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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Review of the gas breakdown physics and nanomaterial-based ionization gas sensors and their applications

Ionization gas sensors are ubiquitous tools that can monitor desired gases or detect abnormalities in real time to protect the environment of living organisms or to maintain clean and/or safe environment in industries. The sensors’ working principle is based on the fingerprinting of the breakdown voltage of one or more target gases using nanostructured materials. Fundamentally, nanomaterial-based ionization-gas sensors operate within a large framework of gas breakdown physics; signifying that an overall understanding of the gas breakdown mechanism is a crucial factor in the technological development of ionization gas sensors. Moreover, many studies have revealed that physical properties of nanomaterials play decisive roles in the gas breakdown physics and the performance of plasma-based gas sensors. Based on this insight, this review provides a comprehensive description of the foundation of both the gas breakdown physics and the nanomaterial-based ionization-gas-sensor technology, as well as introduces research trends on nanomaterial-based ionization gas sensors. The gas breakdown is reviewed, including the classical Townsend discharge theory and modified Paschen curves; and nanomaterial-based-electrodes proposed to improve the performance of ionization gas sensors are introduced. The secondary electron emission at the electrode surface is the key plasma–surface process that affects the performance of ionization gas sensors. Finally, we present our perspectives on possible future directions.

nanomaterial-based gas breakdown characteristics↗
DOE OSTI2019

The Mechanism of Methane Gas Migration Through the Gas Hydrate Stability Zone: Insights From Numerical Simulations

Free gas migration through the gas hydrate stability zone (GHSZ) and subsequent gas seepage at the seabed are characteristic features in marine gas hydrate provinces worldwide. The biogenic or thermogenic gas is typically transported along faults from deeper sediment strata to the GHSZ. Several mechanisms have been proposed to explain free gas transport through the GHSZ. While inhibition of hydrate formation by elevated salinities and temperatures have been addressed previously in studies simulating unfocused, area-wide upward advection of gas, which is not adequately supported by field observations, the role of focused gas flow through chimney-like structures has been underappreciated in this context. Our simulations suggest that gas migration through the GHSZ is, fundamentally, a result of methane gas supply in excess of its consumption by hydrate formation. The required high gas flux is driven by local overpressure, built up from gas accumulating below the base of the GHSZ that fractures the overburden when exceeding a critical pressure, thereby creating the chimney-like migration pathway. Initially rapid hydrate formation raises the temperature in the chimney structure, thereby facilitating further gas transport through the GHSZ. As a consequence, high hydrate saturations form preferentially close to the seafloor, where temperatures drop to bottom water values, producing a prominent subsurface salinity peak. Over time, hydrates form at a lower rate throughout the chimney structure, while initial temperature elevation and salinity peak dissipate. Thus, our simulations suggest that the near-surface salinity peak and elevated temperatures are a result of transient high-flux gas migration through the GHSZ.

58 GEOSCIENCES↗
DOE OSTI2021

Investigating anode off-gas under spark-ignition combustion for SOFC-ICE hybrid systems

Solid oxide fuel cell – internal combustion engine (SOFC-ICE) hybrid systems are an attractive solution for electricity generation. The system can achieve up to 70% theoretical electric power conversion efficiency through energy cascading enabled by utilizing the anode off-gas from the SOFC as the fuel source for the ICE. Experimental investigations were conducted with a single cylinder Cooperative Fuel Research (CFR) engine by altering fuel-air equivalence ratio (φ), and compression ratio (CR) to study the engine load, combustion characteristics, and emissions levels of dry SOFC anode off-gas consisting of 33.9% H 2 , 15.6% CO, and 50.5% CO 2 . The combustion efficiency of the anode off-gas was directly evaluated by measuring the engine-out CO emissions. The highest net-indicated fuel conversion efficiency of 31.3% occurred at φ = 0.90 and CR = 13:1. These results demonstrate that the anode off-gas can be successfully oxidized using a spark ignition combustion mode. The fuel conversion efficiency of the anode tail gas is expected to further increase in a more modern engine architecture that can achieve increased burn rates in comparison to the CFR engine. NO x emissions from the combustion of anode off-gas were minimal as the cylinder peak temperatures never exceeded 1800 K. This experimental study ultimately demonstrates the viability of an ICE to operate using an anode off-gas, thus creating a complementary role for an ICE to be paired with a SOFC in a hybrid power generation plant.

