Absorption Line Of Carbon Monoxide Research Articles

Sub-ppt level detection of carbon monoxide and nitrous oxide enabled by mid-infrared doubly resonant photoacoustic spectroscopy.

We report highly sensitive detection of carbon monoxide (CO) and nitrous oxide (N2O) using doubly resonant photoacoustic spectroscopy paired with a quantum cascade laser (QCL) at 4.57 μm. The butterfly-packaged QCL is used to exploit the CO absorption line at 2190.02 cm-1 and the N2O absorption line at 2191.42 cm-1 by scanning the injection current. Leveraging the simultaneous acoustic and optical resonances and adopting a lower photoacoustic detection frequency, we achieve a minimum detection limit of 0.85 part-per-trillion (ppt) for CO over the 500 s averaging time, and 0.7 ppt for N2O over the 200 s averaging time. Our approach demonstrates record sensitivity for CO and N2O detection compared to state-of-the-art optical gas sensors.

Shear Coaxial Methane–Oxygen Injector Mixing and Combustion Examined by Laser Absorption Tomography

Mixing length scales for methane–oxygen shear-coaxial single-element rocket injectors were experimentally assessed using laser absorption tomography. The laser spectroscopy technique enables quantitative and spatially resolved measurements of carbon monoxide (CO) and temperature within the near-field region, probing rovibrational absorption lines of CO near 5 μm. Multiple injector designs were examined with differing oxidizer post recess depths to compare mixing characteristics. All tests were performed at an oxidizer-to-fuel ratio of 3 with a total propellant flow rate of 0.350 g/s. Planar measurements were taken at 16 axial positions, which collectively captured the first 57 mm of each flame. A tomographic inversion method was applied to obtain radially resolved distributions of temperature and CO mole fraction for each axial position, from which two-dimensional images of the thermochemical structure were generated. Characteristic mixing parameters are defined and extracted from features within the species and temperature profiles to visualize the spatial evolution of CO production. Increasing oxidizer post recess improved mixing due to enhanced shear-induced turbulence and associated radial diffusion of species and temperature; however, the enhancement was nonlinear. This work establishes the first use of laser absorption tomography to directly measure mixing length scales associated with temperature and species profiles in coaxial flames.

Real-time FPGA-based laser absorption spectroscopy using on-chip machine learning for 10 kHz intra-cycle emissions sensing towards adaptive reciprocating engines

Fast emissions sensing is needed to enable rapid optimization on-the-fly for increasingly adaptive engine architectures to improve performance over a wide range of loads and to offer fuel flexibility towards a low-carbon energy future. In this work, a real-time laser absorption spectroscopy technique is developed for 10 kHz on-line measurements of engine exhaust gas temperature and carbon monoxide. Latency due to data reduction is significantly shortened through a machine learning approach to spectral analysis and minimization of post-processing complexity for implementation on a high-bandwidth field-programmable gate array (FPGA). The data reduction method is tested on cycle-resolved laser-absorption thermochemistry measurements in reciprocating piston engine exhaust. The sensor employs a quantum cascade laser to spectrally-resolve two fundamental rovibrational absorption lines of carbon monoxide near 4.9 μm at a rate of 10 kHz. The recorded signals are passed to an FPGA to infer CO concentration and gas temperature through either a pre-trained ridge regression or artificial neural network model. Models are constructed to limit complexity with the aim of minimizing resource utilization and latency on the FPGA. Experimental data are used to evaluate the prediction accuracy of the models, with the neural network achieving RMS errors in CO mole fraction and gas temperature of 0.0390% and 15.0 K, respectively, compared to spectral fitting of the absorption lineshapes. The data reduction latencies are measured through hardware-in-the-loop demonstration, achieving a 10 kHz throughput and 25 μs latency. Computational time of the end-to-end data reduction process on the FPGA is measured at 300 ns and 600 ns for the ridge regression and neural network, respectively. The data reduction methods presented in this work expand the utility of laser absorption spectroscopy for low-latency sensors that match the timescales of combustion and increase the potential for real-time sensing and control to minimize engine exhaust emissions and maximize performance.

