H2 Fraction Research Articles

Effect of low volume fraction of H2 on explosion characteristics and mechanism of AlH3 dust via connected container

During the storage and use of AlH3, a small amount of H2 is easily decomposed, forming a multiphase composite system that increases explosive hazard. This article discussed the AlH3 dust inducing low concentration H2 explosion and venting characteristics by a connected vessel. The results show that when the concentration of H2 was 1 % and 3 %, which was lower than the lower explosive limit of H2 (4 %), H2 was non-flammable, and the explosion was dust-driven explosion. At H2 volume fraction of 5 %, a dual-fuel-driven explosion dominated, culminating in the maximum explosion pressure, reduced pressure, venting flame length, and velocity. The microscopic reaction mechanism of AlH3 with H2 was explored using molecular dynamics simulations. Meanwhile, for the security strategy of AlH3 dust explosion venting with low H2 atmosphere, the NFPA 68 and EN 14491 standards predicted the venting flame length effectively, offering critical insights for the application and safety design of AlH3.

Design and experimental study of solar-driven biomass gasification based on direct irradiation solar thermochemical reactor

Solar-driven biomass steam gasification is a promising technology to produce H2-rich syngas, meanwhile achieve flexible storage of renewable energy. However, the solar gasification application also faces numerous challenges, due to its involved complex chemical reaction characteristics and the inherent the multi-physics energy conversion processes. This work designs a novel direct irradiation solar gasification reactor, with the improved optical acceptance structure and reasonable test module, and the wheat straw particle is selected as experimental sample. Employing a 9 kWe high flux solar simulator, the maximum temperature of reaction bed in this prototype reactor reaches to 1260 °C, with the average solar flux of 1171.3 kW/m2. With adjustable radiation flux as experiment factor, under the highest total radiation of 3.35 kW, the molar fraction of H2 in the produced syngas is 47.1 % with the energy upgrade factor of 1.15, and the cellulose component completes decomposition. Increasing the mass flow rate of steam reduces the syngas output while raising the H2/CO ratio of the syngas. In addition, smaller biomass particle size facilitates the reaction, thereby improving the conversion efficiency of direct irradiation gasification. The investigation results provide a meaningful reference for the efficient utilization of abundant solar and biomass energy.

Study on the influence of Ni/La2O3/CeO2 composite catalysts on the characteristics and stability of biomass pyrolysis components

The impact of adding La2O3 and CeO2 separately or in combination to a Ni-Al2O3 catalyst on the volatile components of biomass pyrolysis is examined in this study. This study focuses on the effects of varying pyrolysis temperatures and catalyst usage cycles on catalytic reforming, evaluating the resulting pyrolysis yield, syngas composition, and catalyst stability. Catalyst characteristics are also analyzed. The results of this study show that the Ni-Al2O3 catalyst modified with La2O3 alone produces a 9 % reduction in tar yield and a 20 % increase in the CO + H2 fraction of the pyrolysis gas compared to the control group. When modified with CeO2 alone, the Ni-Al2O3 catalyst keeps a tar conversion efficiency above 43 % after ten consecutive usage cycles. The addition of La2O3 and CeO2 simultaneously led to a 19 % increase in hydrogen yield, with the absolute content of alcohols, ketones, and esters reaching zero at 850°C.

Anode humidity trade-offs between proton conductivity and concentration overpotentials in protonic ceramic fuel cell: Experiments and numerical simulations

In protonic ceramic fuel cells (PCFCs), the H2 and H2O partial pressures in the anode side vary along the gas flow direction, particularly during high-fuel-utilization operation. This results in different species conductivities and overpotentials, which renders the quantitative evaluation of local performance based on H2 and H2O mole fractions important. A numerical model is developed that can reflect changes in species conductivities and overpotentials resulting from varying gas mole fractions. The numerical current density–voltage characteristic results obtained numerically agree well with those obtained via measurement in a wide range of H2–H2O gas conditions. Numerical modeling confirms a tradeoff, i.e., higher supply humidity levels result in lower electrolyte resistances but higher concentration overpotentials. The maximum output is achieved at a modest humidification level of 20%. The developed numerical model is particularly useful for optimizing the operating conditions of PCFCs with high fuel utilization.