Engineering↗
DOE OSTI2016

Evaluation of Knock Behavior for Natural Gas - Gasoline Blends in a Light Duty Spark Ignited Engine

The compression ratio is a strong lever to increase the efficiency of an internal combustion engine. However, among others, it is limited by the knock resistance of the fuel used. Natural gas shows a higher knock resistance compared to gasoline, which makes it very attractive for use in internal combustion engines. The current paper describes the knock behavior of two gasoline fuels, and specific incylinder blend ratios with one of the gasoline fuels and natural gas. The engine used for these investigations is a single cylinder research engine for light duty application which is equipped with two separate fuel systems. Both fuels can be used simultaneously which allows for gasoline to be injected into the intake port and natural gas to be injected directly into the cylinder to overcome the power density loss usually connected with port fuel injection of natural gas. Adding natural gas at wide open throttle helps to reduce knock mitigating measures and increases the efficiency and power density compared to the other gasoline type fuels with lower knock resistance. The used methods, knock intensity and number of pressure waves, do not show significant differences in knock behavior for the natural gas - gasoline blends compared to the gasoline type fuels. A knock integral was used to describe the knock onset location of the fuels tested. Two different approaches were used to determine the experimental knock onset and were compared to the knock onset delivered by the knock integral (chemical knock onset). The gasoline type fuels show good agreement between chemical and experimental knock onset. However, the natural gas -gasoline blends show higher discrepancies comparing chemical and experimental knock onset.

Advanced Combustion Concept↗
DOE OSTI2018

Numerical simulations of depressurization-induced gas production from an interbedded turbidite gas hydrate-bearing sedimentary section in the offshore India: Site NGHP-02-16 (Area-B)

The recent National Gas Hydrate Program Expedition 02 (NGHP-02) identified the existence of gas hydrate-bearing sand reservoirs at a number of sites in the offshore of India including Site NGHP-02-16 in Area-B of the Krishna-Godavari Basin. The architecture of that gas hydrate accumulation is characterized by thin, gas hydrate-bearing, high quality sand layers interbedded with mud layers within a turbidite sedimentary interval. The lowest gas hydrate-bearing layer contacting a thinly-interbedded saline aquifer designates the base of the gas hydrate stability zone (BGHSZ). The proximity of the BGHSZ and the average temperature around 20 °C make the reservoir a favorable target for hydrate destabilization by means of the depressurization method. The results of the reservoir simulations indicate high gas production potential from this marine gas hydrate deposit with manageable concomitant water production using a well completion design that hydraulically isolates layers with water-saturated sands. Using a detailed geological input model, the predicted cumulative gas rates reach ~3.1 × 10 4 m 3 /day (~1.1 MMscf/day) after 90 days of continuous depressurization and demonstrate sustained production rates ~3.0 × 10 4 m 3 /day (~1.0 MMscf/day) after 5 years of production. The interbedded nature of this gas hydrate occurrence promotes the development of horizontal dissociation interfaces between gas hydrate-bearing sand and mud layers. As a result, non-uniform gas production along the horizontal interfaces becomes a primary determinant of reservoir performance. Simulation cases have been executed to determine the impact of the uncertainty in in situ reservoir permeability and the manner in which intrinsic permeability dynamically changes during dissociation in response to the imposed effective stress increase. Here, the cases based on low initial effective permeability and high sensitivity of compaction to stress result in the least favorable production predictions.

