A motor vehicle exhaust HONO emission measurement system and method based on spectral technology

Abstract

The application discloses a kind of motor vehicle exhaust HONO emission measurement system and method based on spectral technology, the system includes: light source emission section, light beam shaping section, laser modulation and cavity coupling section, resonant cavity section and signal acquisition section;The emergent light of the light source emission section is transmitted to the laser modulation and cavity coupling section by the light beam shaping section, the output light of the laser modulation and cavity coupling section is transmitted to the resonant cavity section, the output light of the resonant cavity section is transmitted to the signal acquisition section, the resonant cavity section includes invar cavity, high-reflection input mirror, high-reflection output mirror and exhaust pretreatment system.The application can utilize spectral technology to detect HONO in motor vehicle exhaust continuously, realize first in motor vehicle vibration / high temperature environment HONO ppb grade detection, fill the quantitative blank of atmospheric radical precursor mobile source emission.

Description

Technical Field

[0001] This invention relates to the field of atmospheric pollutant monitoring technology, specifically to a real-time online measurement system and method for nitrite (HONO) emissions from motor vehicle exhaust based on cavity ring-down spectroscopy (CRDS) technology. Background Technology

[0002] Gaseous nitrous acid (HONO) plays a crucial role in atmospheric oxidation processes as an important precursor to hydroxyl radicals (·OH). Its photolysis reaction is the main source of atmospheric ·OH radicals in urban areas during the daytime, while vehicle exhaust is a significant source of its emissions. However, multiple field measurements and simulation studies have shown that vehicle HONO emissions are systematically underestimated. This gap in understanding restricts the analysis of the generation and dissipation mechanisms of atmospheric OH radicals and the accuracy of air quality models.

[0003] The scientific value of accurately detecting HONO emissions from motor vehicle exhaust is mainly reflected in the following three aspects: First, HONO is a key medium for enhancing atmospheric oxidation, and its source has not yet been clearly identified, which directly affects the accuracy of simulation and prediction of ozone and PM2.5 pollution; Second, the HONO / NOx ratio of motor vehicle emissions has a high degree of uncertainty (the measured value ranges from 0.003% to 4.24%), and the traditional emission inventory uses a fixed ratio method, which leads to significant deviations in emission estimation; Third, with the continuous evolution of after-treatment technologies, the emission characteristics of HONO exhibit dynamic changes, thus requiring continuous updates of measured data as support.

[0004] Currently, the two main methods for detecting HONO gas both domestically and internationally are spectroscopic methods and wet chemical methods, among which:

[0005] Differential absorption spectroscopy (DOAS) in spectroscopic methods and long path absorption spectroscopy (LOPAP) in wet chemical methods are currently widely used HONO measurement techniques in atmospheric monitoring. Their basic principle is to utilize the physical property of gas molecules absorbing light of specific wavelengths and to calculate the relationship function between gas molecule concentration and absorbed light based on the Lambert-Beer law, thereby quantifying the component content in the gas being measured. The main advantages of spectroscopic methods here are short detection response time and high temporal resolution of data.

[0006] The basic principle of wet chemical methods for measuring atmospheric HONO concentration is to use chemical reagents to absorb gaseous nitrous acid in the atmosphere and convert it into nitrite ions. Then, different detection techniques are used to quantitatively analyze the nitrite ions, thereby calculating the concentration of gaseous nitrous acid in the atmosphere. However, in practical applications, wet chemical methods for measuring HONO have the following main drawbacks: low temporal resolution, susceptibility to interference from multiple coexisting pollutants (especially NO2), complex chemical derivatization processes requiring strict condition control, potential positive and negative biases, potentially insufficient detection limits, inability to distinguish between gaseous and particulate phases, and complex automated maintenance. These drawbacks have led to its gradual replacement in the field of atmospheric chemistry, especially in research requiring high temporal resolution, high precision, and online continuous monitoring, by more advanced spectroscopic methods, such as long path absorption spectroscopy (LOPAP), differential absorption spectroscopy (DOAS), cavity ring-down spectroscopy (CRDS), and cavity enhanced absorption spectroscopy (CEAS). These alternative techniques typically offer higher temporal resolution, lower detection limits, less chemical interference, and better automation.

[0007] In summary, existing technologies cannot accurately measure the HONO emissions of motor vehicle exhaust under conventional motor vehicle vibration / high temperature environments. Therefore, this application proposes a motor vehicle exhaust HONO emission measurement system and method based on spectral technology to solve the aforementioned technical problems. Summary of the Invention

[0008] The main objective of this invention is to provide a vehicle exhaust HONO emission measurement system and method based on spectral technology to solve the technical problems mentioned in the background art.

[0009] The present invention solves the above-mentioned technical problems by adopting the following technical solutions:

[0010] A vehicle exhaust HONO emission measurement system based on spectral technology is provided to address the problem of how to continuously and with high sensitivity detect HONO in vehicle exhaust using spectral technology. The system includes: a light source emission section, a beam shaping section, a laser modulation and cavity coupling section, a resonant cavity section, and a signal acquisition section. The emitted light from the light source emission section is transmitted to the laser modulation and cavity coupling section via the beam shaping section. The output light from the laser modulation and cavity coupling section is transmitted to the resonant cavity section, and the output light from the resonant cavity section is transmitted to the signal acquisition section. The resonant cavity section includes an Invar cavity, a high-reflectivity input mirror, a high-reflectivity output mirror, and an exhaust gas pretreatment system. The Invar cavity has the following openings:

[0011] The calibrated gas inlet is designated as port A and connected to a nitrogen cylinder.

