A raman scattering based hydrogen leak detection device and method for a gassing process

Abstract

The application discloses a kind of based on Raman scattering's inflation process hydrogen leakage detection device and method, device includes encircling type sampling cover, pulsed laser source, optical fiber input coupling unit, multiple optical path absorption cell, optical fiber output coupling unit and detection and processing unit;Encircling type sampling cover seal cover is located in the periphery of hydrogen potential leakage source, and its sampling port is communicated with multiple optical path absorption cell by pipeline;Pulsed laser source is used to provide pulsed laser, and is transmitted to multiple optical path absorption cell by optical fiber input coupling unit;Multiple optical path absorption cell adopts Herriott type structure, when there is hydrogen in sampling gas, input laser is reflected in pool multiple times to obtain the Raman scattering signal after multiple optical path enhancement, and is collected by optical fiber output coupling unit Transmission to detection and processing unit;Detection and processing unit are according to Raman scattering signal, by time resolution extract instantaneous Raman signal and suppress long-life fluorescence background, identify hydrogen characteristic Raman peak, the present application can continuously monitor hydrogen leakage at low cost.

Description

Technical Field

[0001] This invention belongs to the field of optical gas detection technology, and specifically relates to a hydrogen leakage detection device and method based on Raman scattering during the inflation process. It is particularly suitable for the safety monitoring of hydrogen leakage during the inflation process of large airborne aerostats such as high-altitude sounding balloons and tethered aerostats on the ground. Background Technology

[0002] Existing hydrogen leak detection technologies are mainly based on the following three categories: Electrochemical / catalytic combustion sensors: such as the Industrial Scientific Tango TX1 and MSA Altair commercial portable detectors. These sensors mainly utilize the redox reaction of hydrogen on the electrode surface to generate a current signal. They are inexpensive ($100), but have long response times (seconds), suffer from zero drift, and their performance degrades in high-altitude and low-temperature environments, making them unable to provide real-time leak warnings.

[0003] Tunable Diode Laser Absorption Spectroscopy (TDLAS): This method uses a near-infrared tunable diode laser (such as the H₂ absorption line near 1.65 μm or 2.3 μm) in conjunction with an InGaAs detector. It is primarily based on Beer-Lambert's law, measuring the absorption attenuation of the laser as it passes through a gas. It can achieve a detection limit at the ppm level. However, hydrogen has a weak absorption line in the near-infrared band, requiring long optical paths (tens of meters) or high-reflectivity cavity enhancement structures. Furthermore, it demands extremely high wavelength stability of the laser (<0.01 cm⁻¹). - ¹), the system is complex.

[0004] Raman spectroscopy: Signal acquisition is performed using a high-power pulsed laser (Nd:YAG, 532 nm) in conjunction with an enhanced charge-coupled device (ICCD, Andor iStar series) or a photomultiplier tube (PMT). Traditional Raman spectroscopy utilizes the inelastic scattering of hydrogen molecules (Raman shift approximately 4155 cm⁻¹). - ¹ and 4161 cm - ¹), signal acquisition is performed through an ICCD camera. ICCD has high sensitivity (single photon level) and gating capability (ns level), but it is expensive (a single unit > $50,000) and requires a picosecond / nanosecond pulsed laser ($100,000) to achieve time resolution. The entire system is bulky and difficult to apply to high-altitude balloon inflation operations in the field.

[0005] Therefore, although Raman spectroscopy has many advantages over electrochemical / catalytic combustion sensors and laser absorption spectroscopy, it still has some shortcomings in practical engineering applications, mainly: 1) Cost barrier: The ICCD + pulsed laser solution costs more than $100,000, making it difficult to promote in high-altitude balloon mass operations.

[0006] 2) Poor engineering adaptability: Existing Raman systems mostly use free space optical paths, which are sensitive to vibration and are not suitable for the wind load and vibration environment at the balloon inflation site.

[0007] 3) Fluorescence interference: The balloon material (polyethylene film) and organic matter in the environment may produce a fluorescent background under laser excitation. Continuous laser or electrochemical methods cannot distinguish between Raman signals and fluorescent background.

[0008] 4) Detection limit contradiction: Simple fiber Raman systems are limited by short optical paths (usually <1 m), and the detection limit for hydrogen (which has a very small Raman cross section) is usually >5%, which cannot meet the safety monitoring requirements (early warning of <4% lower explosion limit is required).

[0009] 5) Limitations of sampling methods: Existing probe-based sampling has a slow response (minutes), cannot capture transient leaks, and cannot actively dilute leaked hydrogen, resulting in insufficient safety. Summary of the Invention

[0010] In order to overcome the shortcomings of the prior art, the present invention aims to provide a hydrogen leakage detection device and method based on Raman scattering during the gas filling process, so as to solve at least one of the problems of high cost, poor engineering adaptability, and difficulty in balancing sensitivity and anti-interference ability in the existing hydrogen leakage monitoring technology.

