High-precision Gas Research Articles

Harnessing sub-comb dynamics in a graphene-sensitized microresonator for gas detection

Since their inception, frequency combs generated in microresonators, known as microcombs, have sparked significant scientific interests. Among the various applications leveraging microcombs, soliton microcombs are often preferred due to their inherent mode-locking capability. However, this choice introduces additional system complexity because an initialization process is required. Meanwhile, despite the theoretical understanding of the dynamics of other comb states, their practical potential, particularly in applications like sensing where simplicity is valued, remains largely untapped. Here, we demonstrate controllable generation of sub-combs that bypasses the need for accessing bistable regime. And in a graphene-sensitized microresonator, the sub-comb heterodynes produce stable, accurate microwave signals for high-precision gas detection. By exploring the formation dynamics of sub-combs, we achieved 2 MHz harmonic comb-to-comb beat notes with a signal-to-noise ratio (SNR) greater than 50 dB and phase noise as low as − 82 dBc/Hz at 1 MHz offset. The graphene sensitization on the intracavity probes results in exceptional frequency responsiveness to the adsorption of gas molecules on the graphene of microcavity surface, enabling detect limits down to the parts per billion (ppb) level. This synergy between graphene and sub-comb formation dynamics in a microcavity structure showcases the feasibility of utilizing microcombs in an incoherent state prior to soliton locking. It may mark a significant step toward the development of easy-to-operate, systemically simple, compact, and high-performance photonic sensors.Graphical

High-sensitive double incidence multi-pass cell for trace gas detection based on TDLAS

A high-precision gas detection system with a dual-incidence multi-pass cell (D-MPC) based on TDLAS was developed, which can simultaneously measure quadruple component gases. Two Distributed Feedback (DBF) Laser Diodes with central wavelength of 1654 nm and 2004 nm were utilized to measure methane (CH4) and carbon dioxide (CO2) for evaluating the performance of the system. High sensitivity and low frequency drift were accomplished by utilizing the second harmonic signals (WMS-2f) detection and peak-locking technology. A LabVIEW-based control and acquisition program, which could be used for direct absorption and wavelength modulation, was developed. Kalman adaptive filtering, Least Mean Squares (LMS) adaptive filtering and S-G filtering were employed for denoising in direct absorption spectroscopy (DAS), respectively, and optimal denoising technology of S-G filtering was selected. According to Allan deviation analysis, the optimal detection precision for CH4 and CO2 was 12 ppb at an integration time of 36 s and 270 ppb at an integration time of 43 s, respectively. A two-day continuous monitoring of atmospheric CO2 and CH4 was implemented to verify the system stability and can be applied to other trace gases monitoring.

Lightweight and High-Precision Gas Identification Neural Network for Embedded Electronic Nose Devices

Lightweight and High-Precision Gas Identification Neural Network for Embedded Electronic Nose Devices

Identification and detection of high NO x emitting inland ships using multi-source shore-based monitoring data

In urban areas situated along busy waterways like the Yangtze River, the diesel engines of inland navigation ships emerge as significant contributors to air pollution. Among these vessels, certain high-emission ships exhibit considerably higher levels of nitrogen oxides (NOx) emissions compared to others. To effectively identify such ships, this study employed a cost-effective ship emission monitoring sensor platform, comprising high-precision gas sensors, automatic identification system receiver, and sensitive meteorological sensors, along the Yangtze River in Wuhan City. By combining multi-source shore-based monitoring data, we identified ship emission signals and proposed a high-emission ship detection method using inverse modeling. Using this method, we successfully detected inland high-emission ships based on two months of monitoring data. Furthermore, the relationship between different ship types, sizes, speeds, and ship NO x emission rates were investigated. The results of this study are beneficial for strengthening the regulation of high-emission vessels in inland waterways, thereby reducing the adverse impact of ship emissions on the environment and climate. It also encourages the inland shipping industry to adopt more environmentally friendly technologies and fuels, as advocated by the International Maritime Organization.

Signal-correction errors in the EasyOne Pro LAB multiple-breath washout device significantly impact outcomes in children and adults.