Dynamic-based artificial intelligence model for simulation and optimization of the single chamber anode brush microbial electrolysis cell

Microbial electrolysis cells (MECs) have become more attractive because they can produce hydrogen (H2) from various organic sources with a low input electrical energy requirement. In this study, a dynamic model for the single-chamber anode brush MEC with acetic acid as a carbon source was developed for the first time. The dynamic model was calibrated and validated using both experimental and literature data, with a high coefficient of determination (R2) of 0.87–0.99, a high Pearson correlation coefficient (PCC) of 0.93–0.99, and a low normalized root mean squared error (NRMSE) of 0.221–0.078. For rapid simulation and optimization, the validated dynamic model was reproduced using an artificial neural network (ANN), and particle swarm optimization (PSO) was then applied to optimize the fitness functions derived from this ANN model (i.e., hydrogen production yield, hydrogen production rate, hydrogen fraction in biogas, and total energy recovery). As a result, the proposed method took about 3 s with an absolute error of <3.5 %. The optimization results revealed that an optimal condition (including applied voltage, operating temperature, substrate concentration, and reactor working volume) cannot exist to obtain the maximum values of all performance parameters simultaneously. Under the same importance, the co-optimal condition was determined at an applied voltage of 0.9 V, temperature of 36.2 °C, substrate concentration of 0.87 g/L, and reactor working volume of 0.05 L. At such co-optimal conditions, MEC achieved an H2 yield of 1168.6 ± 13.3 mL/g with a production rate of 185.6 ± 2.7 mL/L/h, an H2 fraction of 63.6 ± 0.2 %, and a total energy recovery (including electrical, substrate, heat, and mixing input energies) of 16.7 ± 0.2 %. Although these performances increased 1.5–2.3 times compared to non-optimal conditions, the low energy efficiency indicates the need for further investigation into combining MEC with sustainable energy sources, such as solar, wind and osmosis.

Distribution and characterization of products obtained from pyrolysis of cooked food waste- Impact of heating rate

This work offers a comprehensive investigation of the pyrolysis products—liquid, gas, and solid derived from cooked food waste (CFW) at different heating rates (15–100 °C/min). The heating rate significantly influenced the yield of pyrolysis products. The maximum yield of bio-oil (oil + aqueous) was achieved at a heating rate of 50 °C/min, py-gas at 100 °C/min, and biochar at 15 °C/min. The yields were 34 wt% for bio-oil, 30 wt% for py-gas, and 32 wt% for biochar. Analysis of the bio-oil revealed significant proportions of fatty acids (Methyl-methyltetradecanoate) and esters (Oleic acid ethyl ester), constituting 25 %, and 26 % at 15 °C/min but declining with increasing heating rates. Another ester (9-Octadecenoic acid methyl ester) was found across all heating rate with highest concentration of 33 % at 100 °C/min. Aliphatic hydrocarbons (Octane, Dodecene, Heptadecane, Tetradecyne, Undecane, Dimethylhepta-1,3-triene, Tetradecane, Nonadecane), constituted highest concentration of 12 % at 25 °C/min and aromatic hydrocarbons (Toluene) showed maximum presence of 4 % at 50 °C/min. The aqueous phase showcased cyclic nitrogenated compounds (Piperidine), anhydrosugars (DGP), and furanics (Furanmethanol), with the highest concentrations of 46 %, 12 %, and 38 %, respectively observed at 100 °C/min. Instantaneous py-gas analysis indicated an elevated presence of CO2 and CO in the initial pyrolysis stages (up to 70 min) followed by higher H2 in the latter stages (>70 min). While increasing heating rates (15–100 °C/min) boosted cumulative fractions of CO2 and CO, the highest H2 fraction was observed at 50 °C/min. The proximate and ultimate analysis of biochars indicated increased ash, fixed carbon, HHV and H/C compared to raw CFW. The surface area and morphology were positively influenced by an increase in heating rate, resulting in a microporous biochar having maximum surface area of 340.6 m2/g at 50 °C/min.