[0011] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A hydrogen leakage detection device for the filling process based on Raman scattering includes a surround sampling hood, a pulsed laser source, an optical fiber input coupling unit, a multi-path absorption cell, an optical fiber output coupling unit, and a detection and processing unit. The surrounding sampling hood is sealed around the potential hydrogen leak source, and its sampling port is connected to the multi-path absorption cell through a pipeline. The pulsed laser source is used to provide pulsed laser light, which is transmitted to the multi-path absorption cell through the optical fiber input coupling unit. The multi-path absorption cell adopts a Herriott-type structure. When hydrogen is present in the sampling gas, the input laser is reflected multiple times in the cell to obtain a Raman scattering signal enhanced by multiple optical paths, which is then collected by the optical fiber output coupling unit and transmitted to the detection and processing unit. The detection and processing unit extracts the instantaneous Raman signal and suppresses the long-lifetime fluorescence background based on the Raman scattering signal, and identifies the characteristic Raman peak of hydrogen.

[0012] In one embodiment, the sampling port of the surround sampling hood is connected to an explosion-proof air pump via a pipeline, and the outlet of the explosion-proof air pump is connected to or built into the multi-path absorption cell. Gas continuously flows through the multi-path absorption cell under the action of the explosion-proof air pump, thereby achieving continuous sampling.

[0013] In one embodiment, the surround sampling hood has an air inlet and an air outlet connected to the atmosphere, forming an open-loop airflow channel; The gas inlet is positioned lower than the gas outlet, utilizing the characteristic that hydrogen is less dense than air to create a directional upward airflow. The gas flows unidirectionally within the surrounding sampling hood, maintaining a slight negative pressure inside the hood and ensuring continuous gas renewal.

[0014] In one embodiment, the pulsed laser source provides nanosecond or picosecond pulsed lasers with a wavelength of 532 nm, a single pulse energy of 10-100 μJ, and a repetition frequency of 1-20 kHz.

[0015] In one embodiment, the fiber input coupling unit includes a single-mode fiber and a fiber collimator to transmit the laser to the monitoring area and maintain a beam diameter of 1-3 mm and a divergence angle of <1 mrad. An entrance aperture is provided on the first concave mirror of the multi-path absorption cell. The optical fiber input coupling unit is arranged off-axis at the entrance aperture. The incident beam is offset from the optical axis by 5-50 mm and the incident angle is 0.5°-3°, so that the laser forms a closed optical path between the two concave mirrors and is reflected N times, achieving an effective optical path of not less than 10 m and a signal enhancement factor of N times, where N≥40. The fiber optic output coupling unit includes a collecting lens group and a multimode fiber. The collecting lens group is an achromatic double lens group, arranged perpendicular to the optical path direction, with a focal length of 50-100 mm and a numerical aperture NA>0.3, which focuses and couples the Raman scattered light from the central region of the multipath absorption cell to the incident end face of the multimode fiber. The core diameter of the multimode fiber ranges from 200-400 μm. A concave reflector M3 is arranged opposite to the collecting lens group, with a reflectivity of >99.5% at 683 nm, which is used to reflect the backscattered light to the collecting lens group, forming a double-end collecting structure. The fiber input coupling unit and the fiber output coupling unit are located on opposite sides or the same side of the multi-path absorption cell, forming a hybrid optical path structure of fiber input-free space-fiber output.

[0016] In one embodiment, the two coaxial concave mirrors in the Herriott-type structure have a radius of curvature of 1-2 m, are coated with a gold film or dielectric film, have a mirror reflectivity of >99.5% at a wavelength of 532 nm, and are adjustable in distance from 20 to 50 cm. They are adjusted and locked by a precision threaded pair, and the effective optical path of the laser after multiple reflections in the pool is not less than 10 m.

[0017] In one embodiment, the two coaxial concave mirrors are respectively mounted on a stainless steel optical adjustment frame. The stainless steel optical adjustment frame is integrally processed from 440C or 316L stainless steel and is equipped with a flexible adjustment structure. Through the thermal stability and high mechanical rigidity of the stainless steel material itself, as well as the gapless characteristics of the flexible structure, the stability of the mirror spacing under ambient temperature changes and on-site vibration conditions is maintained, preventing the drift of the 40-times reflected light spot pattern.

[0018] In one embodiment, the detection and processing unit includes a SiPM detector and a TCMPC signal processing unit. The SiPM detector is connected to the optical fiber output coupling unit and uses a silicon photomultiplier tube to convert the optical signal into an electrical signal, operating in an overbiased state in Geiger mode. The TCMPC signal processing unit is based on time-correlated multiphoton counting technology, sets a time threshold, is synchronously triggered by a laser pulse, extracts the instantaneous Raman signal with time resolution, suppresses long-lifetime fluorescence background, and identifies the characteristic Raman peak of hydrogen.

[0019] In one embodiment, the front end of the SiPM detector is provided with a narrowband filter group for suppressing Rayleigh scattering and background light. The center wavelength of the narrowband filter group is 683 nm, the bandwidth is 3-10 nm, and it corresponds to the hydrogen vibration Raman shift.