Multiple-breath washout (MBW) is an established technique to assess functional residual capacity (FRC) and ventilation inhomogeneity in the lung. Indirect calculation of nitrogen concentration requires accurate measurement of gas concentrations. To investigate the accuracy of the CO2 concentration and molar mass (MM) values used for the indirect calculation of nitrogen concentration in a commercial MBW device [EasyOne Pro LAB (EOPL), ndd Medizintechnik AG, Switzerland] and its impact on outcomes. We used high-precision gas mixtures to evaluate CO2 and MM sensor output in vivo and in vitro. We developed updated algorithms to correct observed errors and assessed the impact on MBW outcomes and FRC measurement accuracy compared with body plethysmography. The respiratory exchange ratio (RER)-based adjustment of the measured CO2 signal used in the EOPL led to an overestimated CO2 signal (range -0.1% to 1.0%). In addition, an uncorrected dependence on humidity was identified. These combined effects resulted in an overestimation of expired nitrogen concentrations (range -0.7% to 2.6%), and consequently MBW outcomes. Corrected algorithms reduced the mean (SD) cumulative expired volume by 15.8% (9.7%), FRC by 6.6% (3.0%), and lung clearance index by 9.9% (7.6%). Differences in FRC between the EOPL and body plethysmography further increased. Inadequate signal correction causes RER- and humidity-dependent expired nitrogen concentration errors and overestimation of test outcomes. Updated algorithms reduce average signal error, however, RER values far from the population average still cause measurement errors. Despite improved signal accuracy, the updated algorithm increased the difference in FRC between the EOPL and body plethysmography.NEW & NOTEWORTHY We investigated the accuracy of the molar mass (MM) and CO2 sensors of a commercial multiple-breath washout device (ndd Medizintechnik AG, Switzerland). We identified humidity and respiratory exchange ratio-dependent errors that in most measurements resulted in an overestimation of expired nitrogen concentrations, and consequently, MBW results. Functional residual capacity and lung clearance index decreased by 6.6% and 9.9%, respectively. Despite improved signal accuracy, the difference in FRC between the EOPL and body plethysmography increased.

Research on high-precision gas concentration inversion based on adaptive infrared multi-band joint spectral analysis

Research on high-precision gas concentration inversion based on adaptive infrared multi-band joint spectral analysis

Study on the Technique for Wavelength Modulation Spectroscopy with Narrow Band Interference Filter Based External Cavity Diode Laser

In this study, an improved tunable external cavity diode laser (ECDL) is proposed. It is on the basis of narrow band interference filter, and its theoretical research is carried out as the light source of tunable diode laser absorption spectrum-wavelength modulation spectrum (TDLAS-WMS) system. The proposed model can use piezoelectric ceramic actuator to change and modulate its output central wavelength so that the laser central wavelength could periodically scan the absorption spectral band of the desired gas. Compared with the tunable monolithic diode laser, the narrow band interference filter based tunable ECDL might be able to accurately sense the type and concentration of a large variety of gases. Therefore, it can be used in the TDLAS-WMS system for high precision gas sensing and is expected to replace the tunable monolithic diode laser.

A Thermal Fluid–Solid Coupling Simulation of Gas Fuel Control Valves for High-Precision Gas Turbines

Gas fuel control valves play important roles in the control of gas flow in high-precision gas turbines. To clarify the influence of coupling between the structure and the fluid system, a thermal fluid–solid coupling mechanism is presented based on numerical investigations carried out using a dynamic mesh technique. Valve core deformation can affect the outlet gas flow accuracy. At 2% valve opening, the gas temperature contributes 93% to the deformation. The effect of deformation on the flow accuracy at 6% valve opening and 4% valve opening is increased by 4.8% and 7.3%, respectively. The fluctuation range of the gas temperature and pressure in front of the valve should be strictly controlled to ensure the high precision and high stability of the outlet flow. These results help to clarify the processes that occur in the valve flow path, leading to the flow control instability observed in the control valve.

High-precision nanosecond detection of a gas absorption spectrum based on optical frequency comb time-frequency mapping.

There is an increasing demand for high-precision gas absorption spectroscopy in basic research and industrial applications, such as gas tracking and leak warning. In this Letter, a novel, to the best of our knowledge, high-precision and real-time gas detection method is proposed. A femtosecond optical frequency comb is used as the light source, and a broadening pulse containing a range of oscillation frequencies is formed after passing through a dispersive element and a Mach-Zehnder interferometer. Four absorption lines of H13C14N gas cells are measured at five different concentrations within a single pulse period. A single scan detection time of only 5 ns is obtained along with a coherence averaging accuracy of 0.0055 nm. High-precision and ultrafast detection of the gas absorption spectrum is accomplished while overcoming complexities related to the acquisition system and light source that are encountered in existing methods.

Quantum-Enhanced Absorption Spectroscopy with Bright Squeezed Frequency Combs.

