Coal mine roof rock loaded fracture discharge spark testing device and ignition energy evaluation method thereof

Abstract

The invention discloses a coal mine roof rock loaded fracture discharge spark testing device and an ignition energy evaluation method. The coal mine roof rock loaded fracture discharge spark testing device comprises a closed explosion reaction box, a mechanical loading system driven by a hydraulic cylinder, a replaceable compression / shearing mold, a silver pole piece, a high-speed camera, a photoelectric detector, a gas environment control assembly, a data acquisition and processing unit and the like. The underground gas concentration environment is simulated through the gas environment control assembly, rock failure mode simulation is achieved through the mechanical loading system, and the multi-source assembly synchronously collects parameters such as the electric charge quantity, the voltage and the spark form. According to the evaluation method, a direct method and an indirect method are fused, effective ignition energy is output after data verification, and the risk is judged by comparing the effective ignition energy with an explosion threshold. The device can simulate the whole process of discharging electric sparks in a gas-containing environment and perform quantitative evaluation, realizes accurate quantification of ignition energy, provides data support for explosion risk evaluation of roof rocks with different lithology, assists coal mine gas explosion early warning, and ensures safe production.

Description

Technical Field

[0001] This invention relates to the field of coal mine safety testing technology, and in particular to a coal mine roof rock load-induced fracture discharge spark test device and its ignition energy assessment method. Background Technology

[0002] Gas explosions in coal mine goafs are a major hazard threatening safe coal mine production, and their occurrence is often closely related to the dynamic phenomena of roof pressure. During the collapse of roof rock under load, the rock fracture discharges and ionizes the surrounding gas, generating discharge sparks that can ignite premixed gas containing gas / air within the explosive concentration limits (5%-16%). This is a major risk source for inducing gas explosions in goafs. Therefore, accurately simulating the generation process of discharge sparks from roof rock fracture under load and quantitatively assessing their ignition energy is crucial for revealing the explosion mechanism caused by rock fracture discharge and for scientifically preventing and controlling the risk of gas explosions.

[0003] However, current technologies for testing and assessing the ignition energy of discharge sparks from rock fracture under load in coal mines have significant limitations. Regarding experimental setups for qualitatively simulating rock fracture discharge sparks under load, most existing mechanical loading systems can only conduct experiments in air, lacking a closed experimental scenario that can accurately simulate the gas-bearing environment of a goaf, making it difficult to explore the interaction mechanism between rock fracture discharge and gas. Furthermore, existing devices often only achieve a single loading mode, failing to reproduce the combined stress states such as compression and shear that roof rocks may face in actual working conditions, making it difficult to assess the differences in the ability of rocks to generate electric sparks under different fracture modes. In terms of quantitative assessment of ignition energy, it is known that a minimum ignition energy exceeding 0.28 mJ can trigger a gas explosion, but current research has not yet achieved a quantitative assessment of the ignition energy of millisecond-level transient discharge sparks generated by rock under load in a gas-bearing environment, lacking a basis for judging the ignition capability of rock discharge sparks. Although some monitoring devices can collect electrical signals such as charge and voltage when rocks fracture to assess the degree of rock damage, they have failed to achieve synchronous monitoring of electrical signals generated by rock loading and discharge sparks, and the correlation between electrical signals and discharge sparks has not yet been established. Furthermore, existing equipment cannot simultaneously and accurately monitor multi-dimensional parameters such as the luminous intensity, duration, and morphological characteristics of discharge sparks, resulting in a lack of scientific basis for assessing ignition energy and making it difficult to determine whether the spark poses a risk of igniting gas.

[0004] In summary, existing technologies cannot meet the requirements of laboratory simulation of the entire process of roof rock fracture discharge spark under load in underground gas-bearing environments, and there is a lack of reliable quantitative assessment methods for ignition energy. There is an urgent need to construct a technical solution that integrates gas-bearing environment simulation, multimodal mechanical loading, multi-parameter synchronous monitoring, and accurate energy assessment functions to provide data support for the scientific assessment and early warning of coal mine gas explosion risks. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a test device for the discharge spark of rock fracture under load in coal mines and a method for evaluating its ignition energy. This solves the problems of existing technologies, which struggle to simulate the entire process of rock fracture discharge spark under load in underground gas-bearing environments and lack quantitative evaluation of ignition energy. It reveals the explosive potential of rock fracture discharge in different rock types and provides technical support for coal mine gas explosion risk assessment and early warning.