[0020] This invention also provides a method for detecting hydrogen leakage during the filling process based on Raman scattering, which is implemented using the aforementioned Raman scattering-based hydrogen leakage detection device. The main steps are as follows: Start the pulsed laser source and establish a baseline; The sampling gas passes through a pipeline, and the pulsed laser enters the multi-path absorption cell through an optical fiber input coupling unit. When hydrogen is present in the sampling gas, the pulsed laser interacts with the hydrogen molecules to produce Raman scattering. The Raman scattering signal is collected and transmitted to the detection and processing unit through the fiber optic output coupling unit. The detection and processing unit extracts the instantaneous Raman signal by time resolution and suppresses the long-lifetime fluorescence background based on the Raman scattering signal, identifies the characteristic Raman peak of hydrogen, and calculates the real-time concentration according to the calibration curve. When the concentration exceeds the threshold, an audible and visual alarm is triggered.

[0021] Compared with the prior art, the beneficial effects of the present invention are: (1) Significantly reduced costs: SiPM ($50-200) replaces ICCD ($50,000), and nanosecond pulsed laser ($2,000-5,000) replaces picosecond laser ($100,000), reducing the overall cost by two orders of magnitude, making it suitable for mass deployment.

[0022] (2) High time resolution and anti-interference capability: Using TCMPC technology, a time resolution of <100 ps can be achieved, which can effectively distinguish transient Raman signals (ps-ns level) from long-lifetime fluorescence background (ns-μs level). It can still accurately detect hydrogen in the presence of organic fluorescence interference.

[0023] (3) Engineering robustness: The hybrid structure of fiber input-free space-fiber output is adopted, which not only utilizes the multi-path cell to achieve an effective optical path of more than 10 m (ensuring the 1% detection limit), but also isolates vibration through fiber transmission, adapting to the wind load and mobile operation requirements of the high-altitude balloon inflation site.

[0024] (4) Active sampling and continuous monitoring: A surround sampling hood is used in conjunction with an explosion-proof air pump to form an open-loop airflow channel, enabling 10 Hz high-frequency continuous sampling (data is updated every 100 ms), with a response speed two orders of magnitude faster than passive diffusion sampling.

[0025] (5) Integrated safety control of detection and dilution: The pump of the present invention is not only used for sampling, but also for adjusting the pumping rate according to the concentration feedback; when a high concentration of hydrogen (>2%) is detected, it can automatically switch to high flow mode (>100 L / min) to actively pump out the leaked gas for dilution, prevent the local concentration from reaching the lower explosive limit (4%), and realize closed-loop control of monitoring and safety protection.

[0026] (6) Safety: Full optical detection, no risk of electric sparks; open-loop airflow design avoids hydrogen accumulation in confined spaces; explosion-proof pump meets Ex d IIC T4 standard and is suitable for flammable and explosive hydrogen environments. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the measuring device structure of the present invention.

[0028] Figure 2 This is a schematic diagram of a Raman detection cell.

[0029] Figure 3 This is a schematic diagram of the ring-type active sampling section. Detailed Implementation

[0030] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings and examples.

[0031] like Figure 1As shown, a hydrogen leak monitoring device based on time-correlated multiphoton counting according to the present invention includes a photoelectric detection section and a sampling section. The photoelectric detection section mainly includes: The pulsed laser source 101 is used to provide nanosecond or picosecond pulsed laser light, with a preferred wavelength of 532 nm, a single pulse energy of 10-100 μJ, and a repetition frequency of 1-20 kHz. The 532 nm wavelength corresponds to the second-harmonic output of an Nd:YAG laser, which is the most mature and lowest-cost solid-state laser solution in industry, reducing costs by an order of magnitude compared to ultraviolet frequency-doubled or OPO tunable lasers. Furthermore, 532 nm is in the visible green light band, allowing direct visual observation during optical path collimation and adjustment without the need for infrared observers or fluorescent cards, significantly improving on-site safety and maintenance convenience. Simultaneously, this wavelength is far from the hydrogen molecule absorption band, avoiding photoheating effects. The design philosophy for single-pulse energy and repetition frequency is high frequency and low energy. For example, in a specific embodiment, a high repetition frequency of 10 kHz can be selected combined with 50 μJ of single-pulse energy (average power 5 W). Compared with the traditional low repetition frequency and high energy scheme, this is mainly based on considerations of field safety and long-term stability: when the single-pulse energy is <100 μJ, the focused light intensity is much lower than the air laser-induced breakdown (LBS) threshold (approximately 10 μJ). 9 The system, with a pulse strength of W / cm², can operate continuously for extended periods under varying pressure without generating plasma noise or mirror damage. Its high-frequency characteristics allow for a photon counting statistical mode, accumulating 1000 pulse signals within 100ms to achieve a high signal-to-noise ratio, avoiding the thermal effects and optical breakdown risks associated with high single-pulse energy. Furthermore, the pulsed laser pulse width in this embodiment is selected to be approximately 10 ns, which is sufficiently long compared to the vibrational relaxation time of hydrogen molecules (on the order of ps) to ensure quasi-static excitation conditions. Simultaneously, this pulse width matches the time resolution of the SiPM detector (<1 ns), providing a sufficient time window for subsequent TCMPC time resolution to distinguish between the Raman signal (on the same order of magnitude as the laser pulse width) and the long-lived fluorescence background (>10 ns).