Synthesis of nitrogen-doped crystalline Ga2O3 thin films via trimethylgallium doped NH3/H2/N2/O2 premixed stagnation flames

This study presents a novel and cost-effective technique for fabricating nitrogen-doped crystalline α-Ga2O3 and β-Ga2O3 thin films under atmospheric pressure conditions through flame synthesis for the first time. We employ metal–organic ammonia (NH3)-assisted flame synthesis (MO-NAFS) in a quasi-one-dimensional trimethylgallium (TMG) doped NH3/H2/N2/O2 flat flame to achieve a one-step deposition of Ga2O3 onto c-plane α-Al2O3 substrates. We found that hydrogen (H2) addition directly impacts the crystallinity of the Ga2O3 thin film. When only NH3 is employed as the fuel, a thin-film single-crystal nitrogen-doped β-Ga2O3 was observed. Blending the NH3 with 5 % of H2 yields a single-crystal nitrogen-doped α-Ga2O3, while a further increase of H2 fraction up to 10 % results in a mixture of both α-Ga2O3 and β-Ga2O3 crystals. Remarkably, the nitrogen doping through MO-NAFS was found to persistently result in an N/O atomic ratio as high as 1.12, as determined by the XPS analysis. This approach paves the way to a simple and scalable means for producing crystalline nitrogen-doped Ga2O3 thin films with potential control of crystal phase composition through parameter adjustments.

Comparative study on hydrogen losses via microbial byproduct in the presence of methane and nitrogen cushion gas

This study comprehensively investigates H2 loss resulting from injecting two gas mixtures: I (60% H2 + 30% CH4 + 5% N2 + 5% CO2) and II (60% H2 + 30% N2 + 5% CH4 + 5% CO2) into an aqueous solution containing 20,000 ppm sodium chloride and 100 ppm acetic acid (a microbial by-product of acetogenesis) within Bandera clay-rich sandstone reservoirs. Conducted at 42 °C and 1350 psi, various analytical techniques, including X-ray diffraction (XRD), Scanning Electron Microscopy with Energy Dispersive X-ray (SEM-EDX) spectroscopy, Fourier Transform Infrared (FTIR) spectroscopy, porosity and permeability assessments, pH and ion analysis, and gas chromatography, were utilized to assess the relevant properties of rocks, formation water, and gas content before and after 50 days treatment. The results indicate minimal sample reactivity, with dissolution primarily affecting dolomite and albite minerals. On average, porosity increased by 19% in formulation I and 15% in formulation II, while permeability decreased by 4.7% in formulation I and 5.3% in formulation II. In formulation I, H2 fraction decreased by 2.79%, CH4 increased by 7.15%, and CO2 decreased by 9.36%, with N2 remaining constant, whereas in formulation II, H2 only decreased by 1.3%, CH4 increased by 19.22%, and CO2 decreased by 3.58%, with N2 remaining consistent. Overall, the N2 cushion gas condition (i.e., formulation II) slightly outperformed CH4 in minimizing H2 losses. This study thus provides significant insights into potential H2 loss within a microbial-by-product-rich environment for underground hydrogen storage.

Experiment and simulation assessment of supercritical underground coal gasification in deep coal seam

To explain the impact of geological and process factors on underground coal gasification in deep coal seam (>2200 m) and promote the efficient and clean extraction and conversion of coal, this study employs the orthogonal experimental design method to investigate the impact of CO2 coefficient (0–1), moisture content (30–80 wt%), calcite content (0–10 wt%), albite content (0–10 wt%), kaolinite content (0–20 wt%), reaction temperature (550–650 °C), and reaction pressure (23–27 MPa) on the characteristics of coal underground gasification under supercritical H2O/CO2 conditions. Furthermore, range analysis and variance analysis are utilized to determine the degree of influence of each factor and the interaction between factors. Finally, the Gibbs free energy minimization method is used to conduct a thermodynamic equilibrium analysis of coal supercritical H2O/CO2 gasification at high temperatures (750–1000 °C). The results indicate that the three most significant factors affecting the process of coal supercritical H2O/CO2 gasification are the CO2 coefficient, moisture content, and reaction temperature. The maximum carbon gasification efficiency at 650 °C in experimental cases and 1000 °C in simulation cases is 22.2% and 88.1%, respectively. Although the addition of CO2 at lower temperatures reduces the carbon gasification efficiency, at high temperatures (>900 °C), a higher initial CO2 concentration increases the carbon gasification efficiency. The addition of CO2 under conditions of low moisture content increases the mole fraction of H2, but reduces it under conditions of high moisture content (≥70 wt%). Among the three minerals, calcite has the most significant influence on the gasification process.