[0006] The technical solution adopted by the present invention to solve its technical problem is: a coal mine roof rock fracture discharge spark test device, including an explosion reaction chamber, a mechanical loading system, a charge induction sensor, a high-speed camera, a photoelectric detector, a gas environment control component, a data acquisition and processing unit, and an ignition energy assessment module; The explosion reaction chamber is a sealed structure with observation windows on the walls. The explosion reaction chamber is connected to a gas inlet valve and an exhaust valve for filling with a gas-containing mixture to simulate the underground gas environment. The mechanical loading system is located outside the explosion reaction chamber. The force transmission rod of the mechanical loading system is sealed and inserted into the explosion reaction chamber and connected to a mechanical loading mold, which is used to apply uniaxial compression or shear load to the rock sample inside the chamber. Multiple charge sensing sensors are provided and arranged around the rock sample inside the explosion reaction chamber to measure the amount of charge and voltage value when the rock fractures under load. The high-speed camera is mounted on the outside of the observation window and is used to monitor spark phenomena; The photodetector is installed inside the explosion reaction chamber to record the intensity and duration of the spark. The gas environment control component is connected to the gas inlet valve and the gas outlet valve to control the gas concentration inside the box; The data acquisition and processing unit is connected to the charge sensing sensor, high-speed camera, photodetector and mechanical loading system respectively, and is used to receive and integrate monitoring data. The ignition energy assessment module is connected to the data acquisition and processing unit and is used to calculate and assess the effective ignition energy of the discharge spark.

[0007] Furthermore, the main body of the explosion reaction chamber is made of stainless steel, and the top is provided with a through hole for the output end of the mechanical loading system to pass through. The through hole is sealed with an oil-resistant high-pressure sealing ring. The bottom surface inside the explosion reaction chamber is provided with a sample placement platform adapted to the mechanical loading mold. The side wall of the explosion reaction chamber is provided with a gas inlet, a gas outlet, and a pressure relief hole. The gas inlet is connected to a gas inlet valve, and the end of the gas inlet valve away from the explosion reaction chamber forms a branch, which is connected to a gas cylinder and an air cylinder respectively. The gas outlet is connected to an exhaust valve.

[0008] Furthermore, two pressure relief holes are provided and are symmetrically opened on the side wall of the explosion reaction chamber, and each pressure relief hole is equipped with a rupture disc.

[0009] Furthermore, the gas environment control component includes a gas concentration detector, a gas concentration controller, an electromagnetic control valve, and a flow meter. The pipelines between the gas cylinder and the gas inlet valve, and between the air cylinder and the gas inlet valve, are all connected to the flow meter and the electromagnetic control valve. The probe of the gas concentration detector is sealed and extends into the explosion reaction chamber. The signal output terminal of the gas concentration detector is electrically connected to the gas concentration controller. The electromagnetic control valve and the exhaust valve are both electrically connected to the gas concentration controller to regulate the gas concentration in the explosion reaction chamber.

[0010] Furthermore, the charge sensing sensor uses a silver electrode sheet covered with insulating adhesive and attached to the surface of the rock sample as a collection electrode.

[0011] Furthermore, the mechanical loading system includes a hydraulic cylinder, a force transmission rod, and a mechanical loading mold. The hydraulic cylinder is fixed to the top of the explosion reaction chamber, and the output end of the hydraulic cylinder is connected to the force transmission rod. The force transmission rod is sealed and inserted into the explosion reaction chamber and connected to the mechanical loading mold. The mechanical loading mold includes a compression mold and a shear mold. The compression mold and the shear mold are replaced according to the test requirements to apply uniaxial compression or shear loads to the rock sample.

[0012] This invention also provides a method for evaluating the ignition energy of discharge sparks from the fracture of coal mine roof rock under load. Based on the aforementioned test device for discharge sparks from the fracture of coal mine roof rock under load, the ignition energy evaluation method includes the following steps: S1: Multi-source signal synchronous acquisition: Trigger conditions are set through the data acquisition and processing unit, and the trigger signal is synchronously transmitted to the charge induction sensor, high-speed camera, photodetector and mechanical loading system to synchronously acquire four types of signals: charge signal, visual signal, light intensity signal and auxiliary signal. S2. Direct Quantization Calculation: Deriving discharge energy based on the principle of capacitor energy storage, specifically including: Basic energy calculation: Take the average charge collected by the two silver electrodes as Q and the average voltage as U, and calculate the initial discharge energy. ; Environmental correction: Considering the influence of gas concentration inside the explosion reaction chamber on the discharge energy, a correction factor k is introduced to compensate for the effect of gas concentration on energy; Corrected energy ; S3. Indirect Quantitative Evaluation: This involves calculating based on spark characteristics and analogy with standard igniters, specifically including: Spark characteristics extraction: Select the spark area from the high-speed camera video, extract the maximum spark area S and the spark duration t1; calculate the light intensity integral value ∫Idt from the light intensity-time curve output by the photodetector, with the integration interval being the effective luminous duration t2; Standard analogy experiment: Select a standard piezoelectric igniter with a known minimum ignition energy E0, trigger ignition under the same gas concentration conditions as the rock fracture experiment, repeat the experiment 3 times and take the average value, record the maximum area S0, duration t0 and light intensity integral value ∫I0dt of the standard spark, and establish a standard reference benchmark. Indirect energy calculation: By establishing a regression model through multi-parameter analogy, and taking into account the influence of spark area, duration, and light intensity integral, the indirect energy E2 of rock fracture spark is calculated. Where 0.4, 0.3, and 0.3 are the weighting coefficients for spark area, duration, and light intensity integral, respectively; S4: Effective energy fusion is determined, and after removing outlier data, calculations are performed. and The relative error is such that when the error is ≤15%, the arithmetic mean of the two values ​​is taken as the effective ignition energy. ; S4: Effective energy fusion is determined, specifically including: Abnormal data removal: Remove abnormal data acquired by charge sensing sensors, high-speed cameras, and photodetectors; Data validity verification: Calculate the corrected direct energy and indirect energy The relative error, The formula is Only data with a relative error ≤15% are retained; Effective energy calculation: Take the verified qualified energy. and The arithmetic mean of the effective ignition energy The formula is ; Explosion risk assessment: Effective ignition energy Compared to the minimum ignition energy of methane-air premixed gas, when When the discharge spark has an energy ≥ the minimum ignition energy, it is determined that the discharge spark poses a risk of causing explosive gas; when If the minimum ignition energy is less than the threshold, it is determined that there is no risk of explosion.

