Methane Oxygen Research Articles

Versatile methanotrophs form an active methane biofilter in the oxycline of a seasonally stratified coastal basin.

The potential and drivers of microbial methane removal in the water column of seasonally stratified coastal ecosystems and the importance of the methanotrophic community composition for ecosystem functioning are not well explored. Here, we combined depth profiles of oxygen and methane with 16S rRNA gene amplicon sequencing, metagenomics and methane oxidation rates at discrete depths in a stratified coastal marine system (Lake Grevelingen, The Netherlands). Three amplicon sequence variants (ASVs) belonging to different genera of aerobic Methylomonadaceae and the corresponding three methanotrophic metagenome-assembled genomes (MOB-MAGs) were retrieved by 16S rRNA sequencing and metagenomic analysis, respectively. The abundances of the different methanotrophic ASVs and MOB-MAGs peaked at different depths along the methane oxygen counter-gradient and the MOB-MAGs show a quite diverse genomic potential regarding oxygen metabolism, partial denitrification and sulphur metabolism. Moreover, potential aerobic methane oxidation rates indicated high methanotrophic activity throughout the methane oxygen counter-gradient, even at depths with low in situ methane or oxygen concentration. This suggests that niche-partitioning with high genomic versatility of the present Methylomonadaceae might contribute to the functional resilience of the methanotrophic community and ultimately the efficiency of methane removal in the stratified water column of a marine basin.

Modes of interaction of counterflow flames in diluted methane–oxygen mixtures in a closed reactor

The features of the interaction of counterflow flames in diluted methane–oxygen mixtures at a total pressure of up to 200 Torr in a closed reactor were established. It was found that in the mode of interaction of flames propagating in hot reaction products, two-dimensional flame vortices arise due to density stratification; flames, propagating through the initial mixture, interact with the formation of only three-dimensional structures.

On the Nature of the Nonmonotonic Dependence of the Pressure Flame Limits on Temperature CH<sub>4 </sub>+ 2O<sub>2 </sub>Mixtures

In the present work, for the first time for stoichiometric methane–oxygen mixtures, two numerical kinetic methods reproduce the nonmonotonic boundary of the “three pressure limits” region obtained by N.N. Semenov’ coworkers experimentally in a wide pressure range ~20–600 Torr. In where take place the llow pressure ignition peninsula, range of parameters, the simulation of self-ignition delays was carried out. In this case, a nonlinear scheme of methane oxidation (150 reactions) was used to calculate ignition delays. According to the linear part of the same scheme (~20 reactions of the methyl peroxide cycle), formulas for the corresponding Jacobi matrix determinant were obtained for the first time, and for each given temperature, from the equation that determines its zero, three pressure roots were found, from which the boundary line of the region, nonmonotonic in pressure, was constructed self-ignition. Satisfactory convergence of the experimental and calculated data is shown both in terms of delay times and in terms of the position of the limits in the P–T space.

In Situ Propellant Alternatives for a Lunar Ascent/Descent Vehicle

Recently, NASA has pushed for returning humans to the moon sustainably with in situ resource utilization as the central focus. The moon has an abundance of water that is proposed to be electrolyzed into hydrogen and oxygen to be used as propellant. Other volatiles such as ammonia, carbon dioxide, and methane are also present. A mission architecture for a lunar ascent/descent vehicle (LADV) from the Polytechnic University of Turin and nuclear thermal propulsion (NTP) engine models from the University of Alabama in Huntsville were used to compare in-situ-derived propellants for a LADV. This study considered a LADV originating from the lunar surface, delivering a payload in the lunar distant retrograde orbit, and returning to the lunar surface for retanking. This research analyzed the impacts on this mission of using hydrogen NTP, water/ammonia NTP, liquid-oxygen augmented nuclear thermal rocket, and Aeon 1 methane–oxygen engines using the selected architecture and tools. The results were compared to the reference hydrogen–oxygen RL10 engine. The propulsion system comparison analysis showed that combustion engines will offer better overall performance than NTP-based engines due to a 50% decrease in propellant volume, a 20% decrease in dry mass, and a lower propellant mass than the water and ammonia NTP systems. Both the hydrogen–oxygen and methane–oxygen propulsion systems will have similar propellant masses when compared to other systems. This is due to the order of magnitude higher mass of the NTP engines, with the highest mass contribution coming from the reactor. However, both water and ammonia alternative propellant NTP engines can still be viable candidates for the usage of these minimally processed propellants to satisfy this mission.

