Dissertations / Theses: 'Lean hydrogen'

1

Topinka, Jennifer A. (Jennifer Ann) 1977. "Knock behavior of a lean-burn hydrogen-enhanced engine concept." Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/34351.

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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2003.
Includes bibliographical references (p. 89-91).
Experiments to identify the knock trends of lean gasoline-air mixtures, and such mixtures enhanced with hydrogen (H2) and carbon monoxide (CO), were performed on a single-cylinder research engine with boosting capability. The experimental method used to investigate knock trends consisted of determining the octane number (ON) of the primary reference fuel (mixture of isooctane and n-heptane) supplied to the engine that just produced audible knock. All tests were completed at 1500 rpm, MBT spark timing, with coolant temperature at fully warmed-up conditions and intake air temperature at 200 C. Various relative air-fuel ratio (lambda) sweeps were performed, while holding different parameters constant. First, testing with primary reference fuels investigated knock limits of lean operation; selected tests were then repeated with H2 and CO-enhancement. These mixtures simulated 15% and 30% of the engine's gasoline being reformed in a plasmatron fuel.reformer. Experimental results show that leaner operation does not decrease the knock tendency of an engine under conditions where a fixed output torque is maintained; rather it slightly increases the octane requirement. The onset of knock does decrease with lean operation when the intake pressure is held constant, but engine torque is then reduced. When H2 and CO are added to the mixture, the knock susceptibility is reduced, as illustrated by a decrease in the measured octane number of the primary reference fuel resulting in knock. Experiments conducted with the addition of H2 show similar trends, but to a lesser degree. Therefore, both H2 and CO act as octane enhancers when added to a hydrocarbon-air mixture. The extent to which H2 and CO improve the knock resistance of a mixture can be estimated by finding the bond-weighted octane number for the mixture of fuels. To substantiate these. results, a chemical kinetic ignition model was used to predict autoigntion of the end-gas for various conditions and fuel-air mixtures. Predicted model trends of knock onset partially agree with experimental observations. A comprehensive isooctane chemistry mechanism was used to demonstrate that H2 and CO-enhancement are effective in lengthening the ignition delay, and thereby reduce knock tendency.
by Jennifer A. Topinka.
S.M.

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2

Goldwitz, Joshua A. (Joshua Arlen) 1980. "Combustion optimization in a hydrogen-enhanced lean burn SI engine." Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/27061.

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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2004.
Includes bibliographical references (p. 95-97).
Lean operation of spark ignition (SI) automotive engines offers attractive performance incentives. Lowered combustion temperatures inhibit NO[sub]x pollutant formation while reduced manifold throttling minimizes pumping losses, leading to higher efficiency. These benefits are offset by the reduced combustion speed of lean mixtures, which can lead to high cycle-to-cycle variation and unacceptable engine behavior characteristics. Hydrogen-enhancement can suppress the undesirable consequences of lean operation by accelerating the combustion process, thereby extending the "lean limit." Hydrogen can be produced onboard the vehicle with a plasmatron fuel reformer device. Combustion optimization experiments focused on three key areas: the ignition system, charge motion in the inlet ports, and mixture preparation. The ignition system tests compared a standard inductive coil scheme against high-energy discharge systems. Charge motion experiments focused on the impact of turbulence patterns generated by conventional restrictor plates as well as novel inlet flow modification cones. The turbulent motion of each configuration was characterized using swirl and tumble flow benches. Mixture preparation tests compared a standard single-hole pintle injector against a fine atomizing 12-hole injector. Lastly, a further series of trials was also run to investigate the impact of high exhaust gas recirculation (EGR) dilution rates on combustion stability. Results indicate that optimizations of the combustion system in conjunction with hydrogen-enhancement can extend the lean limit of operation by roughly 25% compared against the baseline configuration. Nearly half of this improvement may be attributed to improvements in the combustion system.
(cont.) An inductive ignition system in conjunction with a high tumble-motion inlet configuration leads to the highest levels of combustion performance. Furthermore, hydrogen enhancement affects a nearly constant absolute improvement in the lean misfire limit regardless of baseline combustion behavior. Conversely, the amount of improvement in the point of peak engine NIMEP output is inversely related to the level of baseline performance.
by Joshua A. Goldwitz.
S.M.

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3

Sykes, David Michael. "Design and Evaluation of a Lean-Premixed Hydrogen Injector with Tangential Entry in a Sector Combustor." Thesis, Virginia Tech, 2007. http://hdl.handle.net/10919/31722.

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Hydrogen use in a gas turbine engine has many benefits. Chief among these is the elimination of carbon based emissions. The only products and emissions from the combustion process are water vapor and oxides of nitrogen (NOx). However due to the lower flammability limit of hydrogen, it can be burned at much lower equivalence ratios that typical hydrocarbon fuels, and thus reducing the emissions of NOx. Multiple efforts have been made for the design of premixing injectors for gaseous hydrocarbon fuels, but very few attempts have been made for hydrogen.

To this end a premixing hydrogen injector was designed for the cruise engine condition for a PT6-20 turboprop engine. Swirl generated by tangential entry was utilized as a means to enhance mixing and as a convenient means to stabilize the flame. A prototype was designed to prevent flashback and promote a high degree of mixing, as well as a test combustor to evaluate the performance of the injector at scaled engine conditions. Numerical simulations were also performed to analyze the flowfield at the engine conditions. Performance and emissions data are used to draw conclusions about the feasibility of the injectors in the PT6 engine.
Master of Science

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4

Ivanic, Å½iga 1978. "Predicting the behavior of a lean-burn hydrogen-enhanced engine concept." Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/17932.

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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2004.
Includes bibliographical references (p. 90-91).
(cont.) Lean operation of a spark ignition (SI) internal combustion engine (ICE) offers attractive performance incentives. Lowered combustion temperatures inhibit formation of nitrogen oxides (NOx), while reduced intake manifold throttling minimizes pumping losses leading to higher efficiency. These benefits are offset by the reduced combustion speed of lean mixtures, which can lead to high cycle-to-cycle variation and unacceptable engine behavior characteristics. Hydrogen-enhancement can suppress the undesirable consequences of lean operation by accelerating the combustion process, thereby extending the "lean limit." Hydrogen would be produced on-board the vehicle with a fuel reforming device. Since operating an engine in the lean regime requires a significant amount of air, boosting is required. Hydrogen is also an octane enhancer, enabling operation at higher compression ratios, which results in a further improvement in engine efficiency. The focus of this thesis is on the modeling aspect of the lean boosted engine concept. Modeling provides a useful tool for investigating different lean boosted concepts and comparing them based on their emissions and fuel economy. An existing architectural concept has been tailored for boosted, hydrogen-enhanced, lean-bum SI engine. The simulation consists of a set of Matlab models, part physical and part empirical, that have been developed to simulate performance of a real ICE. The model was calibrated with experimental data for combustion and emissions in regards to changes in air/fuel ratio, load and speed, and different reformate fractions. The outputs of the model are NOx emissions and brake specific fuel consumption (BSFC) maps along with the cumulative NOx emissions and fuel economy for the urban
(cont.) and highway drive cycles.
by Å½iga Ivanic.
S.M.

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5

Ross, Martin C. Shepherd J. E. "Lean combustion characteristics of hydrogen-nitrous oxide-ammonia mixtures in air /." Diss., Pasadena, Calif. : California Institute of Technology, 1997. http://resolver.caltech.edu/CaltechETD:etd-01182008-143226.

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6

Villarreal, Daniel Christopher. "Digital Fuel Control for a Lean Premixed Hydrogen-Fueled Gas Turbine Engine." Thesis, Virginia Tech, 2009. http://hdl.handle.net/10919/34974.

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Hydrogen-powered engines have been gaining increasing interest due to the global concerns of the effects of hydrocarbon combustion on climate change. Gas turbines are suitable for operation on hydrogen fuel. This thesis reports the results of investigations of the special requirements of the fuel controller for a hydrogen gas turbine. In this investigation, a digital fuel controller for a hydrogen-fueled modified Pratt and Whitney PT6A-20 turboprop engine was successfully designed and implemented. Included in the design are safety measures to protect the operating personnel and the engine. A redundant fuel control is part of the final design to provide a second method of managing the engine should there be a malfunction in any part of the primary controller.

Parallel to this study, an investigation of the existing hydrogen combustor design was performed to analyze the upper stability limits that were restricting the operability of the engine. The upstream propagation of the flame into the premixer, more commonly known as a flashback, routinely occurred at 150 shaft horsepower during engine testing. The procedures for protecting the engine from a flashback were automated within the fuel controller, significantly reducing the response time from the previous (manual) method. Additionally, protection measures were added to ensure the inter-turbine temperature of the engine did not exceed published limits. Automatic engine starting and shutdown procedures were also added to the control logic, minimizing the effort needed by the operator. The tested performance of the engine with each of the control functions demonstrated the capability of the controller.

Methods to generate an engine-specific fuel control map were also studied. The control map would not only takes into account the operability limits of the engine, but also the stability limits of the premixing devices. Such a map is integral in the complete design of the engine fuel controller.
Master of Science

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7

Perry, Matthew Vincent. "An Investigation of Lean Premixed Hydrogen Combustion in a Gas Turbine Engine." Thesis, Virginia Tech, 2009. http://hdl.handle.net/10919/43532.