Development and field deployment of a mid-infrared CO and CO2 dual-gas sensor system for early fire detection and location

In order to realize early fire detection and location, a mid-infrared carbon monoxide (CO) and carbon dioxide (CO2) dual-gas sensor system was developed, which mainly includes a gas pretreatment module, a CO2 sensor module, a CO sensor module, and a laptop monitoring platform. CO2 and CO absorption lines located at 4.26 μm and 4.66 μm, respectively, were selected to ensure good selectivity of the sensor system. A series of experiments were carried out to evaluate the sensor performance. The 10–90% response time of the CO and CO2 sensor modules was measured to be ∼ 30 s at a flow rate of 1 L/min, and the limits of detection (LoD) of CO2 and CO were assessed to be 5.66 parts per million by volume (ppmv) and 0.94 ppmv, respectively, when the averaging time was 0.25 s. According to the correlation between CO2 and CO concentration in the early fire stage, a method of early fire detection was studied and proposed using the normalized concentration ratio between CO and CO2 (C(CO)/C(CO2)) as the key alarm parameter. Based on gas turbulent diffusion (GTD) model combined with particle swarm optimization (PSO) algorithm, a mobile early fire location method was presented. Correlative experiment results verified that the reported sensor system has a good performance for early fire detection and location.

Highly precise measurement of atmospheric N2O and CO using improved White cell and RF current perturbation

A highly precise dual gas sensor for measurement of atmospheric nitrous oxide (N2O) and carbon monoxide (CO) was developed and evaluated. A room temperature interband cascade laser emitting at 4.54 μm was used as a laser source to cover the absorption lines of N2O and CO simultaneously. Sensitivity and precision were enhanced by using an improved White cell with 76 m effective optical path length and radio frequency noise perturbation technique to reduce optical interference noise. A method was proposed to correct the laser frequency by calculating the correlation coefficient between the absorption signal with the reference signal, which effectively reduced the long-term drift of the absorption line center to less than 4 × 10−5 cm−1. By further precisely control the temperature and pressure of the absorption cell, a continuous 24 h measurement precision of 65 ppt N2O and 133 ppt CO at 0.1 Hz was demonstrated, with a daily drift less than 1.5 ppt. Finally, the repeatability and reliability of the sensor system were validated by real atmospheric measurements for two consecutive days.

Separation and analysis method of overlapping absorption spectra with cross interference in gas mixture measurement

The interference between overlapping gas absorption lines often occurs in the measurement of multi-component gas mixture with using tunable diode laser absorption spectroscopy (TDLAS). This is also the main problem of the technology in some applications. For instance, in the early application of multi-component gas mixture measurement in coal mines, we found that the absorption lines of carbon monoxide (CO) and methane (CH<sub>4</sub>) seriously overlapped. The absorption signal of trace CO gas was annihilated and could not be effectively demodulated, especially in the presence of high concentration of CH<sub>4</sub>. This problem could not be solved just by accurately selecting the spectral lines due to the band absorption of CH<sub>4</sub>. Therefore, in this paper, we introduce the support vector regression (SVR) model to deal with the interference between CO and CH<sub>4</sub> absorption lines. The spectral signals of 14 groups of mixed gases with different concentrations of CO and CH<sub>4</sub> are used as the training sets, and the five-fold cross-validation is adopted to prevent the model from overfitting. After 15 iterations in 30 seconds, the optimal regression model of CO and CH<sub>4</sub> can be obtained respectively. Furthermore, it is worth noting that based on the experimental data, the linear kernel function is selected to construct the two gas SVR models, and the parameters of the SVR models are optimized by the sequential minimal optimization(SMO) algorithm. With the assistance of the SVR models, the absorption spectra of the two gases can be demodulated effectively, and finally the accurate measurement results are obtained. The measurement results show that the absolute error of trace CO and CH<sub>4</sub> concentration(volume fraction of gas) are less than 2 × 10<sup>–6</sup> and 0.2 × 10<sup>–2</sup> respectively. Meanwhile, the correlation coefficient between the measured values and the actual values of CO and CH<sub>4</sub> are 0.998 and 0.9995, respectively. In addition, the dynamic stability for each of the two regression models is fully verified by the experiment of the inflation process. Consequently, this method can eliminate the interference between the overlapping spectra, and can fully meet the requirements for accurately measuring the gas mixture. We hope that the SVR model can provide an effective solution for the real-time monitoring of multi-component gas mixture, and thus greatly improving the adaptability of TDLAS technology in the future.