Phase diagram to demarcate supercritical, transcritical, and continuous phase regimes for binary fluid equilibrium mixing relevant to combustion applications

A robust methodology to develop phase diagrams of binary fluid mixtures at fixed thermodynamic conditions (pressure, temperature, and mole fraction) as well as of two initially separated fluids undergoing mixing near critical conditions are presented for fluids and conditions relevant to rockets, gas turbines, and diesel engine applications. Phase equilibria of mixtures are first examined to provide insight into the continuous-phase mixing behavior (including but not limited to supercritical behavior), and to develop a broadly applicable phase-diagram for binary fluid mixtures at fixed conditions. Next, adiabatic mixing theory and reduced Helmholtz equations of state are used to predict the thermodynamic conditions required to attain continuous-phase binary fluid mixing near critical conditions. Then, a 3D surface diagram (P, Tfuel, Tamb) separating single and two-phase regions is constructed by varying the ambient pressure and the initial temperatures of the two fluids. Polynomial fits of the 3D surfaces for 10 different binary mixtures are tabulated for nitrogen–alkane and methane–oxygen blends relevant to air-breathing and propellant based engines, respectively.

From Fossil‐Fueled to Hydrogen‐Fueled Annealing Furnaces: Effects on the Oxidation of Stainless Steels

The possibility of replacing methane with hydrogen as the fuel gas in an annealing furnace is studied regarding the oxidation of ferritic AISI 441 and austenitic AISI 304 stainless steels during simulated short‐term annealing. Oxide‐scale formation using the simulated atmospheres based on methane–air, methane–oxygen, and hydrogen–oxygen combustions with different oxidant gas excesses is compared at steel grades’ furnace temperature ranges in an annealing process. Thermogravimetry is used to determine variations of weight gain during oxidation, and field‐emission scanning electron microscopy and glow discharge optical emission spectroscopy are used to characterize oxide scales. The transition to H2 as the fuel gas is more suitable for the ferritic grade than the austenitic grade at the studied temperatures. High water vapor content in hydrogen– and methane–oxygen combustion atmospheres promotes breakaway oxidation for both steel grades. Nodule formation is significantly observed under the most demanding annealing conditions for the ferritic grade, while only the lightest conditions remain without the signs of breakaway oxidation for the austenitic grade. Changes in the oxide‐scale structures produced in both hydrogen–oxygen and methane–oxygen atmospheres are in significant, which can facilitate the exchanges between these atmospheres in relation to methane–air combustion.

Experimental research on the performance of hollow and annular rotating detonation engines with nozzles

• The performance of hollow and annular RDEs with nozzles are compared. • The hollow RDE can reduce the injection pressure loss. • The hollow chamber brings a higher performance loss. Rotating detonation engines (RDEs), which are hoped to achieve significant performance improvements in propulsion systems, have received much attention in recent years. The annular RDE and hollow RDE are two of the major configurations of which the structure is very similar to each other. However, there has been a lack of experimental research discussing the differences in their performance. In the present study, experiments on hollow and annular RDEs are conducted. Four configurations in total are tested at ambient conditions: hollow and annular combustion chambers with two exit throat areas. The gaseous methane and gaseous oxygen are used as propellants. The results reveal that the c*-efficiency of the two hollow combustion chamber configurations is on average 0.7 and 0.79, which is lower than the 0.75 and 0.84 of annular chambers. However, it is exhibited that the hollow RDE can ensure high detonation efficiency at a lower injection pressure ratio. From this perspective, the hollow RDE can be considered a more promising configuration for practical application because it provides a new approach to reducing injection pressure loss. In addition, the analysis of nozzle indicates that the Laval nozzles overperform the aerospike nozzles, which goes against previous studies. The mechanism that accounts for this phenomenon needs further investigation.

Partial oxidation of methane enabling complete coking resistance of Ni-YSZ anode supported solid oxide fuel cells

• Partial oxidation of methane ensures complete coking resistance of Ni-YSZ. • Small decrease in cell performance can be observed with the oxygen content increasing. • Enhanced carbon activity is attributed to the partial oxidation of methane. • Incorporating partial oxidation and electrochemical oxidation is an effective approach. The utilization of natural gas as fuel for Ni-YSZ anode supported solid oxide fuel cells (SOFCs) is a most promising method to accelerate the commercialization process. However, the state-of-art Ni-based anode is sensitive to the natural gas, leading to the carbon formation and cell degradation. Herein, a catalytic partial oxidation approach is proposed by introducing different amounts of oxygen in methane for improving the coking resistance of Ni-based anode. The carbon activity is reduced from 400 to 0.4 when using 15%CH 4 -5%O 2 as fuel, and the electrochemical performance is only decreased by 10 %. Considering the working condition of SOFCs, a complete coking resistance of SOFC can be obtained by introducing only 1.25% O 2 at 0.59 V. This indicates that introducing a small amount of oxygen in methane is beneficial for improving coking resistance of SOFC under working condition.