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As a result of growing concerns about the carbon emissions associated with the combustion of conventional hydrocarbon fuels, hydrogen is gaining more attention as a clean alternative. The combustion of hydrogen in air produces no carbon emissions. However, hydrogen-air combustion does have the potential to produce oxides of nitrogen (NOx), which are harmful pollutants. The production of NOx can be significantly curbed using lean premixed combustion, wherein hydrogen and air are mixed at an equivalence ratio (the ratio of stoichiometric to actual air in the combustion process) significantly less than 1.0 prior to combustion. Hydrogen is a good candidate for use in lean premixed systems due to its very wide flammability range. The potential for the stable combustion of hydrogen at a wide range of equivalence ratios makes it particularly well-suited to application in gas turbines, where the equivalence ratio is likely to vary significantly over the operating range of the machine.

The strong lean combustion stability of hydrogen-air flames is due primarily to high reaction rates and the associated high turbulent burning velocities. While this is advantageous at low equivalence ratios, it presents a significant danger of flashbackâ the upstream propagation of the flame into the premixing deviceâ at higher equivalence ratios. An investigation has been conducted into the operation of a specific hydrogen-air premixer design in a gas turbine engine. Laboratory tests were first conducted to determine the upper stability limits of a single premixer. Tests were then carried out in which eighteen premixers and a custom-fabricated combustor liner were installed in a modified Pratt and Whitney Canada PT6A-20 turboprop engine. The tests examined the premixer and engine operability as a result of the modifications. A computer cycle analysis model was created to help analyze and predict the behavior of the modified engine and premixers. The model, which uses scaled component maps to predict off-design engine performance, was integral in the analysis of premixer flashback which limited the operation of the modified engine.
Master of Science

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8

Farina, Jordan Thomas. "Conversion of a Gas Turbine Engine to Operate on Lean-Premixed Hydrogen-Air: Design and Characterization." Thesis, Virginia Tech, 2010. http://hdl.handle.net/10919/31067.

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The continued use of fossil fuels along with a rise in energy demand has led to increasing levels of carbon emissions over the past years. The purpose of this research was to design a lean premixed hydrogen fuel system that could be readily retrofit into an existing gas turbine engine to provide a clean renewable energy solution to this growing problem. There were major hurdles that had to be overcome to develop a hydrogen fuel system that would be practical, stable, and would fit into the existing space. High flame temperatures coupled with high flame speeds are major concerns when switching from jet fuel or natural gas to hydrogen. High temperatures lead to formations of pollutants such as oxides of nitrogen (NOx) and can potentially cause damage to critical engine components. High flame speeds can lead to dangerous flashbacks in the fuel premixers. Past researches have developed various hydrogen premixers to combat these problems. This research designed and developed new hydrogen premixers using information gathered from these designs and utilized new ideas to address their shortcomings.

A gas turbine engine was modified using 14 premixers and a matching combustor liner to provide lean operation with the existing turbomachinery. The engine was successfully operated using hydrogen while maintaining normal internal temperatures and practically eliminating the NOx emissions when compared to normal Jet-A operation. Even though full power operation was never achieved due to flashbacks in two premixers, this research demonstrated the feasibility of using lean-premixed hydrogen in gas turbine engines.
Master of Science

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9

Speth, Raymond L. 1981. "Effects of curvature and strain on a lean premixed methane-hydrogen-air flame." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/35640.

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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2006.
Includes bibliographical references (leaves 74-77).
The elemental flame is a subgrid model for turbulent combustion, parameterized by time-varying strain rate and curvature. This thesis develops the unsteady one-dimensional governing equations for the elemental flame incorporating detailed chemical kinetics and transport and a robust and efficient numerical method for solving the governing equations. Hydrogen enrichment of some hydrocarbon fuels has been shown to improve stability and extend flammability limits of lean premixed combustion in a number of recent experiments. It is suggested that these trends may be explained by the impact of hydrogen on the flame response to stretch and curvature. The elemental flame model is used to simulate premixed hydrogen-enriched methane flames in positively curved, negatively curved and planar configurations at varying strain rates. Curvature and stretch couple with non-unity species Lewis numbers to affect the burning rates and flame structure. Hydrogen addition is found to increase burning rate and resistance to flame stretch under all conditions. Positive curvature reinforces the effect of hydrogen enrichment, while negative curvature diminishes it.
(cont.) The effects of strong curvature cannot be explained solely in terms of flame stretch. Hydrogen enriched flames display increases in radical concentrations and a broadening of the reaction zone. Detailed analysis of the chemical kinetics shows that high strain rates lead to incomplete oxidation; hydrogen addition tends to mitigate this effect.
by Raymond Levi Speth.
S.M.

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10

Coleman, Marc David. "Catalytic reduction of nitrogen monoxide using hydrogen at low temperatures under lean burn conditions." Thesis, University of Reading, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.246453.

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11

Ayala, Ferran A. (Ferran Alberto) 1976. "Combustion lean limits fundamentals and their application to a SI hydrogen-enhanced engine concept." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/38262.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2006.
Includes bibliographical references (p. 197-199).
Operating an engine with excess air, under lean conditions, has significant benefits in terms of increased engine efficiency and reduced emissions. However, under high dilution levels, a lean limit is reached where combustion becomes unstable, significantly deteriorating drivability and engine efficiency, thus limiting the full potential of lean combustion. Due to hydrogen's high laminar flame speed, adding a hydrogen-rich mixture with gasoline into the engine helps stabilize combustion, extending the lean limit. This work studies the fundamental behavior of lean combustion in a spark ignition (SI) engine, identifying the processes that determine the engine's efficiency curve, and studying practical solutions to extend the peak efficiency and the lean limit. Lean and hydrogen-enhanced combustion data in a SI engine were generated covering a wide range of operating conditions including different compression ratios, loads, types of dilution, types and levels of hydrogen enhancement, and levels of turbulence. Combustion simulations were then performed to quantify the components that determine the efficiency vs. dilution curve. Results showed how burn duration is the primary driver of lean combustion, with a limiting 10-90% burn duration at peak efficiency and a limiting 0-10% burn duration at the onset of rapid combustion variability.
(cont.) These two burn durations, while correlated, are affected differently by laminar flame speed and turbulence. Consequently the effect of hydrogen enhancement on combustion will depend on operating conditions. A flame entrainment combustion model was then used to fundamentally explain the observed criticalities in the experiments. The model properly captured the physics of the combustion process, accurately predicting the data and the basic trends. The model showed that the rapid increase in variability near the lean limit is due to the inverse dependence of the eddy-burning time on the laminar flame speed. This relationship causes the eddy-burning time to grow slowly and then rapidly with decreasing laminar flame speed, amplifying the baseline, normal, random variability associated with the flame initiation process. Due to the effect of initial conditions on combustion phasing, this increasing, but symmetric, variability during flame initiation will lead to asymmetrical variability in the main part of the combustion process. Modeling studies show how by reducing the eddy-burning time, the full burn duration curve can be shifted, extending the location of peak efficiency and the lean limit.
(cont.) This can be done by increasing turbulence, effectively decreasing its microscale structure or by increasing the laminar flame speed through hydrogen enhancement. Hydrogen enhancement using reformate shows diminishing returns at high loads and high compression ratios due to the detrimental effect of high pressures on laminar flame speed. As suggested by the model, reducing the engine's baseline combustion variability during flame initiation can also extend the lean limit. These conclusions are confirmed through experimental results.
by Ferrán A. Ayala.
Ph.D.

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12

Homitz, Joseph. "A Lean-Premixed Hydrogen Injector with Vane Driven Swirl for Application in Gas Turbines." Thesis, Virginia Tech, 2006. http://hdl.handle.net/10919/36334.

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Hydrogen, as an alternative to conventional aviation fuels, has the potential to increase the efficiency of a gas turbine as well as reduce emissions of greenhouse gases. In addition to significantly reducing the number of pollutants due to the absence of carbon, burning hydrogen at low equivalence ratios can significantly reduce emissions of oxides of nitrogen (NOx). Because hydrogen has a wide range of flammability limits, fuel lean combustion can take place at lower equivalence ratios than those with typical hydrocarbon fuels.

Numerous efforts have been made to develop gas turbine fuel injectors that premix methane/natural gas and air in fuel lean proportions prior to the reaction zone. Application of this technique to hydrogen combustion has been limited due to hydrogen's high flame rate and the concern of the reaction zone propagating into the premixing injector, commonly referred to as flashback. In this investigation, a lean-premixing hydrogen injector has been developed for application in small gas turbines. The performance of this injector was characterized and predictions about the injector's performance operating under combustor inlet conditions of a PT6-20 Turboprop have been made.
Master of Science

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13

Karkow, Douglas W. "Combustion instabilities: an experimental investigation on the effects of hydrogen in a lean premixed combustor." Thesis, University of Iowa, 2012. https://ir.uiowa.edu/etd/2911.

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14

Tully, Edward J. (Edward Joseph) 1975. "Lean-burn characteristics of a gasoline engine enriched with hydrogen from a plasmatron fuel reformer." Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/34349.

