Thermal Gases Research Articles

Numerical analysis and machine learning for battery thermal performance cooled with different fluids

A system of parallelly placed Li-ion batteries placed at different spacings and cooled by different coolants is analyzed. The prime focus is on the effect of spacings between the batteries on battery thermal performance. The temperature and heat flux at the coolant and battery interface is taken as continuous. Coolants used belong to thermal oils, gases, conventional oils, liquid metals, and nanofluids. Finite volume method-based numerical analysis is performed upon validation with experimental work reported in the literature, by developing a code in the C language. The simultaneous effect of battery aspect ratio, thermal conductivity, Reynolds number (Ref), and heat generation at different battery spacings for each coolant on average Nusselt number (NuH) is explored. An analytical model is developed and artificial neuro-fuzzy interference system (ANFIS) prediction of NuH is carried out later. Battery aspect ratio, thermal conductivity, and heat generation for any given coolant do not affect the NuH. However, the coolant Prandtl number at different battery spacings has a prominent effect on NuH. Thermal oils and liquid metal coolants show a significant and non-linear variation of NuH with increased battery spacings. The effect of Ref on NuH was linear as expected for all the coolants at different battery spacings. However, NuH variations for liquid metal at different Ref were highly non-linear. The mathematical model developed and ANFIS regression analysis indicated a very comfortable prediction of NuH. The R-squared value of the mathematical model is up to 0.98 while from ANFIS it is up to 0.985 showing a very good fitness of these models.

Theory of multiple quantum coherence signals in dilute thermal gases

Manifestations of dipole–dipole interactions in dilute thermal gases are difficult to sense because of strong inhomogeneous broadening. Recent experiments reported signatures of such interactions in fluorescence detection-based measurements of multiple quantum coherence (MQC) signals, with many characteristic features hitherto unexplained. We develop an original open quantum systems theory of MQC in dilute thermal gases, which allows us to resolve this conundrum. Our theory accounts for the vector character of the atomic dipoles as well as for driving laser pulses of arbitrary strength, includes the far-field coupling between the dipoles, which prevails in dilute ensembles, and effectively incorporates atomic motion via a disorder average. We show that collective decay processes—which were ignored in previous treatments employing the electrostatic form of dipolar interactions—play a key role in the emergence of MQC signals.

Research on the effect of thermal runaway gas components and explosion limits of lithium-ion batteries under different charge states

The combustion and explosion of thermal runaway gases from lithium-ion batteries may accelerate the propagation of thermal runaway from lithium-ion batteries and pose a serious threat to surrounding people and property. Therefore, the research of thermal runaway gas composition and explosion limits of lithium-ion batteries is of great significance for the prevention and control of thermal runaway of lithium-ion batteries. In this paper, we use experiments combined with empirical formulas to investigate the composition of gases generated by the thermal runaway and the explosion limit of 18,650 lithium-ion batteries. The analysis of the thermal runaway gas components of lithium-ion batteries by using gas chromatography-mass spectrometry (GC-MS) shows that as the SOC increases, the number of thermal runaway gases increases. With the increase of SOC, the change of lower explosion limit (LEL) shows the same trend as that in alkanes content, which increases and then decreases; while the change of upper explosion limit (UEL) shows the same trend as that in unsaturated hydrocarbons content, which decreases and then increases. In addition, 50% SOC battery shows the lowest exhausted gas combustion explosion danger.

Thermal transport in solar-reflecting and infrared-transparent polyethylene aerogels

Polyethylene aerogels (PEAs) present a unique combination of optical (solar-reflecting but infrared-transparent) and thermal properties that are ideally suited for applications requiring infrared-transparent thermal insulation such as atmospheric radiative cooling and condensation-free radiant cooling. As the material's thermal resistance plays a large role in these systems’ performance, better understanding of thermal transport within the material is crucial to guide future material development. In this work, we characterize thermal transport in PEAs, elucidating contributions of different heat transfer mechanisms and identifying pathways to further improve their thermal insulation performance. We first present a theoretical model that separates thermal transport via solid conduction through the polyethylene backbone, gaseous conduction within the porous structure and radiative transfer through the semi-transparent material. We then fabricated PEA samples of densities ranging from 12.0 kg/m³ to 82.2 kg/m³ and experimentally characterized their thermal conductivity using a custom-built guarded-hot-plate thermal conductivity setup, with pressures ranging from vacuum to 1 atm, in three gas environments (nitrogen, argon and carbon dioxide), and with low and high emissivity boundaries. The experimental and modeling results indicate that conduction in the gas phase and radiative transfer (for the high emissivity boundary case) dominate heat transfer through the material. We find that reducing the pore size and gas pressure, using lower thermal conductivity gases, adding infrared opacifiers and maintaining low density could all provide significant reduction in thermal conductivity.