Turbulent combustion statistics in a diffusion flame for space propulsion applications

The usage of direct numerical simulations for research of turbulent combustion for space propulsion applications is explored. With this goal in mind, the combustion near the injection of a fuel-rich methane–oxygen flame at 20 bar is simulated using a massively parallelized solver. The statistical properties of the relevant physical fields are examined to study interactions between turbulence and combustion. This analysis is complemented by an investigation and quantification of the error sources in direct numerical simulations of turbulent diffusion flame. A method to estimate the statistical error is derived based on the classical inference theory. In addition, critical resolution criteria are discussed using a mesh sensitivity analysis.

On the role of transverse detonation waves in the re-establishment of attenuated detonations in methane–oxygen

This investigation concerns the problem of detonation attenuation in stoichiometric methane-oxygen and its re-establishment following its interaction with obstacles, using high resolution numerical simulation. The main focus was on the role of the transverse detonation on the re-establishment of the detonation wave, and the importance of applying a numerical combustion model that responds appropriately to the thermodynamic state behind the complex shock wave dynamics. We applied an efficient thermochemically derived four-step global combustion model using an Euler simulation framework to investigate the critical regimes present. While past attempts at using one- or two- step models have failed to capture transverse detonations, for this scenario, our simulations have demonstrated that the four-step combustion model is able to capture this feature. We thus suggest that to correctly model detonation re-initiation in characteristically unstable mixtures, an applied combustion model should contain at least an adequate description to permit the correct ignition and state variable response when changes in temperature and pressure occur, i.e., behind shocks. Our simulations reveal that (1) there is a relationship between the critical outcomes possible and the mixture cell size, and (2) while pockets of unburned gas may exist when a detonation re-initiates, it is not the direct rapid consumption of these pockets that gives rise to transverse detonations. Instead, the transverse detonations are initiated through pressure amplification of reaction zones at burned/unburned gas interfaces whose combustion rates have been enhanced through Richtmyer–Meshkov instabilities associated with the passing of transverse shock waves, or by spontaneous ignition of hot spots, which can form into detonations through the Zeldovich gradient mechanism. In both situations, non-uniform ignition delay times are found to play a role. Finally, we found that the transverse detonations are in fact Chapman–Jouguet detonations, but whose presence contributes to overdriving the re-initiated detonation along the Mach stem.

Numerical Analysis of Wave Characteristics in a Methane-Oxygen Rotating Detonation Engine

Results from the simulation of the U.S. Air Force Research Laboratory methane–oxygen rotating detonation rocket engine from four independent research groups with different flow solvers underpredicted primary detonation wave speeds by a significant margin as compared to experimental values. In a simulation performed by the authors, the average calculated speed of the detonation waves was roughly as compared to the experimentally measured value of . This paper presents a detailed analysis of the wave characteristics in this simulation to provide a more quantitative understanding of the underlying factors leading to this discrepancy. The results show that weaker counter-rotating shock waves have a significant impact on the behavior of the primary detonation waves. The wave speed of the primary detonation wave is reduced by due to collisions with the counter-rotating waves. The presence of these counter-rotating waves also has a strong influence on the flow conditions upstream of the primary detonation waves, as well as the engine heat release rate. In addition, the flow properties upstream of the detonation wave vary significantly in the radial direction. Finally, the subfilter turbulent viscosity is shown to vary radially and with proximity to detonation waves.