[0013] Furthermore, the charge signal is the real-time charge quantity and surface voltage acquired through a silver electrode during rock fracturing. The visual signal is obtained by capturing the dynamics of the spark with a high-speed camera, recording the spark shape, maximum projected area, and duration. The light intensity signal is obtained by capturing the light intensity of a spark through a photodetector, outputting a light intensity-time curve, and determining the peak light intensity and the effective light emission duration. The auxiliary signals are obtained by collecting the gas concentration inside the explosion reaction chamber through a gas concentration detector, and by collecting the displacement of the force transmission rod and the load value of the hydraulic cylinder through an external displacement sensor and a load sensor.

[0014] Furthermore, the triggering conditions in the multi-source signal synchronous acquisition in step S1 are set in two ways. One is that the displacement of the force transmission rod reaches 95% of the rock sample's yield critical displacement, where the yield critical displacement is the maximum elastic displacement of the rock sample before yielding as determined in the pre-experiment. The other is that the hydraulic cylinder load reaches 95% of the rock sample's yield critical load, where the yield critical load is the minimum load value of the rock sample when yielding as determined in the pre-experiment. Meeting either one will trigger the triggering.

[0015] Furthermore, in step S4, the abnormal data removal process removes three types of abnormal data: charge signal fluctuation amplitude > 20%, high-speed camera image blur causing maximum projected area measurement deviation > 15%, and photodetector signal signal-to-noise ratio < 10:1.

[0016] The beneficial effects of this invention are: This invention integrates a sealed explosion reaction chamber with a gas environment control component to accurately simulate the 5%-16% gas explosion limit concentration environment underground, providing a realistic scenario for the study of the interaction between rock fracture discharge and gas, and achieving accurate environmental simulation. Equipped with replaceable compression and shearing molds, it can simulate the dominant failure modes in actual working conditions of roof rock, filling the limitations of single loading modes and achieving full coverage of failure modes. Through the coordinated work of silver electrode plates, high-speed cameras, photoelectric detectors, etc., it simultaneously captures multi-dimensional parameters such as charge, voltage, spark morphology, and light intensity, achieving multi-source synchronous monitoring and providing comprehensive raw data for energy assessment. Combining direct and indirect methods, and introducing environmental correction coefficients and data validity verification, it achieves accurate quantification of ignition energy, which can be directly compared with the explosion threshold to clarify the risk level. The energy assessment is more scientific and standardized, thus providing a quantitative basis for the explosion risk of roof rocks of different lithologies, supporting the scientific assessment and early warning of gas explosion risk in coal mine goaf areas, and ensuring safe production. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the overall structure of the present invention.

[0018] Figure 2 This is a partial structural diagram of the internal structure of the explosion reaction chamber used in this invention.

[0019] Figure 3 This is a flowchart of the ignition energy assessment method of the present invention.

[0020] In the diagram: 1. Hydraulic cylinder; 2. Explosion reaction chamber; 3. Observation window; 4. Gas inlet valve; 5. Flow meter; 6. Electromagnetic control valve; 7. Gas cylinder; 8. Air cylinder; 9. Gas concentration detector; 10. Data acquisition instrument; 11. Computer; 12. High-speed camera; 13. Pressure relief hole; 14. Photoelectric detector; 15. Gas outlet; 16. Force transmission rod; 17. Silver electrode; 18. Rock sample; 19. Shearing mold; 20. Compression mold. Detailed Implementation

[0021] The present invention will be further described in detail below with reference to the accompanying drawings.

[0022] This invention discloses a test device for electrical discharge spark testing of rock fracture under load in coal mine roof.

[0023] Reference Figure 1 and Figure 2 A test device for testing the discharge spark of rock fracture under load in coal mines includes an explosion reaction chamber 2, a mechanical loading system, a charge induction sensor, a high-speed camera 12, a photoelectric detector 14, a gas environment control component, a data acquisition and processing unit, and an ignition energy assessment module. The components work together to simulate the discharge spark of rock fracture under load in a gas-containing environment, monitor multiple parameters synchronously, and accurately quantify the ignition energy, providing reliable technical support for coal mine gas explosion risk assessment.