[0012] The exhaust gas sampling inlet is designated as port B and is connected to the exhaust gas pretreatment system.

[0013] The detection port is designated as port C, and is connected to a gas temperature sensor and a pressure sensor.

[0014] The exhaust port is designated as port D and is connected to a vacuum pump.

[0015] The exhaust gas pretreatment system includes, in sequence: a heat-resistant alloy probe, a cyclone separator, a sintered metal filter element, a PTFE membrane filter, and a heat tracing pipeline.

[0016] Preferably, the light source emitting section includes a laser, and the laser is a quantum cascade laser (QCL).

[0017] Preferably, since the laser beam emitted by the laser initially presents an elliptical spot with significant divergence characteristics, the light source emitting section also includes a set of front lens systems for capturing the emitted laser beam and compressing the divergence angle and converting it into approximately parallel light through precise optical correction.

[0018] After correction, the beam is guided into a set of arsenic selenide (AsSe) optical fibers to isolate mechanical vibrations through flexible conduction while maintaining the polarization stability of the beam. The exit of the arsenic selenide optical fibers is used to guide the beam back into free space for transmission.

[0019] Preferably, the beam shaping section comprises an optical isolator, a collimating lens group, a beam expander, and a cylindrical lens group, specifically including components sequentially connected for receiving the beam emitted by the light source:

[0020] Optical isolators are used to block the back propagation of reflected light using the Faraday magneto-optical effect, preventing feedback interference from cavity mirror reflected light to the laser.

[0021] The collimating lens group uses cemented doublet achromatic lenses to eliminate residual divergence angles of the light beam, thus forming a strictly parallel optical path.

[0022] A beam expander is used to increase the diameter of a beam spot to three times its original size in order to reduce beam diffraction loss.

[0023] A cylindrical mirror assembly, comprising at least one set of orthogonally arranged cylindrical mirrors, is used to correct an elliptical Gaussian beam to be circularly symmetric.

[0024] Furthermore, the free-space propagating beam first passes through an optical isolator, which utilizes the Faraday magneto-optical effect to block any possible back-propagation of reflected light, ensuring that the laser operates without interference. The beam then enters a collimating lens group to further eliminate residual divergence angles and form a strictly parallel optical path. Next, a beam expanding system enlarges the spot diameter to three times its original size. This operation significantly reduces beam diffraction effects, laying the foundation for subsequent resonant cavity coupling. Finally, to correct the elliptic asymmetry of the beam, a set of orthogonally arranged cylindrical mirrors spatially shape the beam, applying differentiated focusing forces in the horizontal and vertical directions, ultimately outputting a circularly symmetrical Gaussian beam.

[0025] Preferably, the optical isolator is arranged with a shut-off element along the path of the mid-infrared continuous laser emitted from the collimating lens group. The shut-off unit includes an acousto-optic modulator, which is controlled by a set of acousto-optic modulator drivers. The signal acquisition segment is connected to the input of the acousto-optic modulator drivers. The acousto-optic modulator is used to shut off the laser when the transmitted light intensity reaches a specified threshold.

[0026] Preferably, the laser modulation and cavity coupling section includes:

[0027] The acousto-optic modulator (AOM) is used to cause the beam shaped by the beam shaping section to undergo Bragg diffraction under the action of the acoustic field driven by the radio frequency signal. By precisely controlling the start and stop of the driving signal, the continuous laser is cut into a laser pulse sequence with a width of microseconds, which is used to be directed at the high-reflectivity input mirror at a small tilt angle.

[0028] The high-reflectivity input mirror features an ultra-smooth surface and an ultra-high-reflectivity coating. When the laser beam is first reflected from the input mirror surface, its spatial mode has been optimized by the pre-optical system, aligning with the fundamental transverse mode (TEM) of the resonant cavity. 00 Highly matched;

[0029] Piezoelectric ceramic PZT is used for dynamic compensation of cavity length drift.

[0030] Preferably, the resonant cavity segment includes a low-loss cavity made of Invar steel, an anti-fouling window with a hydrophobic film coated with fused silica, and a high-reflectivity output mirror with a reflectivity R>99.99%, wherein:

[0031] After the mid-infrared continuous laser beam enters the confocal resonant cavity composed of two highly reflective mirrors in the low-loss cavity, it enters the multiple reflection stage. The beam is reflected tens of thousands of times between the two mirrors that are half a meter apart, forming an equivalent optical path of kilometers. During this process: the curvature design of the cavity mirrors keeps the beam confined within a millimeter-scale diameter range, preventing the beam from spreading and touching the edge of the mirror; the piezoelectric ceramic element attached to the back of the mirror is used to finely adjust the cavity length in real time to counteract the mirror displacement caused by vehicle vibration.

[0032] Each time the laser is reflected, a very small percentage of the light energy leaks through the output mirror, forming an exponentially decaying optical signal sequence.

[0033] The low-loss cavity has several air ports connected to the air pipe. The air pipe is equipped with an air inlet, a nitrogen inlet, an air outlet, and a detection port. An air drying device is arranged on the air pipe on one side of the air inlet. The nitrogen inlet is connected to a nitrogen cylinder. The air outlet is connected to a vacuum pump. The detection port is connected to a gas temperature and pressure sensor.