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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2002.
Includes bibliographical references (leaves 75-76).
If a small amount of hydrogen is added to a gasoline fueled spark ignition engine the lean limit of the engine can be extended. Lean running engines are inherently more efficient, and have the potential for significantly lower NOx emissions. Hydrogen addition reduces the combustion variability. In this engine concept supplemental hydrogen is generated on-board the vehicle by diverting a small fraction of the gasoline to a plasmatron where it is partially oxidized into a stream containing hydrogen, carbon monoxide, nitrogen, and carbon dioxide. It is then mixed in the intake port with the main fuel/air charge to provide hydrogen enhanced lean operation A series of experiments were performed to study the feasibility of this engine concept. Since the plasmatron is still under development the final composition of the plasmatron gas is not yet known. Therefore, two different bottled gases were used to simulate the plasmatron output. An ideal plasmatron gas (H2 , CO, and N2) was used to represent the output of the theoretically best plasmatron. In addition, a typical plasmatron gas (H2 , CO, N2 , and C0 2) was used to represent the current output of the plasmatron. In addition, a series of hydrogen only addition experiments were performed to quantify the impact of the non-hydrogen components in the plasmatron gas. Various amounts of plasmatron gas were used, ranging from the equivalent of 10%-30% of the gasoline being converted in the plasmatron. At each of these fractions a sweep of the relative air/fuel ratio was performed, starting at stoichiometic and slowly increasing lambda until the engine began to misfire. At each operating point data was collected to quantify efficiency, emissions, and combustion stability. All of the data was compared to a baseline case of the engine operating stoichiometrically on gasoline only. It was found that the peak net indicated fuel conversion efficiency of the system increased 12% over the baseline case. In addition, at this peak efficiency point the engine out NOx emissions decrease by 94% (165ppm vs. 2800ppm) while the hydrocarbon emissions decreased by 6% (2210ppm vs. 2350ppm). NOx emissions reductions of 99% were possible although they occured at slightly lower overall efficiency points. In the analysis the relative air/fuel ratio was found to be an inadequate measure of mixture dilution. Two new dilution parameters were defined. The Volumetric Dilution Parameter, VDP, represents the heating value per unit volume of the air/fuel mixture. Pumping work reductions due to dilution correlate with VDP. The Thermal Dilution Parameter, TDP, represents the heating value per unit heat capacity of the fuel/air mixture. Combustion and emissions parameters correlate with TDP.
by Edward J. Tully.
S.M.

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15

Zhang, Qingguo. "Lean blowoff characteristics of swirling H2/CO/CH4 Flames." Diss., Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/22641.

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This thesis describes an experimental investigation of lean blowoff for H2/CO/CH4 mixtures in a swirling combustor. This investigation consisted of three thrusts. The first thrust focused on correlations of the lean blowoff limits of H2/CO/CH4 mixtures under different test conditions. It was found that a classical Damköhler number approach with a diffusion correction could correlate blowoff sensitivities to fuel composition over a range of conditions. The second part of this thesis describes the qualitative flame dynamics near blowoff by systematically characterizing the blowoff phenomenology as a function of hydrogen level in the fuel. These near blowoff dynamics are very complex, and are influenced by both fluid mechanics and chemical kinetics; in particular, the role of thermal expansion across the flame and extinction strain rate were suggested to be critical in describing these influences. The third part of this thesis quantitatively analyzed strain characteristics in the vicinity of the attachment point of stable and near blowoff flames. Surprisingly, it was found that in this shear layer stabilized flame, flow deceleration is the key contributor to flame strain, with flow shear playing a relatively negligible role. Near the premixer exit, due to strong flow deceleration, the flame is negatively strained i.e., compressed. Moving downstream, the strain rate increases towards zero and then becomes positive, where flames are stretched. As the flame moves toward blowoff, holes begin to form in the flame sheet, with a progressively higher probability of occurrence as one moves downstream. It is suggested that new holes form with a more uniform probability, but that this behavior reflects the convection of flame holes downstream by the flow. It has been shown in prior studies, and affirmed in this work, that flames approach blowoff by first passing through a transient phase manifested by local extinction events and the appearance of holes on the flame. A key conclusion of this work is that the onset of this boundary occurs at a nearly constant extinction strain rate. As such, it is suggested that Damköhler number scalings do not describe blowoff itself, but rather the occurrence of this first stage of blowoff. Given the correspondence between this first stage and the actual blowoff event, this explains the success of classical Damköhler number scalings in describing blowoff, such as shown in the first thrust of this thesis. The physics process associated with the actual blowoff event is still unclear and remains a key task for future work.

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16

Kaufman, Kelsey Leigh. "Effect of hydrogen addition and burner diameter on the stability and structure of lean, premixed flames." Thesis, University of Iowa, 2014. https://ir.uiowa.edu/etd/4661.

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Low swirl burners (LSBs) have gained popularity in heating and gas power generation industries, in part due to their proven capacity for reducing the production of NOx, which in addition to reacting to form smog and acid rain, plays a central role in the formation of the tropospheric ozone layer. With lean operating conditions, LSBs are susceptible to combustion instability, which can result in flame extinction or equipment failure. Extensive work has been performed to understand the nature of LSB combustion, but scaling trends between laboratory- and industrial-sized burners have not been established. Using hydrogen addition as the primary method of flame stabilization, the current work presents results for a 2.54 cm LSB to investigate potential effects of burner outlet diameter on the nature of flame stability, with focus on flashback and lean blowout conditions. In the lean regime, the onset of instability and flame extinction have been shown to occur at similar equivalence ratios for both the 2.54 cm and a 3.81 cm LSB and depend on the resolution of equivalence ratios incremented. Investigations into flame structures are also performed. Discussion begins with a derivation for properties in a multicomponent gas mixture used to determine the Reynolds number (Re) to develop a condition for turbulent intensity similarity in differently-sized LSBs. Based on this requirement, operating conditions are chosen such that the global Reynolds number for the 2.54 cm LSB is within 2% of the Re for the 3.81 cm burner. With similarity obtained, flame structure investigations focus on flame front curvature and flame surface density (FSD). As flame structure results of the current 2.54 cm LSB work are compared to results for the 3.81 cm LSB, no apparent relationship is shown to exist between burner diameter and the distribution of flame surface density. However, burner diameter is shown to have a definite effect on the flame front curvature. In corresponding flow conditions, a decrease in burner diameter results a broader distribution of curvature and an increased average curvature, signifying that compared to the larger 3.81 cm LSB, the flame front of the smaller burner contains tighter, smaller scale wrinkling.

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17

Reichel, Thoralf G. [Verfasser], Christian Oliver [Akademischer Betreuer] Paschereit, Christian Oliver [Gutachter] Paschereit, Yeshayahou [Gutachter] Levy, and Arvind [Gutachter] Rao. "Flashback prevention in lean-premixed hydrogen combustion / Thoralf G. Reichel ; Gutachter: Christian Oliver Paschereit, Yeshayahou Levy, Arvind Rao ; Betreuer: Christian Oliver Paschereit." Berlin : Technische Universität Berlin, 2017. http://d-nb.info/1156185807/34.

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18

山本, 和弘, Kazuhiro YAMAMOTO, 義昭小沼, and Yoshiaki ONUMA. "希薄燃焼に及ぼす水素添加の効果 (第3報, 反応機構に着目した管状火炎の数値計算)." 日本機械学会, 1999. http://hdl.handle.net/2237/9326.

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19

山本, 和弘, Kazuhiro YAMAMOTO, 昌幸丸山, Masayuki MARUYAMA, 義昭小沼, and Yoshiaki ONUMA. "希薄燃焼に及ぼす水素添加の効果." 日本機械学会, 1998. http://hdl.handle.net/2237/9318.

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山本, 和弘, Kazuhiro YAMAMOTO, 昌幸丸山, Masayuki MARUYAMA, 義昭小沼, and Yoshiaki ONUMA. "希薄燃焼に及ぼす水素添加の効果 (第2報, 管状火炎の特性と輸送過程に及ぼす回転強さの影響)." 日本機械学会, 1999. http://hdl.handle.net/2237/9322.

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21

Katzy, Peter [Verfasser], Thomas [Akademischer Betreuer] Sattelmayer, Thomas [Gutachter] Sattelmayer, and Marco K. [Gutachter] Koch. "Combustion Model for the Computation of Flame Propagation in Lean Hydrogen-Air Mixtures at Low Turbulence / Peter Katzy ; Gutachter: Thomas Sattelmayer, Marco K. Koch ; Betreuer: Thomas Sattelmayer." München : Universitätsbibliothek der TU München, 2021. http://d-nb.info/1229620877/34.

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22

Katzy, Peter Verfasser], Thomas [Akademischer Betreuer] Sattelmayer, Thomas [Gutachter] Sattelmayer, and Marco K. [Gutachter] [Koch. "Combustion Model for the Computation of Flame Propagation in Lean Hydrogen-Air Mixtures at Low Turbulence / Peter Katzy ; Gutachter: Thomas Sattelmayer, Marco K. Koch ; Betreuer: Thomas Sattelmayer." München : Universitätsbibliothek der TU München, 2021. http://d-nb.info/1229620877/34.