Few-body correlations in two-dimensional Bose and Fermi ultracold mixtures

Few-body correlations emerging in two-dimensional harmonically trapped mixtures, are comprehensively investigated. The presence of the trap leads to the formation of atom-dimer and trap states, in addition to trimers. The Tan’s contacts of these eigenstates are studied for varying interspecies scattering lengths and mass ratio, while corresponding analytical insights are provided within the adiabatic hyperspherical formalism. The two- and three-body correlations of trimer states are substantially enhanced compared to the other eigenstates. The two-body contact of the atom-dimer and trap states features an upper bound regardless of the statistics, treated semi-classically and having an analytical prediction in the limit of large scattering lengths. Such an upper bound is absent in the three-body contact. Interestingly, by tuning the interspecies scattering length the contacts oscillate as the atom-dimer and trap states change character through the existent avoided-crossings in the energy spectra. For thermal gases, a gradual suppression of the involved two- and three-body correlations is evinced manifesting the impact of thermal effects. Moreover, spatial configurations of the distinct eigenstates ranging from localized structures to angular anisotropic patterns are captured. Our results provide valuable insights into the inherent correlation mechanisms of few-body mixtures which can be implemented in recent ultracold atom experiments and will be especially useful for probing the crossover from few- to many-atom systems.

Pulse area dependence of multiple quantum coherence signals in dilute thermal gases.

In the general framework of open quantum systems, we assess the impact of the pulse area on single and double quantum coherence (1QC and 2QC) signals extracted from fluorescence emitted by dilute thermal gases. We show that 1QC and 2QC signals are periodic functions of the pulse area, with distinctive features that reflect the particles' interactions via photon exchange, the polarizations of the laser pulses, and the observation direction.

Anisotropic thermalization of dilute dipolar gases

We study collisional rethermalization in ultracold dipolar thermal gases, made intricate by their anisotropic differential cross sections. Theoretical methods are provided to derive the number of collisions per rethermalization, which for dipolar gases, is highly dependent on the dipole alignment axis. These methods are formulated to be easily applied in experimental contexts, even reducing to analytic expressions if the route to thermal equilibrium is governed by short-time dynamics. In the analytic case, collisional rethermalization is fully characterized by the dipole magnitude and orientation, scattering length, and thermalization geometry. These models compare favorably to Monte Carlo simulations, and are shown to model well a recent experimental result on the rethermalization of polar molecular samples.

Doping hematite with bismuth to enhance its catalytic and oxidizing properties

• Doping Fe 2 O 3 with Bi can significantly enhance its intrinsic reactivity. • The catalytic decomposition mechanism of HMX has been studied. • The ignition delay time is greatly shortened with the increase of Bi amount. • A high ignition performance of Al/Bix-Fe 2 O 3 can be obtained. Bismuth-cation modulated hematite (Bi-Fe 2 O 3 ) was prepared by a one-step hydrothermal method and used as a catalyst for the thermolysis of energetic materials (EMs) and oxidant in an Al-based thermite. The effects of the amount of Bi doped Fe 2 O 3 on the catalytic property and thermite behavior were investigated using differential scanning calorimetry (DSC). Thermogravimetry–infrared spectroscopy-mass spectrometry (TG/IR/MS) was used to study the thermal decomposition gases of cyclotetramethylenetetranitramine (HMX) with or without catalyst. Bi-Fe 2 O 3 was found to reduce the initial thermal decomposition temperature and activation energy of HMX, and change the decomposition mechanism. In addition, the thermite reaction of Al/Bi-Fe 2 O 3 is exothermic and faster than that of undoped Al/Fe 2 O 3 , resulting in more rapid energy release. Al/Bi-Fe 2 O 3 also shows a shorter ignition delay time than Al/Fe 2 O 3 . This study demonstrates Al/Bi-Fe 2 O 3 as an efficient advanced combustion catalyst for solid propellants.