[0034] Preferably, the signal acquisition segment is used to calculate the cavity ring-off time when there is no HONO gas absorption in the optical resonant cavity, and to calculate the ring-off time when there is HONO gas absorption in the cavity, specifically including:

[0035] Achromatic focusing lens is used to focus the ring-down beam transmitted from the output mirror onto the PMT cathode to converge the diffuse spot to a micron-scale size. The focused beam is then used to pass through a narrow bandpass filter.

[0036] The bandpass filter allows only light of a specified wavelength (light near the wavelength of HONO's characteristic absorption) to pass through, thereby suppressing stray light and effectively blocking interference from specified radiation sources in the exhaust gas.

[0037] A photomultiplier tube (PMT) is used to convert light signals into electrical signals after receiving a converging light spot projection through a photosensitive cathode surface.

[0038] Mid-infrared detector, high-speed data acquisition card and data processing equipment.

[0039] A method for measuring HONO emissions from motor vehicle exhaust based on spectral technology, implemented using any of the aforementioned HONO emission measurement systems based on spectral technology, includes:

[0040] S1. High-purity nitrogen gas (purity ≥ 99.999%) is introduced into the resonant cavity of the resonant section. The laser is started to perform wavelength scanning. Continuous test pulses are generated by AOM. The PMT acquires the cavity ring-down curve. The single exponential decay function is fitted using the least squares method to calculate the cavity ring-down time. Store as baseline parameters;

[0041] S2. By adjusting the laser drive current, a triangular wave scanning wavelength of 100 Hz is specified, and the ring-down time is monitored in real time. The change in absorption peak when scanning to the characteristic absorption peak of HONO. When the value drops sharply, this wavelength is identified as the central operating point.

[0042] S3. Start PZT closed-loop control, apply a 1 kHz dither signal to the piezoelectric ceramic, detect the error voltage through the lock-in amplifier, and adjust the cavity length in real time through the PID controller to ensure that the laser frequency resonates with the cavity mode;

[0043] S4. Insert the heat-resistant alloy probe into the central flow channel of the vehicle's exhaust pipe to extract the raw exhaust gas. The exhaust gas then passes sequentially through a cyclone separator, where centrifugal force removes carbon soot particles >10μm; a sintered metal filter element for deep filtration, retaining particles of 2-10μm; and a PTFE membrane filter for surface filtration, removing submicron particles of 0.2-2μm. A heated sampling pipeline is wrapped around the sampling line, and a PID temperature control module is used to prevent HONO from condensing and adsorbing on the pipe wall.

[0044] S5. After receiving the TTL trigger signal, the acousto-optic modulator (AOM) generates a high diffraction efficiency (>80%) laser pulse during the turn-on phase and cuts off the incident light path during the turn-off phase.

[0045] S6. After the mid-infrared continuous laser is coupled into the cavity through the input mirror (R > 99.998%), the beam is reflected more than 500 times between the cavity mirrors, and the light intensity inside the cavity reaches the saturation value. The transmitted light intensity follows the... Attenuation, in which The initial light intensity is then introduced, followed by data acquisition from a key window of 20-60 μs using a photomultiplier tube (PMT).

[0046] The S7 high-speed acquisition card synchronously records the output voltage of the photomultiplier tube (PMT), acquiring 5000 data points for each oscillation event and transmitting them to the data processing device in real time via USB.

[0047] Preferably, the data processing device includes a ring-down time calculation module, used to fit a single exponential decay function using the Levenberg-Marquardt algorithm to solve for the ring-down time. The calculation formula is as follows:

[0048]

[0049] in, It is the initial voltage amplitude of the ring-down. It is the decay time constant. It is the first Sampling time for each data point At a certain point in time The voltage value measured by the photomultiplier tube (PMT). This represents the total number of sampling points;

[0050] At this point, an absorption coefficient exists. for:

[0051]

[0052] in, It is the speed of light in a vacuum (3 × 10⁸ m / s). It is gas at laser frequency The absorption coefficient at that location, It is the cavity decay time. It is the sample decay time.

[0053] Preferably, the data processing device includes a concentration decoupling module and an early warning module. The early warning module triggers an audible and visual alarm when the HONO concentration is too high. The concentration decoupling module is used to construct a partial least squares regression (PLSR) model. The calculation formula for the PLSR model is as follows:

[0054]

[0055] in, At frequency The total absorption coefficient measured at the location, It is HONO gas at frequency Absorption cross section at the location, yes In frequency The absorption cross section at that point yes In frequency The absorption cross section at that point It is the fitting residual or error term;

[0056] The partial least squares regression (PLSR) model is also used to decouple cross-sensitive components using multi-wavelength scanning data, to calculate HONO number density, and to convert it into volume concentration. The calculation formula is as follows:

[0057]

[0058]

[0059] in, It is the number density of HONO gas. The absorption coefficient contributed by HONO. It is the absorption cross section of HONO. It is the volume concentration of HONO. The temperature of the gas inside the optical resonant cavity. This refers to the gas pressure inside the optical resonant cavity. It is a set of conversion constants based on the Loschmidt constant, which has a physical origin.

[0060] In another aspect, the present invention also discloses a computer-readable storage medium storing a computer program, which, when executed by a processor, causes the processor to perform the calculation steps of the method described above.

[0061] In another aspect, the present invention also discloses a computer device, including a memory and a processor, wherein the memory stores a computer program, and when the computer program is executed by the processor, the processor performs the calculation steps of the method described above.