[0032] The fiber optic input coupling unit 103 is used to transmit pulsed laser light to the monitoring area and maintain beam quality. In this embodiment, it includes a single-mode fiber 102 and a fiber collimator to control the beam diameter to 1-3 mm and the divergence angle to <1 mrad. Furthermore, it uses a single-mode fiber with a core diameter of approximately 9 μm to transmit the laser, ensuring that the output is a fundamental mode Gaussian beam and avoiding mode noise and pointing jitter caused by multimode transmission. The fiber is several meters long, which isolates the laser source from the on-site sampling area, protecting the laser from vibration interference during the inflation process and facilitating flexible optical path arrangement. The fiber collimator uses a short focal length collimator (e.g., f=11mm), thereby collimating the divergent beam output from the fiber into parallel light with a diameter of 1-3 mm and controlling the divergence angle to less than 1 mrad. The beam diameter is matched with the size of the Herriott cavity entrance aperture, which can couple into the cavity through the off-axis entrance aperture (5 mm from the edge of the mirror) and also reserve margin for the beam spread after at least 40 reflections, ensuring that the beam does not overflow the effective light transmission area of ​​the mirror and maintains multi-path transmission efficiency.

[0033] The multi-path absorption cell 104 is the core component of this invention. It employs a conventional Herriott-type structure and features two coaxial concave mirrors, providing a monitoring area for the interaction between the pulsed laser and hydrogen gas. Specifically, when the sampled gas contains hydrogen, Raman scattering occurs. The input laser undergoes multiple reflections between the two coaxial concave mirrors within the cell, resulting in a Raman scattering signal enhanced by the multi-path absorption. (Reference) Figure 2 As shown, in this embodiment, the curvature radius of the two coaxial concave mirrors is 1-2 m, and the mirror reflection at a wavelength of 532 nm is >99.5%, which can be achieved by plating a gold film or dielectric film on the concave mirrors. The mirror spacing is adjustable from 20 to 50 cm, and can be adjusted and locked by a precision threaded pair. In this invention, the concave mirror at the incident end is defined as the first concave mirror. An incident aperture is opened on the first concave mirror. The optical fiber input coupling unit 103 is arranged off-axis at the incident aperture. The offset of the incident beam relative to the optical axis is 5-50 mm, and the incident angle is 0.5°-3°, so that the laser forms a closed optical path between the two concave mirrors and forms a circular light spot pattern after N reflections. The effective optical path is not less than 10 m, and the signal enhancement factor is N times. In this embodiment of the invention, N is not less than 40. This invention reduces the sensitivity to mirror processing tolerances by selecting concave mirrors with a curvature radius of 1-2 m, while maintaining a compact pool structure and improving adaptability to the on-site environment. The 99.5% reflection ensures almost no energy loss during the reflection process, and the effective optical path of more than 10 m guarantees sufficient Raman signals to enter the signal acquisition system.

[0034] The fiber optic output coupling unit 105 is used to collect and transmit the Raman scattering signal enhanced by multiple optical paths to the detection and processing unit 107. (Reference) Figure 1 and Figure 2As shown, in this embodiment, it includes a collecting lens group and a multimode fiber 106. The collecting lens group is an achromatic double lens group, arranged perpendicular to the optical path direction, with a focal length of 50-100 mm and a numerical aperture (NA) > 0.3, which focuses and couples the Raman scattered light from the central region of the multipath absorption cell 4 to the incident end face of the multimode fiber 106. The core diameter of the multimode fiber 106 ranges from 200-400 μm. The collecting lens group is arranged perpendicular to the laser optical path direction (90° scattering configuration) and adopts an achromatic double lens design to correct spherical aberration and chromatic aberration, efficiently focusing the scattered light from the measurement area in the center of the cell to the end face of the multimode fiber. The numerical aperture of the lens group is greater than 0.3, matching the multimode fiber to ensure that the Raman signal within a large solid angle is effectively collected. The multimode fiber 106 has a core diameter ranging from 200 to 400 μm. By selecting a large-core multimode fiber to transmit signal light, its core diameter can match the photosensitive area of ​​the SiPM detector (on the order of millimeters), avoiding coupling loss caused by excessive spot expansion. At the same time, the larger core diameter tolerance reduces alignment difficulty and adapts to the assembly and maintenance needs in the field. Furthermore, in this embodiment, a concave reflector M3 (corresponding to the hydrogen Raman wavelength of 683 nm, which is highly reflective) is set on the opposite side of the collecting lens group. Its reflectivity at 683 nm is >99.5%, reflecting the backscattered light back to the collecting lens group, realizing dual-end collection. The signal strength is about twice that of single-end collection, compensating for signal attenuation after long-distance transmission in a multi-path cell.

