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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Measurement and modeling of methane diffusion in hydrocarbon mixtures

Methane (CH 4 ) dissolution and diffusive mass transfer in liquid hydrocarbon mixtures is of key interest in the context of enhanced oil recovery from tight shales. In this paper, we have studied CH 4 dissolution and diffusion in normal alkane mixtures at a temperature of 50 ⁰C and at pressures of ~8 MPa. For the measurement of CH 4 dissolution/diffusion in bulk liquid hydrocarbon mixtures, we have utilized a high pressure and temperature, constant-volume diffusion (CV-D) setup. Here, we have studied CH 4 diffusion in mixtures with three long-chain normal alkanes: decane (C 10 ), dodecane (C 12 ) and hexadecane (C 16 ). We have measured CH 4 solubility and diffusion in its binary mixtures with each of these three normal alkanes, as well as in ternary and quaternary mixtures. During the experiments, the swelling of the liquid mixture due to CH 4 dissolution was measured in situ via a cathetometer and was subsequently integrated into the data analysis. A key conclusion from this study is that the solubility and transport properties of the multicomponent mixtures can be predicted accurately from binary mixture measurements using an appropriate Equation of State (EOS) and Wilke’s simplification of the classical Maxwell-Stefan (MS) diffusion theory. This observation can facilitate accurate prediction of diffusive mass transfer in more complex liquid hydrocarbon mixtures.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Low diffusive methane emissions from the main channel of a large Amazonian run-of-the-river reservoir attributed to high methane oxidation

The global development of hydropower dams has rapidly expanded over the last several decades and has spread to historically non-impounded systems such as the Amazon River's main low land tributaries in Brazil. Despite the recognized significance of reservoirs to the global methane (CH4) emission, the processes controlling this emission remain poorly understood, especially in Tropical reservoirs. Here we evaluate CH4 dynamics in the main channel and downstream of the Santo Antônio hydroelectric reservoir, a large tropical run-of-the-river (ROR) reservoir in Amazonia. This study is intended to give a snapshot of the CH4 dynamics during the falling water season at the initial stage after the start of operations. Our results show substantial and higher CH4 production in reservoirs' littoral sediment than in the naturally flooded areas downstream of the dam. Despite the large production in the reservoir or naturally flooded areas, high CH4 oxidation in the main channel keep the concentration and fluxes of CH4 in the main channel low. Similar CH4 concentrations in the reservoir and downstream close to the dam suggest negligible degassing at the dam, but stable isotopic evidence indicates the presence of a less oxidized pool of CH4 after the dam. ROR reservoirs are designed to disturb the natural river flow dynamics less than traditional reservoirs. If enough mixing and oxygenation remain throughout the reservoir's water column, naturally high CH4 oxidation rates can also remain and limit the diffusive CH4 emissions from the main channel. Nevertheless, it is important to highlight that our results focused on emissions in the deep and oxygenated main channel. High emissions, mainly through ebullition, may occur in the vast and shallow areas represented by bays and tributaries. However, detailed assessments are still required to understand the impacts of this reservoir on the annual emissions of CH4.

Amazon, aquatic, biogeochemistry, carbon cycling, ↗
NASA NTRS1977

High pressure flame system for pollution studies with results for methane-air diffusion flames

A high pressure flame system was designed and constructed for studying nitrogen oxide formation in fuel air combustion. Its advantages and limitations were demonstrated by tests with a confined laminar methane air diffusion flame over the pressure range from 1 to 50 atm. The methane issued from a 3.06 mm diameter port concentrically into a stream of air contained within a 20.5 mm diameter chimney. As the combustion pressure is increased, the flame changes in shape from wide and convex to slender and concave, and there is a marked increase in the amount of luminous carbon. The height of the flame changes only moderately with pressure.