58 GEOSCIENCES↗
DOE OSTI2013

Life Cycle Water Consumption for Shale Gas and Conventional Natural Gas

Shale gas production represents a large potential source of natural gas for the nation. The scale and rapid growth in shale gas development underscore the need to better understand its environmental implications, including water consumption. This study estimates the water consumed over the life cycle of conventional and shale gas production, accounting for the different stages of production and for flowback water reuse (in the case of shale gas). This study finds that shale gas consumes more water over its life cycle (13–37 L/GJ) than conventional natural gas consumes (9.3–9.6 L/GJ). However, when used as a transportation fuel, shale gas consumes significantly less water than other transportation fuels. When used for electricity generation, the combustion of shale gas adds incrementally to the overall water consumption compared to conventional natural gas. The impact of fuel production, however, is small relative to that of power plant operations. The type of power plant where the natural gas is utilized is far more important than the source of the natural gas.

03 NATURAL GAS↗
DOE OSTI2016

Performance, Efficiency and Emissions Assessment of Natural Gas Direct Injection compared to Gasoline and Natural Gas Port-Fuel Injection in an Automotive Engine

Interest in natural gas as a fuel for light-duty transportation has increased due to its domestic availability and lower cost relative to gasoline. Natural gas, comprised mainly of methane, has a higher knock resistance than gasoline making it advantageous for high load operation. However, the lower flame speeds of natural gas can cause ignitability issues at part-load operation leading to an increase in the initial flame development process. While port-fuel injection of natural gas can lead to a loss in power density due to the displacement of intake air, injecting natural gas directly into the cylinder can reduce such losses. A study was designed and performed to evaluate the potential of natural gas for use as a light-duty fuel. Steady-state baseline tests were performed on a single-cylinder research engine equipped for port-fuel injection of gasoline and natural gas, as well as centrally mounted direct injection of natural gas. Experimental results suggest that similar efficiencies can be achieved in part-load operation for both gasoline and natural gas. While the effects of injection timing are generally minimal for port-fuel injection, varying the injection timing for direct injection, especially after intake valve closure, can speed up the early flame development process by nearly 18°CA. Results at full-load suggest that operation with natural gas regardless of fuel system allows for an efficiency increase. While port-fuel injection of natural gas leads to a power density loss, direct injection of natural gas allows for up to a 10% improvement in full-load power density over liquid and gaseous port-fuel injection for a naturally aspirated engine. In addition to increasing full-load efficiencies, natural gas operation allows for up to a 30% reduction in engine out carbon dioxide emissions at full-load.

Sevik, James M↗
DOE OSTI2014

Modelling the deployment of CO₂ storage in U.S. gas-bearing shales

The proliferation of commercial development in U.S. gas-bearing shales helped to drive a twelve-fold increase in domestic gas production between 2000 and 2010, and the nation's gas production rates continue to grow. While shales have long been regarded as a desirable caprock for CCS operations because of their low permeability and porosity, there is increasing interest in the feasibility of injecting CO₂ into shales to enhance methane recovery and augment CO₂ storage. Laboratory work published in recent years observes that shales with adsorbed methane appear to exhibit a stronger affinity for CO₂ adsorption, offering the potential to drive additional CH₄ recovery beyond primary production and perhaps the potential to store a larger volume of CO₂ than the volume of methane displaced. Recent research by the authors on the revenues associated with CO₂-enhanced gas recovery (CO₂-EGR) in gas-bearing shales estimates that, based on a range of EGR response rates, the average revenue per ton of CO₂ for projects managed over both EGR and subsequent storage-only phases could range from $0.50 to $18/tCO₂. While perhaps not as profitable as EOR, for regions where lower-cost storage options may be limited, shales could represent another “early opportunity” storage option if proven feasible for reliable EGR and CO₂ storage. Significant storage potential exists in gas shales, with theoretical CO₂ storage resources estimated at approximately 30-50 GtCO₂. However, an analysis of the comprehensive cost competitiveness of these various options is necessary to understand the degree to which they might meaningfully impact U.S. CCS deployment or costs. This preliminary analysis shows that the degree to which EGR-based CO₂ storage could play a role in commercial-scale deployment is heavily dependent upon the offsetting revenues associated with incremental recovery; modeling the low revenue case resulted in only five shale-based projects, while under the high revenue case, shales accounted for as much as 20 percent of total U.S. storage in the first 20 years of deployment. Interestingly, even in this highest revenue case, there appear to be no negative-cost projects that would be profitable in a no-policy environment as modeled under the assumptions employed. While this reflects a very first look at the potential for shales, it is clear that more laboratory and experimental work are needed to reduce uncertainty in key variables and begin to differentiate and identify high-potential shales for early pilot study.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2018