Absorption spectroscopy is a widely used technique that permits the detection and characterization of gas species at low concentrations. We propose a sensing strategy combining the advantages of frequency modulation spectroscopy with the reduced noise properties accessible by squeezing the probe state. A homodyne detection scheme allows the simultaneous measurement of the absorption at multiple frequencies and is robust against dispersion across the absorption profile. We predict a significant enhancement of the signal-to-noise ratio that scales exponentially with the squeezing factor. An order of magnitude improvement beyond the standard quantum limit is possible with state-of-the-art squeezing levels facilitating high precision gas sensing.

Synergistic coupling of 0D–2D heterostructure from ZnO and Ti3C2Tx MXene-derived TiO2 for boosted NO2 detection at room temperature

2D MXenes are highly attractive for fabricating high-precision gas sensors operated at room temperature (RT) due to their high surface-to-volume ratio. However, the limited selectivity and low sensitivity are still long-standing challenges for their further applications. Herein, the self-assembly of 0D–2D heterostructure for highly sensitive NO2 detection was achieved by integrating ZnO nanoparticles on Ti3C2Tx MXene-derived TiO2 nanosheets (designated as ZnO@M−TiO2). ZnO nanoparticles can not only act as spacers to prevent the restacking of M−TiO2 nanosheets and ensure effective transfer for gas molecules, but also enhance the sensitivity of the sensor the through trapping effect on electrons. Meanwhile, M−TiO2 nanosheets facilitate gas diffusion for rapid sensor response. Benefiting from the synergistic effect of individual components, the ZnO@M−TiO2 0D–2D heterostructure-based sensors revealed remarkable sensitivity and excellent selectivity to low concentration NO2 at RT. This work may facilitate the sensing application of MXene derivative and provide a new avenue for the development of high-performance gas sensors in safety assurance and environmental monitoring.

Real-time monitoring of toxic CS2 with high concentrations using a suitable terahertz photonic crystal fiber

Detection of toxic carbon disulfide ( C S 2 ) at high concentration, arising due to heavy industrial utilities, is an essential requirement for a sustainable ecosystem and healthcare. However, research and development of appropriate sensor devices to monitor a very high concentration of C S 2 are lacking. We design a polyethylene (PE) photonic crystal fiber (PCF) consisting of two interpenetrating periodic hexagonal lattices of teflon inclusions and air holes in the cladding, which can monitor ambient C S 2 with extremely high precision in a wide concentration range. Here, we measure the time delay difference (TDD) associated with the difference between group velocities of the two supported modes due to changes in C S 2 concentration in the prescribed holes. For a 10 cm long variant of the designed PCF operating at 0.75 THz frequency, we observe a linearly increasing TDD variation from ∼ 2 to 13 ps due to change in C S 2 concentration from 17 to 50%. However, when the C S 2 concentration exceeds the 50% range, we observe decreasing TDD characteristics. In this high concentration regime ( > --> 50 % ), we monitor C S 2 by analyzing second mode loss (SML) variation due to concentration change (at 0.98 THz frequency), where SML increases up to ∼ 30 d B for ∼ 100 % ambient C S 2 concentration. Here, we achieve a high concentration sensitivity where a variation of 1.6 dB SML is observed with a unit concentration change of C S 2 . The proposed scheme has an immense potential to boost the technologies for high-precision gas monitoring devices.

Dual Fabry-Perot interferometers gas pressure sensor in a parallel configuration based on a hollow core Bragg fiber and the harmonic Vernier effect.

An ultra-high sensitivity parallel-connected Fabry-Perot interferometers (FPIs) pressure sensor is proposed and demonstrated based on hollow core Bragg fiber (HCBF) and harmonic Vernier effect. The HCBF functions as a micro Fabry-Perot cavity and possesses low transmission loss. One FPI acts as the sensing unit while the other FPI is used as the reference unit to generate the Vernier effect. The sensing FPI was prepared by fusion splicing a section of HCBF between a single-mode fiber (SMF) and a hollow silica tube (HST), and the reference FPI was fabricated by sandwiching a piece of HCBF between two SMFs. Two FPIs with very different free spectral ranges (FSRs) in the fringe pattern were connected to the 2 × 2 coupler parallelly, which realizes the harmonic Vernier effect and ensures the stability of the interference fringe. Laboratory results exhibited that the pressure sensitivity can be enhanced to 119.3 nm/MPa within 0-0.5 MPa by the proposed sensor. Moreover, low-temperature crosstalk of 0.074 kPa/° was achieved. Compared with the traditional optical fiber gas pressure sensor, the advanced sensor features high sensitivity, stability, easy fabrication, and fast response, which can be a promising candidate for real-time and high-precision gas pressure monitoring.

