Ratio Of Hydrogen Research Articles

Experimental Investigation and Chemical Kinetics Analysis of Carbon Dioxide Inhibition on Hydrogen-Enriched Liquefied Petroleum Gas (LPG) Explosions

The utilization of hydrogen-enriched liquefied petroleum gas (LPG) is an effective means of reducing carbon emissions, but the special physical and chemical properties of hydrogen have raised concerns among the public. To delve into the intricate chemical kinetic mechanisms governing the inhibitory effect of CO2 on the explosion of hydrogen-enriched LPG, this study systematically investigated the influence of varying CO2 concentrations (3%, 6%, and 9%) on the explosion characteristics of hydrogen-enriched LPG (hydrogen ratio ranging from 0 to 0.5) within a 20 L spherical explosion chamber. Subsequently, a chemical kinetic analysis was conducted, focusing on the explosion reaction dynamics of the H2/LPG/CO2/Air mixture, encompassing temperature sensitivity assessments and the production rates of key free radicals. The findings reveal that although hydrogen incorporation does not significantly alter the maximum explosion pressure of LPG, it markedly accelerates the explosion reaction rate, posing a challenge for CO2 in effectively inhibiting the explosion of hydrogen-enriched LPG. CO2 functions as a stabilizing third body within the reaction system, diminishing the collision frequency among free radicals, hydrogen molecules, hydrocarbon molecules, and oxygen molecules, thereby slowing down the reaction rate. As the proportion of hydrogen increases, the concentration of ·H radicals, known for their high reactivity, escalates, rapidly completing the propagation phase of the chain reaction and intensifying the overall generation rates of critical free radicals, including ·H, ·O, and ·OH. Notably, the key reaction H+O2⇋O+OH, which governs the reaction temperature, undergoes significant enhancement, further accelerating the explosion reaction rate and ultimately diminishing the inhibitory efficacy of CO2 against the hydrogenated LPG explosion. Furthermore, as the amount of hydrogen added increases, hydrogen’s competitiveness for oxygen within the reaction system markedly improves, attenuating the oxidation of hydrocarbons. Concurrently, the alkane recombination reaction, exemplified by C3H6+CH3(+M)⇋sC4H9(+M), is strengthened. These insights provide valuable understanding of the complex interactions and mechanisms during the explosion of hydrogen-enriched LPG in the presence of CO2, with implications for the safe application of hydrogen-enriched LPG.

Laser-induced plasma analysis of ammonia-oxygen and ammonia-oxygen-enriched-air flames at elevated pressures

This study employed Laser-induced breakdown spectroscopy (LIBS) to measure the fuel-oxidizer ratio (FOR) of ammonia combustion with oxygen-enriched air and pure oxygen flames at elevated pressures (100 - 300 kPa). The correlations between the spectral line intensity ratios of nitrogen (N), hydrogen (H), oxygen (O), and equivalence ratio were used to quantify the FOR of flames at various pressures. The effect of pressure on the stability and precision of the calibration profiles for the elemental intensity ratios in flames was investigated. It was observed that the H/O correlation decreases with pressure increase for both ammonia flames. N/O correlations decrease with elevated pressure for the ammonia-oxygen flame. Furthermore, the nitrogen (NII) spectral emission lines at 568 nm and 595 nm were used to estimate the plasma temperature, while the hydrogen (Hα) line at 656 nm was used for electron number density measurements.

Optimizing the Pore Structure of Lotus-Type Porous Copper Fabricated by Continuous Casting.