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23

Ruel, Fiona. "Contribution électrochimique à l’étude de la corrosion sous contrainte des aciers inoxydables lean duplex en milieu purement chloruré et sous présence de sulfure d’hydrogène." Thesis, Saint-Etienne, EMSE, 2014. http://www.theses.fr/2014EMSE0743/document.

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Les aciers inoxydables lean duplex, à faible teneur en nickel et sans molybdène, représentent une alternative économique pour les usines de dessalement et l’industrie pétrolière. Celles-ci ont la particularité d’être exposées à des milieux très agressifs dont la présence de chlorure, de sulfure d’hydrogène, de hautes températures ou encore d’acides peut provoquer des phénomènes de fissuration sous contrainte.Cette étude est divisée en deux parties, la première se consacre aux milieux purement chlorurés et la seconde aux milieux contenant du sulfure d’hydrogène. Dans les deux parties, la compréhension des phénomènes liés à la fissuration sous contrainte des lean duplex est effectuée sur la nuance S32304, puis est comparée aux comportements des nuances S32202 et S32101. L’influence des milieux bouillants sur la résistance à la fissuration des aciers inoxydables, les mécanismes de dépassivation et de dissolution sélective des lean duplex, les différents modes de fissuration en présence de sulfure d’hydrogène ou encore l’amorçage de la corrosion sous contrainte assistée par le sulfure d’hydrogène sont abordés dans ce rapport
Lean duplex stainless steels, with low content of nickel and without molybdenum, represent an economic alternative for desalting plants and petroleum industry. For these uses, steel have the particularity to be exposed to very aggressive environments inducing phenomenon of Stress Corrosion Cracking as chlorides, hydrogen sulphur, high temperatures or acids.This study is divided in two parts dedicated to two different environments. The first part is devoted to chloride middles and the second to hydrogen sulphur middles. In both parts, the understanding of phenomenon linked to the stress corrosion cracking of lean duplex is studied on the grade steel S32304, then is compared to the behaviour of grade steels S32202 and S32101. The topics treated in this report are notably the influence of boiling environments on the cracking resistance of stainless steels, the mechanism of unpassivation and selective dissolution of lean duplex, the different modes of cracking in presence of hydrogen sulphur, and the initiation of stress corrosion cracking assisted by hydrogen sulphur

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24

Saffari, Yasaman. "Leak Test on High-Speed Separator." Thesis, KTH, Kemiteknik, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-90477.

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High speed separators from Alfa Laval are widely in use for processing flammable and non-flammable liquids. The following work is focusing on the case of non-flammable liquid as the process liquid in case the working area around the equipment may contain quantities of explosive gases. As stated by Alfa Laval documentation, the major risk is leaking of the explosive atmosphere into the separator from the surrounding environment which may result in producing zone 1 or zone 2 of hazardous area classification. Zone 1: Area in which an explosive gas-air mixture is likely to occur for short periods in normal operation.1 Zone 2: Area in which an explosive gas-air mixture is not likely to occur, and if it occurs it will only exist for a very short time due to an abnormal condition.1 According to Alfa Laval design package, there is a need of continuous inert gas injection into the separator during the process in order to reduce the oxygen concentration and keep it in the safe level (inert gas purging) and this policy is aimed to meet the requirements of ATEX-directive 94/9/EC/2003. The objective of the current thesis is a wish to have a better understanding of the potential risks, evaluating them and try to find ways to ease the process. The outcome can be useful to make a basic instruction for further tests and simplifications as well. The separator GTN 50 is selected and hydrogen (1% concentration) is used to simulate the explosive atmosphere. The result of the tests indicates that the cooling down stage after normal operation is the only period in which hydrogen will leak into the separator, frame top part and it should be cleaned up before the next start up. A number of recommendations -Ventilation to the fresh air, Water discharges, Pressurized air injectionare also being tested and discussed. Ventilation to the fresh air and injection of pressurized air seem to be applicable A Standard Testing Flow chart is suggested and calculation on real case is considered. A number of additional ideas are also included in the last section.

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25

De, Santis Donato. "Hydrogen reduction of lead from Kelex 100." Thesis, McGill University, 1987. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=66077.

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26

Mohammadabadi, Ali Shafiei. "Hydrogen‐induced damage of lead‐zirconate‐titanate (PZT)." Thesis, University of British Columbia, 2013. http://hdl.handle.net/2429/44320.

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Lead-Zirconate-Titanate Pb(Zr,Ti)O₃ (PZT) based actuators are evaluated by automotive industry for advanced fuel-injection systems, including hydrogen injection. However, hydrogen can have deleterious effect on the PZT's functionality and properties. The general objective of this work is to study the interactions between PZT and hydrogen. The results of long-term (200-1200 hours) high-pressure (10 MPa) hydrogen exposure on the PZT microstructure show that hydrogen has only superficial effects on the microstructure of bare PZT. However, when an electrode is attached to PZT, the hydrogen damage increased; a porous layer developed immediately adjacent to the electrodes on the PZT surface due to hydrogen spillover. The kinetics of the PZT structural modifications due to hydrogen was investigated by online monitoring of the electrical properties of PZT above the Curie temperature, up to 650°C. The results show that the structural changes can be described by the classical nucleation and growth theory. The growth of the new structure appears to be limited by the diffusion of protons into PZT, with a calculated activation energy of 0.44± 0.09 eV, at 450-650°C. Two relaxation peaks were observed in the dissipation factor curves of the hydrogen-treated PZT. While the kinetics of one of the relaxation peaks obeys the classical Arrhenius law with the activation energy of 0.66 eV, the other peak shows an unusual relaxation kinetic. The mechanisms for the formation of these relaxation peaks are determined. Low temperature (20°C) diffusion of hydrogen into the PZT was also studied, using the water electrolysis technique. Based on the microstructural observations, the diffusion coefficient of hydrogen in PZT was calculated as 9×10-¹¹ cm²/sec. The Maxwell-Wagner polarization mechanism is determined to be responsible for the changes in the hydrogen-affected PZT capacitance. In the last part of the project, alumina coatings were applied to PZT plates using the sol-gel technique, to explore the possibilities of decreasing H₂ damage to PZT. The functionality of the coating against hydrogen damage was evaluated by the water electrolysis technique. Significant decrease of hydrogen damage was observed even for highly porous coatings. The mechanisms by which the alumina coating decreases the hydrogen damage were tentatively proposed.

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27

Villenave, Nicolas. "Étude expérimentale des propriétés fondamentales de la combustion de l'hydrogène pour des applications de propulsion." Electronic Thesis or Diss., Orléans, 2025. http://www.theses.fr/2025ORLE1001.

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En vue d'atteindre la neutralité carbone d'ici 2050, l’Union européenne envisage l'hydrogène comme un vecteur énergétique prometteur afin de réduire la consommation des ressources fossiles. Alors que les piles à combustible et les véhicules électriques occupent déjà une place importante dans la décarbonation du secteur des transports, l'hydrogène est également considéré comme une alternative aux carburants conventionnels pour les véhicules lourds. Toutefois, de nombreux obstacles liés aux propriétés physico-chimiques ainsi qu’à la combustion pauvre en hydrogène sont encore à l’étude : apparition de phénomènes de combustion anormale, production d'oxydes d'azote, instabilités dues aux effets thermodiffusifs. Cette thèse contribue à la compréhension du processus d’auto-inflammation des mélanges pauvres hydrogène/air ainsi qu’au phénomène de propagation des flammes prémélangées laminaires et turbulentes. Dans une première partie, des mesures de délais d’auto-inflammation hydrogène/air et hydrogène/air/oxydes d’azote sont réalisées à l’aide d’une machine à compression rapide afin de revisiter et valider un mécanisme cinétique dans des conditions similaires à celles rencontrées dans un moteur à allumage commandé. Dans une deuxième partie, des flammes laminaires prémélangées en expansion sont étudiées au sein d’une chambre de combustion sphérique à volume constant, en faisant varier la température initiale ainsi que la dilution à la vapeur d’eau et en considérant les instabilités intrinsèques liées aux propriétés physico-chimiques de l’hydrogène : instabilités thermodiffusives, hydrodynamiques et liées à la pesanteur. Dans une dernière partie,des flammes turbulentes prémélangées en expansion sont caractérisées par génération d’une turbulence homogène et isotrope au sein d’une chambre sphérique. Une étude paramétrique est réalisée par rapport à un cas de référence en faisant varier l’intensité turbulente, la pression initiale et la richesse. Finalement, une corrélation turbulente est proposée afin de décrire la propagation de ces flammes et en vue d’être utilisée dans des modèles numériques
In order to reach carbon neutrality by 2050, the European Union is considering hydrogen as a promising energy carrier to reduce reliance on fossil fuels. While fuel cells and electric vehicles already play an important role in decarbonizing the transport sector, hydrogen is also seen as an alternative to conventional fuels for heavy-duty vehicles. Yet, a number of challenges linked to the physico-chemical properties of lean hydrogen combustion are still under investigation: abnormal combustion phenomena, production of nitrogen oxides,instabilities due to thermodiffusive effects, to state a few. This thesis contributes to the understanding of the auto-ignition process in lean hydrogen/air mixtures, as well as the propagation of laminar and turbulent premixed flames. First, measurements of hydrogen/air and hydrogen/air/nitrogen oxides ignition delay times are carried out using a rapid compression machine, to update and validate a kinetic mechanism under spark ignition engine-like conditions. Second, outwardly propagating spherical premixed laminar flames were studiedin a constant-volume combustion chamber, varying the initial temperature and steam dilution, and considering the intrinsic instabilities linked to the physico-chemical properties of hydrogen namely thermodiffusive,hydrodynamic and gravity-related instabilities. Then, expanding premixed turbulent flames are characterized by the generation of a homogeneous and isotropic turbulence zone within a spherical chamber. A parametric study is conducted by varying turbulent intensity, initial pressure and equivalence ratio. Finally, a turbulent correlation is proposed to describe the turbulent propagation of such flames, for use in numerical models

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28

Halici, Safak. "Development Of Lead Alloys For Valve-regulated Lead-acid (vrla) Batteries." Master's thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12612422/index.pdf.