CO 2 storage in depleted oil and gas fields in the Gulf of Mexico

Depleted oil and gas reservoirs are one of the prime-candidate formations for geologic CO 2 storage. Although both the geological structure and the physical properties of most of them have been extensively studied and characterized, there is limited data on the assessment of the CO 2 storage capacity, especially in the offshore fields. The purpose of this study is to develop a high-level quantitative assessment of the CO 2 volume that can be stored in depleted oil and gas fields in the Federal offshore regions of the Gulf of Mexico (GOM), both on a field-by-field and on a reservoir-by-reservoir basis. In this study, we simulated CO 2 storage in 461 of the depleted oil and gas reservoirs (73 fields) among 3514 reservoirs (675 fields) in the GOM (2013 BOEM Reserves database). Based on the simulation results, we improved the Department of Energy (DOE) CO 2 Storage Resource Estimate Equation to make more refined and accurate estimates of storable CO 2 volumes. Newly revised efficiency factor (ERoil/gas) correlates better with hydrocarbon recovery factor (HCRF), which is found to be a strong indicator of the CO 2 storage capacity of the reservoir. The higher HCRF results in higher ERoil/gas. The further investigations resulted in an improved, material balance-based correlation—which is called the Production-CO 2 Storage Correlation—between cumulative production (free gas, oil and water) at reservoir conditions and CO 2 storage volume at standard conditions. This relationship, which is unique for all three types of reservoirs (gas, oil and combination), allows for making direct estimates of CO 2 storage volume using only existing production data. Application of these correlations to all of the depleted fields (3514 reservoirs) yields CO 2 storage capacities of 4748 MMtons, and the CO 2 storage capacity in all 1295 depleted and active fields (13,289 reservoirs) in the GOM calculated to be 21.57 Billion tons. If a 5000 psia surface injection pressure constraint was applied, these volumes would be reduced to 4075 MMtons for all depleted fields only and to 15.80 Billion tons for all depleted and active fields in the GOM. Therefore, the production-CO 2 storage correlations can be used to make more accurate CO 2 storage volume estimates in all onshore and offshore depleted oil and gas fields.

03 NATURAL GAS↗
DOE OSTI2017

Gas Gun Model and Comparison to Experimental Performance of Pipe Guns Operating with Light Propellant Gases and Large Cryogenic Pellets

Injection of multiple large (~10 to 30 mm diameter) shattered pellets into ITER plasmas is presently part of the scheme planned to mitigate the deleterious effects of disruptions on the vessel components. To help in the design and optimize performance of the pellet injectors for this application, a model referred to as “the gas gun simulator” has been developed and benchmarked against experimental data. The computer code simulator is a Java program that models the gas-dynamics characteristics of a single-stage gas gun. Following a stepwise approach, the code utilizes a variety of input parameters to incrementally simulate and analyze the dynamics of the gun as the projectile is launched down the barrel. Using input data, the model can calculate gun performance based on physical characteristics, such as propellant-gas and fast-valve properties, barrel geometry, and pellet mass. Although the model is fundamentally generic, the present version is configured to accommodate cryogenic pellets composed of H2, D2, Ne, Ar, and mixtures of them and light propellant gases (H2, D2, and He). The pellets are solidified in situ in pipe guns that consist of stainless steel tubes and fast-acting valves that provide the propellant gas for pellet acceleration (to speeds ~200 to 700 m/s). The pellet speed is the key parameter in determining the response time of a shattered pellet system to a plasma disruption event. The calculated speeds from the code simulations of experiments were typically in excellent agreement with the measured values. With the gas gun simulator validated for many test shots and over a wide range of physical and operating parameters, it is a valuable tool for optimization of the injector design, including the fast valve design (orifice size and volume) for any operating pressure (~40 bar expected for the ITER application) and barrel length for any pellet size (mass, diameter, and length). Key design parameters and proposed values for the pellet injectors for the ITER disruption mitigation systems are discussed.