Helium and carbon isotopic signatures of thermal spring gases in southeast Yunnan, China

Late Palaeozoic and Cenozoic magmatism, including Pingbian Quaternary basaltic volcanoes, occurs in southeast Yunnan, China, where seismic tomography evidence indicates magma activity in the uppermost mantle. However, the characteristics of mantle fluid release remain poorly understood. Here, we report the chemical compositions of hot spring gases in SE Yunnan and measure the 3He/4He ratios, 4He/20Ne ratios, and δ13C-values (CO2, CH4) to determine their origins and the factors influencing their migration. Except for five samples contaminated by the atmosphere (4He/20Ne ratios, 0.39 ̶2.39), the Rc/Ra ratios (Rc is the air-corrected 3He/4He ratio, Ra is the air ratio with 1.4 × 10−6) range from 0.042 Ra to 0.470 Ra, indicating that the helium is mostly of crustal origin with minor addition of mantle-derived helium. The calculated maximum proportion of mantle helium was ~5% of total helium, indicating that mantle 3He leakage correlates with the ductile lower crust. The hot spring gases are fractionated by the partial dissolution of CO2 in groundwater, and the initial δ13CCO2 values are modelled by Rayleigh fractionation within a range of −26.5‰ to −6.14‰. The modelled CO2 in samples estimated by the HeC isotope coupling model originates from the mixing of limestone and organic sediment end-members. The isotopic signature of CH4 (−69.2‰ to 35.9‰) suggests a thermogenic source and microbial oxidation in some samples. Furthermore, the apparent isotopic temperatures are estimated using fractionation factors for CH4 and CO2, suggesting a lack of magmatism in the crust beneath the Red River fault zone (188–318 °C), but partial melting under the Bozhushan granitoid plutons (572–688 °C). The low emission of mantle-derived helium is attributed to the low fault permeability and minor active crustal deformation in present-day SE Yunnan, which restrain the upward migration of mantle fluids.

Surface coordination of black phosphorene for excellent stability, flame retardancy and thermal conductivity in epoxy resin

Black phosphorus (BP) are shining for its promising properties. Due to the instability and agglomeration problem, the surface coordination strategy is a key point in practical applications. Herein, a ruthenium sulfonate ligand is synthesized to coordinate black phosphorus (BP) nanosheets. By virtue of Ru-P coordination, the lone pair electrons in BP are occupied, thus the RuL3@BP displays excellent stability in environment and different solvents. Subsequently, the resulting RuL3@BP is added into epoxy resin (EP) to fabricate EP nanocomposites. RuL3@BP can effectively enhance the dispersibility of BP in EP due to the surface coordination. When the RuL3@BP is added into epoxy in an amount of 3 wt%, the char yield is distinctly improved by 96.83%, which is ascribed to the cooperative catalytic charring effect between BP and RuL3. EP/RuL3@BP nanocomposites can easily pass the UL-94 V-0 rating, and its limiting oxygen index (LOI) value rises by 26.72%. The peak of heat release rate (PHRR) is decreased by 62.21% and the total heat release (THR) reduces by 35.22%, which is assigned to the restriction of heat transfer and inhibition of flammable gas by the dense char residues. The smoke production and diffusion of thermal pyrolysis gases are dramatically suppressed in the combustion. Meanwhile, owing to strong interfacial interactions between RuL3@BP and EP, EP nanocomposites filled with 3 wt% RuL3@BP exhibit a high thermal conductivity of 0.376 W m−1 K−1, which is enhanced by 52.23% and 65.64% compared with that of EP/BP composite (0.247 W m−1 K−1) and pure EP (0.227 W m−1 K−1), respectively. This surface coordination strategy provides a novel approach for fabricating advanced-performance nanocomposites.