[0062] As can be seen from the above technical solution, the present invention provides a system and method for measuring HONO emissions from motor vehicle exhaust based on spectral technology. Compared with the prior art, the present invention has the following advantages:

[0063] 1. This invention, through the design of an ultra-high reflectivity confocal resonant cavity, can extend the effective absorption path by three orders of magnitude. Compared with traditional optical methods (such as FTIR and DOAS, which are limited to the detection limit of HONO at only ppm level due to the limitations of optical path length and light source stability), it can achieve the first ppb-level detection of HONO under vehicle vibration / high temperature environment, filling the quantitative gap in the emission of atmospheric free radical precursors from mobile sources.

[0064] 2. By employing an Invar cavity (thermal expansion coefficient 0.5×10-6 / K) in conjunction with active temperature control, this invention can maintain the stability of the cavity well in ambient temperatures ranging from -20 to 50℃. At the same time, by combining the heat tracing pipeline structure to suppress HONO adsorption, it can further achieve adaptability under extreme working conditions.

[0065] 3. This invention addresses the high dust characteristics of motor vehicle exhaust (diesel vehicle particulate matter concentration reaches 80mg / m³). 3 A physical-thermal synergistic filter chain was designed, which can significantly reduce the attenuation rate of optical cavity transmittance and at the same time significantly extend the maintenance cycle.

[0066] 4. The present invention adopts a coaxial optical path system layout, which significantly reduces the structural volume, makes the optical cavity smaller, allows for faster gas replacement, and provides a more sensitive response.

[0067] 5. This invention combines a light source emission section, a beam shaping section, a laser modulation and cavity coupling section, a resonant cavity section, and a signal acquisition section to form a HONO gas measurement system, which can use spectral technology to continuously and in real-time detect HONO in motor vehicle exhaust with high sensitivity.

[0068] It should be understood that the descriptions in this section are not intended to identify key or essential features of embodiments of the invention, nor are they intended to limit the scope of the invention. Other features of the invention will become readily apparent from the following description. Of course, implementing any product of the invention does not necessarily require achieving all of the advantages described above simultaneously. Attached Figure Description

[0069] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0070] Figure 1 This is a schematic diagram of the system structure of the present invention;

[0071] Figure 2 This is a schematic diagram of the workflow of the system of the present invention;

[0072] Figure 3 This is a schematic diagram of the method usage flow of the system of the present invention.

[0073] in:

[0074] 1. Quantum Cascade Laser (QCL); 2. Optical Isolator; 3. Acousto-Optical Modulator; 4. Acousto-Optical Modulator Driver; 5. Collimating Lens Group; 6. Beam Expander; 7. Cylindrical Lens Group; 8. Arsenic Selenide (AsSe) Fiber; 9. High-Reflectivity Input Mirror; 10. Piezoelectric Ceramic; 11. Invar Cavity; 12. High-Reflectivity Output Mirror; 13. Heat-Resistant Alloy Probe; 14. Cyclone Separator; 15. Sintered Metal Filter; 16. PTFE Membrane Filter; 17. Heating Pipeline; 18. Achromatic Focusing Lens; 19. Bandpass Filter; 20. Photomultiplier Tube; 21. High-Speed ​​Data Acquisition Card; 22. Data Processing Equipment; 23. Nitrogen Cylinder; 24. Vacuum Pump; 25. Gas Temperature Sensor; 26. Gas Pressure Sensor. Detailed Implementation

[0075] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0076] For details in the embodiments, please refer to Figures 1 to 3 .

[0077] like Figure 1As shown. The HONO emission measurement system for motor vehicle exhaust based on spectral technology proposed in this embodiment of the invention includes the following steps:

[0078] The system includes: a light source emission section, a beam shaping section, a laser modulation and cavity coupling section, a resonant cavity section, and a signal acquisition section. The emitted light from the light source emission section is transmitted to the laser modulation and cavity coupling section via the beam shaping section. The output light from the laser modulation and cavity coupling section is transmitted to the resonant cavity section, and the output light from the resonant cavity section is transmitted to the signal acquisition section. A shut-off element is arranged between the light source section and the beam shaping section. By combining these components, a HONO gas measurement system is formed, capable of continuous, real-time, and highly sensitive detection of HONO in vehicle exhaust using spectroscopic technology.

[0079] (1) The light source emitting section includes a laser, which is a quantum cascade laser (QCL). Further, the light source emitting section includes a quantum cascade laser (QCL1) for generating mid-infrared continuous laser light, and the mid-infrared continuous laser light emitted from the quantum cascade laser (QCL1) is on the path. In a further embodiment, the scanning frequency of the quantum cascade laser (QCL1) is set in the Hz range. A suitable measurement band is selected based on the spectral characteristics of HONO gas in motor vehicle exhaust. Through the quantum cascade laser (QCL1), the output wavelength can be locked near the target absorption spectral wavelength of HONO gas. Then, a set of arsenic selenide (AsSe) optical fibers 8 can be arranged on the output optical path of the quantum cascade laser (QCL1). It can isolate mechanical vibration through flexible conduction while maintaining the polarization state stability of the beam. Here, the exit of the arsenic selenide optical fiber is used to reintroduce the beam into free space for transmission.

[0080] (2) The beam shaping section includes an optical isolator 2, a collimating lens group 5, a beam expander 6, and a cylindrical lens group 7; the collimating lens group 5 is arranged on the path of the first-order diffracted light emitted from the acousto-optic modulator 3, the beam expander 6 is arranged on the output light path of the collimating lens group 5, and the cylindrical lens group 7 is arranged on the output light path of the beam expander 6.