[0035] The detection and processing unit 107 is used to identify the characteristic Raman peaks of hydrogen. In this embodiment, it mainly includes a SiPM detector and a TCMPC signal processing unit. The SiPM detector is connected to a multimode fiber 106 and uses a silicon photomultiplier tube (such as the Hamamatsu S13360 series, with a photosensitive area of ​​3×3 mm) to convert the optical signal into an electrical signal, operating in Geiger mode under over-voltage conditions (over-voltage 2-5 V). This parameter achieves a balance between high sensitivity and low cost. Specifically, the SiPM can achieve single-photon level detection sensitivity under over-voltage conditions, meeting the detection requirements of hydrogen Raman scattering (extremely small cross-section). Compared to ICCDs ($50,000), the SiPM costs only a few hundred US dollars and does not require a high-voltage power supply or cooling system, significantly reducing the overall cost and complexity, making it suitable for mass deployment. At the same time, it can achieve fast time response and has a wide dynamic range. The SiPM output pulse rise time is less than 1 nanosecond, enabling nanosecond-level time resolution when combined with subsequent electronics. This is sufficient to distinguish transient Raman signals (on the same order of magnitude as the laser pulse width) from long-lived fluorescence background (nanosecond to microsecond level), which is crucial for achieving time-resolved interference immunity. By adjusting the overbias and count rate, the SiPM can adapt to a wide range of signal intensities, from trace amounts of hydrogen (<1%) to higher concentrations (>4%), avoiding detector saturation. The TCMPC signal processing unit, based on time-correlated multiphoton counting technology, sets a time threshold (gate width 20-100 ns), uses the laser pulse trigger signal as the time reference (T0), and sets nanosecond-level time windows (signal window covering the laser pulse width, background window delayed by tens of nanoseconds). By comparing the photon counts within the two windows, transient Raman signals are extracted and long-lived fluorescence background is suppressed, improving the signal-to-noise ratio. Utilizing a 10 kHz high-repetition-rate laser pulse sequence, shot noise is reduced through statistical averaging, achieving stable detection at low concentrations while maintaining a data update rate of 10 Hz. The detection and processing unit 107 is synchronously triggered by the laser pulse, extracts the instantaneous Raman signal by time resolution and suppresses the long-lifetime fluorescence background, and identifies the characteristic Raman peak of hydrogen (4155 cm⁻¹). - ¹or 4161 cm - ¹).

[0036] The sampling section is a surround active sampling system, reference Figure 3 As shown, it mainly includes: The surround sampling hood 201 is sealed around the outer periphery of a potential leak source (such as a balloon inflation port, hydrogen refueling gun interface, or valve). It can be cylindrical or horseshoe-shaped, forming an annular gap with the outer wall of the leak source. It has a sampling port, which is connected to the multi-path absorption cell 104 via a pipeline.

[0037] Furthermore, the sampling section also includes an explosion-proof air extraction pump 204. The explosion-proof air extraction pump 204 is connected to the sampling port of the surround sampling hood 201 via a pipeline. The surround sampling hood 201 has a gas inlet 202 communicating with the atmosphere and a gas extraction port 203, forming an open-loop airflow channel. The outlet of the explosion-proof air extraction pump 204 is connected to or built into the multi-path absorption cell 104. The gas continuously flows through the multi-path absorption cell 104 under the action of the explosion-proof air extraction pump 204, thereby achieving continuous sampling.

[0038] Furthermore, the air inlet 202 of the surround sampling hood 201 is located at the bottom or low side wall of the surround sampling hood 201, and can adopt a mesh structure to prevent large dust particles from clogging the explosion-proof air pump 204. The air outlet 203 is located at the top or high side wall of the surround sampling hood 201. Utilizing the characteristic that hydrogen has a lower density than air, a directional upward airflow is formed. The gas generates a unidirectional flow (bottom in, top out or side in, side out) in the sampling hood, maintaining a slight negative pressure (-50~-100 Pa) inside the hood and ensuring continuous gas renewal.

[0039] In a further embodiment of the present invention, the fiber input coupling unit 103 and the fiber output coupling unit 105 can be located on both sides or on the same side of the multi-path absorption cell 104, forming a hybrid optical path structure of fiber input-free space-fiber output (FSF), which conforms to the geometric relationship that the Raman scattering signal is perpendicular to the laser direction. This not only utilizes the flexible transmission of optical fiber to adapt to the needs of mobile operations on site, but also realizes the multi-path enhancement of the Herriott cavity through the collimated free space beam, thus taking into account both system compactness and optical stability.

[0040] In a further embodiment of the present invention, a narrowband filter group is provided at the front end of the SiPM detector to suppress Rayleigh scattering and background light, thereby ensuring that the signals of other components (such as air) do not interfere with the analysis of the hydrogen signal. For example, the center wavelength of the narrowband filter group is 683 nm, the bandwidth is 3-10 nm, and it corresponds to the hydrogen vibration Raman shift.

[0041] In a further embodiment of the present invention, the detection device further includes a highly stable stainless steel flexible optical adjustment frame to prevent spot drift caused by temperature changes and mechanical vibrations. Two coaxial concave mirrors are respectively mounted on the stainless steel optical adjustment frame, which is integrally machined from 440C or 316L stainless steel and has a flexible adjustment structure.

[0042] In a further embodiment of the present invention, the explosion-proof air pump 204 is a diaphragm pump (such as the KNF N86 series) and uses a brushless DC motor with an explosion-proof rating of Ex d IIC T4. The pumping speed is adjustable, with a normal sampling mode of 10-30 L / min and a high-concentration dilution mode of >100 L / min.