The best absorption lines for the detection of carbon monoxide at 2.35 micron with tunable diode lasers

A modeling of high-resolution absorption spectra of carbon monoxide (CO) and other interfering gases at 2.35 um was conducted. Several CO absorption lines have been determined as the best for the use in laser based spectral analysis of CO under conditions of high humidity and high concentrations of CO2 in complex gas mixtures. Measurements of resonance absorption in these lines allow one to obtain maximum sensitivity and selectivity of CO analysis in the near-infrared spectral region.

A Sensitive and Reliable Carbon Monoxide Monitor for Safety-Focused Applications in Coal Mine Using a 2.33-$\mu$ m Laser Diode

In this paper, a stable and reliable carbon monoxide (CO) monitoring system with high sensitivity (at sub-ppm level) was designed and demonstrated with particular reference to use in the mining industry, tailoring the design specifically for forecasting spontaneous combustion, a major hazard to miners. An appropriate strong CO absorption line was used to minimize the interferences expected from gases present in ambient air, with several preferred CO absorption lines selected and investigated, therefore choosing a distributed feedback (DFB) laser operating at a wavelength of 2330.18 nm as the excitation source. Through a detailed investigation, a minimum detection limit of ~0.2 ppm and a measurement precision of <50 ppb were achieved with a 1 s averaging time. Further in tests, a long-term continuous monitoring evaluation was carried out, demonstrated the excellent stability and reliability of the developed CO monitor. The results obtained have validated the potential of this design of a CO monitoring system for practical monitoring applications underground to enhance safety in the mining industry.

Retrieval of Carbon Monoxide Total Column in the Atmosphere from High Resolution Atmospheric Spectra

Carbon monoxide (CO) is a marker of the atmospheric pollution caused by fires and combustion engine emissions. The regular monitoring of the CO content in the atmosphere is needed to control air quality. In this work, the results of CO atmospheric total column retrievals from the solar spectra recorded by Fourier -transform spectrometers at the St. Petersburg (59.88° N, 29.83° E) and Kourovka (57.038° N, 59.545° E) stations are presented. The impact of differences in CO absorption line parameters in modern spectroscopic databases on the accuracy of the CO atmospheric total column retrieved from high resolution spectra is estimated.

Development of an early warning fire detection system based on a laser spectroscopic carbon monoxide sensor using a 32-bit system-on-chip

A distributed feedback laser-based carbon monoxide (CO) sensor has been developed for early warning detection of fire. The sensor, based on a system-on-chip with high-performance 32-bit microcontroller (MCU), features a digital lock-in amplifier (DLIA) for wavelength modulation spectroscopy (WMS) to improve detection sensitivity. The ramp scanning signal and a sinusoidally modulated signal were generated and superimposed by the MCU, and converted by a digital-to-analog converter to scan the absorption line of CO around 2.327 μm. The n-harmonic components obtained through multiplication of the n-th cosine wave data of the spectral signal, were then processed by integration and filter algorithms. The Allan-Werle deviation was used to evaluate the long-term performance of the sensor. The limit of detection (LoD) for CO was calculated to be 0.0875 ppm based on an optimal integration time of ∼24 s. In field tests, five small-scale standard fires were investigated in accord with EN54 and the results for the test substances – cotton rope (smoldering fire), polyurethane foam (smoldering fire), beech wood, a sheet of A4 paper and polyvinylchloride – verified the reliability and robustness of the developed sensor. Relatively fast response times (110 s for foam and A4 paper; 250 s for PVC, beech wood and cotton rope) were realized based on a threshold of 5 ppm CO. The CO sensor is considered suitable for integration into portable devices for industrial application, particularly for in-situ early warning fire detection.