Lotus-type porous copper was fabricated using a continuous casting method in pressurized hydrogen and nitrogen gas atmospheres. This study evaluates the effects of process parameters, such as the hydrogen ratio, total pressure, and transference velocity, on the resulting pore structure. A continuous casting process was developed to facilitate the mass production of lotus-type porous copper. To achieve the desired porosity and pore diameter for large-scale manufacturing, a systematic evaluation of the influence of each process parameter was conducted. Lotus-type porous copper was produced within a hydrogen ratio range of 25-50%, a transference velocity range of 30-90 mm∙min-1, and a total pressure range of 0.2-0.4 MPa. As a result, the porosity ranged from 36% to 55% and the pore size varied from 300 to 1500 µm, demonstrating a wide range of porosities and pore sizes. Through process optimization, it is possible to control the porosity and pore size. The hydrogen ratio and total pressure were found to primarily affect porosity, whereas the hydrogen ratio, transference velocity, and total pressure significantly influenced pore diameter. When considering these parameters together, porosity was most influenced by the hydrogen ratio, whereas the total pressure and transference velocity had a greater influence on pore diameter. Reducing the hydrogen ratio and increasing the transference velocity and total pressure reduced the pore diameter and porosity. This optimization of the continuous casting process enables the control of porosity and pore diameter, facilitating the production of lotus-type porous copper with the desired pore structures.

Investigation on the effects of swirl-strength on flashback phenomenon of premixed CH[formula omitted]/H[formula omitted]/air flame in a bluff-body swirl burner

Blending a low ratio of hydrogen into traditional hydrocarbon fuels can reduce the modification in structure of existing combustors. However, even a low hydrogen ratio can increase the propensity of flashback due to the extremely high reactivity of hydrogen. Swirl number is a key parameter of swirl combustors which determines the flow structure. To design reliable gas turbine combustors for hydrogen-blended fuels, the study in the effect of swirl strength on flashback characteristic and the underlying mechanism is necessary. In this study, the flashback characteristics of premixed 30% H2/70% CH4/air flame in a bluff-body swirl burner is investigated via both experiment and large-eddy simulations with the flamelet-generated-manifold method (FGM-LES). The flashback mode and flame-flow interaction are analyzed based on the LES results. It is found that the increase in swirl strength will increase the propensity of flashback and promote the flashback speed of premixed 30% H2/70% CH4/air flame in the bluff-body swirl burner. The turns from Mode II (small-scale flame bulges leading flashback) to Mode I (large-scale swirling flame tongue leading flashback) during flashback of hydrogen-blended flames due to the production of stronger reversed flow by swirling flow. It is also found that stronger swirl strength will result in a smoother flame front and narrower strain rate distribution range which suppresses the local hydrogen enrichment due to preferential diffusion of hydrogen, thus suppressing the flame propagating speed. However, this effect is not dominant in flashback process compared to the promotion of reversed flow by increased swirl strength.

Numerical simulation of the effects of pulsed injection on combustion and flow processes in a supersonic combustor

This paper describes two-dimensional numerical simulations of pulsed injection to a hydrogen-fueled air-breathing ramjet using the Reynolds-averaged Navier–Stokes method. We analyze the effects of sinusoidal pulsed injection on the start-up ignition time, start-up ignition range, combustion efficiency, and flow field evolution of the ramjet and compare the performance with that of steady injection. The results show that pulsed injection shortens the ignition time and optimizes the ignition equivalence ratio of hydrogen. Pulsed injection also improves the combustion efficiency of hydrogen, increasing the thrust of the engine by 7.79% compared with steady injection under the same equivalence ratio. We find that pulsed injection can cause oscillations in the ramjet combustion flow field, and show that the oscillation frequency is affected by the pulsed injection frequency.

Experimental analysis and optimization of the variable valve timing on attaining high efficiency with low NOx emission of a direct-injected hydrogen engine

The direct-injection hydrogen engine (DI-H2ICE) has demonstrated zero carbon emissions with high brake thermal efficiencies (BTE). Due to the high stoichiometric air–fuel ratio of hydrogen, with a lean burn strategy the gas exchange process of a hydrogen engine is different to a gasoline engine, and the valve timing controlling strategy requires reinvestigation. In this research, the optimal variable valve timing (VVT) is investigated in a 2.0 L DI H2ICE. The intake and exhaust valve timing controlling strategies are analyzed experimentally over the whole operating map. A multi-indicator decision-making method is applied to determine the entropy weight of BTE and NOx emissions. Results indicate that BTE greatly benefits from advanced intake valve timing, and exhaust valve timing affects BTE through pumping losses. Advanced intake and exhaust valve timings are employed in the hydrogen engine to enhance the BTE until the NOx emissions rise rapidly at high loads. The retarded exhaust valve timing helps reduce NOx emissions and avoid the risk of abnormal combustion at high loads. Therefore, earlier IVO and later EVC are applied simultaneously for DI-H2ICE compared to the gasoline engine. A maximum power of 124.8 kW at an engine speed of 4500 rpm and a BTE of 42.57 % is achieved with optimized VVT. Furthermore, NOx emissions are controlled to under 20 ppm over nearly half of the engine operating map. The conclusions are valuable in the development of high-performance H2ICEs, the numerical simulation studies, and hydrogen fuel applications.