[0043] In a further embodiment of the present invention, the contact surface between the surround sampling cover 201 and the leakage source is provided with a replaceable sealing interface (such as clamp type, magnetic suction type or clamp type), so as to be able to adapt to the air inlet or valve of different pipe diameters.

[0044] Based on the above structure, the workflow of the detection method of the present invention is as follows: 1) System initialization and baseline establishment: Start the explosion-proof air pump (204) in advance and operate in normal sampling mode (10-30L / min) to establish a stable "bottom in, top out" directional airflow in the surrounding sampling hood (201) and maintain a slight negative pressure (-50~-100 Pa) inside the hood to ensure that leaked hydrogen can be captured in time and prevented from escaping. Simultaneously start the pulsed laser source (101) and preheat it to the working state. At this time, there is only ambient air in the multi-path absorption cell (4). The TCMPC signal processing unit collects 30 seconds of background data, establishes the dark counting baseline and the optical background baseline, and stores them as a reference.

[0045] 2). Active sampling and renewal of multi-path absorption cell: High-pressure hydrogen (10-15 MPa) is ejected from the gas filling port. If there is a leak in the interface or valve, the hydrogen will naturally accumulate at the top of the surrounding sampling hood (201) because its density is less than that of air. Under the directional airflow generated by the explosion-proof gas pump (204), it will continuously flow into the multi-path absorption cell (4) through the pipeline, realizing the active enrichment and continuous renewal of the leaked gas.

[0046] 3). Multi-path Raman excitation in a multi-path absorption cell: After the laser pulse is transmitted and collimated through a single-mode fiber, it enters the multi-path absorption cell (4) off-axis and is reflected 40 times between two concave mirrors, forming an effective optical path of 12 m. During this process, the laser repeatedly interacts with hydrogen molecules in the gas flow, generating vibrational Raman scattering light at 683 nm (corresponding to 4155 cm⁻¹). - ¹Raman shift), signal intensity is accumulated 40 times to obtain multi-path enhancement.

[0047] 4) Scattered signal collection and electrical conversion: Raman scattered light perpendicular to the laser path is coupled to a multimode fiber (106) via a collection lens group and transmitted to the SiPM detector. The SiPM operates in overbiased state in Geiger mode, converting each incident photon into a nanosecond-level electrical pulse signal.

[0048] 5) Time-Resolved Photon Count: The TCMPC signal processing unit uses the laser trigger signal as the time reference (T0) and records the arrival time of each photon pulse with a time accuracy of <100 ps to construct a time-correlated histogram. A signal window (0-20 ns) is set to capture transient Raman signals synchronized with the laser pulse width, and a background window (50-200 ns) is set to capture long-lived fluorescence and dark counting.

[0049] 6) Background Suppression and Signal Extraction: By comparing the photon counts of the signal window and the background window using an algorithm, the fluorescence background and dark counts are subtracted to extract the net Raman photon count rate. This differential method can effectively suppress fluorescence interference generated by balloon materials and environmental organic matter under laser excitation.

[0050] 7) Concentration Inversion and Safety Judgment: Based on the pre-stored multi-point calibration curves (usually established with standard hydrogen concentrations of 1%, 2%, and 4%), the net Raman photon count rate is converted into real-time volumetric concentration. When the concentration exceeds 1% (25% of the lower explosive limit, the warning threshold), the system triggers an audible and visual alarm; when the concentration exceeds 2%, the explosion-proof gas pump (204) automatically switches to high-flow dilution mode (>100 L / min) to actively pump out leaked gas for dilution, preventing the local concentration from reaching the lower explosive limit (4%), thus achieving closed-loop control of monitoring and safety protection.

[0051] 8) Data Output and Recording: The system continuously outputs concentration data at a frequency of 10 Hz, while simultaneously recording operating parameters such as ambient temperature and air flow rate for subsequent traceability and analysis. After the detection is completed, the laser and air pump are turned off, and the system enters standby mode.

[0052] Based on the above structure, this invention enables Raman monitoring of hydrogen leaks using time-correlated multiphoton counting (TCMPC). The main hardware components used are two orders of magnitude cheaper than existing ICCDs and picosecond lasers, saving at least $5,000 based on current market prices. Furthermore, the constructed fiber-free space hybrid structure is more stable, adaptable to vibration environments in the field, and enables portable monitoring. Algorithm-wise, this invention utilizes time-resolved technology to suppress fluorescence background, achieving a detection limit of 1% volume fraction, far below the hydrogen explosion limit of 4%. In terms of sampling technology, this invention employs surround active sampling, enabling continuous monitoring at 10Hz high frequency, and also features leak gas extraction and dilution functions, significantly improving on-site safety.

[0053] Accordingly, this invention can be applied not only to the safety monitoring of hydrogen leakage during the ground inflation process of large airborne aerostats such as high-altitude sounding balloons and tethered aerostats, but also to the monitoring of micro-leakage of hydrogen in scenarios such as hydrogen refueling stations for hydrogen-powered vehicles, fuel cell workshops, and chemical pipelines.

[0054] The following is a specific embodiment of the present invention for monitoring the inflation port of a high-altitude balloon.