On Ozone Addition in Ignition and Explosion Characteristics of Methane–Oxygen Mixtures

On Ozone Addition in Ignition and Explosion Characteristics of Methane–Oxygen Mixtures

Comparative study on the onset of detonation in methane–oxygen mixtures: initiation in a smooth tube and re-initiation downstreamof a single orifice plate

Comparative study on the onset of detonation in methane–oxygen mixtures: initiation in a smooth tube and re-initiation downstreamof a single orifice plate

Experimental validation of multiphysics model simulations of the thermal response of a cement clinker rotary kiln at laboratory scale

AbstractAn increasing demand for buildings, transportation systems and civil infrastructure development has driven expansion of cement consumption world‐wide, producing a significant increase in related global energy demand. With approximately 7% of the world‐wide industrial energy consumption (10.7 exajoules [EJ]), the cement industry is the third most energy intensive industrial processes and a key component for concrete, the most consumed composite material in the global construction industry. In cement manufacturing, the cement kiln accounts for most of the energy consumption in the production process. As the heart of a cement plant, the cement kiln is where the kiln feed primarily containing calcium oxide (CaO), silica (SiO2), alumina (Al2O3), and iron (Fe2O3) are thermally and chemically transformed into clinker minerals. The presented work developed a multiphysics model, designed and built a laboratory‐scale rotary cement clinker kiln, and produced cement clinker at laboratory‐scale. The model was developed to study the interaction between the various thermal, fluid dynamic and chemical interactions involved in the sintering process used to form Portland cement clinker in an effort to reduce energy use. The analytical model was validated through experimental testing using a unique laboratory‐scale rotary cement kiln developed during the investigation. Also demonstrated was the feasibility of producing clinker at laboratory scale. This modeling and lab scale tests were designed to better understand the clinker sintering process so that operational and quality decisions can be made to optimize energy consumption without compromising cement clinker quality. The computational fluid dynamics modeling was developed in COMSOL Multiphysics 6.0. The characteristics of the combustion fluid flow, concentration of species, temperature and heat transfer were studied for a turbulent flow of methane (CH4) gas and oxygen (O2). Theory suggests that heat transfer impacts the cement production process but the multiphysics model more accurately describes the convection, conduction, and radiant heat transfer in the kilning process and thus allows for a better understanding of the energy exchange driving the chemical reactions that produce Portland cement. Clinker minerals were formed because of appropriate burning conditions implemented during experimental model validation.

Exploring the connection of physical habitat health of the wetland with its gas regulating services

Many scholars assessed habitat health and measured gas regulation service of wetlands separately. However, no such targeted work was done to answer how habitat health can control gas regulation? Therefore, the present study investigated the role of habitat health on the gas regulation service of wetlands. Multi-parametric Machine Learning (ML) based modelling approach was applied to assess habitat health considering physical wetland hydrological factors and habitat degrading factors. Three primary atmospheric gas regulation functions of wetland, namely Methane (CH4) emission, Carbon (C) sequestration, and Oxygen (O2) release, were observed associating with habitat health. Very poor habitat health prevailed over 227 km2 of wetland, whereas very good habitat health covered 299 km2 of wetland. But out of the very good habitat health zone, 69% belonged to the perennial river of this region. On the other hand, it was estimated that the amount of annual CH4 emission, C sequestration, and O2 release from the wetlands of this region were respectively 8.01 × 1000 tons, 908.98 × 1000 tons and 664.51 × 1000 tons. The association of habitat health was positive with CH4 emission and negative with C sequestration and O2 release. Following the association, habitat health zone-wise variation of emission, sequestration, and release was also very prominent. The very good zone of habitat health was observed to have 60% higher CH4 average emission and 56% lesser C sequestration than very poor habitat health.

Thermodynamic modeling of in-situ rocket propellant fabrication on Mars

SummaryIn-situ resource utilization (ISRU) to refuel rockets on Mars will become critical in the future. The current effort presents a thorough feasibility analysis of a scalable, Matlab-based, integrated ISRU framework from the standpoint of the second law of thermodynamics. The ISRU model is based on existing technology that can utilize Martian resources (regolith and atmosphere) to produce rocket propellants. Model simulations show that the system analysis is theoretically consistent with a positive entropy generation, and the achievable mass flow rates of liquid methane and liquid oxygen can potentially meet the 16-month rocket refueling deadline (on Mars) as desired by the National Aeronautics and Space Administration. However, the model is sensitive to liquid oxygen storage temperatures, and lower temperatures are necessary to minimize compressor work. This proof-of-concept model can open avenues for further experimental evaluation of the system to achieve a higher technology readiness level.