Miller, I. M.↗
NASA NTRS1996

Regulation of Methane Oxidation in a Freshwater Wetland by Water Table Changes and Anoxia

The effects of water table fluctuations and anoxia on methane emission and methane oxidation were studied in a freshwater marsh. Seasonal aerobic methane oxidation rates varied between 15% and 76% of the potential diffusive methane flux (diffusive flux in the absence of aerobic oxidation). On an annual basis, approximately 43% of the methane diffusing into the oxic zone was oxidized before reaching the atmosphere. The highest methane oxidation was observed when the water table was below the peat surface. This was confirmed in laboratory experiments where short-term decreases in water table levels increased methane oxidation but also net methane emission. Although methane emission was generally not observed during the winter, stems of soft rush (Juncus effusus) emitted methane when the marsh was ice covered. Indigenous methanotrophic bacteria from the wetiand studied were relatively anoxia tolerant. Surface peat incubated under anoxic conditions maintained 30% of the initial methane oxidation capacity after 32 days of anoxia. Methanotrophs from anoxic peat initiated aerobic methane oxidation relatively quickly after oxygen addition (1-7 hours). These results were supported by culture experiments with the methanotroph Methylosinus trichosporium OB3b. This organism maintained a greater capacity for aerobic methane oxidation when starved under anoxic compared to oxic conditions. Anoxic incubation of M. trichosporium OB3b in the presence of sulfide (2 mM) and a low redox potential (-110 mV) did not decrease the capacity for methane oxidation relative to anoxic cultures incubated without sulfide. The results suggest that aerobic methane oxidation was a major regulator of seasonal methane emission front the investigated wetland. The observed water table fluctuations affected net methane oxidation presumably due to associated changes in oxygen gradients. However, changes from oxic to anoxic conditions in situ had relatively little effect on survival of the methanotrophic bacteria and thus on methane oxidation potential per se.

Roslev, Peter↗
DOE OSTI2021

Three-Dimensional Free Gas Flow Focuses Basin-Wide Microbial Methane to Concentrated Methane Hydrate Reservoirs in Geological System

Here, we present a systematic model that links the generation, migration, phase partitioning, and accumulation of methane into a closed loop as the sediment is deposited from the seafloor and buried through the base of hydrate stability zone (BHSZ). In our model, methane is generated by biodegradation of organic carbon in muds. Hydrate does not form and methane is not trapped until a coarse-grained layer is deposited, because the small pores prevent hydrate formation in muds. Instead, methane diffuses into sands/silts where methane solidifies into hydrate. As hydrate-bearing sands/silts pass through the BHSZ during sediment burial, methane hydrate dissociates, and releases free gas. The released and the newly generated free gas below the BHSZ concentrates into a vertical/dipping zone with low capillary entry pressure and high permeability and flows upward driven its buoyancy. When free gas reaches the hydrate stability zone (HSZ), capillary forces drive free gas to flow laterally, preferentially enter sands/silts, feed hydrate growth, and elevate hydrate saturation. With three-dimensional focused free gas flow, microbial methane that is generated from a much larger fetch area of the entire basin, both above and below the BHSZ, is concentrated into coarse-grained layers at structural closures for hydrate formation. Our model illustrates how geological evolution, microbial methane generation, and gas flow by buoyancy couple to generate concentrated hydrate deposits in geological system. These insights can be used to explore for high-concentration methane hydrate and are important for understanding the methane budget and carbon cycle under the seafloor.

58 GEOSCIENCES↗
NASA NTRS1996

In Situ Analyses of Methane Oxidation Associated with the Roots and Rhizomes of a Bur Reed, Sparganium Eurycarpum, in a Maine Wetland

Methane oxidation associated with the belowground tissues of a common aquatic macrophyte, the burweed Sparganium euryearpum, was assayed in situ by a chamber technique with acetylene or methyl fluoride as a methanotrophic inhibitor at a headspace concentration of 3 to 4%. Acetylene and methyl fluoride inhibited both methane oxidation and peat methanogenesis. However, inhibition of methanogenesis resulted in no obvious short-term effect on methane fluxes. Since neither inhibitor adversely affected plant metabolism and both inhibited methanotrophy equally well, acetylene was employed for routine assays because of its low cost and ease of use. Root-associated methanotrophy consumed a variable but significant fraction of the total potential methane flux; values varied between 1 and 58% (mean +/- standard deviation, 27.0% +/- 6.0%), with no consistent temporal or spatial pattern during late summer. The absolute amount of methane oxidized was not correlated with the total potential methane flux; this suggested that parameters other than methane availability (e.g., oxygen availability) controlled the rates of methane oxidation. Estimates of diffusive methane flux and oxidation at the peat surface indicated that methane emission occurred primarily through aboveground plant tissues; the absolute magnitude of methane oxidation was also greater in association with roots than at the peat surface. However, the relative extent of oxidation was greater at the latter locus.