Retrofitting Natural Gas–Fired Boiler for Hydrogen Combustion: Operational Performance and NOx Emissions

Abstract The effects of hydrogen fraction (HF: volumetric fraction of H2 in the fuel mixture of CH4 + H2) from 0% to 100% by volume, on the thermal and environmental performance of a 207-MW industrial water tube boiler, are investigated numerically at a fixed excess air factor, λ = 1.15. This study aims to determine the hardware modifications required for boilers to be retrofitted for pure hydrogen operation and investigates how NOx emissions are affected by hydrogen enrichment. The results showed insignificant increases in maximum combustion temperature with increasing the HF, though the distributions of temperature profiles are distinct. In reference to the basic methane combustion, H2 flames resulted in a positive temperature rise in the vicinity of the burner. Increasing the HF from 0% to 2% resulted in higher average thermal NOx emissions at the boiler exit section from 37 up to 1284 ppm, then it decreased to 1136 ppm at HF = 30%, and later it leveled up to 1474 ppm at HF = 100%. The spots for higher differences in NO formation compared to the reference case are shifted downstream at higher HFs. The effect of hydrogen enrichment on CO2 and H2O as radiation sources, as well as the volumetric absorption radiation of the furnace wall and the heat flux at furnace surfaces, has all been presented in relation to the effect of hydrogen addition on boiler performance.

Coupled multi-dimensional modelling of warm plasmas: Application and validation for an atmospheric pressure glow discharge in CO2/CH4/O2

To support experimental research into gas conversion by warm plasmas, models should be developed to explain the experimental observations. These models need to describe all physical and chemical plasma properties in a coupled way. In this paper, we present a modelling approach to solve the complete set of assumed relevant equations, including gas flow, heat balance and species transport, coupled with a rather extensive chemistry set, consisting of 21 species, obtained by reduction of a more detailed chemistry set, consisting of 41 species. We apply this model to study the combined CO2 and CH4 conversion in the presence of O2, in a direct current atmospheric pressure glow discharge. Our model can predict the experimental trends, and can explain why higher O2 fractions result in higher CH4 conversion, namely due to the higher gas temperature, rather than just by additional chemical reactions. Indeed, our model predicts that when more O2 is added, the energy required to reach any set temperature (i.e., the enthalpy) drops, allowing the system to reach higher temperatures with similar amounts of energy. This is in turn related to the higher H2O fraction and lower H2 fraction formed in the plasma, as demonstrated by our model. Altogether, our new self-consistent model can capture the main physics and chemistry occurring in this warm plasma, which is an important step towards predictive modelling for plasma-based gas conversion.

An experimental study on the flame instability of NH3/DME blends with H2 addition

It is of significance to investigate the effect of H2 on the combustion of NH3/DME blends since NH3 can partially decompose to produce hydrogen (H2) in the combustion process. However, few studies were conducted on NH3/DME/H2 mixtures, especially for flame instability. This work presents an experimental study of the flame instability of NH3/DME blends with H2 addition. Experiments were conducted using the spherical constant-volume combustion method at φ = 0.7 – 1.4, Tu = 298 K. The influences of NH3/DME blend ratio (BNH3/DME = 80/60, 60/40, 40/60, and 20/80), initial pressure (Pu = 0.1 – 0.5 MPa), and H2 fraction (XH2 = 0%, 20%, and 40%) on the flame instability were examined in detail. The results show that increasing either DME fraction or initial pressure can promote the hydrodynamic instability of NH3/DME/air flames because of the decreased flame thickness. For both XH2 = 0% and 20%, the cellular flame instability with BNH3/DME = 40/60 and 20/80 increases with increasing equivalence ratio. For XH2 = 40%, the flame instability shows a similar trend with BNH3/DME = 20/80, but the most unstable flame appears around stoichiometric combustion with BNH3/DME = 40/60. This is due to the compound effects of the diffusive-thermal imbalance and hydrodynamic instability for lean or rich fuel, while the diffusive-thermal instability can be neglected for stoichiometric combustion. Therefore, an effective control of H2 or DME addition can help enhance the combustion performance of the fuel while reducing the occurrence of dangerous events caused by potential flame instabilities. In addition, critical parameters, i.e., critical flame radius rcr, critical Peclet number Pecr, and critical Karlovitz stretch factor Kacr were analyzed to quantify the onset of flame instability. This work provides insights into the flame instabilities of NH3/DME with H2 addition.