Metrological quantification of CO in biogas using laser absorption spectroscopy and gas chromatography

Biogas has a vital role in the future market for renewable energy. When upgraded to biomethane, it can be injected into natural gas grids if the level of certain impurities complies with the specifications in EN16723. For some of these impurities, suitable measurement methods are lacking which hamper the quality control of biomethane to be injected into natural gas networks. Here, we report on the evaluation of three detection methods suitable for carbon monoxide (CO) in biogas and biomethane applications for which EN16723 specifies an upper limit of 0.1% (1000 µmol ⋅ mol−1). Two of these methods are based on laser absorption spectroscopy (LAS) and one on gas chromatography (GC). Both LAS spectrometers employ direct absorption spectroscopy and operate at 4.6 µm, probing a single CO absorption line in the fundamental CO band. One of them, direct tunable diode laser absorption spectroscopy (dTDLAS), is based on a new interband cascade laser specially designed for biogas and biomethane applications, while the other is based on quantum cascade laser absorption spectroscopy (QCLAS). The GC is equipped with two packed columns (HayeSep Q and molecular sieve 5A) and a thermal conductivity detector. CO amount fraction results in biogas matrices derived using these three measurement methods and are compared to amount fraction values of different, gravimetrically prepared reference gas standards of CO in biogas. These were used to validate the measurement capabilities. The measured CO amount fraction results from LAS and GC covered 10–30 000 µmol ⋅ mol−1 (system measurement ranges, LAS: 3–1000 µmol ⋅ mol−1, GC: 500–30 000 µmol ⋅ mol−1) and were in excellent agreement with the gravimetric values of the gas standards. At 400 µmol ⋅ mol−1, the guide to the expression of uncertainty in measurement compliant relative standard uncertainties of our calibration-free dTDLAS and the gas-calibrated QCLAS systems are estimated to be 1.4% versus 0.5%, respectively. The relative standard uncertainty of the GC CO measurements at 5075 µmol ⋅ mol−1 is 1.3%. This work demonstrates that, by means of GC and LAS, relative standard uncertainties of 1.4% and below can be reached for CO measurements in biogas and that cost-optimized calibration-free approaches not requiring frequent use of gas standards have become available.

Characterization of a commercial software defined radio as high frequency lock-in amplifier for FM spectroscopy.

A commercial software defined radio based on a Rafael Micro R820T2 tuner is characterized for the use as a high-frequency lock-in amplifier for frequency modulation spectroscopy. The sensitivity limit of the receiver is 1.6 nV/Hz. Frequency modulation spectroscopy is demonstrated on the 6406.69 cm-1 absorption line of carbon monoxide.

Development and Integration of a CO Detection System Based on Wavelength Modulation Spectroscopy Using Near-Infrared DFB Laser

A wavelength modulation spectroscopy- (WMS-) based gas sensing system was established to measure concentration of carbon monoxide (CO) in the range 0–100%. The CO absorption line at 1563.06 nm was scanned with a tunable distributed feedback (DFB) laser, and two InGaAs photodiodes were applied to perform optic-electric conversion. Without using commercial instruments, essential electrical circuits were self-developed and integrated, including laser temperature controller, laser current driver, signal generator, and digital lock-in amplifier. The gas cell deployed in the system was fiber coupled with a total effective optical path length of 50 cm. The second-order harmonic signal was extracted, and experiments of gas detection were carried out to investigate the performance of the sensor, including detection repeatability, detection accuracy, response time, and limit of detection (LoD). Experiment results show that the sensor is reliable and has acceptable probing performance. The maximum relative detection error is less than 3.8%, suggesting good detection stability. Benefiting from the self-developed sensor, the whole CO detection system has small size, affordable expense, and application potential.