Combs, Stephen Kirk↗
DOE OSTI2011

THE STATE OF THE GAS AND THE RELATION BETWEEN GAS AND STAR FORMATION AT LOW METALLICITY: THE SMALL MAGELLANIC CLOUD

We compare atomic gas, molecular gas, and the recent star formation rate (SFR) inferred from H{alpha} in the Small Magellanic Cloud (SMC). By using infrared dust emission and local dust-to-gas ratios, we construct a map of molecular gas that is independent of CO emission. This allows us to disentangle conversion factor effects from the impact of metallicity on the formation and star formation efficiency of molecular gas. On scales of 200 pc to 1 kpc (where the distributions of H{sub 2} and star formation match well) we find a characteristic molecular gas depletion time of {tau}{sup mol} d{sub ep} {approx} 1.6 Gyr, similar to that observed in the molecule-rich parts of large spiral galaxies on similar spatial scales. This depletion time shortens on much larger scales to {approx}0.6 Gyr because of the presence of a diffuse H{alpha} component, and lengthens on much smaller scales to {approx}7.5 Gyr because the H{alpha} and H{sub 2} distributions differ in detail. We estimate the systematic uncertainties in our dust-based {tau}{sup mol}{sub dep} measurement to be a factor of {approx}2-3. We suggest that the impact of metallicity on the physics of star formation in molecular gas has at most this magnitude, rather than the factor of {approx}40 suggested by the ratio of SFR to CO emission. The relation between SFR and neutral (H{sub 2} + H{sub i}) gas surface density is steep, with a power-law index {approx}2.2 {+-} 0.1, similar to that observed in the outer disks of large spiral galaxies. At a fixed total gas surface density the SMC has a 5-10 times lower molecular gas fraction (and star formation rate) than large spiral galaxies. We explore the ability of the recent models by Krumholz et al. and Ostriker et al. to reproduce our observations. We find that to explain our data at all spatial scales requires a low fraction of cold, gravitationally bound gas in the SMC. We explore a combined model that incorporates both large-scale thermal and dynamical equilibrium and cloud-scale photodissociation region structure and find that it reproduces our data well, as well as predicting a fraction of cold atomic gas very similar to that observed in the SMC.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

A quantitative phase-field model for gas bubble evolution in UO2

Due to the large formation energy of vacancies and noble gas atoms in the form of interstitials or substitutional atoms in nuclear fuel (UO2), the thermodynamic equilibrium concentrations of these species are very low in the nuclear fuel matrix even at very high temperatures, which imposes difficulties upon the quantitative study of bubble evolution via the phase-field method. In this study, a quantitative phase-field model is proposed to deal with this problem. The system’s free energy density is derived according to the principles of thermodynamics, with consideration of the elastic effect and with the use of real material parameters from experiments. The model is useful for the study of the kinetics of gas bubble growth with very dilute concentrations of vacancy and gas atoms in the matrix. This model is applied to study single bubble growth and multiple bubble growth under various concentrations of vacancy and gas atoms and at various temperatures. The elastic effect and the effects of the generation rate of vacancies and gas atoms on bubble growth are analyzed.

low defect concentration, nuclear fuel, gas bubble↗
DOE OSTI2021

Numerical simulation of gas production from natural gas hydrate deposits with multi-branch wells: Influence of reservoir properties