Efficient cooling strategies for liquid hydrogen pipelines: A comparative analysis

Liquid hydrogen (LH2) stands out for its high energy density, efficient transportation, and safe low-pressure storage. However, the challenge lies in achieving rapid cooling of LH2 pipelines while minimizing hydrogen loss. This paper introduces a robust three-dimensional model for simulating the unsteady-state heat transfer and the gas-liquid two-phase flow within LH2 pipelines. Throughout the cooling cycle, the pipe undergoes transitions in flow patterns, including stratified smooth flow, wavy flow, and intermittent flow, in which wavy flow dominates due to the extremely low liquid-to-gas density ratio of hydrogen. A comprehensive comparative analysis is conducted for three cooling modes: constant flow, variable flow, and pulsing flow. Finally, an evaluative framework for distinct pipeline cooling modes has been proposed. A reasonable variable flow cooling mode exhibits certain advantages in both cooling time and liquid hydrogen consumption when compared with the constant flow cooling mode, and the pulse flow cooling method adeptly capitalizes on the performance benefits derived from intermittent flow. Specifically, within the cooling range of 40 K–20 K, it substantially economizes liquid hydrogen consumption (15%–20 %), albeit concomitant with an extended total cooling time (40%–60 %). This study can offer theoretical insights to guide the high-efficiency cooling of liquid hydrogen pipelines.

Time-dependent variations in desorbed gas composition: methodological analysis of asphaltite vein investigation results

In this study, a phenomenon that can have significant technical and economic impacts in the mining and unconventional gas production of hydrocarbon resources is discussed, change of gas composition during desorption period. The change is analyzed, related findings are obtained and engineering tools are forged. In this scope, a member of the Southeastern Turkey asphaltite’s gas content and composition character was examined. 12+1 samples were collected at equal intervals from an inclined drillhole that cut through the asphaltite vein. The United States Bureau of Mines (USBM) direct method was employed to determine the gas content. Gas composition analysis was performed on gas samples, which were collected four times throughout the desorption period. Residual gas composition is determined as well. During desorption period, methane and hydrogen ratios exhibited decreasing trends, while others have increasing trends. In evaluating of the collected data, the desorption order between gas compounds are revealed. Logarithmic trend functions are generated to estimate the concentrations of gas compounds at specific time points. With these functions and gas content measurement data, weighted average concentrations for gas compounds are determined. These concentration functions and the weighted average results are used to create engineering tools showing unit energy content of desorbed gas through desorption period both instantaneous and cumulative. Similarly, change in lower explosive limit and auto-ignition temperature during desoption period is shown. The weighted average gas concentrations obtained are used to interpret geological insights as they are the actual gas composition of the samples. In the study, gas content characteristic properties of Üçkardeşler asphaltite vein is comprehensively presented. Accordingly, the mean gas content, excluding one sample with a value of 2.78 m3/t at a location near a fault intersection, was found to be 1.66 m3/t. The average volumetric concentrations of methane, ethane, propane, and acetylene in the desorbed gas were determined as 61.6%, 24.5%, 10.7%, and 2.3%, respectively. The remaining part primarily consisted of heavier hydrocarbons, with low amounts of carbon dioxide and hydrogen.