Heavy black hole seed formation in high-z atomic cooling halos

Context. Halos with masses in excess of the atomic limit are believed to be ideal environments in which to form heavy black hole seeds with masses above 103 M⊙. In cases where the H2 fraction is suppressed, this is expected to lead to reduced fragmentation of the gas and the generation of a top-heavy initial mass function. In extreme cases this can result in the formation of massive black hole seeds. Resolving the initial fragmentation scale and the resulting protostellar masses has, until now, not been robustly tested. Aims. We run zoom-in simulations of atomically cooled halos in which the formation of H2 is suppressed to assess whether they can truly resist fragmentation at high densities and tilt the initial mass function towards a more top-heavy form and the formation of massive black hole seeds. Methods. Cosmological simulations were performed with the moving mesh code AREPO, using a primordial chemistry network until z ∼ 11. Three haloes with masses in excess of the atomic cooling mass were then selected for detailed examination via zoom-ins. A series of zoom-in simulations, with varying levels of maximum spatial resolution, captured the resulting fragmentation and formation of metal-free stars using the sink particle technique. The highest resolution simulations resolved densities up to 10−6 g cm−3 (1018 cm−3) and captured a further 100 yr of fragmentation behaviour at the centre of the halo. Lower resolution simulations were then used to model the future accretion behaviour of the sinks over longer timescales. Results. Our simulations show intense fragmentation in the central region of the halos, leading to a large number of near-solar mass protostars. Even in the presence of a super-critical Lyman-Werner radiation field (JLW &gt; 105J21), H2 continues to form within the inner ∼2000 au of the halo. Despite the increased fragmentation, the halos produce a protostellar mass spectrum that peaks at higher masses relative to standard Population III star-forming halos. The most massive protostars have accretion rates of 10−3–10−1 M⊙ yr−1 after the first 100 years of evolution, while the total mass of the central region grows at 1 M⊙ yr−1. Lower resolution zoom-ins show that the total mass of the system continues to accrete at ∼1 M⊙ yr−1 for at least 104 yr, although how this mass is distributed amongst the rapidly growing number of protostars is unclear. However, assuming that a fraction of stars can continue to accrete rapidly, the formation of a sub-population of stars with masses in excess of 103 M⊙ is likely in these halos. In the most optimistic case, we predict the formation of heavy black hole seeds with masses in excess of 104 M⊙, assuming an accretion behaviour in line with expectations from super-competitive accretion and/or frequent mergers with secondary protostars.

Reduction in environmental hazards and enhance the energy conversion from microalgae wastewater: Characteristics evaluation

AbstractThe formation of algae blooms can influence uncontrolled growth, causing hazards to aquatic ecosystems. The attention of microalgae wastewater treatment is gathering significance in bio‐energy conversion, resulting in environmental sustainability. Gasification technology is found to improve energy conversion with improved environmental sustainability. The novel research is to treat microalgae wastewater via hydrothermal gasification process with the assistance of a potassium hydroxide catalyst (KOH). During the gasification process, the gasification time is varied from 10, 20, and 30 min under a higher gasification temperature of 900°C is maintained throughout the gasification process. Effect of gasification processing time with KOH catalyst action on the percentage of molar fractions including carbon monoxide (CO), carbon dioxide (CO2), hydrogen (H2) and methane (CH4), lower heating value (LHV), syngas H2 yield, and gasification efficiency of hydrothermal gasification process for microalgae wastewater are experimentally investigated. The results of the present investigation are exposed with higher processing time with maximum gasification temperature processed with KOH catalyst offered maximum H2 fraction of 59%, reduced CH4 and LHV of 15% and 10 MJ/Nm3, optimum H2 yield of 22 mol/kg, and attained maximum gasification efficiency of 55%, respectively. The optimum gasification process parameters, including a 30‐min processing time with a higher gasification temperature of 900°C gained H2, will be suggested for energy/alternative fuel applications.