[0024] The explosion reaction chamber 2 is a sealed structure, with its main body made of 304 stainless steel to ensure structural stability during the experiment and resistance to corrosion in a gas-containing environment. A through-hole is provided at the top for the output end of the mechanical loading system to pass through. This through-hole is sealed with an oil-resistant high-pressure sealing ring, maintaining the airtightness of the chamber while the force transmission rod 16 moves up and down, preventing gas leakage from affecting experimental accuracy. The walls of the explosion reaction chamber 2 are equipped with a quartz glass observation window 3, measuring 300mm × 200mm × 10mm. This window is characterized by high temperature resistance (≤600℃ without gas evolution), impact resistance >1.5MPa, and light transmittance ≥90%, providing a clear view for the high-speed camera 12 to capture the dynamics of the sparks. The bottom of the chamber is equipped with a sample placement platform adapted to the mechanical loading mold, ensuring the rock sample is centered and that the loading force is transmitted evenly.

[0025] The side wall of the explosion reaction chamber 2 is provided with a gas inlet, a gas outlet 15, and two pressure relief holes 13 arranged symmetrically. The gas inlet is connected to a gas inlet valve 4. The end of the gas inlet valve 4 away from the explosion reaction chamber 2 forms a branch, which is connected to a gas cylinder 7 and an air cylinder 8 respectively, so as to achieve precise gas and air mixing. The gas outlet 15 is connected to an exhaust valve for residual gas discharge after the experiment and concentration adjustment during the experiment. The pressure relief hole 13 is equipped with a rupture disc with a burst pressure of 0.3 MPa. When the pressure inside the chamber exceeds the standard due to a gas explosion, the rupture disc can quickly rupture and release pressure to protect the chamber and surrounding equipment.

[0026] The mechanical loading system is located outside the explosion reaction chamber 2 and includes a hydraulic cylinder 1, a force transmission rod 16, and a mechanical loading mold. The hydraulic cylinder 1 is fixed to the top of the explosion reaction chamber 2, and its output end is rigidly connected to the force transmission rod 16. The force transmission rod 16 is sealed and inserted into the explosion reaction chamber 2 and centered and connected to the mechanical loading mold to ensure that the loading force is accurately transmitted to the rock sample along the axial direction. The mechanical loading mold includes a compression mold 20 and a shear mold 19, which adopts a quick positioning and limiting structure and can be flexibly replaced according to the test requirements. It can simulate the uniaxial compression and shear failure modes of coal mine roof rock commonly seen in actual working conditions, covering the dominant fracture morphology of the roof, and providing an experimental basis for exploring the characteristics of discharge sparks under different failure modes.

[0027] Multiple charge sensing sensors are arranged around the rock sample inside the explosion reaction chamber 2. They are made of pure silver electrodes 17 with a thickness of 0.1 mm, backed with insulating adhesive and attached to the surface of the rock sample 18 as collection electrodes. The pure silver material has excellent conductivity and can quickly respond to the charge change when the rock fractures. The attached installation and multi-electrode arrangement can reduce single-point acquisition error and ensure accurate measurement of the real-time charge and voltage value when the rock fractures under load, providing core raw data for direct calculation of ignition energy.

[0028] The high-speed camera 12 is located outside the observation window 3. It has a resolution of 1280×800 and a maximum frame rate of 2000fps. The lens is aimed at the fracture area of ​​the rock sample, and the trigger logic is linked with the loading signal of the hydraulic cylinder 1. It can synchronously capture the millisecond-level transient spark dynamics at the moment of rock fracture, clearly record the spark shape, maximum projected area and duration, and provide visual data support for indirect evaluation of ignition energy. At the same time, it avoids direct contact between the equipment and the gas-containing environment, thus improving the safety of the experiment.

[0029] The photodetector 14 is installed inside the explosion reaction chamber 2. It adopts a silicon photodiode array with a response wavelength of 400-700nm, a light intensity range of 0.01-1000cd, and a resolution of 0.01cd. It can capture the changes in the luminous intensity of the spark in real time and output a precise light intensity-time curve. By analyzing the light intensity-time curve, the peak light intensity and the effective luminous duration can be determined, providing an optical characteristic basis for the indirect quantification of ignition energy. It works in conjunction with the high-speed camera 12 to realize the synchronous acquisition of multi-dimensional parameters of the spark.

[0030] The gas environment control component is connected to the gas inlet valve 4 and the exhaust valve to precisely control the gas concentration inside the chamber. It includes a gas concentration detector 9, a gas concentration controller, an electromagnetic control valve 6, and a gas mass flow meter 5. The pipelines between the gas cylinder 7 and the gas inlet valve 4, and between the air cylinder 8 and the gas inlet valve 4, are connected to the flow meter 5 and the electromagnetic control valve 6. The flow meter 5 can display and fine-tune the inlet flow rate in real time, while the electromagnetic control valve 6 controls the pipeline flow. The probe of the gas concentration detector 9 extends into the chamber through a sealed interface on the side wall of the explosion reaction chamber 2, approximately 100mm from the rock sample 18, to avoid damage to the probe if the rock sample fractures. It can monitor the gas concentration inside the chamber in real time and transmit signals to the gas concentration controller. The gas concentration controller has a preset gas concentration range of 5%-16%, covering the gas explosion limit. By receiving the concentration detection signal, it automatically controls the opening and closing of the electromagnetic control valve 6 and the operation of the exhaust valve, achieving closed-loop regulation of the gas concentration and ensuring that the gas concentration inside the chamber remains stable at the set value, realistically simulating the gas-containing environment in a coal mine.

