The effect of hydrogen injection parameters on the quality of hydrogen–air mixture formation for a PFI hydrogen internal combustion engine

To research the quality of the hydrogen–air mixture formation and the combustion characteristics of the hydrogen fueled engine under different hydrogen injection timings, nozzle hole positions and nozzle hole diameter, a three-dimensional simulation model for a PFI hydrogen internal combustion engine with the inlet, outlet, valves and cylinder was established using AVL Fire software. In the maximum torque condition, research focused on the variation law of the total hydrogen mass in the cylinder and inlet and the space distribution characteristics and variation law of velocity field, concentration field and turbulent kinetic energy under different hydrogen injection parameters (injection timings, nozzle hole positions and nozzle hole area) in order to reveal the influence of these parameters on hydrogen–air mixture formation process. Then the formation quality of hydrogen–air mixture was comprehensively evaluated according to the mixture uniformity coefficient, the remnant hydrogen percentage in the inlet and restraining abnormal combustion (such as preignition and backfire). The results showed that the three hydrogen injection parameters have important influence on the forming quality of hydrogen–air mixture and combustion state. The reasonable choice of the nozzle hole position of hydrogen, nozzle hole diameter and the hydrogen injection time can improve the uniformity of the hydrogen–air mixing in the cylinder of the hydrogen internal combustion engine, and the combustion heat release reaction is more reasonable. At the end of the compression stroke, the equivalence ratio uniform coefficient increased at first and then decreased with the beginning of the hydrogen injection. When hydrogen injection starting point was with 410–430°CA, equivalence ratio uniform coefficient was larger, and ignition delay period was shorter so that the combustion performance index was also good. And remnant hydrogen percentage in the inlet was less, high concentration of mixed gas in the vicinity of the inlet valve also gathered less, thus suppressing the preignition and backfire. With the increase of the distance between the nozzle and the inlet valve, the selection of the hydrogen injection period is narrowed, and the optimum hydrogen injection time was also ahead of time. The results also showed that it was favorable for the formation of uniform mixing gas when the nozzle hole diameter was 4 mm.     

The processing of Mg–Ti for hydrogen storage; mechanical milling and plasma synthesis

A study was carried out into the processing of Mg-10 vol.% Ti powder mixture for hydrogen storage purposes. Two processing routes were evaluated; mechanical milling and plasma synthesis. Mechanical milling, carried out with a high speed planetary mill, yielded a particulate structure made up of large Mg agglomerates, 90–100 μm, with embedded Ti fragments of approx. 1 μm in size with a uniform distribution. Mg agglomerates were made up of coherently diffracting volumes that were less than 50 nm in size. Plasma processing was carried out with an RF plasma torch of 25–27 kW applied power, the powder mixtures fed with 1–3 g/min axially into the torch. The mixture Mg-10 vol.% Ti after plasma processing comprised Mg powders which were extremely fine, <100 nm. Ti occurred as separate particles mixed with Mg nanopowders. The powders had a coherently diffracting volumes that were comparable to the size of the particles themselves indicating that the plasma processing yields relatively defect free crystals. The formation of the nano-size particulate structures is evaluated with regard to their possible implications on the hydrogenation of Mg–Ti alloys.     

Molecular dynamics simulation on the effect of water uptake on hydrogen bond network for OH− conduction in imidazolium-g-PPO membrane

OH⁻ conduction involved in the hydrophilic channel of anion exchange membrane strongly depends on the water uptake. To investigate the effect of water uptake on the hydrogen bond network for OH⁻ conduction, a series of molecular dynamics simulations based on all-atom force field were performed on the hydrated imidazolium-g-PPO membranes with different water uptakes. The systems were well verified by comparing the membrane density and OH⁻ conductivity with previous experiments. By means of local structural properties and pair-potential energy, reasonable hydrogen bond criteria were determined to describe the hydrogen bond network confined in the membrane. Increasing water uptake enhances the hydration structures of water and OH⁻, and facilitates the reorganization of the hydrogen bond network. Water and OH⁻ are nearly saturated with water when the water uptake reaches λ = 10, where well-connected hydrogen bond network is produced. Further increasing water uptake has much less contribution to improving the hydrogen bond network, but inevitably swells the membrane channel. This work provides a molecular-level insight into the effect of water uptake on the hydrogen bonding structures and dynamics of OH⁻ and water confined in the imidazolium-g-PPO membrane.     