Effect of {010} crystal facets of Bi2MoO6 and 1D/2D heterostructures for conductometric room temperature NH3 gas sensors

High working temperature and the insufficient limits of detection limit the broad applications of semiconductor chemiresistive gas sensors. Herein, pure Bi2MoO6 nanosheets and a series of one-dimensional/two-dimensional (1D/2D) multi-walled CNTs/Bi2MoO6 nanocomposites were developed via a facile hydrothermal route for room-temperature ammonia monitoring. The as-synthesized samples were characterized by various analytical techniques. 0.5 wt% MWCNTs/Bi2MoO6 nanocomposites showed the best sensing properties to 10–50 ppm NH3, including low limit of detection (157 ppb), high response (Ra/Rg = 44.2 @ 50 ppm), good selectivity, reproductivity, and anti-humidity sensing ability. The enhanced gas sensing mechanism was proposed based on the synergetic effect of high-energy crystal facets, modified surface characteristics and p-n heterojunction. Density functional theory (DFT) studies were also carried out to further clarify the gas sensing mechanisms. This work provides a practical approach to design and fabricate high-precision gas sensors working at room temperature.

Hybrid Modeling Method of SDR Interstage Valve Based on Mechanism and Data-Driven

Variable-throat adjustment is the most practical flow regulation method of solid ducted rocket ramjet (SDR). The high-fidelity mathematical model of the interstage valve is the basis for realizing high-precision gas flow and thrust regulation. In this paper, the complex effect of gas was divided into load and throat deformation effect. The load was mainly determined by the clearance, friction torque, and pneumatic torque that the valve was subjected to during operation. And the throat deformation was determined primarily by the deposition and ablation of the valve faced in the gas. Therefore, we could divide the valve model into three parts: the servo motor model, the load characteristic model, and the deformation model of the actual acting throat (referred to as the throat). Given, we have designed a cold-air experiment program, using cold air to equalize the valve load. Furthermore, we analyzed its mechanism of action and established the load model using the experimental data and neural network. Finally, the deformation mechanism of the throat was investigated, and simultaneously, the deformation model was shown based on the flight test data. Compared with the traditional interstage valve model, the model established in this paper is closer to the actual working conditions, which is helpful to carry out the more comprehensive and practical ground simulation. It has essential reference value for further realizing the precise regulation of gas flow.

Suitability Assessment of NOx Emissions Measurements with PTI Equipment

The measurement of NOx emissions in vehicles has so far been exclusively carried out during the type-approval process. For this purpose, high-precision gas measurement laboratory equipment and Portable Emission Measurement Systems (PEMS) are used. Both types of equipment are costly in terms of price, maintenance, complexity, and time of use (calibration and maintenance requirements). Currently, NOx emissions measurements in Periodic Technical Inspections (PTIs) are being considered, but PEMS or laboratory equipment is unsuitable for this function, and PTI-grade equipment has to be used. Although CO and O2 are currently being reliably measured with this equipment, there is not enough information about its accuracy for NOx measurements. Accordingly, in this paper, simultaneous measures have been performed over the same engine in a test cell, with a laboratory and a PTI gas analyser to assess the accuracy of the latter. When performing the test with the most similar conditions found in PTI, our results show that the PTI gas analyser shows an average deviation of 2.6 ppm and 9% rel. with respect to high-precision laboratory equipment for concentrations below 700 ppm NOx, which can be considered acceptable for periodic technical inspections.

Progress and challenges in exploration of powder fueled ramjets

• A detailed review of the research progress on powder fueled ramjets is presented. • The key technologies and scientific issues in powder fueled ramjets are proposed. • Some suggestions are proposed for the development of powder fueled ramjets. The powder fueled ramjet is a developing propulsion system, which makes use of metal powder as the propellant and presents noticeable advantages, for instance, high specific impulse and density-specific impulse, thrust adjustment, simple structure, and suitability for high Mach flight vehicles. In this paper, the basic work characteristics are introduced and the exploration progress is reviewed and summarized for powder fueled ramjets. Furthermore, several key technologies are proposed, which mainly include the powder feeding system, ignition and combustion processes of the powder fuel, combustion organization technology, multiple start, thrust adjustment, and thermal protection technology. The development of the powder fueled ramjet is in the proof-of-concept stage, and a large number of individual technology breakthroughs have been achieved in subsonic conditions. However, in both subsonic and supersonic conditions, the combustion mechanism of powder fuel needs to be investigated by high precision gas–solid two-phase numerical simulation methods, and ground tests, thus, to guide combustion chamber design. In order to achieve thrust regulation, coupling studies on powder fuel delivery and combustion are required. Besides, new thermal protection schemes based on the lattice structural and supercritical fluid active cooling have great potential to meet the demands of complicated two-phase combustion thermal environments.