[0055] like Figure 1 As shown, the hydrogen leak monitoring device in this embodiment is used for ground inflation operations of high-altitude sounding balloons, wherein: The pulsed laser source 101 is a 532 nm passively Q-switched Nd:YAG nanosecond pulsed laser (such as Teem Photonics SB-532-10), with a pulse width of approximately 10 ns, a single pulse energy of 50 μJ, and a repetition frequency of 10 kHz. The laser output is connected to a 9 μm core diameter, 5 m long single-mode optical fiber 102 via an FC / PC interface.

[0056] The fiber input coupling unit 103 includes a single-mode fiber 102, a fiber collimator (f=11 mm, ThorlabsF220FC-532) and an optical isolator, which collimates the laser into parallel light with a diameter of about 2 mm and a divergence angle of <0.5 mrad, and incident it into the multi-path absorption cell 104.

[0057] The multi-path absorption cell 4 includes two coaxial concave mirrors M1 and M2, with a mirror curvature radius R = 1 m and a spacing d = 30 cm. The mirrors are coated with a gold film (reflectivity > 99.5% at 532 nm). Incident light is incident at an off-axis height of approximately 45 mm (offset relative to the optical axis) and reflects 40 times between the two mirrors, forming a circular light spot pattern. The effective optical path is L = 12 m. An optical fiber output coupling unit (105) is arranged perpendicular to the laser path direction on the side of the cell. A concave reflector M3 is placed opposite the signal collection end, with a mirror coating (reflectivity > 99.5% at 683 nm). The cell body is made of stainless steel and equipped with an air inlet and outlet, allowing it to be placed near the inflation port of a balloon.

[0058] The fiber optic output coupling unit 105 has a collecting lens group (f=25 mm, NA=0.5, M4) set on the side of the multipath cell perpendicular to the optical path direction (90° scattering configuration), which focuses the light onto the fiber optic probe 108 and connects to the multimode fiber 106. The multimode fiber 106 has a core diameter of 200 μm, NA=0.39, and a length of 2 m. This large-core multimode fiber matches the photosensitive area of ​​the SiPM (3×3 mm) and has a collection solid angle of approximately 0.1 sr.

[0059] The detection and processing unit 107 includes a narrowband filter (Semrock, 683 / 10 nm), a SiPM detector (Hamamatsu S13360-3025CS, 3 V overbias), and a TCMPC module (based on Becker & Hickl SPC-150 or equivalent TCSPC card). The SiPM detector output signal is connected to the TCMPC signal processing unit via a preamplifier (Femto HSA-X-2-40).

[0060] Surround active sampling section such as Figure 3As shown, the surrounding sampling hood 201 is made of aluminum alloy, cylindrical in shape, with an inner diameter of 25 cm and a height of 30 cm, and is fixed to the outer periphery of the balloon inflation port by a clamp. A grid-like air inlet 202 is provided at the bottom of the sampling hood, and an air extraction port 203 is provided at the top. The explosion-proof air extraction pump 204 is a KNF N86KNE diaphragm pump with an explosion-proof rating of Ex d IICT4. It connects the air extraction port at the top of the sampling hood to the air inlet of the multi-path absorption cell via a DN10 PTFE tube. The pump outlet is connected to the multi-path absorption cell 104, and an exhaust port is provided at the rear of the cell leading to a safe area. Its airflow organization is as follows: The explosion-proof air pump 204 operates at a flow rate of 30 L / min, forming a directional airflow of "bottom in, top out" inside the surrounding sampling hood 201, maintaining a slight negative pressure of -80 Pa inside the hood; the leaked hydrogen gas, due to its low density, naturally floats to the top air extraction port and is forcibly drawn into the multi-path absorption cell 104.

Claims

1. A hydrogen leakage detection device for a gas filling process based on Raman scattering, characterized in that, It includes a surround sampling hood (201), a pulsed laser source (101), an optical fiber input coupling unit (103), a multi-path absorption cell (4), an optical fiber output coupling unit (105), and a detection and processing unit (107). The surrounding sampling hood (201) is sealed around the potential hydrogen leak source, and its sampling port is connected to the multi-path absorption cell (4) through a pipeline. The pulsed laser source (101) is used to provide pulsed laser light and transmits it to the multi-path absorption cell (4) through the optical fiber input coupling unit (103). The multi-path absorption cell (4) adopts a Herriott-type structure. When hydrogen is present in the sampling gas, the input laser is reflected multiple times in the cell to obtain the Raman scattering signal enhanced by the multi-path, which is then collected and transmitted to the detection and processing unit (107) by the fiber output coupling unit (105). The detection and processing unit (107) extracts the instantaneous Raman signal by time resolution and suppresses the long-lifetime fluorescence background based on the Raman scattering signal, and identifies the characteristic Raman peak of hydrogen.

2. The hydrogen leakage detection device based on Raman scattering during the gas filling process according to claim 1, characterized in that, The sampling port of the surrounding sampling hood (201) is connected to the explosion-proof air pump (204) through a pipeline. The outlet of the explosion-proof air pump (204) is connected to or built into the multi-path absorption cell (4). The gas flows continuously through the multi-path absorption cell (4) under the action of the explosion-proof air pump (204) to achieve continuous sampling.