King, Gary M.↗
NASA NTRS1993

Comparison of Numerical Model Results with Diffusion Flames in Microgravity

The effects of gravity on methane diffusion flames were studied using a finite difference numerical model. Variables under consideration included velocity, pressure, temperature, enthalpy, reactive species, and inert carrier gas. Results obtained showed that flames in zero gravity were wider and taller than those in normal gravity. The use of a six reaction scheme produced similar predictions of flame width and height compared to those of the single reaction case. The numerical models predicted a considerable difference in the flame base region between normal gravity and low gravity. This region is considered to be beyond the boundaries of current analytical models.

Hyer, Paul V.↗
DOE OSTI2023

Effects of MOF linker rotation and functionalization on methane uptake and diffusion

The flexible degrees of freedom in metal–organic frameworks (MOFs) can have significant effects on guest molecule behavior. However, in the majority of studies applying molecular simulations to MOFs, the framework is assumed to be rigid in order to minimize computational cost. Here, in this work, we assess the significance of this assumption on a representative example of methane uptake and diffusion in UiO-66. We introduce an open-source code to modify MOFs through functionalization and linker rotation and we perform Grand Canonical Monte Carlo and molecular dynamics simulations of methane in each of the functionalized and linker-rotated derivatives of UiO-66. We find that linker rotation moderately influences methane uptake and significantly influences methane diffusion. Our assessment provides ranges of property values that serve as measures of uncertainty of these two properties associated with linker rotation. We further determine that void volume fraction and minimum pore size are the features that govern methane uptake and diffusion, respectively. These findings illustrate the impact of linker rotation on MOFs and provide design principles to guide future investigations.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Cryptic Methane-Cycling by Methanogens During Multi-Year Incubation of Estuarine Sediment

As marine sediments are buried, microbial communities transition from sulfate-reduction to methane-production after sulfate is depleted. When this biogenic methane diffuses into the overlying sulfate-rich sediments, it forms a sulfate-methane transition zone (SMTZ) because sulfate reducers deplete hydrogen concentrations and make hydrogenotrophic methanogenesis exergonic in the reverse direction, a process called the anaerobic oxidation of methane (AOM). Microbial participation in these processes is often inferred from geochemistry, genes, and gene expression changes with sediment depth, using sedimentation rates to convert depth to time. Less is known about how natural sediments transition through these geochemical states transition in real-time. We examined 16S rRNA gene amplicon libraries and metatranscriptomes in microcosms of anoxic sediment from the White Oak River estuary, NC, with three destructively sampled replicates with methane added (586-day incubations) and three re-sampled un-amended replicates (895-day incubations). Sulfate dropped to a low value (∼0.3 mM) on similar days for both experiments (312 and 320 days, respectively), followed by a peak in hydrogen, intermittent increases in methane-cycling archaea starting on days 375 and 362 (mostly Methanolinea spp. and Methanosaeta spp., and Methanococcoides sp. ANME-3), and a methane peak 1 month later. However, methane δ 13 C values only show net methanogenesis 6 months after methane-cycling archaea increase and 4 months after the methane peak, when sulfate is consistently below 0.1 mM and hydrogen increases to a stable 0.61 ± 0.13 nM (days 553–586, n = 9). Sulfate-reducing bacteria (mostly Desulfatiglans spp. and Desulfosarcina sp. SEEP-SRB1) increase in relative abundance only during this period of net methane production, suggesting syntrophy with methanogens in the absence of sulfate. The transition from sulfate reduction to methane production in marine sediments occurs through a prolonged period of methane-cycling by methanogens at low sulfate concentrations, and steady growth of sulfate reducers along with methanogens after sulfate is depleted.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS1992

Carbon and hydrogen isotopic characterization of methane from wetlands and lakes of the Yukon-Kuskokwim Delta, Western Alaska

The results are reported of a study of the carbon and hydrogen isotopic composition of methane from tundra environments of the Yukon-Kuskokwin Delta of western Alaska. The delta C-13 value of diffusive methane emissions from wet meadow tundra of the Delta is -65.82 +/- 2.21 per mil (n=18). Detritus-rich sediments of tundra lakes are loaded with methane-rich gas bubbles during the warm season. Spatial trend is the major gas concentration and isotopic values of methane in these gas bubbles appear to reflect processes associated with production rate and mechanisms; high methane concentrations, lightest delta C-13 values, the heaviest delta D value occur in detritus-rich sediments isolated from emergent vegetation. Heavier delta C-13 and lighter delta D values in methane from heavily vegetated lake margins suggest a shift toward a larger role for acetate fermentation in association with aquatic plants and plant detritus. Bubble ebullition is estimated to account for up to 17 percent of total Delta methane emissions.