Defect evolution in pure iron under simultaneous in-situ irradiation with Fe+-He+-H2+: Impact of hydrogen & helium-dose ratios

The properties of materials in irradiation environments are significantly influenced by hydrogen and helium. However, the effects of gas-dose ratio on the evolution of defects, which are crucial for material application assessment in various nuclear reactors and for understanding fundamental irradiation mechanisms, remain unclear. In this paper, defect evolution within pure iron was investigated in-situ through simultaneous triple-beam irradiation at 723 K using 400 keV Fe+, 50 keV He+ and 50 keV H2+. Four different gas-dose ratios were used: 10 appm He/dpa & 45 appm H/dpa, 10 appm He/dpa & 100 appm H/dpa, 100 appm He/dpa & 100 appm H/dpa, and 45 appm He/dpa & 10 appm H/dpa. It was observed that the gas-dose ratio significantly influenced the evolution of defects, including the size and density of dislocation loops and bubbles. It was found that an increased hydrogen-dose ratio, when paired with a constant helium-dose ratio, resulted in smaller loop sizes, but increased the density of loops and bubbles. Conversely, maintaining a constant hydrogen dose ratio while increasing the helium dose ratio proved advantageous for raising the density of loops and bubbles, and for reducing loop size. Additionally, an increase in both hydrogen and helium-dose ratios was associated with heightened swelling due to bubble formation. Moreover, hydrogen was found to have a less impact on loop nucleation compared to helium, and helium exhibited a more pronounced inhibitory effect on loop migration than hydrogen.

Laminar burning velocity, cellular instability, and the superadiabatic flame temperature phenomenon for NH3/syngas/air premixed flames

The laminar burning velocity (LBV) and cellular instability of ammonia/syngas/air were investigated using the spherically expanding flame method at an initial pressure of 3 atm and temperatures of 298–448 K. The impacts of equivalence ratio, temperature, and hydrogen ratio on LBV were scrutinized. The results demonstrate that the LBV varies non-monotonically with the equivalence ratio and increases with increasing temperature and hydrogen ratio. Flame instability was analyzed using flame uplift rate, Lewis number, thermal expansion ratio, flame thickness, critical radius, critical Peclet number and logarithmic growth rate of perturbation in combination with the schlieren images. Of these, the flame uplift rate is used to quantify buoyancy instability, a flame instability that has received little attention. At high pressures, lower LBV makes the flame susceptible to buoyancy instability. The flame uplift rate increases with increasing flame radius, suggesting that the buoyancy instability becomes increasingly significant as the spherical flame expands. The diffusional-thermal instability is weaker at the fuel-rich side and enhanced at the leaner side. As the hydrogen ratio increases, the flame instability increases. Hydrodynamic instability is not susceptible to temperature, which is only slightly weakened with increasing temperature. Additionally, the phenomenon of superadiabatic flame temperature (SAFT) in ammonia/syngas/air flames was first found and analyzed its temperature dependence. Increasing the initial temperature suppresses SAFT occurrence.

Chemical effect of H2 on NH3 combustion in an O2 environment via molecular dynamics simulations

Due to the imperative to reduce carbon emissions, NH3-H2 mixed combustion has garnered significant attention. However, the knowledge of the reaction kinetics of NH3-H2-O2 mixtures at the molecular level remains limited. In this paper, the reactive force-field (ReaxFF) method was employed to study the microscale reaction kinetics of the NH3-H2-O2 mixture with varying hydrogen ratios (HR). The results of the microcanonical ensemble simulations indicated that the addition of H2 significantly increased the combustion performance of NH3. However, H2 did not change the two primary reaction paths of NH3 oxidation (NH3 → N2H2 → N2 and NH3 → NO → N2). The addition H2 not only led to a shift in the initiation reactions from NH3-O2 to H2-O2 reactions, but also notably enhanced the concentration of HO2 and OH radicals (e.g., O2 + H2 → HO2 + H), which accelerated the extraction of H from NxHy and subsequently facilitated the immediate formation of N2. Furthermore, the ignition delay decreased from 120 ps to 40 ps, and the activation energies decreased from 295.46 kJ/mol to 162.12 kJ/mol as HR increased from 0 to 0.3 under the equivalence ratio of 0.4. These key findings can guide the development of clean NH₃ combustion technology.