[0081] The first-order diffracted light passes sequentially through the collimating lens group 5, the beam expander 6, the cylindrical lens group 7, the arsenic selenide (AsSe) fiber 8, and the high-reflection input mirror 9, and then is transmitted into the Invar cavity 11, where it oscillates and propagates between the plano-concave mirrors at both ends of the cavity.

[0082] A shutdown unit is arranged along the path of the mid-infrared continuous laser emitted from the optical isolator 2. The shutdown unit includes at least one set of arranged acousto-optic modulators. The acousto-optic modulators are controlled by a driver of the acousto-optic modulators. The signal acquisition section is connected to the input of the acousto-optic modulator driver. The acousto-optic modulators are used to shut off the laser when the transmitted light intensity reaches a specified threshold.

[0083] Specifically, in this embodiment, a shutdown unit is set on the mid-infrared continuous laser path output by optical isolator 2. The light source emission section outputs mid-infrared continuous laser near the selected HONO gas absorption line wavelength, and after being allowed by optical isolator 2, it enters acousto-optic modulator 3. The acousto-optic modulator driver 4 controls the acousto-optic modulator 3 to output first-order diffracted light. First-order diffracted light is generally adjusted using visible linearly polarized light to see the first-order diffracted spot. However, considering that the refractive index of the crystal is different for visible light and mid-infrared light, it is possible to try adjusting directly using mid-infrared light. The intensity of the received transmitted light signal can be observed with an oscilloscope, and it will decrease when adjusted to first-order diffracted light; it can also be adjusted by observing the square wave signal. When a signal with the same change as the high and low levels appears, it indicates that first-order diffracted light has appeared.

[0084] (3) The laser modulation and cavity coupling section includes a high-reflection input mirror 9 and a piezoelectric ceramic 10; the high-reflection input mirror 9 is arranged on the output optical path of the arsenic selenide (AsSe) fiber 8, and the piezoelectric ceramic 10 is bonded to the back of the high-reflection input mirror 9.

[0085] (4) The resonant cavity section includes an Invar cavity 11, a high-reflectivity output mirror 12 and an exhaust gas pretreatment system; the high-reflectivity output mirror 12 and the high-reflectivity input mirror 9 are arranged coaxially with a reflectivity >99.99%; the exhaust gas pretreatment system includes a heat-resistant alloy probe 13, a cyclone separator 14, a sintered metal filter element 15, a PTFE membrane filter 16 and a heat tracing pipeline 17.

[0086] Specifically, such as Figure 1 As shown, the Inductor cavity 11 has four gas ports on its exterior for gas replacement and sampling: First, the lower end of the input mirror (port A) is the calibration gas inlet, connected to the nitrogen cylinder 23; second, the upper end of the output mirror (port B) is the exhaust gas sampling inlet, connected to the three-stage filtration system; then, the middle part of the cavity (port C) is the detection port, used to connect the temperature and pressure sensor; finally, the bottom of the cavity (port D) is the exhaust port, connected to the vacuum pump 24. Ports A and B are located perpendicular to the optical axis to avoid disturbing the optical path; port C is located at the geometric center of the cavity to ensure representativeness of the detection; port D is located at the lowest point for easy drainage.

[0087] In summary, this application, through the design of an ultra-high reflectivity confocal resonant cavity, can extend the effective absorption path by three orders of magnitude in practical implementation. Compared with traditional optical methods (such as FTIR and DOAS, which are limited to the ppm level for HONO detection due to the limitations of optical path length and light source stability), it can achieve ppb-level detection of HONO for the first time under vehicle vibration / high temperature environment, filling the quantitative gap in the emission of atmospheric free radical precursors from mobile sources. Furthermore, by using an Invar cavity (thermal expansion coefficient 0.5×10-6 / K) in conjunction with active temperature control, it can maintain the stability of the cavity length in an ambient temperature range of -20 to 50℃. At the same time, combined with the heat tracing pipeline structure to suppress HONO adsorption, it can further achieve adaptability under extreme operating conditions.

[0088] (5) The signal acquisition section includes an achromatic focusing lens 18, a bandpass filter 19, a photomultiplier tube 20, a high-speed data acquisition card 21, and a data processing device 22. The achromatic focusing lens 18 is arranged on the transmission light path of the high-reflectivity output mirror 12, the bandpass filter 19 is arranged on the output light path of the achromatic focusing lens 18, the photomultiplier tube 20 is arranged on the output light path of the bandpass filter 19, and the output end of the photomultiplier tube 20 is connected to the data processing device 22 via the high-speed data acquisition card 21.

[0089] The high-speed data acquisition card 21 is used to record the electrical signal converted from the transmitted light intensity signal and transmit it to the data processing device 22 for processing and storage. When the transmitted light intensity signal reaches the shutdown threshold set by the data processing device 22, the data processing device 22 sends a shutdown signal to the controller of the acousto-optic modulator 3, causing the acousto-optic modulator 3 to quickly interrupt the first-order diffraction light. At the same time, it controls the high-speed data acquisition card 21 to record a light intensity decay event and transmit it to the data processing device 22 for calculation, processing and storage to obtain the HONO gas concentration. The data processing device 22 sets a concentration threshold, and when the detected concentration reaches the set threshold, an alarm is issued.

[0090] In summary, this system addresses the high dust characteristics of motor vehicle exhaust (diesel vehicle particulate matter concentration reaches 80 mg / m³). 3 A physical-thermal synergistic filter chain was designed, which can significantly reduce the attenuation rate of optical cavity transmittance and significantly extend the maintenance cycle. At the same time, it adopts a coaxial optical path system layout, which greatly reduces the structural volume, makes the optical cavity smaller, and allows for faster gas replacement and more sensitive response.