Combustion Simulation of 82-Injector Rocket Engine

A computational study of the nonlinear rocket-engine combustion instability is presented for an engine with 82 coaxial methane–oxygen injector ports, a choked nozzle, and a combustion chamber that models a Rocketdyne experiment. Computations use a three-dimensional unsteady shear-stress transport delayed detached-eddy simulation method. Four different one-step chemical kinetic rates are simulated on the resolved scale to determine the effect of the burning rate. Application of kinetic rates on the resolved scale give faster rates than expected with turbulent combustion where the final mixing and chemical reaction in the cascade occurs on the smallest scales; thus, reduction of the kinetic rate is examined here. When the normalized kinetic rate is 1, implying the nominal Westbrook–Dryer rate, only the longitudinal-mode instability is observed. As the kinetic rate decreases, less of the combustion occurs upstream near the longitudinal-mode pressure antinode, the longitudinal-mode instability becomes weak, and the first-tangential-mode instability emerges, which fits better with experiment. The proximity of the domain of major heat release to the longitudinal mode pressure antinode is found to be critical. Evidence is presented for the need for an improved combustion model that will provide a more accurate and lower burning rate.

Effects of a significant boundary layer on the flame acceleration and transition to detonation in millimeter-scale tubes

Experiments using three different mixtures (ethylene–oxygen, methane–oxygen, and acetylene–oxygen–argon) and four different tube diameters (0.5, 1, 2, and 4 mm) were carried out to investigate the entire process of flame propagation in narrow tubes. Flame propagation in the four sizes of tubes was recorded synchronously by a high-speed camera. The results show that the deflagration-to-detonation transition (DDT) process goes through four stages according to velocity evolution, in the sequence of (i) exponential acceleration, (ii) “hesitation” period, (iii) linear acceleration, and (iv) velocity jump. The DDT run-up distance decreases with decreasing tube diameter, which arises from the effect of the significant boundary layer during flame acceleration. The area divergence is introduced by analyzing how tube diameter and initial pressure affect the DDT run-up distance. The critical value of 0.1 for the area divergence can be used to distinguish the variation characteristics of the normalized DDT run-up distance between millimeter-scale tubes and the large tubes (centimeter-scale). Moreover, an empirical formula with a unified form is obtained, which describes the DDT run-up distance as a function of tube diameter and initial pressure. It allows a good prediction of the experimental results regardless of the tube size as well as the type of mixture.

Analysis of turbulence generation and dissipation in shear layers of methane–oxygen diffusion flames using direct numerical simulations

A turbulent methane–oxygen diffusion flame is studied using a direct numerical simulation setup. The operating regime and turbulence characteristics are chosen to resemble those of a modern methane rocket combustor. Local flame characteristics and dimensionless numbers are defined and evaluated, and their relationship with the turbulent kinetic energy transport budget is studied. Positive net turbulence generation is observed in the reaction shear layer. It is found that the underlying mechanisms for these results are similar to those encountered in premixed flames, with pressure terms acting as the primary turbulent kinetic energy sources. Models for predicting turbulent transport through mean pressure gradients, fluctuating pressure gradients, and turbulent flux of turbulent kinetic energy are adapted. The accuracy of the proposed formulations is assessed, and the involved challenges are discussed.

The influence of bio-plastics for food packaging on combined anaerobic digestion and composting treatment of organic municipal waste

The use of bio-plastic-based packaging as an alternative to conventional plastic packaging is increasing. Among the plethora of different bio-based plastics, the most relevant ones are those that, at the end of their life, can be treated with the organic fraction of municipal solid waste. Even in these cases, their impact on the waste processing and recycling is not always positive. This study aim to assess on a laboratory scale the influence on combined anaerobic digestion and composting industrial processes of a bio-based plastic film, namely cellulose acetate (CA), in pure and modified (additions of additive) forms. CA films were mixed with organic waste and subjected to: (i) anaerobic digestion; (ii) active composting and (iii) two stages of curing composting. Anaerobic digestion and composting were monitored through methane yield and oxygen uptake respectively; additionally, the bio-plastics degree of disintegration was assessed during all the processes. The final disintegration of pure and modified CA was 73.82% and 54.66%, respectively. Anaerobic digestion contributes to the disintegration of the material, while aerobic treatment appears to be nearly ineffective, especially for modified CA. The presence of cellulose acetate during anaerobic digestion of food waste increased the methane yield by about 4.5%. Bioassay confirmed the absence of possible toxic effects on the final compost from the bio-plastic treatment. Although bio-based materials are not the only solution to plastic pollution, the findings confirm the need to upgrade the organic waste treatment plants and the necessity to revise the requirements for the use of compost in agriculture.