Evaluation of the use of ammonia/hydrogen blends in turbocharged gas engines

The potential for ammonia/hydrogen (NH3/H2) blends as fuel in modern, turbocharged, gas engines is evaluated by comparing the combustion properties of these blends with those of methane. To ensure proper combustion phasing in existing spark-ignited (SI) engines, the laminar burning velocity (LBV) is used, while the ignition delay times (IDT) of the mixtures are compared to assess the risk of engine knock. The chemical mechanisms used for the computation of IDT and/or LBV of NH3/H2 mixtures are selected from 8 chemical mechanisms based on their ability to predict experimental data. The application of a turbocharger is shown to “boost” the temperature in the cylinder after compression to values that admit the use of NH3/H2 mixtures in natural-gas SI engines without increasing the compression ratio (CR). The analysis also identifies regions of temperature and H2 fraction that increase the risk of knock. Using the conditions in a practical turbocharged SI engine as an example, 40–50% H2 in NH3 yields combustion phasing equivalent to that obtained with methane, while avoiding the risk of knock. Analysis of the IDT for the conditions in a high-pressure direct-injection natural-gas engine also shows that the use of a turbocharger in compression-ignition (diesel-type) engines strongly reduces the demands on CR for achieving the conditions necessary for reliable ignition of NH3/H2 mixtures. Increasing the temperature by only a few tens of degrees above the conditions studied will yield an IDT for ∼20% H2 in NH3 that satisfies the ignitibility requirements for use in a turbocharged diesel engine.

Modeling and exergy-economy analysis of residential building energy supply systems combining torrefied biomass gasification and solar energy

A novel hybrid energy system driven by torrefied biomass gasification and solar energy is proposed for the first time, and their complementarity to enhance the system’s energy efficiency is analyzed and shown. The system mainly combines biomass torrefaction, biomass gasification subsystem, solar heat collection and absorption refrigeration technology. The effects of different operating parameters on the gasification products were studied. The economic analysis is carried out based on the theory of exergy economy. The results show that torrefaction pretreatment of biomass can significantly improve its fuel quality and gasification performance. With the increase of torrefied temperature, the volume fraction of CO2 and H2 decreased while the volume fraction of CH4 and CO increased. The economic analysis shows that the expected annual income is $72,735, and the investment recovery period is 2.89 years. Through the calculation of the energy-saving and environmental benefits, it can be concluded that the hybrid energy system can save 1.05 × 106 MJ of heat per year. This equates to about 358.26 tons of standard coal or a CO2 emission reduction of 550.59 tons, the participation of solar energy is conducive to the system emission reduction. By tuning the parameter sensitivity, the influence of biomass price change on the unit exergy cost of system products was more obvious.

Numerical Study of Ignition and Combustion of Hydrogen-Enriched Methane in a Sequential Combustor

Ignition and combustion behavior in the second stage of a sequential combustor are investigated numerically at atmospheric pressure for pure CH4\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\ ext{CH}}_{4}$$\\end{document} fueling and for two CH4\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\ ext{CH}}_{4}$$\\end{document}-H2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\ ext{H}}_{2}$$\\end{document} fuel blends in 24:1 and 49:1 mass ratios , respectively, using Large Eddy Simulation (LES). Pure CH4\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\ ext{CH}}_{4}$$\\end{document} fueling results in a turbulent propagating flame anchored by the hot gas recirculation zones developed near the inlet of the sequential combustion chamber. As the H2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\ ext{H}}_{2}$$\\end{document} content increases, the combustion process changes drastically, with multiple auto-ignition kernels produced upstream of the main flame brush. Analysis of the explosive modes indicates that, for the highest H2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\ ext{H}}_{2}$$\\end{document} amount investigated, flame stabilization in the combustion chamber is strongly supported by auto-ignition chemistry. The analysis of fuel decomposition pathways highlights that radicals advected from the first stage flame, in particular OH, induce a rapid fuel decomposition and cause the reactivity enhancement that leads to auto-ignition upstream of the sequential flame. This behavior is promoted by the relatively large mass fraction of OH radicals found in the flow reaching the second stage, which is approximately one order of magnitude greater than it would be at chemical equilibrium. The importance of the out-of-equilibrium vitiated air on the ignition behavior is proven via an additional LES that features weak auto-ignition kernel formation when equilibrium is artificially imposed. It is therefore concluded that parameters affecting the relaxation towards chemical equilibrium of the vitiated flow can have an important influence on the operability of sequential combustors fueled with varying fractions of H2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\ ext{H}}_{2}$$\\end{document} blending.