[0091] Furthermore, the workflow of the HONO gas measurement system in motor vehicle exhaust gas based on cavity ring-down spectroscopy proposed in this embodiment is as follows: Figure 2 As shown, it specifically includes:

[0092] L1. Inject 99.999% high-purity nitrogen into the Invar cavity 11 through a trachea for 5 minutes. With the Invar cavity 11 filled with high-concentration nitrogen and no HONO gas absorption, the drive current of the quantum cascade laser QCL1 is controlled by the quantum cascade laser QCL1 controller. The output wavelength of the quantum cascade laser QCL1 is tuned according to the selected HONO gas measurement band and wavelength scanning range, so that the center frequency of a single longitudinal mode in the Invar cavity 11 is within the wavelength change period of the output light of the quantum cascade laser QCL1. Thus, the incident transmitted light resonates with the single longitudinal mode in the cavity, thereby achieving periodic transient excitation of the cavity mode.

[0093] L2. The quantum cascade laser QCL1 is activated, outputting mid-infrared continuous laser light. The acousto-optic modulator driver 4 controls the acousto-optic modulator 3 to generate laser pulses. The photomultiplier tube 20 detects the transmitted light intensity signal. The high-speed data acquisition card 21 acquires the decay signal of the transmitted light intensity output from the Invar cavity as it decays over time and records the decay curve. This data is then transmitted to the data processing device 22. The data processing device 22 processes and calculates the decay signal by fitting a single exponential decay function using the least squares method, obtaining the cavity decay time of the HONO gas absorbed within the cavity. .

[0094] L3. The laser driver outputs a triangular wave modulation signal at a frequency of 100Hz, causing the output wavelength of the quantum cascade laser QCL1 to scan near the wavelength range of the HONO gas absorption spectrum. The change in the ring-down time τ is monitored in real time. When the scanning reaches the wavelength of the HONO gas absorption spectrum, the value of τ drops sharply, and the system automatically locks that wavelength as the operating point.

[0095] L4. Apply a 1kHz dither signal to the piezoelectric ceramic 10, detect the error voltage through a lock-in amplifier, and then use a set of PID temperature control modules to adjust the driving voltage of the piezoelectric ceramic 10 in real time to compensate for the cavity length change caused by vehicle vibration.

[0096] L5. Insert the heat-resistant alloy probe 13 into the central flow channel of the vehicle exhaust pipe; turn on the vacuum pump to extract the exhaust gas, which passes through the following in sequence: cyclone separator 14 to remove particles >10μm; sintered metal filter element 15 to remove particles 2-10μm; PTFE membrane filter 16 to remove particles 0.2-2μm; and heat tracing pipeline 17 to prevent HONO adsorption.

[0097] L6. Acousto-optic modulator 3 generates laser pulses with a turn-off time of <100ns; the pulses are reflected multiple times in the resonant cavity; photomultiplier tube 20 collects the decaying signal of the acquisition window; high-speed data acquisition card 21 records the signal.

[0098] L7. Data processing device 22 performs the following calculations: optimizes the oscillation time using the Levenberg-Marquardt algorithm; calculates the absorption coefficient; substitutes the parameters from the HITRAN database, decouples interference using PLSR; and performs concentration conversion to obtain the HONO concentration.

[0099] On the other hand, such as Figure 3 As shown, this invention also discloses a method for using a system for measuring HONO gas in motor vehicle exhaust based on cavity ring-down spectroscopy technology, the method comprising the following steps:

[0100] S1. Inject high-concentration nitrogen into the Invar cavity through the vent on the Invar cavity, and adjust the flow rate by adjusting valve 23 of the high-purity nitrogen cylinder; continue inflating for 5 minutes to replace the cavity; measure and store the gas. value;

[0101] S2. Set the laser to 100Hz triangular wave scan; tune the output wavelength of the light source emission section according to the selected HONO gas measurement band and wavelength scan range; automatically lock. The minimum value corresponds to the wavelength;

[0102] S3. Activate the dither control mode of the piezoelectric ceramic 10; set a set of parameters for the PID temperature control module, such as integral time, derivative time, etc.

[0103] S4. Insert the heat-resistant alloy probe 13 into the exhaust pipe; start the three-stage filtration system: cyclone separator 14 → sintered metal filter element 15 → PTFE membrane filter 16; set the temperature of the heat tracing pipeline 17.

[0104] S5. Set the pulse width of the acousto-optic modulator 3; calibrate the turn-off delay; set the gain of the photomultiplier tube 20;

[0105] S6. Introduce external air into the Invar cavity and stop introducing high-concentration nitrogen into the Invar cavity. Based on the gas temperature sensor 25 and the gas pressure sensor 26, control the temperature and pressure of the extracted external gas to ensure that the Invar cavity is filled with high-concentration nitrogen and that there is HONO gas absorption. Calculate the decay time when there is HONO gas absorption in the cavity. ;

[0106] S7. Data processing device 22 based on cavity ring-off time The decay time of HONO gas absorption in the cavity It calculates the HONO gas concentration and issues a warning signal when the HONO gas concentration exceeds the set concentration threshold.

[0107] Finally, it should be noted that other embodiments or specific implementations of the method for using the HONO gas measurement system in motor vehicle exhaust gas based on cavity ring-down spectroscopy technology of the present invention can be referred to the above-described embodiments of the HONO gas measurement system based on spectral technology, and will not be repeated here.