Pressure-Dependent Detection of Carbon Monoxide Employing Wavelength Modulation Spectroscopy Using a Herriott-Type Cell.

Wavelength modulation spectroscopy (WMS) combined with a multipass absorption cell has been used to measure a weak absorption line of carbon monoxide (CO) at 1.578 µm. A 0.95m Herriott-type cell provides an effective absorption path length of 55.1 m. The WMS signals from the first and second harmonic output of a lock-in amplifier (WMS-1 f and 2 f, respectively) agree with the Beer-Lambert law, especially at low concentrations. After boxcar averaging, the minimum detection limit achieved is 4.3 ppm for a measurement time of 0.125 s. The corresponding normalized detection limit is 84 ppm m Hz-1/2. If the integrated time is increased to 88 s, the minimum detectable limit of CO can reach to 0.29 ppm based on an Allan variation analysis. The pressure-dependent relationship is validated after accounting for the pressure factor in data processing. Finally, a linear correlation between the WMS-2 f amplitudes and gas concentrations is obtained at concentration ratios less than 15.5%, and the accuracy is better than 92% at total pressure less than 62.7 Torr.

Performance of discrete wavelet technique in the de-noising of noisy spectrum in the mid-infrared region near 4.5 µm

We applied discrete wavelet transform (DWT) technique for de-noising of carbon monoxide (CO) spectrum which is experimentally obtained in the mid-infrared region using a difference-frequency-based spectrometer. The performance of DWT is firstly examined by de-noising of a simulated P(16) CO absorption line based on the real data associated with the experimental setup we arranged in laboratory. It is found that when the db20 function from Daubechie wavelet family is used at level 7 of composition, highest signal-to-noise ratio (SNR) ~23 can be achieved. Similar results are obtained in the experiment in which a noisy CO trace is de-noised using the same procedure as described in the simulation. Subsequently, highest SNR of ~9.2 and lowest residuals is experimentally obtained using the db20 function which confirms the merit of DWT technique in detection of low-level absorption signals.

Research on high sensitivity detection of carbon monoxide based on quantum cascade laser and quartz-enhanced photoacoustic spectroscopy

Quartz-enhanced photoacoustic spectroscopy (QEPAS) technology was invented lately. Therefore it is an innovative method for trace gas detection compared with other existing technologies. In this paper, trace gas detection for carbon monoxide (CO) based on QEPAS technology is demonstrated. In order to realize high sensitive detection, a novel mid-infrared, state-of-art 4.6 m high power, continuous wave (CW), distributed feedback (DFB) quantum cascade laser (QCL) with single mode output is used as the laser exciting source. Therefore, the strongest absorption of fundamental frequency band of CO is achieved. Using the wavelength modulation spectroscopy and the 2nd harmonic detection, the influence of laser wavelength modulation depth on QEPAS signal level is investigated. Two important parameters of Q-factor and resonant frequency for quartz tuning fork as a function of gas pressure are measured. After optimization of the modulation depth of laser wavelength, the gas pressure of CO:N2 gas mixture and the improving speed of the V-R relaxation rate through the addition of water vapor, a minimum detection limit (MDL) of 1.95 parts per billion by volume (ppbv) for CO at gas pressure of 500 Torr and modulation depth of 0.2 cm-1 is achieved with a 1 sec acquisition time and the addition of 2.6% water vapor in the analyzed gas mixture. Finally, the influence of level lifetime of the targeted gas on QEPAS signal amplitude is investigated by comparison of CO QEPAS sensor performance using two different CO absorption lines of R(5) and R(6) located at 2165.6 cm-1 and 2169.2 cm-1respectively. The expression of the QEPAS signal amplitude is modified by adding the level lifetime parameter for a better precision.