Synthesis and characterization of mesoporous MOF UMCM-1 for CO2/CH4 adsorption; an experimental, isotherm modeling and thermodynamic study

Abstract In this work, a metal-centered organic framework (UMCM-1) demonstrating microporous nature was prepared by the combination of the organic linker 1,3,5-tris(4-carboxyphenyl) benzene (H2BTB) and the salt Zinc Nitrate Hexahydrate (Zn-(NO3)2·6H2O) via solution-based, catalyst-free, and direct mixing method. The structural characteristics and porous properties of UMCM-1 were investigated by surface morphology, functional groups analysis, crystallinity, thermal stability, texture characteristics via FESEM, FTIR, PXRD, thermal stability analysis, porous properties, respectively, and pure gases (CO2 and CH4) uptake behaviour. The pure CO2 and CH4 adsorption were acquired out at a pressure of 1 bar and at three various temperatures i.e. 298.15 K, 323.15 K, and 348.15 K. The N2 adsorption-desorption isotherms reveal their highly microporous nature with specific surface area (3481.0667 m2/g), pore size (19.9373 A), and the pore volume (0.0178 cm3/g). The UMCM-1 was found crystalline and highly stable under harsh thermal conditions. The CO2 uptake capacity (1.0732 mmol/g) was found to be 138.48% approximately higher than CH4 uptake capacity (0.45 mmol/g). By increasing temperature, 10.7% approximately loss in the uptake capacities of CO2 and CH4 was observe demonstrating the exoergic in nature i.e. energy-releasing adsorption phenomenon. Furthermore, the isotherms and thermodynamic study demonstrated that the adsorption phenomenon is favorable adsorption behaviour with the heterogeneous system, demands higher pressure adsorption to activate the pores and physical in nature. The results presented herein demonstrated the UMCM-1 as a promising candidate for the energy-efficient CO2 separation.

Origin and fate of hydrothermal fluids at Piton des Neiges volcano (Réunion Island): A geochemical and isotopic (O, H, C, Sr, Li, Cl) study of thermal springs

As many ocean basaltic volcanoes worldwide, Piton des Neiges (Réunion Island) hosts a hydrothermal system that represents a potential geothermal resource. Despite several prospection campaigns over the past decades, this potential has never been confirmed because many aspects of fluid supply and circulation remain unclear. To track the origin and fate of hydrothermal fluids, we analyzed the geochemistry of thermal springs (water and gas), by combining conventional tracers (major-trace elements and O, H, C, Sr, Li isotopes) with Cl isotopes, a geochemical tool under development. Added to literature data, our new results allow us to compare the composition of thermal springs with cold waters, rocks, gas, and fumarolic deposits from La Réunion and elsewhere, and to untwine the complex history of fluid mixing that constitutes the geothermal system of Piton des Neiges.δ18OH2O and δDH2O values of springs (-8.67 to -4.9 and -56.3 to -23.5 ‰ VSMOW, respectively) are positioned close to the local meteoric water line, showing that thermal waters are of meteoric origin. However, their depletion in heavy isotopes relative to cold waters suggests a recharge strongly influenced by cyclones, with a possible contribution from high altitude (≥ 2000 m) rainfalls. Their absence of 18O enrichment relative to the local meteoric water line indicates that the isotopic exchange between rocks and water is very limited, and therefore suggests that their deep temperatures are relatively low and/or the water/rock ratios are high. δ13C values in thermal waters (-8.0 to +3.2 ‰ PDB) and gases (-6.7 to -5.3 ‰ PDB) confirm that carbon is essentially of magmatic origin, which we interpret as supplied by regional degassing of La Réunion hotspot. Major-trace elements and 87Sr/86Sr (0.704142 to 0.704336), δ7Li (+2 ‰ and +34.8 ‰ LSVEC), and δ37Cl (-0.35 ‰ and +0.40 ‰ SMOC) compositions show that three additional processes contribute to the mineralization of thermal waters: 1) interaction with basalt at temperatures ≥50 °C, 2) very limited seawater contamination (< 3 mol%), and/or 3) leaching of trachyte or scrubbing of fumarolic gas or condensates emitted by a shallow trachytic magma in the volcanic edifice.The geothermal system of Piton des Neiges is thus the result of meteoric water interaction with a trachytic heat source (as a solidified intrusion or a magma pocket), unrelated to the CO2 flux. We also emphasize that thermal waters at Piton des Neiges are exceptionally isolated from seawater compared to other geothermal systems in ocean island volcanoes worldwide, which implies a heat source located above the seawater/freshwater interface. These inferences are of critical importance for the future geothermal exploration on the island, as they suggest that the geothermal resource is within reach of relatively shallow drilling depths (≤1000 m).