Martens, Christopher S.↗
NASA NTRS1991

Infrared radiation parameterizations in numerical climate models

This study presents various approaches to parameterizing the broadband transmission functions for utilization in numerical climate models. One-parameter scaling is applied to approximate a nonhomogeneous path with an equivalent homogeneous path, and the diffuse transmittances are either interpolated from precomputed tables or fit by analytical functions. Two-parameter scaling is applied to parameterizing the carbon dioxide and ozone transmission functions in both the lower and middle atmosphere. Parameterizations are given for the nitrous oxide and methane diffuse transmission functions.

Chou, Ming-Dah↗
NASA NTRS1994

Observations of Methane and Ethylene Diffusion Flames Stabilized Around a Blowing Porous Sphere Under Microgravity Conditions

This paper presents the experimental and theoretical results for expanding methane and ethylene diffusion flames in microgravity. A small porous sphere made from a low-density and low-heat-capacity insulating material was used to uniformly supply fuel at a constant rate to the expanding diffusion flame. A theoretical model which includes soot and gas radiation is formulated but only the problem pertaining to the transient expansion of the flame is solved by assuming constant pressure infinitely fast one-step ideal gas reaction and unity Lewis number. This is a first step toward quantifying the effect of soot and gas radiation on these flames. The theoretically calculated expansion rate is in good agreement with the experimental results. Both experimental and theoretical results show that as the flame radius increases, the flame expansion process becomes diffusion controlled and the flame radius grows as gamma t. Theoretical calculations also show that for a constant fuel mass injection rate a quasi-steady state is developed in the region surrounded by the flame and the mass flow rate at any location inside this region equals the mass injection rate.

Atreya, Arvind↗
NASA NTRS1997

Shapes of Buoyant and Nonbuoyant Methane Laminar Jet Diffusion Flames

Laminar gas jet diffusion flames represent a fundamental combustion configuration. Their study has contributed to numerous advances in combustion, including the development of analytical and computational combustion tools. Laminar jet flames are pertinent also to turbulent flames by use of the laminar flamelet concept. Investigations into the shapes of noncoflowing microgravity laminar jet diffusion flames have primarily been pursued in the NASA Lewis 2.2-second drop tower, by Cochran and coworkers and by Bahadori and coworkers. These studies were generally conducted at atmospheric pressure; they involved soot-containing flames and reported luminosity lengths and widths instead of the flame-sheet dimensions which are of Greater value to theory evaluation and development. The seminal model of laminar diffusion flames is that of Burke and Schumann, who solved the conservation of momentum equation for a jet flame in a coflowing ambient by assuming the velocity of fuel, oxidizer and products to be constant throughout. Roper and coworkers improved upon this model by allowing for axial variations of velocity and found flame shape to be independent of coflow velocity. Roper's suggestion that flame height should be independent of gravity level is not supported by past or present observations. Other models have been presented by Klajn and Oppenheim, Markstein and De Ris, Villermaux and Durox, and Li et al. The common result of all these models (except in the buoyant regime) is that flame height is proportional to fuel mass flowrate, with flame width proving much more difficult to predict. Most existing flame models have been compared with shapes of flames containing soot, which is known to obscure the weak blue emission of flame sheets. The present work involves measurements of laminar gas jet diffusion flame shapes. Flame images have been obtained for buoyant and nonbuoyant methane flames burning in quiescent air at various fuel flow-rates, burner diameters and ambient pressures. Soot concentrations were minimized by selecting conditions at low flowrates and low ambient pressures; this allows identification of actual flame sheets associated with blue emissions of CH and CO2. The present modeling effort follows that of Roper and is useful in explaining many of the trends observed.