Cryogenic vacuum distillation vs Cavitron methods in ecohydrology: Extraction protocol effects on plant water isotopic values

Stable isotope ratios of hydrogen and oxygen in plant water are widely used for water tracing in ecohydrology studies. In this approach, plant water is extracted for isotopic analysis of δ2H and δ18O. Among the extraction methods, cryogenic vacuum distillation (CVD) has been the most popular, but its impact on the isotopic composition of plant water is currently under debate. Newer Cavitron method have been proposed to replace CVD method for xylem water extraction. These recommendations have been largely based on comparisons between Cavitron-xylem water with low temperatures CVD-xylem water. However, the CVD protocol (extraction temperature and time) varies widely across laboratories, and no direct, systematic comparison has yet been made between extraction temperature and time protocols vs. the Cavitron approach. Here we compared the isotopic values of xylem water from the same tree obtained through CVD extraction at 60 °C (60, 120, 240, 360 min), 100 °C (30, 60, 120, 240 min), 140 °C (15, 30, 60, 120, 240 min), and 200 °C (15, 30 min). Subsequently, we compared the results of CVD-xylem water with Cavitron-xylem water. Our data show that isotopic values for CVD-xylem water became more positive with increasing extraction time under the same extraction temperature. Such extractions also became more isotopically positive with increasing extraction temperature for the same extraction time. When total extraction efficiency exceeded 98 %, there was no δ18O difference in CVD-xylem water among any of the different protocols (p > 0.05). However, lower extraction temperatures resulted in more negative δ2H when compared to higher temperature extraction (p < 0.05). Cavitron-xylem water was close to CVD-xylem water (average difference of 3 ‰ for δ2H and 0.5 ‰ for δ18O, n = 79) when total extraction efficiency for CVD was below 98 %. But for extraction efficiencies beyond 98 %, the Cavitron-xylem water was more negative in δ2H (17.3 ‰, n = 70) and δ18O (1.7 ‰, n = 70) than CVD-xylem water. Compared to Cavitron-xylem water, CVD-xylem water at 200 °C with extraction efficiency > 98 % was closer to the soil water. Further study is necessary to conduct a complete cross-comparison between Cavitron and CVD at different temperatures with different species at various water and salt stress conditions. But our results suggest that abandoning CVD for plant water maybe premature until such complete comparison work is done.

From swamp to sea: Quantifying terrestrial dissolved organic carbon in a tropical shelf sea using hydrogen isotope ratios

Dissolved organic carbon (DOC) is a key component of coastal biogeochemical cycles, but its composition and reactivity depend on the relative contribution of autochthonous aquatic versus allochthonous terrigenous DOC (tDOC). In complex coastal waters, tDOC is commonly quantified using the bulk DOC stable carbon isotope ratio (δ13CDOC). However, several limitations can hamper the use of δ13CDOC in marine ecosystems, such as (1) the narrow and often overlapping separation of the autochthonous and allochthonous endmembers, and (2) mineralization of tDOC to dissolved inorganic carbon creates a reservoir effect such that autochthonous DOC can acquire a terrigenous-like δ13CDOC. The stable isotope ratio of non-exchangeable hydrogen in the DOC (δ2Hn) has emerged as a new tool that can potentially overcome these limitations: (1) δ2Hn has a large separation between aquatic and terrigenous endmembers (>50‰) and (2) it is not subject to reservoir effects caused by tDOC mineralization. Here, we evaluate the potential of δ2Hn obtained from solid phase-extracted dissolved organic matter (SPE-DOM), by comparing it to δ13CDOC and chromophoric DOM (CDOM) optical properties. We collected samples at a site in Southeast Asia’s Sunda Shelf that experiences substantial seasonal variation in tDOC input, driven primarily by the monsoon-induced physical advection of peatland-derived tDOC. Over a 1-year monthly time series, the terrigenous fraction of DOC (fterr) determined using δ2Hn of SPE-DOM and δ13CDOC of bulk DOC was well correlated (r2 = 0.42), and there was no significant difference in fterr between the two isotope systems. In fact, δ2Hn displayed slightly stronger correlations with salinity and CDOM optical properties compared to δ13CDOC. Our results indicate that δ2Hn of SPE-DOM is effective for quantifying tDOC across coastal gradients, potentially offering greater sensitivity than δ13CDOC, and is a viable alternative in settings where δ13CDOC is inadequate.