3. The hydrogen leakage detection device based on Raman scattering during the gas filling process according to claim 1 or 2, characterized in that, The surrounding sampling hood (201) has an air inlet (202) and an air outlet (203) that are connected to the atmosphere, forming an open-loop airflow channel; The gas inlet (202) is positioned lower than the gas outlet (203). By utilizing the characteristic that hydrogen has a lower density than air, a directional upward airflow is formed. The gas generates a unidirectional flow within the surrounding sampling hood (201), maintaining a slight negative pressure inside the hood and ensuring continuous gas renewal.

4. The hydrogen leakage detection device based on Raman scattering during the gas filling process according to claim 1, characterized in that, The pulsed laser source (101) provides nanosecond or picosecond pulsed lasers with a wavelength of 532 nm, a single pulse energy of 10-100 μJ, and a repetition frequency of 1-20 kHz.

5. The hydrogen leakage detection device based on Raman scattering during the gas filling process according to claim 1, characterized in that, The fiber input coupling unit (103) includes a single-mode fiber (102) and a fiber collimator, which transmits the laser to the monitoring area and maintains the beam diameter of 1-3 mm and the divergence angle of <1 mrad. An entrance hole is provided on the first concave mirror of the multi-path absorption cell (4). The optical fiber input coupling unit (103) is arranged off-axis at the entrance hole. The incident beam is offset from the optical axis by 5-50 mm and the incident angle is 0.5°-3°, so that the laser forms a closed optical path between the two concave mirrors and is reflected N times, so that the effective optical path is not less than 10m and the signal enhancement factor is N times, where N≥40; The fiber output coupling unit (105) includes a collecting lens group and a multimode fiber (106). The collecting lens group is an achromatic double lens group, which is set along the direction perpendicular to the optical path, with a focal length of 50-100 mm and a numerical aperture NA>0.

3. It focuses and couples the Raman scattered light from the central region of the multipath absorption cell (4) to the incident end face of the multimode fiber (106). The core diameter of the multimode fiber (106) is in the range of 200-400 μm. A concave reflector M3 is set opposite to the collecting lens group. Its reflectivity at 683 nm is >99.5%. It is used to reflect the backscattered light to the collecting lens group to form a double-end collecting structure. The fiber input coupling unit (103) and the fiber output coupling unit (105) are located on opposite sides or on the same side of the multi-path absorption cell (4), forming a hybrid optical path structure of fiber input-free space-fiber output.

6. The hydrogen leakage detection device based on Raman scattering during the gas filling process according to claim 1, characterized in that, The Herriott-type structure has two coaxial concave mirrors with radii of curvature of 1-2 m. The concave mirrors are coated with gold or dielectric film, and the mirror reflectivity at a wavelength of 532 nm is >99.5%. The mirror spacing is adjustable from 20 to 50 cm and can be adjusted and locked by a precision threaded pair. The effective optical path of the laser after multiple reflections in the pool is not less than 10 m.

7. The hydrogen leakage detection device based on Raman scattering during the gas filling process according to claim 6, characterized in that, The two coaxial concave mirrors are respectively mounted on a stainless steel optical adjustment frame, which is made of 440C or 316L stainless steel and is equipped with a flexible adjustment structure.

8. The hydrogen leakage detection device based on Raman scattering during the gas filling process according to claim 1, characterized in that, The detection and processing unit (107) includes a SiPM detector and a TCMPC signal processing unit. The SiPM detector is connected to the optical fiber output coupling unit (105) and uses a silicon photomultiplier tube to convert the optical signal into an electrical signal. It operates in the overbiased state of Geiger mode. The TCMPC signal processing unit is based on time-correlated multiphoton counting technology, sets a time threshold, and is synchronously triggered by a laser pulse. It extracts the instantaneous Raman signal by time resolution and suppresses the long-lifetime fluorescence background to identify the characteristic Raman peak of hydrogen.

9. The hydrogen leakage detection device based on Raman scattering during the gas filling process according to claim 8, characterized in that, The front end of the SiPM detector is equipped with a narrowband filter group for suppressing Rayleigh scattering and background light. The center wavelength of the narrowband filter group is 683 nm, the bandwidth is 3-10 nm, and it corresponds to the hydrogen vibration Raman shift.

10. A method for detecting hydrogen leakage during a gas filling process based on Raman scattering, implemented using the hydrogen leakage detection device for a gas filling process based on Raman scattering as described in any one of claims 1 to 9, characterized in that, The steps are as follows: Start the pulsed laser source (101) and establish a baseline; The sampling gas passes through the pipeline, and the pulsed laser passes through the optical fiber input coupling unit (103) and both enter the multi-path absorption cell (4). When hydrogen is present in the sampling gas, the pulsed laser interacts with the hydrogen molecules to produce Raman scattering. The Raman scattering signal is collected and transmitted to the detection and processing unit (107) through the fiber optic output coupling unit (105). The detection and processing unit (107) extracts the instantaneous Raman signal by time resolution and suppresses the long-lifetime fluorescence background according to the Raman scattering signal, identifies the characteristic Raman peak of hydrogen, and calculates the real-time concentration according to the calibration curve. When the concentration exceeds the threshold, an audible and visual alarm is triggered.

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