[0031] The data acquisition and processing unit includes a data acquisition instrument 10 and a computer 11, which work together to form a complete data acquisition, conditioning, display, and processing chain. It is connected to a charge sensing sensor, a high-speed camera 12, a photodetector 14, and a mechanical loading system to achieve synchronous reception, integration, and in-depth processing of multi-source data. The data acquisition instrument 10, as the front-end acquisition and display core, can display the surface charge and voltage of the rock sample 18 in real time and has an over-limit alarm function. It receives signals from the photodetector 14 and the silver electrode 17 via a shielded wire, amplifies and conditions the signals, and outputs synchronized digital data to the computer 11. It also provides a trigger synchronization port for time synchronization with the high-speed camera 12 to ensure the time axis of the monitoring signal is aligned.

[0032] Computer 11, as the core of backend data processing and storage, is responsible for receiving the charge, voltage, and mechanical loading parameters transmitted by data acquisition instrument 10. It also receives the video stream from high-speed camera 12 and the light intensity signal from photodetector 14. Through supporting software, it extracts key parameters such as the maximum projected area of ​​the spark, duration, and light intensity integral value, and uniformly stores all experimental data, including mechanical loading parameters, gas concentration, photoelectric intensity, video, and displacement. It supports exporting to Excel / TXT format, which facilitates subsequent correlation analysis and regression modeling of "displacement-discharge energy-spark characteristics", providing a complete and accurate dataset for the ignition energy assessment module.

[0033] This invention also discloses a method for evaluating the ignition energy of discharge sparks from load-induced fractures of coal mine roof rocks.

[0034] Reference Figure 3 A method for evaluating the ignition energy of discharge sparks from the fracture of coal mine roof rock under load, based on the aforementioned test device for discharge sparks from the fracture of coal mine roof rock under load, includes the following steps: S1. Multi-source signal synchronous acquisition: The data acquisition instrument 10 of the data acquisition and processing unit sets the trigger conditions. There are two trigger conditions, and the system can be triggered if either one is met. The first is: the displacement of the force transmission rod 16 reaches 95% of the rock sample's yield critical displacement. The yield critical displacement is the maximum elastic displacement of the rock sample before yielding, which is determined by loading rock samples of the same lithology and specifications and recording the displacement value at the time of yielding. The second is: the load of the hydraulic cylinder 1 reaches 95% of the rock sample's yield critical load. The yield critical load is the minimum load value of the rock sample at the time of yielding, which is determined by loading rock samples of the same lithology and specifications and recording the minimum load value at the time of yielding.

[0035] The trigger signal is synchronously transmitted to the charge sensing sensor, high-speed camera 12, photodetector 14, and mechanical loading system via a BNC cable. The device start-up time difference is ≤1μs to ensure that all signals are synchronized. Four types of signals are acquired synchronously: charge signal, visual signal, light intensity signal, and auxiliary signal. Among them, the charge signal is the real-time charge and surface voltage of the rock when it fractures, which are collected by the silver electrode 17. After being amplified by the signal amplification module built into the data acquisition instrument 10, it is transmitted to the data acquisition card and then uploaded to the computer 11. The visual signal is captured by a high-speed camera 12 to capture the dynamics of the spark, and the video stream is transmitted to a computer 11 in real time. The computer 11 then uses software to clearly record the spark shape, maximum projection area, and duration. The light intensity signal is captured by the photodetector 14 to capture the intensity of the spark light emission. The output light intensity-time curve is transmitted to the computer 11 via the data acquisition instrument 10. The computer 11 determines the peak light intensity and the effective light emission duration. The auxiliary signals are the gas concentration inside the explosion reaction chamber 2 collected by the gas concentration detector 9, the displacement of the force transmission rod 16 collected by the external displacement sensor, and the load value of the hydraulic cylinder 1 collected by the load sensor. All kinds of auxiliary signals are synchronously transmitted to the computer 11 to provide support for environmental correction of energy calculation and traceability of experimental conditions.

[0036] S2. Direct Quantitative Calculation: This method derives the discharge energy based on the principle of capacitor energy storage. The core of this principle is that the rock fracturing discharge process can be equivalent to capacitor discharge, and the product of charge and voltage can reflect the energy released during the discharge process. Specifically, it includes: Basic energy calculation: Computer 11 retrieves data from multiple sets of silver electrode plates 17 transmitted by data acquisition instrument 10, and calculates the energy using the formula: Calculate the initial discharge energy; In the above formula, Q is the average charge collected by the two silver electrodes 17, in pC; U is the average voltage of the corresponding two silver electrodes 17, in V. This represents the initial discharge energy, expressed in μJ.