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In this study, Mg, Sn, Cd, Bi and Sb containing, five binary, three ternary and two quaternary different alloys to be used in a Valve-Regulated Lead-Acid (VRLA) batteries have been studied in terms of their mechanical and electrochemical properties. The investigated properties are hardness, passivity, corrosion rate, hydrogen gassing and the conductivity of the passive film. All electrochemical tests were carried out in 3.75 M H2SO4 solution by using open-circuit potential, anodic polarization, polarization resistance measurement and gas collection techniques. The results showed that while the minimum hardness values were observed in Pb and Pb-Bi alloy, Mg containing alloys have the highest hardness values among all alloys. According to corrosion measurements, lowest icritical value was obtained for Pb, Pb-Bi and Pb-Sn, which reached to passivation region earlier than others. Passive film formation was seen for all specimens. The noble Ecorr value and minimum corrosion rates belonged to Pb and Pb-Mg. Pb-Bi and Pb-Cd have the highest gas evolution rate. Besides, there were not seen much difference in the gassing behavior of Pb-Sn and Pb-Sb alloys. Mg is found to have a superior effect on hydrogen gassing. Addition of Sn, as an alloying element, to lead increases the conductivity of the passivation layer. Mg containing alloys did not show good conductivity characteristic. As a result, Mg containing alloy seemed to have an important role because of the desired hardness, corrosion and, gas evolution behavior. However, conductivity of passivation layer of these alloys came up to be low due to the higher tendency of Mg to oxidation. Even so, Mg seems to be a promising alloying element for lead grid alloys in Valve-Regulated Lead-Acid (VRLA) batteries.

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29

Ball, Allen Joseph. "Investigation of gaseous hydrogen leak detection using Raman scattering and laser-induced breakdown spectroscopy." [Gainesville, Fla.] : University of Florida, 2005. http://purl.fcla.edu/fcla/etd/UFE0010545.

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30

Saini, Alpna. "An investigation of the cause of leak formation in palladium composite membranes." Link to electronic thesis, 2006. http://www.wpi.edu/Pubs/ETD/Available/etd-050406-133412/.

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31

Barakat, Waël. "Chimie de coordination supramoléculaire avec des porphyrines à anses greffées en positions méso 5,10." Thesis, Rennes 1, 2019. http://www.theses.fr/2019REN1S049.

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Ce travail de thèse traite de la synthèse de porphyrines à une ou deux anses (6, 11, 8i and 14i) greffées sur les positions méso adjacentes 5,10 et 15,20 et portant une fonction acide carboxylique suspendue avec ou sans un autre groupement fonctionnel (cyano, pyridine) en position alpha. Cette conformation génère une flexibilité de l'anse avec deux positions clairement identifiées de l'acide carboxylique (intérieure/extérieure). Ainsi la synthèse et la caractérisation des composés sont discutées en détails puis la coordination des ligands 6, 11, et 8i avec les métaux Zn(II), Hg(II), Pb(II) et Bi(III) est décrite. Dans le cas du zinc, cation penta-coordiné en géométrie pyramidale à base carrée, ce dernier est stabilisé soit par le groupement acide carboxylique intramoléculaire soit par une molécule de solvant exogène (DMSO ou H2O). Dans le cas du mercure, des complexes des deux types, monométalliques et bimétalliques, sont obtenus alors que pour le plomb, deux espèces monométalliques sont formées dans lesquelles le cation est soit du même côté, soit du côté opposé à l'anse, mais dans des proportions différentes. Enfin, le cation Bi(III) induit une seconde sphère de coordination inédite, responsable de l'insertion stéréosélective du métal. Qui plus est, un processus de transmétallation augmente la cinétique d'insertion du bismuth. Également, la présence d'un groupement cyano en position alpha de l'acide carboxylique génère une gêne stérique en coordination dans le cas du plomb, l'obligeant à coordiner la porphyrine sur sa face nue
This thesis work concerns the synthesis of 5,10 single and bis-strapped porphyrin ligands (6, 11, 8i and 14i) bearing an overhung carboxylic acid group with/without an additional functional group (cyano and pyridine). The 5,10 meso linkage promotes a flexibility of the strap which allows the carboxylic acid group to be in two identified positions (in/out). The synthesis and characterization of the compounds are discussed in details, and the coordination of the ligands (6, 11, and 8i) with metals Zn(II), Hg(II), Pb(II) and Bi(III) have been investigated. In the case of Zn(II), five-coordinated metal in a square pyramidal geometry, the metal was stabilized by either an intramolecular carboxylic acid group or an exogenous molecule (DMSO or H2O). In the case of Hg(II), both monometallic and bimetallic species were obtained where for lead, two monometallic species were formed in which Pb(II) is coordinated from the same / opposite side of the strap with different ratios. Finally, Bi(III) promotes a new second sphere of coordination which is responsible for the side selective insertion of the metal. Beside, a transmetalation process speeds up the kinetic insertion of bismuth. In addition, the presence of a cyano group in the α position of the carboxylic acid group creates a steric effect on coordination (in case of Pb(II)) which forces the metal to coordinate from the opposite side of the strap

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32

Vempati, Venkata Surya Raghuram. "Remote detection of hydrogen leak using Nd:YAG pulsed laser induced dual line detection Rayleigh light scattering." [Gainesville, Fla.] : University of Florida, 2005. http://purl.fcla.edu/fcla/etd/UFE0008640.

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33

Deshpande, Sameer Arun. "DIMESIONALITY ASPECTS OF NANO MICRO INTEGRATED METAL OXIDE BASED EARLY STAGE LEAK DETECTION ROOM TEMPERATURE HYDROGEN SENSOR." Doctoral diss., University of Central Florida, 2007. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/2131.

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Detection of explosive gas leaks such as hydrogen (H2) becomes key element in the wake of counter-terrorism threats, introduction of hydrogen powered vehicles and use of hydrogen as a fuel for space explorations. In recent years, a significant interest has developed on metal oxide nanostructured sensors for the detection of hydrogen gas. Gas sensors properties such as sensitivity, selectivity and response time can be enhanced by tailoring the size, the shape, the structure and the surface of the nanostructures. Sensor properties (sensitivity, selectivity and response time) are largely modulated by operating temperature of the device. Issues like instability of nanostructures at high temperature, risk of hydrogen explosion and high energy consumption are driving the research towards detection of hydrogen at low temperatures. At low temperatures adsorption of O2- species on the sensor surface instead of O- (since O- species reacts easily with hydrogen) result in need of higher activation energy for hydrogen and adsorbed species interaction. This makes hydrogen detection at room temperature a challenging task. Higher surface area to volume ratio (resulting higher reaction sites), enhanced electronic properties by varying size, shape and doping foreign impurities (by modulating space charge region) makes nanocrystalline materials ideal candidate for room temperature gas sensing applications. In the present work various morphologies of nanostructured tin oxide (SnO2) and indium (In) doped SnO2 and titanium oxide (titania, TiO2) were synthesized using sol-gel, hydrothermal, thermal evaporation techniques and successfully integrated with the micro-electromechanical devices H2 at ppm-level (as low as 100ppm) has been successfully detected at room temperature using the SnO2 nanoparticles, SnO2 (nanowires) and TiO2 (nanotubes) based MEMS sensors. While sensor based on indium doped tin oxide showed the highest sensitivity (S =Ra/Rg= 80000) and minimal response time (10sec.). Highly porous SnO2 nanoparticles thin film (synthesized using template assisted) showed response time of about 25 seconds and sensitivity 4. The one dimensional tin oxide nanostructures (nanowires) based sensor showed a sensitivity of 4 and response time of 20 sec. Effect of aspect ratio of the nanowires on diffusion of hydrogen molecules in the tin oxide nanowires, effect of catalyst adsorption on nanowire surface and corresponding effect on sensor properties has been studied in detail. Nanotubes of TiO2 prepared using hydrothermal synthesis showed a sensitivity 30 with response time as low as 20 seconds where as, TiO2 nanotubes synthesized using anodization showed poor sensitivity. The difference is mainly attributed to the issues related to integration of the anodized nanotubes with the MEMS devices. The effect of MEMS device architecture modulation, such as, finger spacing, number and length of fingers and electrode materials were studied. It has been found that faster sensor response (~ 10 sec) was observed for smaller finger spacing. A diffusion model is proposed for elucidating the effect of inter-electrode distance variation on conductance change of a nano-micro integrated hydrogen sensor for room temperature operation. Both theoretical and experimental results showed a faster response upon exposure to hydrogen when sensor electrode gap was smaller. Also, a linear increase in the sensor sensitivity from 500 to 80000 was observed on increasing the electrode spacing from 2 to 20 μm. The improvement in sensitivity is attributed to the higher reactive sites available for the gaseous species to react on the sensor surface. This phenomenon also correlated to surface adsorbed oxygen vacancies (O-) and the rate of change of surface adsorbed oxygen vacancies. This dissertation studied in detail dimensionality aspects of materials as well as device in detecting hydrogen at room temperature.
Ph.D.
Department of Mechanical, Materials and Aerospace Engineering
Engineering and Computer Science
Materials Science & Engr PhD