Sunderland, Peter B.↗
NASA NTRS1987

A theoretical analysis of the extinction limits of a methane-air opposed-jet diffusion flame

A theoretical analysis is described for a methane-air diffusion flame stabilized in the forward stagnation region of a porous metal cylinder in a forced convective flow. The analysis includes effects of radiative heat loss from the porous metal surface and finite rate kinetics but neglects the effects of gravity. The theoretically predicted extinction limits compare well with experimentally observed extinction limits from the literature. After the predicted limits compared well with the experimental limits, a parametric study of the effect of fuel surface emissivity and Lewis number was conducted with the numerical model. It was found that the computed blowoff limit is independent of radiative heat loss for high fuel blowing velocities but is a strong function of Lewis number. At low fuel blowing velocities, the extinction limit varies with both radiative heat loss and Lewis number. It is discovered, however, that even if thermal losses from the fuel surface are absent, the flame can extinguish at the fuel surface independently of Lewis number due to excessive reaction zone thinning.

Olson, S. L.↗
NASA NTRS2015

A Numerical and Experimental Study of Coflow Laminar Diffusion Flames: Effects of Gravity and Inlet Velocity

In this work, the influence of gravity, fuel dilution, and inlet velocity on the structure, stabilization, and sooting behavior of laminar coflow methane-air diffusion flames was investigated both computationally and experimentally. A series of flames measured in the Structure and Liftoff in Combustion Experiment (SLICE) was assessed numerically under microgravity and normal gravity conditions with the fuel stream CH4 mole fraction ranging from 0.4 to 1.0. Computationally, the MC-Smooth vorticity-velocity formulation of the governing equations was employed to describe the reactive gaseous mixture; the soot evolution process was considered as a classical aerosol dynamics problem and was represented by the sectional aerosol equations. Since each flame is axisymmetric, a two-dimensional computational domain was employed, where the grid on the axisymmetric domain was a nonuniform tensor product mesh. The governing equations and boundary conditions were discretized on the mesh by a nine-point finite difference stencil, with the convective terms approximated by a monotonic upwind scheme and all other derivatives approximated by centered differences. The resulting set of fully coupled, strongly nonlinear equations was solved simultaneously using a damped, modified Newton's method and a nested Bi-CGSTAB linear algebra solver. Experimentally, the flame shape, size, lift-off height, and soot temperature were determined by flame emission images recorded by a digital camera, and the soot volume fraction was quantified through an absolute light calibration using a thermocouple. For a broad spectrum of flames in microgravity and normal gravity, the computed and measured flame quantities (e.g., temperature profile, flame shape, lift-off height, and soot volume fraction) were first compared to assess the accuracy of the numerical model. After its validity was established, the influence of gravity, fuel dilution, and inlet velocity on the structure, stabilization, and sooting tendency of laminar coflow methane-air diffusion flames was explored further by examining quantities derived from the computational results.

microgravity↗
NASA NTRS2001

Suppression of Low Strain Rate Nonpremixed Flames by an Agent

The agent concentration required to achieve the suppression of low strain rate nonpremixed flames is an important consideration for fire protection in a microgravity environment such as a space platform. Currently, there is a lack of understanding of the structure and extinction of low strain rate (<20 s(exp -1)) nonpremixed flames. The exception to this statement is the study by Maruta et al., who reported measurements of low strain rate suppression of methane-air diffusion flames with N2 added to the fuel stream under microgravity conditions. They found that the nitrogen concentration required to achieve extinction increased as the strain rate decreased until a critical value was obtained. As the strain rate was further decreased, the required N2 concentration decreased. This phenomenon was termed "turning point" behavior and was attributed to radiation-induced nonpremixed flame extinction. In terms of fire safety, a critical agent concentration assuring suppression under all flow conditions represents a fundamental limit for nonpremixed flames. Counterflow flames are a convenient configuration for control of the flame strain rate. In high and moderately strained near-extinction nonpremixed flames, analysis of flame structure typically neglects radiant energy loss because the flames are nonluminous and the hot gas species are confined to a thin reaction zone. In counterflowing CH4-air flames, for example, radiative heat loss fractions ranging from 1 to 6 percent have been predicted and measured. The objective of this study is to investigate the impact of radiative emission, flame strain, agent addition, and buoyancy on the structure and extinction of low strain rate nonpremixed flames through measurements and comparison with flame simulations. The suppression effectiveness of a number of suppressants (N2, CO2, or CF3Br) was considered as they were added to either the fuel or oxidizer streams of low strain rate methane-air diffusion flames.

Hamins, A.↗