Influence of the H2 proportion on NH3/H2/air combustion in hot and low-oxygen coflows

This study investigated the effect of the H2 fraction on reaction dynamics and NOx formation in a premixed NH3/H2/air jet flame within a hot coflow (JHC) through numerical simulations. We found that even a small mole fraction of H2 (e.g., XH2, F = 5%) significantly enhances the ignition of the premixed NH3/air flame. However, the presence of H2 markedly intensifies the main combustion reactions only when XH2, F ≥ 30%, resulting in a sharp increase in temperature and heat release rate. Moreover, as XH2, F increases, the NOx emission first increases until XH2, F = 75% and then decreases. Without any H2 addition, a high emission of unburned NH3 occurs in the pure NH3 JHC flame. On the other hand, when XH2, F ≥ 50%, the emissions of unburned H2 and OH increase rapidly due to extremely high temperatures. Notably, maintaining XH2, F between 5% and 20% minimizes the emissions of NOx, NH3, H2, and OH. Furthermore, the preferential diffusion of H2 plays a key role in enhancing the production of active radicals (OH, O, and H), thereby significantly boosting the initiation and combustion reactions of NH3/H2 blended fuel.

Study of hydrogen injection strategy on fuel mixing characteristics of a free-piston engine

The formation of the gas mixture in the cylinder has a significant effect on the combustion and emission of the engine. The main difference between a conventional engine and a free piston engine is that the piston movement mode is different. Therefore, a new coupled iterative method is adopted in this paper to study the injection position and duration of hydrogen fuel in a free piston engine where diesel fuels hydrogen, and reveal its influence on gas mixing and combustion in the cylinder of a free piston engine. The results show that it is suitable to spray hydrogen 55 mm from TDC. At this time, the mass fraction of H2 in the cylinder is relatively uniform, the cumulative heat release is about 620 J, and the pressure and temperature are relatively low, which are 7.2 MPa and 1529 K respectively. The duration of hydrogen injection is 0.4 ms, at this time, the mixing degree in the cylinder and the gas flow speed are better, although there is a little shortage of unburned equivalent ratio, but this has little impact on the overall, and the final cumulative heat release reaches 655 J.

Laminar burning velocity of lithium-ion battery thermal runaway vent gas in air

In this study, a spherically propagating flame of vent gas generated during the thermal runaway of lithium-ion batteries with different states of charge (SOC) was experimentally and numerically investigated. The vent gas is mainly composed of H2, CO, CO2, and some hydrocarbons. With increasing SOC, the CO2 fraction tends to decrease while the H2 and CO fractions tend to increase. Combustion experiments were conducted using a closed vessel, and the combustion progression was captured using a high-speed Schlieren image system to measure the unstretched laminar burning velocity, Su0. In addition, the combustion was computationally estimated under the experimental conditions by performing 1D planar flame simulations using Chemkin-Pro with the Aramco Mech 1.3 reaction model. Remarkably, the calculated values of Su0 closely matched the experimental ones, demonstrating good agreement. The results showed that Su0 tended to increase with increasing SOC. Furthermore, the effects of the chemical reaction mechanism, which plays a pivotal role in driving this increase in Su0 with increasing SOC, were investigated. Specifically, the heightened SOC levels promoted the H2 branching reaction led to an increased concentration of OH radicals in the mixture. This consequently accelerated the rate-determining reaction for the oxidation of hydrocarbons, leading to an increase in Su0. As an effect of the hydrocarbons in the vent gas mixtures, the number of moles of CO increased slightly near the flame because the rate of CO production in the flame zone was more dominant than that of consumption under the condition of SOC 50.