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34

Can, Mukaddes. "Hydrogen Generation From Conventional Fuels Over Mesoporous Mixed Oxide Catalysts Under Time Interrupted Reaction Conditions." Phd thesis, METU, 2011. http://etd.lib.metu.edu.tr/upload/12614520/index.pdf.

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In this study, catalytic activity of the Co and/or Pb-SBA-15 mesoporous catalysts in methane partial oxidation reaction was investigated. By using sol-gel, incipient wetness impregnation and post grafting method, SBA-15 samples are incorporated with Co and/or Pb at different weight loadings to provide a controlled geometry in nanometer scale. The characterization of the synthesized samples was done by XRD, N2 adsorption isotherms, FTIR, TEM images, Raman and XPS analysis. In the present study also, gas phase methane partial oxidation modeling and the synthesizing of mesoporous SBA-15 silica with different pore sizes were investigated. For the samples prepared by sol-gel method, XRD analysis showedthat cobalt exists in the form of Co3O4and Pb exist in the form of PbO. BET surface areas of the Co loaded catalysts are in the range of 479.5-640.1 m2/g. However, in Pb loaded samples, higher metal loading decrease the surface area up to 4.63 m2/g. Considering the both Co and Pb containing bi-metallic samples, TEM and BET results revealed that the ordered hexagonal mesostructure was fully destroyed. The samples prepared by incipient wetness impregnation and post grafting method characterized by using BET, TEM, Raman and XPS analysis. According to the BET results all the samples show ordered mesostructure in agreement with TEM results for all Co and/or SBA-15 mesoporous samples. TEM results also revealed that, the Co(5%) Pb(5%)-SBA-15 catalyst prepared by incipient wetness impregnation method possess big cobalt and lead oxide crystallines on the mesoporous structure. Raman analysis results indicated that cobalt exist in Co3O4 form. According to XPS results all samples containing cobalt include Co3O4. The partial oxidation of methane was carried out in a fixed bed flow-type reactor in a temperature range of 50&ndash
850°
C under atmospheric pressure.According to the reaction test results, the 0.5%Rh-Co-SBA15 catalyst shows the highest methane conversion (82%) and H2 selectivity. The non-precious metal show lower reactivities, addition of Pb to the Co-SBA-15 catalyst increases the catalytic activity and decrease the H2 production temperature.

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35

Bates, Benjamin R. "Within Lake Spatial Variability of Long-chain n-alkanes and their Hydrogen Isotopic Compositions Adirondack Mountains, NY." University of Cincinnati / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1535373859284956.

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36

Rogoff, Eric Brian 1960. "Characterization of water interaction with the Apache Leap Tuff, Superior, Arizona, using stable isotopes of oxygen and hydrogen." Thesis, The University of Arizona, 1988. http://hdl.handle.net/10150/191988.

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Alteration of rock by water is observed in all levels of the Apache Leap Tuff, Superior, Arizona. Possible alteration conditions range from hydrothermal circulation after eruption of the tuff to percolation of low temperature modern water. This study uses stable isotopes of oxygen and hydrogen in matrix phenocrysts and whole rocks to determine temperature and timing of alteration, and the extent of water-rock interaction at progressive distances from fractures. Data indicate low temperatures (20 to 30°C) of water-rock interaction. Water/rock ratios increase stratigraphically upward. Water/rock ratios decrease as distance from fractures decrease, suggesting that fractures may not have been major flow conduits. Calculations indicate a water oxygen isotopic composition similar to modern water, although the water hydrogen isotopic composition is heavier than modern water due to evaporation.

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37

Tierney, Jessica E., Francesco S. R. Pausata, and Peter B. deMenocal. "Rainfall regimes of the Green Sahara." AMER ASSOC ADVANCEMENT SCIENCE, 2017. http://hdl.handle.net/10150/622881.

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During the "Green Sahara" period (11,000 to 5000 years before the present), the Sahara desert received high amounts of rainfall, supporting diverse vegetation, permanent lakes, and human populations. Our knowledge of rainfall rates and the spatiotemporal extent of wet conditions has suffered from a lack of continuous sedimentary records. We present a quantitative reconstruction of western Saharan precipitation derived from leaf wax isotopes in marine sediments. Our data indicate that the Green Sahara extended to 31 degrees N and likely ended abruptly. We find evidence for a prolonged "pause" in Green Sahara conditions 8000 years ago, coincident with a temporary abandonment of occupational sites by Neolithic humans. The rainfall rates inferred from our data are best explained by strong vegetation and dust feedbacks; without these mechanisms, climate models systematically fail to reproduce the Green Sahara. This study suggests that accurate simulations of future climate change in the Sahara and Sahel will require improvements in our ability to simulate vegetation and dust feedbacks.

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38

Suh, Yeon Jee. "Leaf Wax Stable Isotopes as Paleovegetation and Paleohydrologic Proxies: From a Modern Calibration Study to a Paleoclimate Application." University of Cincinnati / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1512045032087257.

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SENNA, ROQUE M. de. "Desenvolvimento e demonstração de funcionamento de um sistema híbrido de geração de energia elétrica, com tecnologia nacional, composto por módulo de células a combustível tipo PEMFC e acumulador chumbo ácido." reponame:Repositório Institucional do IPEN, 2012. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10121.

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Made available in DSpace on 2014-10-09T12:35:00Z (GMT). No. of bitstreams: 0
Made available in DSpace on 2014-10-09T13:59:32Z (GMT). No. of bitstreams: 0
Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

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40

Möller, Lena [Verfasser]. "Funktionalisierung von Oberflächen und Hyaluronsäure-basierte Hydrogele für die Anwendung in der regenerativen Medizin / Lena Möller." Hannover : Technische Informationsbibliothek und Universitätsbibliothek Hannover (TIB), 2012. http://d-nb.info/1023627116/34.

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Mittlmeier, Lena [Verfasser], and Matthias [Akademischer Betreuer] Schieker. "Evaluation der Wirkung eines BMP-7-beladenen Hydrogels im murinen intramedullären Injektionsmodell / Lena Mittlmeier ; Betreuer: Matthias Schieker." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2019. http://d-nb.info/1182899617/34.

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42

Bubnová, Kateřina. "Využití nízkotlakého plazmatu pro čistění olověných archeologických nálezů." Master's thesis, Vysoké učení technické v Brně. Fakulta chemická, 2021. http://www.nusl.cz/ntk/nusl-449329.

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This diploma thesis builds on my bachelor thesis, which was focused on the application of low-pressure hydrogen plasma and argon-hydrogen plasma on layers of corrosion products. According to results of the experiments, an appropriate temperature for plasma chemical treatment of lead samples was detected. However, the process of corrosion removal through plasma chemical treatment needs to be further optimized to prevent potential damage to the original historical artefacts. Optimization of the treatment process is therefore the main subject of this work’s research. The model samples with artificial corrosion layers with dual composition were prepared. These samples were put to desiccator with sand and organic acid. The samples corroded in environment of acetic acid or formic acid with the aim of creating the corrosion, which would be at least partially simulated with corrosion on the original artefacts. The process of corrosion lasted for eleven months. After that, the samples were dried out under reduced pressure, put to the protecting foil with humid and oxygen absorbers. In contrast with my bachelor thesis where the continuous regime was chosen for the treatment, the pulse regime with three different condition settings is used. Process of experiment was monitored by OES, surface of samples was analyzed by SEM, EDX, XRD methods. Results from experiments with model samples were used for treatment of original artefacts with missing documentation, so their eventual damaging was acceptable.

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43

Shaw, Caitlin H. "A Preliminary Investigation of Treating Metal Pollutants in Water by Slow-Release Hydrogen Peroxide." Ohio University / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1493820099202382.

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44

Deloule, Etienne. "Analyses isotopiques à l'échelle intra-cristalline : une contribution à l'étude des systèmes géologiques." Vandoeuvre-les-Nancy, INPL, 1991. http://docnum.univ-lorraine.fr/public/INPL_T_1991_DELOULE_E.pdf.