MXene-derived TiO2 nanosheets decorated with Ag nanoparticles for highly sensitive detection of ammonia at room temperature

• A novel AgNPS-anchored Ti 3 C 2 T x MXene–derived TiO 2 nanocomposite is fabricated for high-precision gas sensors. • The Ag@TiO 2 gas sensor exhibited a response value of 71.8 to 50 ppm NH 3 at room temperature with a detection limit of 5 ppm. • Enhanced NH 3 sensing response mechanism of the Ag@TiO 2 nanocomposite is discussed. Due to their large surface-to-volume ratio and low electronic noise, two-dimensional transition metal carbides (Ti 3 C 2 T x MXene) and their derived transition metal oxides have demonstrated significant potential for use in high-precision gas sensing. However, the construction of high-sensitivity Ti 3 C 2 T x MXene–based gas sensors operated at room temperature (RT) is still a major challenge. Herein, we demonstrate a sensitive nanocomposite prepared by uniformly anchoring silver nanoparticles (AgNPs) on Ti 3 C 2 T x MXene–derived transition metal oxide (TiO 2 ) nanosheets for high-sensitivity NH 3 detection. AgNPs can not only serve as spacers to effectively prevent the restacking of MXene-derived TiO 2 nanosheets and ensure an effective transmission highway for target gas molecules, but also enhance the sensitivity of the sensor through chemical and electronic sensitization. By integrating the unique merits of the individual components and the synergistic effects of the composites, the optimized Ag@TiO 2 nanocomposite–based sensors revealed an extraordinary response value of 71.8 to 50 ppm NH 3 at RT with a detection limit as low as 5 ppm. In addition, the Ag@TiO 2 NH 3 sensor also exhibits excellent selectivity and outstanding repeatability. This strategy provides an avenue for the development of MXene derivatives for advanced gas sensors.

THEORETICAL AND EXPERIMENTAL INVESTIGATIONS OF IDENTIFYING PRESSURE LOSS IN FILTER ELEMENTSOF COARSE AND FINE GAS PURIFICATION WHEN PLACED IN ONE BODY

Statement of the problem. Reliable operation of modern high-precision gas flow reduction and control systems located in cabinet, block and capital gas distribution points calls for the use of two-stage cylindrical gas purification plants containing preliminary and fine filters. An urgent task is to design and scientifically substantiate the use of cost-effective two-stage natural gas purification devices located at gas distribution points as well as the development of analytical calculation methods for identifying pressure losses in the filter elements of two-stage cylindrical installations and the timing of their regeneration.Results. Theoretical and experimental identification of pressure losses depending on the degree of clogging of a multilayer filter element with mechanical impurities is given.Conclusions. Analytical equations for identifying pressure losses are obtained which differ from the known solutions in that the effect of clogging with mechanical impurities in a multilayer filter cloth is first presented as the sum of pressure losses on a number of clean calibrated grids located one after another, with the cell sizes of each subsequent grid less than the previous one.

Vacuum Based Gas Sensing Material Characterization System for Precise and Simultaneous Measurement of Optical and Electrical Responses.

Gas sensing performance characterization systems are essential for the research and development of gas sensing materials and devices. Although existing systems are almost completely automatically operated, the accuracies of gas concentration control and of pressure control and the ability to simultaneously detect different sensor signals still require improvement. In this study, a high-precision gas sensing material characterization system is developed based on vacuum technology, with the objective of enabling the precise and simultaneous measurement of electrical responses. Because of the implementation of vacuum technology, the gas concentration control accuracy is improved more than 1600 times, whereas the pressure of the test ambient condition can be precisely adjusted between vacuum and 1.2 bar. The vacuum-assisted gas-exchanging mechanism also enables the sensor response time to be determined more accurately. The system is capable of performing sensitivity, selectivity, and stability tests and can control the ambient relative humidity in a precise manner. More importantly, the levels of performance of three different optical signal measurement set-ups were investigated and compared in terms of detection range, linearity, noise, and response time, based on which of their scopes of application were proposed. Finally, single-period and cyclical tests were performed to examine the ability of the system to detect optical and electrical responses simultaneously, both at a single wavelength and in a spectral region.