[0108] In another aspect, the present invention also discloses a computer-readable storage medium storing a computer program, which, when executed by a processor, causes the processor to perform the steps of the method described above.

[0109] In another aspect, the present invention also discloses a computer device, including a memory and a processor, wherein the memory stores a computer program, and when the computer program is executed by the processor, the processor performs the steps of the method described above.

[0110] In another embodiment provided in this application, a computer program product containing instructions is also provided, which, when run on a computer, causes the computer to execute the calculation process in any of the above embodiments of the motor vehicle exhaust HONO emission measurement system based on spectral technology.

[0111] It is understood that the system provided in the embodiments of the present invention corresponds to the method provided in the embodiments of the present invention, and the explanation, examples and beneficial effects of the relevant content can be referred to the corresponding parts of the above methods.

[0112] This application also provides an electronic device, including a processor, a communication interface, a memory, and a communication bus, wherein the processor, communication interface, and memory communicate with each other via the communication bus.

[0113] Memory, used to store computer programs;

[0114] The processor, when executing the program stored in the memory, implements the calculation process in the above-mentioned HONO emission measurement system for motor vehicle exhaust gas based on spectral technology.

[0115] The communication bus mentioned in the above-mentioned electronic devices can be a standard bus for interconnecting peripheral components or an extended industrial standard structure bus, etc. This communication bus can be divided into address bus, data bus, control bus, etc.

[0116] The communication interface is used for communication between the aforementioned electronic devices and other devices.

[0117] The memory may include random access memory or non-volatile memory, such as at least one disk storage device. Optionally, the memory may also be at least one storage device located remotely from the aforementioned processor.

[0118] The processors mentioned above can be general-purpose processors, including central processing units, network processors, etc.; they can also be digital signal processors, application-specific integrated circuits, field-programmable gate arrays or other programmable logic devices, discrete gate or transistor logic devices, or discrete hardware components.

[0119] In the above embodiments, implementation can be achieved, in whole or in part, through software, hardware, firmware, or any combination thereof. When implemented using software, it can be implemented, in whole or in part, as a computer program product. The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, all or part of the processes or functions described in the embodiments of this application are generated.

[0120] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

[0121] Furthermore, it should be noted that if any directional indication (such as up, down, left, right, front, back, etc.) is involved in the embodiments of the present invention, the directional indication is only used to explain the relative positional relationship and movement of each component in a specific posture. If the specific posture changes, the directional indication will also change accordingly.

[0122] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the meaning of "and / or" throughout the text includes three parallel solutions; for example, "A and / or B" includes solution A, solution B, or a solution where both A and B are satisfied simultaneously. Furthermore, in the embodiments of this invention, "multiple" refers to two or more. Moreover, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

Claims

1. A vehicle exhaust HONO emission measurement system based on spectral technology, characterized in that, include: The system comprises a light source emitting section, a beam shaping section, a laser modulation and cavity coupling section, a resonant cavity section, and a signal acquisition section. The emitted light from the light source emitting section is transmitted through the beam shaping section to the laser modulation and cavity coupling section. The output light from the laser modulation and cavity coupling section is transmitted to the resonant cavity section, and the output light from the resonant cavity section is transmitted to the signal acquisition section. The resonant cavity section includes an Invar cavity, a high-reflectivity input mirror, a high-reflectivity output mirror, and a tail gas pretreatment system. The Invar cavity has the following openings: The calibrated gas inlet is connected to a nitrogen cylinder. The exhaust gas sampling inlet is connected to an exhaust gas pretreatment system. The detection port is connected to a gas temperature sensor and a pressure sensor. The exhaust port is connected to a vacuum pump. The light source emitting section includes a laser and a set of front lens systems, which are used to capture the laser emitted by the laser and compress the divergence angle and convert it into approximately parallel light through optical correction. After correction, the beam is guided into a set of arsenic selenide optical fibers to isolate mechanical vibrations through flexible conduction while maintaining the polarization stability of the beam. The exit of the arsenic selenide optical fibers is used to guide the beam back into free space for transmission. The signal acquisition segment includes: Achromatic focusing lenses are used to focus the ring-down beam transmitted from the output mirror onto the PMT cathode, so as to converge the diffuse spot to a micron-scale size. The bandpass filter allows only light of a specified wavelength absorbed by the HONO feature to pass through, thereby suppressing stray light and effectively blocking interference from specified radiation sources in the exhaust gas. A photomultiplier tube (PMT) is used to convert light signals into electrical signals after receiving a converging light spot projection through a photosensitive cathode surface. Mid-infrared detector, high-speed data acquisition card and data processing equipment.

2. The HONO emission measurement system for motor vehicle exhaust based on spectral technology as described in claim 1, characterized in that, The beam shaping section specifically includes sections sequentially connected to receive the beam emitted by the light source: Optical isolators are used to block the back propagation of reflected light using the Faraday magneto-optical effect, preventing feedback interference from cavity mirror reflected light to the laser. Collimating lens group is used to eliminate the residual divergence angle of the light beam in order to form a perfectly parallel light path. A beam expander is used to increase the diameter of a beam spot to three times its original size in order to reduce beam diffraction loss. A cylindrical mirror assembly, comprising at least one set of orthogonally arranged cylindrical mirrors, is used to correct an elliptical Gaussian beam to be circularly symmetric.

3. The HONO emission measurement system for motor vehicle exhaust based on spectral technology as described in claim 2, characterized in that, An acousto-optic modulator is arranged on the path of the mid-infrared continuous laser emitted from the optical isolator to the collimating lens group. The acousto-optic modulator is controlled by a set of drivers. The signal acquisition segment is connected to the input of the acousto-optic modulator driver. The acousto-optic modulator is used to turn off the laser when the transmitted light intensity reaches a specified threshold.