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La composition isotopique du Plomb a été mesurée sur des lessivages progressifs des minéraux de sulfures des gisements métallifères de la ceinture archéenne de l'Abitibi (Québec). La signature isotopique des gisements en milieu sédimentaire montre que les métaux proviennent d'une croute continentale antérieure à la ceinture de roches vertes, âgée de 2,7 milliards d'années. Les minéralisations associées au volcanisme résultent d'un mélange entre cette source crustale et une source mantellique. L'analyse isotopique à la sonde ionique du plomb et du soufre des galènes de Tristate et du Viburnum trend (Mississippi Valley) met en évidence des variations à courte échelle (100 micromètres) pour ces deux éléments. L'absence de corrélations entre les deux éléments montre l'existence de plusieurs sources de compositions isotopiques différentes et une croissance épisodique. Ces zonations suggèrent que les solutions hydrothermales à l'origine des gisements ont circule dans des fractures avec des débits importants. La modélisation numérique montre que ce type de circulation joue vraisemblablement un rôle important pour la mise en place des gisements du type de la vallée du Missouri. La calibration de la mesure isotopique de l'hydrogène par sonde ionique permet l'analyse de quelques nanogrammes d'échantillons, avec une précision meilleur que 10 %, quand les méthodes classiques en requièrent des milligrammes. L'analyse d'amphiboles dans des xénolites mantelliques équilibres à haute température et haute pression montre des zonations isotopiques importantes à l'échelle du minéral, jusqu'a 60% sur une échelle intra-millimétrique, pour des parasites d'Hawaii et du massif central. Ceci implique la présence d'hétérogénéités isotopiques importantes dans le manteau et une relation temporelle étroite entre les échanges d'hydrogène minéraux phases fluides et le volcanisme qui entraine les xénolites

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45

DIAS, André Luís de França. "Perfil fisiológico e bioquímico de três variedades de cana-de-açúcar (Saccharum spp.) durante a aclimatização." Universidade Federal Rural de Pernambuco, 2014. http://www.tede2.ufrpe.br:8080/tede2/handle/tede2/4723.

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Made available in DSpace on 2016-06-14T15:47:03Z (GMT). No. of bitstreams: 1 Andre Luis de Franca Dias.pdf: 1058700 bytes, checksum: 0141cbefc140d89e9bd8891c383caa9b (MD5) Previous issue date: 2014-02-14
The cultivation of sugarcane in Brazil has notoriety for contributing significantly to the economy. The micropropagation is a tool for tissue culture plants to produce on a large scale genetically identical to the mother plant in a relatively short time compared with the conventional spread, environmental, and controlled aseptic conditions. The acclimatization stage is considered critical by large losses of micropropagated material, caused by the changing environment of the laboratory plants for greenhouses. Objective was to evaluate plants of varieties sugarcane RB931011 , RB92579 and RB98710 in different acclimatization conditions. These varieties were micropropagated in temporary immersion bioreactor (BIT) and acclimatized in a greenhouse whose structural roofing material consisted of milky plastic (PL), half of the area covered in association with black mesh shade (MS) (70% shading ). The plants were subjected to full sun (SP), after 30 days in the greenhouse. The acclimatization period under PL and MS was 15 days. The three varieties were planted in the substrate Carolina Soil® in volumes of 55 cm3 and 95 cm3, establishing the following treatments : T1 (RB931011 - 55 cm3), T2 (RB931011 - 95 cm3), T3 (RB92579 - 55 cm3), T4 (RB92579 - 95 cm3), T5 (RB98710 - 55 cm3) and T6 (RB98710 - 95 cm3). Every 15 days were evaluated: number of leaves (NF), plant height (AP) and percentage of plants with tillers (% P). At the end of the experimental period were determined: dry shoot weight (MSa) and roots (MSr), percentage of survival (S%), leaf area (AF), high water content (CHR), stomatal density, activity of superoxide dismutase (SOD), ascorbate peroxidase (APX) and catalase (CAT), content of malondialdehyde (MDA) and hydrogen peroxide. The experimental design was completely randomized in a 2x3 factorial design with 20 replications. Each replicate was represented by one plant per pot. The RB92579 and RB98710 varieties showed more robustness reaching the largest biometric medium and higher survival rate in the acclimatization. The largest volume of substrate provided better average height, dry weight, leaf area and lower SOD activity after 45 days of acclimatization, highlighting the influence of stress reduction and balance in plants. The substrate volume of 95 cm3 is the most suitable for acclimatization and plant production of sugarcane.
A cultura da cana-de-açúcar tem destaque no Brasil por contribuir consideravelmente com a economia. A micropropagação é uma ferramenta da cultura de tecidos de plantas para produção de plantas em larga escala geneticamente idênticas à planta mãe, em um tempo relativamente curto em comparação com a propagação convencional, em condições ambientais, assépticas e controladas. A fase de aclimatização é considerada crítica pelas grandes perdas do material micropropagado, causada pela mudança de ambiente das plantas do laboratório para as estufas e casas de vegetação. Objetivou-se avaliar mudas de cana-de-açúcar das variedades RB931011, RB92579 e RB98710 em diferentes condições de aclimatização. Essas variedades foram micropropagadas em biorreator de imersão temporária (BIT) e aclimatizadas em estufa cujo material estrutural de cobertura era constituído de plástico leitoso (PL), sendo metade da área coberta em associação à malha de sombreamento (MS) preta (70% de sombreamento). As plantas foram submetidas a sol pleno (SP), após 30 dias em estufa. O período de aclimatização sob PL e MS foi de 15 dias. As três variedades foram plantadas no substrato Carolina Soil® nos volumes de 55 cm3 e 95 cm3, estabelecendo-se os seguintes tratamentos: T1 (RB931011 – 55 cm3), T2 (RB931011 – 95 cm3), T3 (RB92579 – 55 cm3), T4 (RB92579 – 95 cm3), T5 (RB98710 – 55 cm3) e T6 (RB98710 – 95 cm3). A cada 15 dias foram avaliados: número de folhas (NF), altura da planta (AP) e porcentagem de plantas com perfilhos (% P). Ao final do período experimental determinaram-se: massa seca da parte aérea (MSa) e das raízes (MSr), porcentagem de sobrevivência (S%), área foliar (AF), teor relativo de água (CHR), densidade estomática, atividade das enzimas superóxido dismutase (SOD), ascorbato peroxidase (APX) e catalase (CAT), teor do aldeído malônico (MDA) e de peróxido de hidrogênio. O delineamento experimental foi inteiramente casualizado, em um fatorial 2x3, com 20 repetições. Cada repetição foi representada por uma planta por tubete. As variedades RB92579 e RB98710 apresentaram mais robustez atingindo as maiores médias biométricas e maior taxa de sobrevivência na aclimatização. O maior volume de substrato proporcionou maior média de altura, peso da matéria seca, área foliar e menor atividade da SOD aos 45 dias de aclimatação, destacando-se na influência da redução e equilíbrio do estresse nas mudas. O volume de substrato de 95 cm3 é o mais indicado para a aclimatização e produção de mudas de cana-de-açúcar.

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46

Peigat, Laurent. "Modélisation d'un joint viscoplastique pour la filière hydrogène." Phd thesis, Ecole Nationale Supérieure des Mines de Paris, 2012. http://pastel.archives-ouvertes.fr/pastel-00756297.

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L'Electrolyse de la Vapeur d'eau à Haute Température (EVHT) est l'un des procédésde production d'hydrogène les plus prometteurs. Dans l'optique d'une économie del'hydrogène produit par EVHT, de nombreux verrous restent à lever. L'un d'entre euxporte sur l'étanchéité. En effet, dans un EVHT, la gestion des gaz est primordiale. Ilfaut pouvoir gérer et prévoir dans le temps le comportement des joints afin d'éviter unedégradation des performances. Or, en EVHT, les températures de fonctionnement sontélevées (classiquement autour de 800 °C), des phénomènes de fluage ou de relaxationapparaissent, le différentiel de dilatation thermique entre les cellules électrochimiques encéramique et les interconnecteurs métalliques doit être pris en compte. Enfin, il convientde maintenir l'étanchéité de l'empilement à faible niveau d'effort pour ne pas risquerd'endommager la partie céramique.L'objet du travail de cette thèse démarre par un constat simple : nous ne disposons pasd'outils de prédimensionnement des joints à haute température permettant de prévoirun débit de fuite. Dès lors que l'on est amené à changer un paramètre de fonctionnement,comme la température, la pression, la stratégie de chargement, la géométrie ou la naturedu joint, une nouvelle expérience doit être menée.A partir d'essais d'étanchéité et de simulations numériques aux éléments finis, un modèleoriginal est proposé. Ce modèle qui a été validé en fonction de différents paramètresexpérimentaux permet d'estimer le débit de fuite associé à un joint en Fecralloy (Fe-CrAl) selon sa forme, ses conditions de serrage et du temps de maintien. Offrant ainsila possibilité de concevoir à moindre coût des joints spécifiques pour l'application visée.

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47

Tsvetkova, Galina Valeryevna. "An autonomous long-term fast reactor system and the principal design limitations of the concept." Diss., Texas A&M University, 2003. http://hdl.handle.net/1969.1/36.