Unexpected increase of the deuterium to hydrogen ratio in the Venus mesosphere

This study analyzes H2O and HDO vertical profiles in the Venus mesosphere using Venus Express/Solar Occultation in the InfraRed data. The findings show increasing H2O and HDO volume mixing ratios with altitude, with the D/H ratio rising significantly from 0.025 at ~70 km to 0.24 at ~108 km. This indicates an increase from 162 to 1,519 times the Earth's ratio within 40 km. The study explores two hypotheses for these results: isotopic fractionation from photolysis of H2O over HDO or from phase change processes. The latter, involving condensation and evaporation of sulfuric acid aerosols, as suggested by previous authors [X. Zhang et al., Nat. Geosci. 3, 834-837 (2010)], aligns more closely with the rapid changes observed. Vertical transport computations for H2O, HDO, and aerosols show water vapor downwelling and aerosols upwelling. We propose a mechanism where aerosols form in the lower mesosphere due to temperatures below the water condensation threshold, leading to deuterium-enriched aerosols. These aerosols ascend, evaporate at higher temperatures, and release more HDO than H2O, which are then transported downward. Moreover, this cycle may explain the SO2 increase in the upper mesosphere observed above 80 km. The study highlights two crucial implications. First, altitude variation is critical to determining the Venus deuterium and hydrogen reservoirs. Second, the altitude-dependent increase of the D/H ratio affects H and D escape rates. The photolysis of H2O and HDO at higher altitudes releases more D, influencing long-term D/H evolution. These findings suggest that evolutionary models should incorporate altitude-dependent processes for accurate D/H fractionation predictions.

Efficient and low-cost Ni-NiO/Al2O3 catalysts with dual-active-sites for selective catalytic conversion of phthalic anhydride to phthalide

A efficient and low-cost nickel-based catalyst with abundant Ni/NiO heterojunctions was constructed and applied in the hydrodeoxygenation of phthalic anhydride to phthalide. The Ni/NiO heterojunction catalysts were prepared by treating mixed metal oxides derived from NiAl-LDH with different ratio in hydrogen at 400 °C, as confirmed by the XRD, H2-TPR, TEM and XPS characterization results. The developed Ni-NiO/Al2O3(3) sample with maximal Ni/NiO heterojunction possessed significant activity in phthalic anhydride hydrogenation with 99.7 % conversion and 90.6 % selectivity of phthalide at 170 °C and 4 MPa H2, as a result the amazing activity of 15.8 mmol·g−1·s−1 was achieved. Besides, Ni-NiO/Al2O3(3) catalyst exhibited good stability in this reaction, which indicated the Ni-NiO/Al2O3(3) catalyst haswideapplicationprospect in the hydrodeoxygenation of phthalic anhydride to phthalide. The Ni/NiO heterojunction in the catalyst was the key to achieve the amazing activity. Based on the kinetic analysis and theoretical calculations, the cooperative catalytic mechanism was found inthis reaction. The design of synergetic catalyst with dual-active-sites can by achieved by partly reduced with metal oxides.

(Invited) Dynamic Operation of Solid Oxide Electrolyzers

Electrolysis of steam to generate hydrogen is expected to be a highly dynamic operation if renewable resources such as wind and solar are used as the electrical power input. Rapid fluctuation of input power and intermittent operation of the solid oxide electrolysis stack will result in transient operating conditions at the cell level. All operating variables such as temperature, steam content, voltage, flow rate, etc. may change rapidly in these conditions.To address this situation, this work operates Ni/YSZ-supported and metal-supported cells under highly dynamic conditions, with individual variables isolated. The cells are remarkably robust to dynamic operation. A safe range is found for each operating variable, with accelerated degradation observed outside that range in certain cases. For example, cycling Ni/YSZ-supported cells between 1.3 V and 1.6V at 750°C and 50:50 H2O:H2 is tolerated well, but increasing the upper voltage to 1.7 V and higher leads to increased degradation. Additionally, Steam:hydrogen ratio is cycled between 3:97 and 75:25. Temperature is cycled between 150 and 800°C. Operation is cycled between fuel cell and electrolysis modes, with synchronized steam content. Metal-supported cells tolerate steam cycling, voltage cycling, temperature cycling and redox cycling, and results for button cells and 50 cm2 planar cells will be reported. In many cases, hold times are 1 minute, allowing thousands of cycles to be accumulated over hundreds of hours of operation.Figure 1. Dynamic cycling of a Ni/YSZ-supported button cell at 750C. (Top) Cycling between 1.3 and 1.7V with 1 min holds and 50/50 H2/H2O. (Bottom) Cycling between various steam contents at 1.3 V. Figure 1