[0037] Environmental correction: Computer 11, in conjunction with the effect of gas concentration in the cavity of the explosion reaction chamber 2 on the discharge energy, introduces a correction coefficient k to compensate for the effect of gas concentration on energy. Corrected energy When the gas concentration is 9%, k=1, and k increases by 0.03 for every 1% increase in gas concentration; this makes the calculation results more consistent with the actual downhole gas environment; and the direct energy after environmental correction can truly reflect the discharge energy level of the rock at the target gas concentration.

[0038] S3. Indirect Quantitative Evaluation: Combining spark characteristics with analogy calculations using standard igniters, and leveraging the correlation between the physical characteristics of the spark and ignition energy, a reference benchmark is established using a standard igniter with known energy, enabling indirect deduction of ignition energy. Specifically, this includes: Spark feature extraction: Using Image-ProPlus software on a computer, the spark area was selected from the high-speed camera video, and the maximum spark area S was extracted (unit: mm). 2 The spark duration t1 is in milliseconds; the light intensity-time curve is integrated using Origin software to calculate the light intensity integral value ∫Idt, in cd·ms; the integration interval is the effective luminous duration t2; this integral value can comprehensively reflect the total luminous energy of the spark.

[0039] Standard analogy experiment: A standard piezoelectric igniter with a known minimum ignition energy of E0=0.3mJ was selected and ignited under the same gas concentration conditions as the rock fracture experiment. The experiment was repeated 3 times and the average value was taken to reduce random errors. The maximum area S0, duration t0, and light intensity integral value ∫I0dt of the standard spark were recorded by computer to establish a standard reference benchmark. Indirect energy calculation: A regression model is established through multi-parameter analogy, taking into account the influence of spark area, duration, and light intensity integral, and calculated using the formula. Calculate the indirect energy E2 of the sparks from rock fracture; Where 0.4, 0.3, and 0.3 are the weighting coefficients for spark area, duration, and light intensity integral, respectively; S4. Effective Energy Fusion Determination: To further improve the reliability of ignition energy assessment, data verification and fusion are used to combine the advantages of direct and indirect methods; specifically including: Abnormal data removal: Computer 11 automatically filters and removes three types of abnormal data: charge signal fluctuation amplitude >20%, high-speed camera image blur causing maximum projected area measurement deviation >15%, and photodetector 14 signal-to-noise ratio <10:1. Data validity verification: Calculate the corrected direct energy and indirect energy The relative error is given by the formula: Only data with a relative error ≤15% are retained to ensure consistency in the evaluation results of the two methods; Effective energy calculation: Take the verified qualified energy. and The arithmetic mean of the effective ignition energy The formula is ; Explosion risk assessment: Effective ignition energy Compared to the minimum ignition energy of a methane-air premixed gas, the known minimum ignition energy is approximately 0.28 mJ. When When the discharge spark is ≥0.28mJ, it is determined that the discharge spark poses a risk of causing explosive gas; when When the concentration is <0.28 mJ, it is determined that there is no risk of explosion, providing a quantitative basis for early warning of gas explosion risk in coal mine goaf areas.

[0040] Specific Implementation Example 1: Fine Sandstone Experiment and Ignition Energy Assessment Based on Shear and Compression Dies 1. Experimental parameters The sample was fine sandstone, processed into cylinders (φ50mm×100mm), discs (φ50mm×25mm), and cubes (70mm×70mm×70mm), and dried at 100℃ for 24 hours to remove moisture and reduce interference from the discharge signal. A compression mold 20 or a shearing mold 19 was installed, and two silver electrode sheets 17 were attached to the front and back of the sample. After the airtightness of the chamber was tested and qualified, all pipelines were connected. The chamber volume was 10L, and the gas concentration in the chamber was adjusted to 9.2%. The high-speed camera 12 was set to a resolution of 1280×800 and a frame rate of 1000fps. The photodetector 14 was set to a sampling rate of 10kHz and a response wavelength calibration of 400-700nm. The gain of the built-in signal amplification module of the data acquisition instrument 10 was adjusted to ×1000. Compression test: loading speed 2.5 kN / s, trigger condition is that the displacement of force transmission rod 16 reaches 95% of the rock sample's yield critical displacement; Shear test: loading speed 1.5 kN / s, trigger condition is that the shear load of hydraulic cylinder 1 reaches 95% of the shear strength of fine sandstone, i.e., the yield critical load.

[0041] 2. Energy Assessment The evaluation is conducted following the steps S1-S4 described above: simultaneous acquisition of multi-source signals, direct quantization calculation, indirect quantization evaluation, and effective energy fusion determination. Compression test: average voltage 30V, charge 3nC, no sparks; ≈0.0225mJ<0.28mJ.

[0042] Shear test: average voltage 250V, charge 45nC, spark area 10mm² 2 Duration: 0.8ms; ≈2.92mJ>0.28mJ.

[0043] 3. Conclusions and Post-processing The discharge sparks generated by the compression fracture of fine sandstone do not pose a potential risk of igniting gas, while the discharge sparks generated by shear fracture pose a risk of explosion. After the experiment, residual gas was discharged, the specimens were collected, and the device was cleaned.

