized in that, The gas supply and control system mentioned in step 1 includes: a fuel gas mass flow controller with a range of 0-15 L / min and an accuracy of ±0.3%FS; an air mass flow controller with a range of 0-150 L / min and an accuracy of ±0.3%FS; a pressure stabilizing valve to control inlet pressure fluctuation ≤±0.08 kPa; a cooling water pump with a flow rate of 10-20 L / min to control the burner base temperature ≤75℃; and a nitrogen protective gas flow rate of 5-15 L / min, which is axially introduced from the top of the quartz cover.

6. The method for measuring the spatial distribution of pollutants and the flameout / temper limit in a flat-flame burner according to claim 1, characterized in that, In the coordinate calibration process of step 2, the feature points are selected according to the principle of 4 points on the edge + 4 points in the center + 2 points on the diagonal, and the distance between adjacent feature points is 20-30mm; image processing is performed using Matlab software, and the probe tip is identified through a sub-pixel positioning algorithm.

7. The method for measuring the spatial distribution of pollutants and the flameout / temper limit in a flat-flame burner according to claim 1, characterized in that, The criteria for determining stable combustion in step 3 are: the flame center position shift ≤2mm within 5 consecutive minutes, and the pollutant concentration fluctuation ≤5%.

8. The method for measuring the spatial distribution of pollutants and the flameout / temper limit in a flat-flame burner according to claim 1, characterized in that, In step 4, the starting coordinates of the grid scanning path are -40mm, -40mm, and the ending coordinates are 40mm, 40mm. The step size is selected according to the accuracy requirements: 3-5mm for high-precision measurement and 6-8mm for fast measurement. The sampling probe moving speed is 5-10mm / s, and the concentration data is collected 3 times at each sampling point. The average value is taken as the final result. The flame image capture frequency is 1-3 frames / second, and the image with a time difference of ≤0.5 seconds from the concentration data acquisition time is selected for correlation.

9. The method for measuring the spatial distribution of pollutants and the flameout / temper limit in a flat-flame burner according to claim 1, characterized in that, The criteria for flameout in step 5 are: the flame completely detaches from the burner surface for ≥3 seconds and cannot recover on its own; the criteria for flashback are: the flame retracts into the burner and the burner outlet temperature rises sharply by ≥50℃ / s.

10. The method for measuring the spatial distribution of pollutants and the flameout / temper limit in a flat-flame burner according to claim 1, characterized in that, Step 6 post-processing also includes: analyzing flame images using ImageJ software, calculating flame area error ≤2% and average brightness error ≤3%; plotting air-fuel ratio-pollutant concentration curves using Origin software, and determining limit values ​​using linear interpolation; the data report must include a device parameter table, calibration error analysis, relative standard deviation of repeatability verification results ≤3%, and attach pollutant distribution cloud maps and flame images under typical operating conditions.

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