Vast amounts of natural gas hydrate are buried in subseafloor sediments without impermeable boundaries, which is recognized as an essential energy source for the future. Previously, the multi-branch well was proposed to enhance the recovery efficiency of natural gas hydrate, and the gas production rate has been dramatically improved comparing with the vertical well. However, the multi-branch well shows a terrible performance in gas production duration. Here, as a continuation of the previous study, numerical simulations were conducted to investigate the influence of hydrate reservoir properties on the gas production potential. Results indicate that it is hard to extract hydrate commercially for hydrate accumulations without impermeable boundaries. A high initial hydrate saturation leads to a long gas production duration but a low gas production rate. An increase in the intrinsic permeability of isotropic reservoirs would shorten the gas production duration and result in a low gas recovery ratio. Permeability anisotropy shows a noticeable effect on enhancing the gas recovery ratio and the gas production duration due to the improved pressure propagation pattern. Therefore, in the upcoming field tests, reservoir reconstructions that enhance permeability anisotropy are strongly suggested to obtain better outcomes.

03 NATURAL GAS↗
DOE OSTI2017

Percolation connectivity, pore size, and gas apparent permeability: Network simulations and comparison to experimental data: Connectivity, Pore Size, and Gas Permeability

We modeled single-phase gas flow through porous media using percolation networks. Gas permeability is different from liquid permeability. The latter is only related to the geometry and topology of the pore space, while the former depends on the specific gas considered and varies with gas pressure. As gas pressure decreases, four flow regimes can be distinguished as viscous flow, slip flow, transition flow, and free molecular diffusion. Here we use a published conductance model presumably capable of predicting the flow rate of an arbitrary gas through a cylindrical pipe in the four regimes. We incorporated this model into pipe network simulations. We considered 3-D simple cubic, body-centered cubic, and face-centered cubic lattices, in which we varied the pipe radius distribution and the bond coordination number. Gas flow was simulated at different gas pressures. The simulation results showed that the gas apparent permeability k app obeys an identical scaling law in all three lattices, k app ~ (z-z c ) β , where the exponent β depends on the width of the pipe radius distribution, z is the mean coordination number, and z c its critical value at the percolation threshold. Surprisingly, (z-z c ) had a very weak effect on the ratio of the apparent gas permeability to the absolute liquid permeability, k app /k abs , suggesting that the Klinkenberg gas slippage correction factor is nearly independent of connectivity. We constructed models of k app and k app /k abs based on the observed power law and tested them by comparison with published experimental data on glass beads and other materials.

58 GEOSCIENCES↗
DOE OSTI2019

A preliminary study of the gas hydrate stability zone in a gas hydrate potential region of China

Abstract Due to its significance for gas hydrate accumulation, the gas hydrate stability zone (GHSZ) is an essential condition for successful gas hydrate exploration and is usually controlled by three main factors: gas components, geothermal gradient, and permafrost thickness. Based on the core and conventional log data of gas hydrate potential region, the CSMHYD program was adopted to simulate the influences of above three factors on the thickness of the GHSZ. When the gas components of the gas hydrate were CH 4 , C 2 H 6 , and C 3 H 8 , with the CH 4 percentage ranging from 50% to 100%, the average GHSZ thickness can reach 1000 m according to the forward simulation results. When the gas hydrate was composed of CH 4 and one of C 2 H 6 , C 3 H 8 , H 2 S, and CO 2 , the influence order of the above four gases on the thickness of GHSZ is as follows: H 2 S ＞ C 2 H 6 ＞ C 3 H 8 ＞ CO 2 . Under the gas components of 90% CH 4 , 5% C 2 H 6, and 5% C 3 H 8 , the thickness of GHSZ decreased rapidly as the geothermal gradient increased following an exponential relation with a correlation of 99.92% and increased slowly as permafrost thickness increased following a linear relation with a correlation of 99.9%. In addition, the thickness of a gas hydrate favorable reservoir was determined by comprehensive log methods as 500 m. We conclude that a reservoir within 500 m below the permafrost layer is favorable for gas hydrate reservoir formation.

Xiao, Kun↗