4. The HONO emission measurement system for motor vehicle exhaust based on spectral technology as described in claim 1, characterized in that, The laser modulation and cavity coupling section includes: The acousto-optic modulator (AOM) is used to cause the beam shaped by the beam shaping section to undergo Bragg diffraction under the action of the acoustic wave field driven by the radio frequency signal, and to cut the continuous laser into a laser pulse sequence with a width of microseconds, which is used to shoot towards the high reflection input mirror at a small tilt angle. High-reflection input mirror, with an ultra-smooth surface and ultra-high reflective coating; Piezoelectric ceramic PZT is used for dynamic compensation of cavity length drift.

5. The HONO emission measurement system for motor vehicle exhaust based on spectral technology as described in claim 4, characterized in that, The resonant cavity segment includes a low-loss cavity made of Invar steel, an anti-fouling window with a hydrophobic film coated with fused silica, and a high-reflection output mirror, wherein: After the laser beam enters the confocal resonant cavity composed of two highly reflective mirrors in the low-loss cavity, it enters the multiple reflection stage. The beam is reflected tens of thousands of times between the two mirrors that are half a meter apart, forming an equivalent kilometer-level optical path. The piezoelectric ceramic element attached to the back of the mirror is used to finely adjust the cavity length in real time to counteract the mirror displacement caused by vehicle vibration. Each time the laser is reflected, a very small percentage of the light energy leaks through the output mirror, forming an exponentially decaying optical signal sequence. The low-loss cavity has several air ports connected to the air pipe. The air pipe is equipped with an air inlet, a nitrogen inlet, an air outlet, and a detection port. An air drying device is arranged on the air pipe on one side of the air inlet. The nitrogen inlet is connected to a nitrogen cylinder. The air outlet is connected to a vacuum pump. The detection port is connected to a gas temperature and pressure sensor.

6. A method for measuring HONO emissions from motor vehicle exhaust based on spectral technology, implemented using the HONO emission measurement system for motor vehicle exhaust based on spectral technology as described in any one of claims 1-5, characterized in that, include: S1. High-purity nitrogen gas is introduced into the resonant cavity of the resonant cavity section. The laser is started to perform wavelength scanning. Continuous test pulses are generated through AOM. The PMT acquires the cavity ring-down curve. The single exponential decay function is fitted using the least squares method to calculate the cavity ring-down time. Store as baseline parameters; S2. By adjusting the laser drive current to specify the triangular wave scanning wavelength, the ring-down time is monitored in real time. The change in absorption peak when scanning to the characteristic absorption peak of HONO. When the value drops sharply, this wavelength is identified as the central operating point. S3. Start PZT closed-loop control, apply a dither signal to the piezoelectric ceramic, detect the error voltage through a lock-in amplifier, and adjust the cavity length in real time to ensure that the laser frequency resonates with the cavity mode; S4. Insert the heat-resistant alloy probe into the central flow channel of the vehicle's exhaust pipe to extract the raw exhaust gas; S5. After receiving the trigger signal, the acousto-optic modulator generates a high-diffraction-efficiency laser pulse and cuts off the incident light path during the turn-off phase. S6. After the mid-infrared continuous laser is coupled into the cavity through the input mirror, the beam is reflected between the cavity mirrors, and the light intensity reaches the saturation value. The transmitted light intensity follows... Attenuation, in which The initial light intensity is then introduced, and then the photomultiplier tube (PMT) collects key window data. S7. Synchronously record the output voltage of the photomultiplier tube (PMT), collect data for each oscillation event, and transmit it to the data processing device in real time via USB.

7. The method for measuring HONO emissions from motor vehicle exhaust based on spectral technology as described in claim 6, characterized in that, The data processing device includes a ring-out time calculation module, used to fit a single exponential decay function using the Levberg-Marquardt algorithm to solve for the ring-out time. The calculation formula is as follows: in, It is the initial voltage amplitude of the ring-down. It is the decay time constant. It is the first Sampling time for each data point At a certain point in time The voltage value measured by the photomultiplier tube (PMT). This represents the total number of sampling points; At this point, an absorption coefficient exists. for: in, It is the speed of light in a vacuum. It is gas at laser frequency The absorption coefficient at that location, It is the cavity decay time. It is the sample decay time.

8. The method for measuring HONO emissions from motor vehicle exhaust based on spectral technology as described in claim 6, characterized in that, The data processing device is equipped with a concentration decoupling module and an early warning module. The early warning module triggers an audible and visual alarm when the HONO concentration is too high. The concentration decoupling module is used to construct a partial least squares regression (PLSR) model. The calculation formula for the PLSR model is as follows: in, At frequency The total absorption coefficient measured at the location, It is HONO gas at frequency The absorption cross section at that point yes In frequency The absorption cross section at that point yes In frequency The absorption cross section at that point It is the fitting residual or error term; The partial least squares regression (PLSR) model is also used to decouple cross-sensitive components using multi-wavelength scanning data, to calculate HONO number density, and to convert it into volume concentration. The calculation formula is as follows: in, It is the number density of HONO gas. The absorption coefficient contributed by HONO. It is the absorption cross section of HONO. It is the volume concentration of HONO. The temperature of the gas inside the optical resonant cavity. This refers to the gas pressure inside the optical resonant cavity. It is a set of conversion constants based on the Loschmidt constant.

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