[0044] Specific Example 2: Spark Test and Ignition Energy Assessment of Load-Bearing Fracture in Coarse Sandstone 1. Experimental parameters The specimen was coarse sandstone, and the gas concentration was adjusted to 9.1%. The specimen specifications, drying treatment, device installation and other experimental parameters were the same as in Specific Example 1.

[0045] 2. Energy Assessment The evaluation is conducted following the steps S1-S4 described above: simultaneous acquisition of multi-source signals, direct quantization calculation, indirect quantization evaluation, and effective energy fusion determination. Compression test: average voltage 25V, charge 2nC, no sparks; ≈0.0125mJ<0.28mJ.

[0046] Shear test: average voltage 40V, charge 5nC, spark area 1mm 2 Duration: 0.15ms; ≈0.066mJ<0.28mJ.

[0047] 3. Conclusions and Post-processing The discharge sparks generated by the compression and shear fracture of coarse sandstone pose no risk of explosion; after the experiment, residual gas was discharged, the specimens were collected, and the device was cleaned.

[0048] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A test device for electrical discharge spark testing of rock fracture under load in coal mine roof, characterized in that: It includes an explosion reaction chamber (2), a mechanical loading system, a charge sensing sensor, a high-speed camera (12), a photoelectric detector (14), a gas environment control component, a data acquisition and processing unit, and an ignition energy assessment module; The explosion reaction chamber (2) is a sealed structure with an observation window (3) on the wall. The explosion reaction chamber (2) is connected to a gas inlet valve (4) and an exhaust valve for filling with a gas-containing mixed gas to simulate the underground gas environment. The mechanical loading system is set outside the explosion reaction chamber (2). The force transmission rod (16) of the mechanical loading system is sealed and inserted into the explosion reaction chamber (2) and connected to a mechanical loading mold for applying uniaxial compression or shear load to the rock sample inside the chamber. Multiple charge sensing sensors are provided and arranged around the rock sample inside the explosion reaction chamber (2) to measure the amount of charge and voltage value when the rock is subjected to load and fractures. The high-speed camera (12) is located outside the observation window (3) and is used to monitor spark phenomena; The photodetector (14) is installed inside the explosion reaction chamber (2) to record the luminous intensity and duration of the spark; The gas environment control component is connected to the gas inlet valve (4) and the exhaust valve to control the gas concentration in the box; The data acquisition and processing unit is connected to the charge sensing sensor, the high-speed camera (12), the photodetector (14) and the mechanical loading system respectively, and is used to receive and integrate monitoring data; The ignition energy assessment module is connected to the data acquisition and processing unit and is used to calculate and assess the effective ignition energy of the discharge spark.

2. The coal mine roof rock under load fracture discharge spark test device according to claim 1, characterized in that: The main body of the explosion reaction chamber (2) is made of stainless steel. The top is provided with a through hole for the output end of the mechanical loading system to pass through. The through hole is sealed with an oil-resistant high-pressure sealing ring. The bottom surface inside the explosion reaction chamber (2) is provided with a sample placement platform adapted to the mechanical loading mold. The side wall of the explosion reaction chamber (2) is provided with a gas inlet, an outlet (15) and a pressure relief hole (13). The gas inlet is connected to the gas inlet valve (4). The gas inlet valve (4) forms a branch at the end away from the explosion reaction chamber (2) and is connected to the gas cylinder (7) and the air cylinder (8) respectively. The outlet (15) is connected to the exhaust valve.

3. The coal mine roof rock under load fracture discharge spark test device according to claim 2, characterized in that: Two pressure relief holes (13) are provided and are symmetrically opened on the side wall of the explosion reaction chamber (2). The pressure relief holes (13) are filled with rupture discs.

4. The coal mine roof rock under load fracture discharge spark test device according to claim 3, characterized in that: The gas environment control component includes a gas concentration detector (9), a gas concentration controller, an electromagnetic control valve (6), and a flow meter (5). The pipelines between the gas cylinder (7) and the gas inlet valve (4) and between the air cylinder (8) and the gas inlet valve (4) are connected to the flow meter (5) and the electromagnetic control valve (6). The probe of the gas concentration detector (9) is sealed and extends into the explosion reaction chamber (2). The signal output terminal of the gas concentration detector (9) is electrically connected to the gas concentration controller. The electromagnetic control valve (6) and the exhaust valve are both electrically connected to the gas concentration controller to regulate the gas concentration in the explosion reaction chamber (2).

5. The coal mine roof rock under load fracture discharge spark test device according to claim 4, characterized in that: The charge sensing sensor uses a silver electrode (17) with an insulating adhesive backing, which is attached to the surface of the rock sample (18) as a collection electrode.

6. The coal mine roof rock under load fracture discharge spark test device according to claim 5, characterized in that: The mechanical loading system includes a hydraulic cylinder (1), a force transmission rod (16), and a mechanical loading mold. The hydraulic cylinder (1) is fixed to the top of the explosion reaction chamber (2). The output end of the hydraulic cylinder (1) is connected to the force transmission rod (16). The force transmission rod (16) is sealed and inserted into the explosion reaction chamber (2) and connected to the mechanical loading mold. The mechanical loading mold includes a compression mold (20) and a shear mold (19). The compression mold (20) and the shear mold (19) are replaced according to the test requirements to apply uniaxial compression or shear load to the rock sample (18).