Interplay between thermal Rydberg gases and plasmas

We investigate the phenomenon of bistability in a thermal gas of cesium atoms excited to Rydberg states. We present both measurements and a numerical model of the phenomena based on collisions. By directly measuring the plasma frequency, we show that the origin of the bistable behavior lies in the creation of a plasma formed by ionized Rydberg atoms. Recombination of ions and electrons manifests as fluorescence which allows us to characterize the plasma properties and study the transient dynamics of the hysteresis that occurs. We determine scaling parameters for the point of plasma formation, and verify our numerical model by comparing measured and simulated spectra. These measurements yield a detailed microscopic picture of ionization and avalanche processes occurring in thermal Rydberg gases. From this set of measurements, we conclude that plasma formation is a fundamental ingredient in the optical bistability taking place in thermal Rydberg gases and imposes a limit on usable Rydberg densities for many applications.

The chemical and isotopic compositions of thermal waters and gases in the Republic of Buryatia, Russia

The chemical and isotopic compositions of waters and associated gases in the Republic of Buryatia are investigated in this report. Results show the thermal waters are predominantly enriched in N2. They are alkaline, low salinity and have high concentrations of HCO3-, SO42-, F, Si but low values for Ca2+, Mg2+, K+. According to isotopic composition, the thermal waters are meteoric in origin. Despite the low salinity, the thermal waters are in equilibrium with calcite, magnesite, fluorite, albite, laumontite and other minerals but are not equilibrium with respect to primary aluminosilicates. This indicates that the thermal waters and water-bearing rocks represent the equilibrium-nonequilibrium system.

Universal prethermal dynamics of Bose gases quenched to unitarity.

Understanding strongly correlated phases of matter, such as the quark-gluon plasma and neutron stars, and in particular the dynamics of such systems, for example, following a Hamiltonian quench(a sudden change in some Hamiltonian parameter, such as the strength of interparticle interactions) is a fundamental challenge in modern physics. Ultracold atomic gases are excellent quantum simulators for these problems, owing to their tunable interparticle interactions and experimentally resolvable intrinsic timescales. In particular, they provide access to the unitary regime, in which the interactions are as strong as allowed by quantum mechanics. This regime has been extensively studied in Fermi gases1,2. The less-exploredunitary Bose gases3-11 offer possibilities12 such as universal physics controlled solely by the gas density13,14 and new forms of superfluidity15-17. Here, through momentum- and time-resolved studies, we explore degenerate and thermal homogeneous Bose gases quenched to unitarity. In degenerate samples, we observe universal post-quench dynamics in agreement with the emergence of a prethermal state18-24 with a universal non-zero condensed fraction22,24. In thermal gases, the dynamic and thermodynamic properties generally depend on the gas density and the temperature, but we find that they can still be expressed in terms of universal dimensionless functions. Surprisingly, we find that the total quench-induced correlation energy is independent of the gas temperature. These measurements provide quantitative benchmarks and challenges for the theory of unitary Bose gases.

Flow transportation inside shale rocks at low-temperature combustion condition: A simple scaling law

The gas flow inside the shale undergoes a complicated process from continuum-flow to Knudsen diffusion during combustion. In this study, a shale sample obtained from Shanxi province with burial depth of 643 m was combusted at a constant temperature to study the transient internal pressure variation. In the beginning, a cylinder-shaped shale was combusted above an electric heater at a constant temperature 450 °C. The transient internal pressures and surface temperatures of the shale sample were recorded every 15 s. With the thermal wave propagating from the electric heater to the top of shale, the shale surface temperature gradually increased. The pressure inside the sample was quickly built up because of the thermal cracking of kerogen. It reached a peak value of 12,000 Pa. Afterwards, the pressure gradually declined with the improvement of the permeability of the shale. By the observations during the experiment, a combustion model based on the scaling power law was used to simulate the transient internal pressure changes of a cylinder shaped shale sample during the combustion process. The simulated results showed a good agreement with experimental data. Based on the pressure variation data, it was found that not only the original trapped/storage gas (free state gas, adsorbed state gas, and dissolved state gas) but also the thermal cracking hydrocarbon gases produced from kerogen could be extracted from tight shale formation for gas recovery. Thus, combustion can further improve the production rate of gas from shale reservoirs.