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The objectives of this dissertation were to find a principal domain of promising and technologically feasible reactor physics characteristics for a multi-purpose, modular-sized, lead-cooled, fast neutron spectrum reactor fueled with an advanced uranium-transuranic-nitride fuel and to determine the principal limitations for the design of an autonomous long-term multi-purpose fast reactor (ALM-FR) within the principal reactor physics characteristic domain. The objectives were accomplished by producing a conceptual design for an ALM-FR and by analysis of the potential ALM-FR performance characteristics. The ALM-FR design developed in this dissertation is based on the concept of a secure transportable autonomous reactor for hydrogen production (STAR-H2) and represents further refinement of the STAR-H2 concept towards an economical, proliferation-resistant, sustainable, multi-purpose nuclear energy system. The development of the ALM-FR design has been performed considering this reactor within the frame of the concept of a self-consistent nuclear energy system (SCNES) that satisfies virtually all of the requirements for future nuclear energy systems: efficient energy production, safety, self-feeding, non-proliferation, and radionuclide burning. The analysis takes into consideration a wide range of reactor design aspects including selection of technologically feasible fuels and structural materials, core configuration optimization, dynamics and safety of long-term operation on one fuel loading, and nuclear material non-proliferation. Plutonium and higher actinides are considered as essential components of an advanced fuel that maintains long-term operation. Flexibility of the ALM-FR with respect to fuel compositions is demonstrated acknowledging the principal limitations of the long-term burning of plutonium and higher actinides. To ensure consistency and accuracy, the modeling has been performed using state-of-the-art computer codes developed at Argonne National Laboratory. As a result of the computational analysis performed in this work, the ALM-FR design provides for the possibility of continuous operation during about 40 years on one fuel loading containing mixture of depleted uranium with plutonium and higher actinides. All reactor physics characteristics of the ALM-FR are kept within technological limits ensuring safety of ultra-long autonomous operation. The results obtained provide for identification of physical features of the ALM-FR that significantly influence flexibility of the design and its applications. The special emphasis is given to existing limitations on the utilization of higher actinides as a fuel component.

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Ross, Martin C. "Lean combustion characteristics of hydrogen-nitrous oxide-ammonia mixtures in air." Thesis, 1997. https://thesis.library.caltech.edu/227/1/Ross_mc_1997.pdf.

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We report experimental studies on the combustion of lean hydrogen-nitrous oxide-ammonia-air mixtures. This project is in support of the waste tank safety assessment for the storage facility at Hanford, WA. This study focuses on combustion limits, pressure histories, and flame speeds of flammable gas mixtures characteristic of this facility. A facility was constructed to study the lean combustion characteristics of mixtures containing ammonia. This facility consists of a gas-handling system, a remotely-controlled 400-liter pressure vessel, a vacuum system capable of pumping and disposing of the unburned ammonia, and a data acquisition system. A total of 208 experiments were conducted for this study. All experiments were performed using air as a primary oxidizer. Separate experiments were carried out for binary and ternary mixtures containing air, hydrogen, ammonia, hydrogen-nitrous oxide, ammonia-hydrogen, and ammonia-nitrous oxide. Other experiments examined quaternary mixtures of ammonia-nitrous oxide-hydrogen-air. Mixtures were burned under quiescent and turbulent conditions and, in some cases, with an inert substitute (nitrogen) for the nitrous oxide. The pressure and temperature were recorded in the tank throughout the combustion events. A schlieren video photography system was used to observe flame propagation and measure flame speeds. The final equilibrium pressures were also measured in the experiments. The results demonstrate that nitrous oxide is inert in lean mixtures of hydrogen-air-nitrous oxide and reactive in lean mixtures of ammonia-air-nitrous oxide. For mixtures of hydrogen-nitrous oxide-ammonia-air, the reactivity of the nitrous oxide depends on the hydrogen-ammonia ratio. A correlation between the adiabatic, constant-pressure, flame temperature of the mixture and the reactivity threshold of the nitrous oxide is proposed. It was found that the nitrous oxide began reacting when the adiabatic flame temperature was between 1100 and 1300 K. It was found that for flame temperatures above this threshold, presence of nitrous oxide affects the flammability limit, the pressure history, and the flame speed.

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Schlup, Jason Robert. "Numerical Investigations of Transport and Chemistry Modeling for Lean Premixed Hydrogen Combustion." Thesis, 2018. https://thesis.library.caltech.edu/10991/1/schlup_jason_2018.pdf.

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The use of hydrogen as a fuel for power generation applications has been suggested as an additive to, or replacement of, hydrocarbon fuels. The safety of hydrogen combustion has also received recent attention due to nuclear power plant disasters and the rise of hydrogen refuelling stations. In these uses and scenarios, lean hydrogen--air flames are prone to thermo-diffusive instabilities which can be dangerous to equipment and personnel. These instabilities are heavily influenced by two mechanisms: transport properties (e.g., diffusion) and chemical species production rates. This thesis investigates lean premixed hydrogen combustion using direct numerical simulations. A wide range of flame configurations are considered, spanning one-dimensional steady configurations to three-dimensional unsteady laminar and turbulent flames with high curvature. In particular, the two controlling mechanisms of thermo-diffusive instabilities are carefully investigated.

The effects of transport properties, in particular the importance of thermal diffusion in these mixtures, are quantified through global and local evaluations. Thermal diffusion is found to change flame speeds in one-dimensional flat flames, and also modify species profiles due to the increased diffusivity of light reactants. The impact of thermal diffusion is greatly enhanced in the presence of flame curvature, resulting in higher flame speeds (20% to 30% for two- and three-dimensional laminar and turbulent flames), fuel consumption, and flame surface area relative to simulations neglecting thermal diffusion. The mixture-averaged thermal diffusion model proposed by Chapman and Cowling (1970) is found to accurately reproduce global and local flame statistics (including enhanced burning and local extinction) computed using multicomponent transport at significantly reduced costs. Further cost reductions of the mixture-averaged thermal diffusion method are undertaken, and a new model is developed with constant computational requirements for large (~100 species) chemical models. The resulting reduced thermal diffusion model additionally improves upon the accuracy of the mixture-averaged thermal diffusion technique.

The effects of fluctuating chemical source terms on flame instabilities are then investigated using tabulated chemistry. One-dimensional unstretched flames including non-equal diffusion and thermal diffusion are incorporated into a chemistry table. This table successfully captures the interaction of differential diffusion and flame curvature. The chemistry tabulation approach is applied to a similar set of flame configurations, and accurate predictions of global and local statistics are found. The tabulated chemistry method reproduces flame curvature, local enhanced burning, and local extinction of unstable flames using one-dimensional, flat, burning flames in its construction. The proposed reduced-order thermal diffusion and chemistry tabulation models significantly reduce computational costs while simultaneously including physical properties necessary to predict lean premixed hydrogen--air flame instabilities.

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Hernandez, Perez Francisco Emanuel. "Subfilter Scale Modelling for Large Eddy Simulation of Lean Hydrogen-enriched Turbulent Premixed Combustion." Thesis, 2011. http://hdl.handle.net/1807/29744.

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Hydrogen (H2) enrichment of hydrocarbon fuels in lean premixed systems is desirable since it can lead to a progressive reduction in greenhouse-gas emissions, while paving the way towards pure hydrogen combustion. In recent decades, large-eddy simulation (LES) has emerged as a promising tool to computationally describe and represent turbulent combustion processes. However, a considerable complication of LES for turbulent premixed combustion is that chemical reactions occur in a thin reacting layer at small scales which cannot be entirely resolved on computational grids and need to be modelled. In this thesis, subfilter-scale (SFS) modelling for LES of lean H2-enriched methane-air turbulent premixed combustion was investigated. Two- and three-dimensional fully-compressible LES solvers for a thermally perfect reactive mixture of gases were developed and systematically validated. Two modelling strategies for the chemistry-turbulence interaction were pursued: the artificially thickened flame model with a power-law SFS wrinkling approach and the presumed conditional moment (PCM) coupled with the flame prolongation of intrinsic low-dimensional manifold (FPI) chemistry tabulation technique. Freely propagating and Bunsen-type flames corresponding to stoichiometric and lean premixed mixtures were considered. Validation of the LES solvers was carried out by comparing predicted solutions with experimental data and other published numerical results. Head-to-head comparisons of different SFS approaches, including a transported flame surface density (FSD) model, allowed to identify weaknesses and strengths of the various models. Based on the predictive capabilities of the models examined, the PCM-FPI model was selected for the study of hydrogen-enrichment of methane. A new progress of reaction variable was proposed to account for NO. The importance of transporting species with different diffusion coefficients was demonstrated, in particular for H2. The proposed approach was applied to a Bunsen-type configuration, reproducing key features observed in the experiments: the enriched flame was shorter, which is attributed to a faster consumption of the blended fuel; and the enriched flame displayed a broader two-dimensional curvature probability density function. Furthermore, reduced levels of carbon dioxide (CO2), increased levels of nitrogen monoxide (NO), and a slight increase in the carbon monoxide (CO) levels in areas of fully burned gas were predicted for the enriched flame.

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Dissertations / Theses on the topic 'Lean hydrogen'

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