7. A method for evaluating the ignition energy of sparks from load-bearing fractures of coal mine roof rock, characterized in that: Based on the coal mine roof rock fracture discharge spark test device according to claim 6, the ignition energy assessment method includes the following steps: S1: Multi-source signal synchronous acquisition: Trigger conditions are set through the data acquisition and processing unit, and the trigger signal is synchronously transmitted to the charge sensing sensor, high-speed camera (12), photodetector (14) and mechanical loading system to synchronously acquire the corresponding charge signal, visual signal, light intensity signal and auxiliary signal. S2. Direct Quantization Calculation: Deriving discharge energy based on the principle of capacitor energy storage, specifically including: Basic energy calculation: Take the average charge collected by the two silver electrodes (17) as Q and the average voltage as U, and calculate the original discharge energy. ; Environmental correction: Combining the effect of gas concentration in the cavity of the explosion reaction box (2) on the discharge energy, a correction coefficient k is introduced to compensate for the effect of gas concentration on energy; Corrected energy ; S3. Indirect Quantitative Evaluation: This involves calculating based on spark characteristics and analogy with standard igniters, specifically including: Spark characteristics extraction: Select the spark area from the high-speed camera video, extract the maximum spark area S and the spark duration t1; calculate the light intensity integral value ∫Idt from the light intensity-time curve output by the photodetector (14), and the integration interval is the effective light emission duration t2; Standard analogy experiment: Select a standard piezoelectric igniter with a known minimum ignition energy E0, trigger ignition under the same gas concentration conditions as the rock fracture experiment, repeat the experiment 3 times and take the average value, record the maximum area S0, duration t0 and light intensity integral value ∫I0dt of the standard spark, and establish a standard reference benchmark. Indirect energy calculation: By establishing a regression model through multi-parameter analogy, and taking into account the influence of spark area, duration, and light intensity integral, the indirect energy E2 of rock fracture spark is calculated. Where 0.4, 0.3, and 0.3 are the weighting coefficients for spark area, duration, and light intensity integral, respectively; S4: Effective energy fusion is determined, and after removing outlier data, calculations are performed. and The relative error is such that when the error is ≤15%, the arithmetic mean of the two values ​​is taken as the effective ignition energy. ; S4: Effective energy fusion is determined, specifically including: Abnormal data removal: Abnormal data acquired by the charge sensing sensor, high-speed camera (12) and photodetector (14) are removed; Data validity verification: Calculate the corrected direct energy and indirect energy The relative error, The formula is Only data with a relative error ≤15% are retained; Effective energy calculation: Take the verified qualified energy. and The arithmetic mean of the effective ignition energy The formula is ; Explosion risk assessment: Effective ignition energy Compared to the minimum ignition energy of methane-air premixed gas, when When the discharge spark has an energy ≥ the minimum ignition energy, it is determined that the discharge spark poses a risk of causing explosive gas; when If the minimum ignition energy is less than the threshold, it is determined that there is no risk of explosion.

8. The method for evaluating the ignition energy of discharge sparks from load-bearing fractures of coal mine roof rock according to claim 7, characterized in that: The charge signal is the real-time charge and surface voltage collected by the silver electrode (17) when the rock fractures. The visual signal is obtained by capturing the dynamics of the spark using a high-speed camera (12), recording the spark shape, maximum projected area, and duration. The light intensity signal is obtained by capturing the spark luminescence intensity through a photodetector (14), outputting a light intensity-time curve, and determining the light intensity peak and effective luminescence duration. The auxiliary signals are the gas concentration in the explosion reaction chamber (2) collected by the gas concentration detector (9), the displacement of the force transmission rod (16) collected by the external displacement sensor and load sensor, and the load value of the hydraulic cylinder (1).

9. The method for evaluating the ignition energy of discharge sparks from load-bearing fractures of coal mine roof rock according to claim 7, characterized in that: The triggering conditions for the multi-source signal synchronous acquisition in step S1 are set in two ways. One is that the displacement of the force transmission rod (16) reaches 95% of the rock sample yield critical displacement, where the yield critical displacement is the maximum elastic displacement of the rock sample before yielding as determined in the pre-experiment. The other is that the load of the hydraulic cylinder (1) reaches 95% of the rock sample yield critical load, where the yield critical load is the minimum load value of the rock sample when yielding as determined in the pre-experiment. The triggering condition can be met if either condition is met.

10. The method for evaluating the ignition energy of discharge sparks from load-bearing fractures of coal mine roof rock according to claim 7, characterized in that: In step S4, the abnormal data removal process removes three types of abnormal data: charge signal fluctuation amplitude > 20%, high-speed camera image blur causing maximum projection area measurement deviation > 15%, and photodetector (14) signal signal-to-noise ratio < 10:1.

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