Nanocrystalline Diamond Lateral Overgrowth for High Thermal Conductivity Contact to Unseeded Diamond Surface

We demonstrate diamond lateral overgrowth as a way of increasing the thermal conductivity of thin layers of diamond. The technique can be used as a way of growing diamond on top of semiconductors, creating a thin layer of high thermal conductivity diamond in direct contact with semiconductors and allowing for the encasement of GaN in high thermal conductivity diamond.As we move to higher and higher power densities, the requirements for heat removal become extreme. The best passive way to remove heat from a semiconductor is to have a high thermal conductivity heat spreader near the heat source. Having diamond under the substrate is good. Having diamond under the epi is better and having diamond on top and bottom of the epi is better still.As-grown thin layers of diamond on non-diamond substrates have nano-diamond seeds as the starting material. The diamond thermal conductivity is a function of the grain size (Especially for small grain material) [1]. If we can increase the grain of the diamond near the junction, we can increase the thermal conductivity near the junction and more efficiently spread the heat away from the source before rejecting it into the surrounding material.In the experiment, we start with a bare silicon wafer seeded with nano-diamond seeds then grow about one micron of diamond. We coat it with a few nanometers of SiN. Then pattern the SiN layer with 2μm wide features to facilitate the coalescence of LOG-NCD over the SiN. Then we grow a 2μm thick microwave-plasma CVD NCD film (800W, 15Torr, 750°C, 0.3% CH4/H2) over the patterned SiN film initiating directly from the exposed areas of the host NCD. The diamond growth does not initiate on the patterned silicon nitride without seeds. The exposed diamond acts as a nucleating center initiating the diamond regrowth. The regrown diamond spreads from the diamond crystals exposed from the first growth. The edge crystals closest to the SiN patterned area expand over the silicon nitride forming diamond conformal to the SiN surface. This creates large crystals over the unseeded area. Figure 1 is a transmission electron microscope (TEM) image of the sample. The TEM, the image can be split into two regions. The left has no patterning, the called-out grain is 100nm wide. The right is patterned, and the diamond grains are between 1,000 to 2,000nm wide.We measured the thermal conductivity of the diamond on this samples using the TDTR method. This method uses a laser many times larger in diameter than the thickness of the film. As such, we probe the out-of-plane thermal conductivity. The initial diamond growth near the silicon had an average thermal conductivity of 100W/mK. We measured the second micron of growth without patterns to have Tc of 130W/mK. The diamond directly above the patterns had Tc of 260W/mK with grains 10X larger than the un-patterned diamond.Since the diamond grains are columnar, the difference in thermal conductivity between the patterned and un-patterned diamonds was 2X. Lateral measurements would likely show even larger changes in thermal conductivity. With grain sizes of 100 nm to 250 nm (as is the case with seeded diamond), the in-plane thermal conductivity will be dominated by the quality of the grain/grain interfaces and the lateral grain size dimensions rather than for the quality of the lattice. [1] We used lateral overgrowth to increase the grains to microns rather than 100s of nm. This means that we move into a regime where thermal conductivity is dominated by the quality of the diamond in the grains rather than the grain boundaries. As such the thermal conductivity is increased and can be further improved by improving the crystal quality - a parameter which is controlled by the diamond growth conditions. Typically, samples grown with more than 1% methane / hydrogen ratio show lower thermal conductivity [2]. However higher concentrations are important to establish the initial diamond film without damage to the underlying semiconductor. Here, the lateral overgrowth and methane concentration can be balanced to achieve both high thermal conductivity and low damage to the underlying substrate.