A Modified Empirical Mode Decomposition Algorithm in TDLAS for Gas Detection

Based on the research of the traditional empirical mode decomposition (EMD) method, we proposed a modified EMD algorithm for the detected signal processing in tunable diode laser absorption spectroscopy. The modified EMD algorithm introduced Savitzky–Golay filtering and cross-correlation operation into the traditional EMD algorithm and reconstructed the signal by using the cross-correlation coefficients effectively. Based on the modified EMD algorithm in theory, the second harmonic component analysis was simulated by comparing with some other filtering algorithms. The experiments system was performed for carbon monoxide (CO) concentration detection. Comparing the sensing performances without and with using EMD-FCR and other filtered methods, the experimental results show that the signal-to-noise ratio of the system was significantly improved from 7.32 to 14.31 dB by EMD-FCR corresponding to one absorption line of CO at 1567.32 nm, leading to the minimum detection limit of 2 ppm. The accuracy and stability of the system are both improved by proposing the modified EMD algorithm.

IMPROVEMENT IN QCL ABSORPTION BASED CO TRACE GAS SENSOR SYSTEM

This paper describe development of Trace gas sensor that can detect Carbon Monoxide (CO) gas by using a wavelength tuned Distributed feedback-Quantum Cascade LASER (DFB-QCL). Trace gas sensor design is based on principle of Direct Infrared Absorption Spectroscopy. High Resolution Transmission Molecular Spectroscopic (HITRAN) Analysis is carried out for selecting fundamental absorption line of CO R(12) near 2190.0175 cm -1 and the characteristics of wavelength tunable DFB-QCL has been analyzed, for detection of CO R(12) at same wavenumber. Fixed length gas cell of 10 cm is used to achieve highest sensitivity and improved detection limit. We are improving the response time and reducing the various noises present in the gas sensor using signal processing with the help of NI LabVIEW software and hardware. Also effect of chopper frequency variation, Mercury Cadmium Telluride (MCT) detector distance variation on Full Width Half Maxima (FWHM), Intensity of DFB-QCL is observed with and without gas sample present in fixed gas cell.

QEPAS based ppb-level detection of CO and N_2O using a high power CW DFB-QCL

An ultra-sensitive and selective quartz-enhanced photoacoustic spectroscopy (QEPAS) sensor platform was demonstrated for detection of carbon monoxide (CO) and nitrous oxide (N2O). This sensor used a state-of-the art 4.61 μm high power, continuous wave (CW), distributed feedback quantum cascade laser (DFB-QCL) operating at 10°C as the excitation source. For the R(6) CO absorption line, located at 2169.2 cm(-1), a minimum detection limit (MDL) of 1.5 parts per billion by volume (ppbv) at atmospheric pressure was achieved with a 1 sec acquisition time and the addition of 2.6% water vapor concentration in the analyzed gas mixture. For the N2O detection, a MDL of 23 ppbv was obtained at an optimum gas pressure of 100 Torr and with the same water vapor content of 2.6%. In both cases the presence of water vapor increases the detected CO and N2O QEPAS signal levels as a result of enhancing the vibrational-translational relaxation rate of both target gases. Allan deviation analyses were performed to investigate the long term performance of the CO and N2O QEPAS sensor systems. For the optimum data acquisition time of 500 sec a MDL of 340 pptv and 4 ppbv was obtained for CO and N2O detection, respectively. To demonstrate reliable and robust operation of the QEPAS sensor a continuous monitoring of atmospheric CO and N2O concentration levels for a period of 5 hours were performed.

Broadening of rovibrational absorption lines of carbon monoxide and dioxide molecules as a result of collisions with walls

The mechanisms determining the absorption line profiles of CO and СО2 molecules enclosed in cells with sizes changing from a few tens of nanometers to a few centimeters are considered. Frequencies of molecular transitions from several reciprocal centimeters (rotational transitions) to 2000 cm−1 (rovibrational transitions) are considered. Doppler and intermolecular collisional broadening and line broadening as a result of collisions with walls of the cell filled with the gas are discussed. It is demonstrated that the contribution of line broadening as a result of collisions with cell walls to the total line width can change from several fractions to several tens of percent depending on the cell size. The temperature dependence of the contributions of line broadening and their dependence on the absorption wavelength are discussed.