Interpretation of turn-to-turn insulation fault by dissolved gas analysis

The purpose of dissolved gas analysis (DGA) in utilities is to help detect the presence of abnormality within transformer. When faults occur in transformers, transformer engineers need to determine the location and risk of the faults. Ultimately, they have to decide, based on DGA, whether to continue operating or not, perform internal inspection, or dispose the transformer. In this study, the fault and failure types in the transformer are suggested to determine the location and risk of the faults. In particular, turn-to-turn insulation faults are classified as degradation and breakdown. These faults are difficult to identify during internal inspection, and have a high possibility of failure. Urgent decision and action are thus required to avoid failure. In degradation of turn-to-turn insulation faults, failures may occur by generating thermal gases in paper during a long period of time. In breakdown of turn-to-turn insulation faults, thermal gases are not generated in paper, and failures are rather due to sudden breakdown of insulation. This study also presents a typical example of a turn-to-turn insulation fault. This example shows the progress of the fault from thermal to discharge, which is common phenomena in winding fault. Based on the findings of this work, transformer engineers can determine by DGA if transformers can be operated with or without internal inspection, or disposed when the fault has not been identified during internal inspection.

The origin and secondary alteration of dissolved gas in oil: A case study from the western Tu-Ha Basin, China

The Tu-Ha Basin is a typical Jurassic coal-derived petroliferous basin in western China. Seventeen natural gas samples were collected from the Jurassic Sanjianfang and Qiketai Formations, the Cretaceous Tugulu Formation, and the Paleogene Shanshan Formation to analyze the source and secondary alteration of natural gas. The natural gas samples were characterized by molecular and stable carbon (δ13C) and hydrogen (δD) isotope compositions. The results indicate that the natural gases are wet gases, in which methane is the main alkane component. Nitrogen (N2) and carbon dioxide (CO2) are the two non-hydrocarbons. The N2 values (>12%) are relatively higher, which increase rapidly at the burial depth of 1500–2000 m. Some natural gases have suffered secondary alteration at this depth. The natural gases are thermal genetic coal-derived gases (humic gas), coming from the Jurassic coal measure source rocks, which are chiefly in the low mature to early mature stage. Nitrogen in the shallow is chiefly derived from the atmosphere, while nitrogen at the deeper burial depth is mainly derived from the thermal decomposition of organic matter (OM). The shallow natural gas samples have the heaviest carbon isotope composition of ethane (δ13C2) and a carbon isotope sequence of (δ13C1 < δ13C2 > δ13C3 > δ13n-C4 < δ13i-C4), which is mainly caused by the biodegradation. The higher nitrogen content illustrates that a large amount of surface water is running into the reservoirs. Water washing occurs in the reservoirs, which decreases the molecular methane content and increases the amount of heavier hydrocarbons at 1500–2000 m depth.

Matter-Wave-Optical-Wave Mixing-Induced Transparency and a Nonhyperbolic Matter-Wave Quasisoliton in Quantum Gases.

The realization of atomic quantum gases has brought out surprising effects that have no correspondence in nonlinear optics with thermal gases, presenting intriguing and exciting challenges to the research discipline of nonlinear optics which has matured since the invention of the laser. Here, we show an unexpected optical wave-mixing gain cancellation effect in a quantum gas that restricts an, otherwise, strongly enhanced backward-propagating light-matter wave-mixing process. This results in a wave-mixing induced transparency and a nonhyperbolic quasi-matter-wave soliton that opens new research opportunities in hydrodynamic fluid research of degenerate quantum gases, such as phonon scattering in a two-dimensional sonic black hole horizon.

Low thermal fault gases of various natural monoesters and comparison with mineral oil

Natural ester oils began to be implemented in higher voltage of power transformer in 2002. Gases generated by such oils need to be examined in order to anticipate the use of dissolved gas analysis (DGA) method to diagnose the presence of faults in natural ester filled transformer in service. This paper deals with an analysis of the gas generations of natural monoesters of different molecular structures derived from palm and rice bran oils under localized and low thermal faults ranging from 200 to 300 °C. Types of gases and their generation rates at various temperature levels were investigated. An attempt is made to compare the gas generation tendency between tested oils and commercially available natural ester insulation oil reported in the previous literature as well as mineral oil. The phenomenon of ethane generation by fatty acid monoesters having C-C double bond in their hydrocarbon chains and those without C-C double bond are discussed. Due to the expectation of overheating temperature, the possible implementation of CO/CH 4 gas ratio is also evaluated.