Analysis of combustion characteristics of ammonia/hydrogen mixed fuel in HCCI engine

Abstract A zero-dimensional HCCI combustion model for ammonia/hydrogen mixed gases was established to study the influence of hydrogen on the combustion characteristics of ammonia fuel. The effects of compression ratio, intake temperature, and hydrogen ratio on the combustion performance of ammonia were analyzed. The results suggest that due to the high ignition point of ammonia, the intake temperature must reach 523 K when the compression ratio is 18 for ammonia fuel to be compression ignited. At the same time, it was found that under this condition, ammonia fuel can burn under lean conditions (ϕ=0.2). The study also found that when the intake temperature is 523 K, the minimum-to-compression ratio during ammonia compression ignition decreases from 18 to 10 as the hydrogen doping ratio increases from 0 to 0.2.

Experimental study and correlation analysis for the effect of hydrogen pressure on biomass fluidized hydropyrolysis under N2-H2 mixed atmosphere

The utilization of fluidized bed reactors for the biomass hydropyrolysis vapor upgrading is essential in the conversion of biomass into liquid fuels. Conducting pyrolysis experiments in fluidized bed reactors with a N2-H2 mixed atmosphere is advantageous for system operation as it allows for lower minimum operating velocities, enhances pyrolysis efficiency, and reduces heat loss. This research examines the impact of hydrogen pressure in a bubbling fluidized bed reactor using a N2-H2 mixed carrier gas, with poplar wood as the feedstock and Ni-Moγ/Al2O3 as the catalyst. Through experimental and correlation analyses, significant relationships are observed between hydrogen pressure and the production of liquid and gas-phase products, with varying effects attributed to changes in hydrogen ratio and reaction pressure. Elevated hydrogen ratios facilitate secondary reactions such as the CO2 hydrogenation, resulting in a decline in CO2 production and an elevation in the yields of light hydrocarbons and aqueous phase products. Augmenting the reaction pressure to enhance hydrogen pressure aids in promoting hydrogen saturation and cracking, and amplifying the hydrogen pressure through an increase in the reaction pressure at a specific hydrogen ratio proves more efficacious in enhancing both the quantity and quality of bio-oil produced. In the context of poplar hydropyrolysis vapor upgrading utilizing a Ni-Moγ/Al2O3 catalyst, a hydrogen ratio of 50 % at a reaction pressure of 1.5 MPa emerged as the preferred option for achieving a 12 % bio-oil yield with a moderate average bio-oil carbon number and satisfactory hydrogenation levels. This comprehensive investigation examines the influence of hydrogen pressure on biomass hydropyrolysis, highlighting variations in the impacts of changes in hydrogen ratio and reaction pressure on pyrolysis results. These results offer a theoretical framework for discerning distinctions between hydropyrolysis investigations carried out in pure hydrogen atmospheres versus mixed N2-H2 atmospheres.

Effect and mechanism of ionic liquid-polymer composite coating on enhancing hydrogen embrittlement resistance of X80 pipeline steel for hydrogen blended natural gas transportation

Blending hydrogen into existing natural gas pipelines is a cost-effective method for large-scale hydrogen transportation. However, high hydrogen ratios cause hydrogen embrittlement in pipeline steel, limiting transportation efficiency. Due to complex structures and harsh application conditions, existing coatings are difficult to apply on pipelines. To tackle such issues, we propose an ionic liquid-polymer composite coating using epoxy resin as coating substrate, based on the competitive adsorption of methane and hydrogen on pipeline steel. Ionic liquids with high methane selectivity were selected via quantum chemical calculation. The protective effect of coatings was characterized using hydrogen pre-charging constant strain tensile tests. Simulation and experimental results demonstrate that epoxy resin coatings reduce hydrogen embrittlement in X80 steel. Modified with selective CH4/H2 permeability ionic liquids, the epoxy resin coating enhances methane and hydrogen competitive adsorption on the steel surface, improving hydrogen embrittlement resistance. This novel coating offers a viable solution for achieving safe and high ratio hydrogen blended transportation in natural gas pipeline.