The value chain of green hydrogen for fuel cell buses – A case study for the Rhine-Main area in Germany

As an immanent necessity to reduce global greenhouse gas emissions, the energy transition poses a major challenge for the next 30 years, as it includes a cross-sectoral increase of fluctuating renewable energy production, grid extension to meet regional electricity supply and demand as well as an increase of energy storage capacity. Within the power-to-gas concept, hydrogen is considered as one of the most promising solutions.The paper presents a scenario-based bottom-up approach to analyse the hydrogen supply chain to substitute diesel with fuel cell buses in the Rhine-Main area in central Germany for the year 2025. The analysis is based on field data derived from the 6 MW power-to-gas plant “Energiepark Mainz” and the bus demonstration project “H₂-Bus Rhein-Main”. The system is modelled to run simulations on varying demand scenarios. The outcome is minimised hydrogen production costs derived from the optimal scheduling of a power-to-gas plant in terms of the demand. The assessment includes the energy procurement for hydrogen production, different hydrogen delivery options and spatial analysis of potential power-to-gas locations.     

The lithium-lithium hydride process for the production of hydrogen: Comparison of two concepts for 950 and 1300°C HTR helium outlet temperature

The lithium-lithium hydride process serves to generate hydrogen from water efficiently, using the high temperature heat of a nuclear reactor. Thermodynamic analyses show that hydrogen can be produced with an overall thermal efficiency of 48% at conventional HTR outlet temperatures of 950°C. Assuming helium heat of 1300°C, 56% overall thermal efficiency can be achieved.     

Mechanisms for adsorption,dissociation and diffusion of hydrogen in hydrogen permeation barrier of α-Al2O3: The role of crystal orientation

The mechanisms of adsorption of hydrogen on α-Al₂O₃(1-102) surface and of its diffusion in bulk are investigated, using first principles thermodynamics and kinetics, and compared with similar results obtained for the diffusion of hydrogen on α-Al₂O₃(0001) surface. Because of the different oxygen environments on both surfaces, the H binding energies on the (1-102) surface are 0.3–1.2 eV smaller than in the (0001) surface. The H₂ binding energies on (1-102) and (0001) surfaces are resembled. We have identified four main mechanisms, leading to dissociation of H₂, H migration on the surface, H diffusion into and inside the bulk. Equilibrium constant and activation barrier show that H₂ dissociation is the most favorable process and significant diffusion of H into the bulk can occur more readily from the (1-102) surface compared to the (0001) surface. Based on the hydrogen interaction with α-Al₂O₃(1-102) surface, a mechanism of α-Al₂O₃ suppressing H-permeation is identified.     

How can hydrothermal treatment impact the performance of continuous two-stage fermentation for hydrogen and methane co-generation?

Hydrothermal treatment can facilitate hydrolysis of biomass wastes such as algae and livestock manures, by converting high-molecular weight carbohydrates and proteins to monosaccharides and amino acids. However, further decomposition and reciprocal reaction of monosaccharides and amino acids are usually accompanied with hydrothermal treatment, which have negative impacts on microbial fermentation performance. In this study, glucose and glycine were used as model substrates during hydrothermal treatment coupled with semi-continuous hydrogen and methane fermentation. The results showed that thermal decomposition of glucose was stronger than glycine, due to the binary interactions between carbonyl group and amino group. Acidic condition could suppress conversion of intermediate compounds to polymers, thereby improving 5-HMF concentration to 7.59 g/L. Hydrothermal by-products had adverse impacts on hydrogen fermentation stability, resulting in a wide fluctuation of hydrogen production rate of around 0.55 L/L/d. Adding sulfuric acid for treatment would increase the competition of sulphate reducing bacteria, and cause a stuck methane fermentation. Additionally, by-products degradation promoted the growth of hydrogenotrophic and mixotrophic methanogens.     

Is platinum necessary for efficient hydrogen evolution? – DFT study of metal monolayers on tungsten carbide

In this work WC-supported metal monolayers (Cu, Ru, Rh, Pd, Ag, Ir, Pt and Au) are investigated using Density Functional Theory in order to establish general trends regarding monolayer stability, electronic structure and reactivity. Using calculated hydrogen–metal bond energies and available data on the exchange current densities (j₀) for hydrogen evolution reaction (HER) volcano-type curve is obtained enabling prediction of HER j₀ for the entire series of M_ML/WC systems not considered so far as HER electrocatalysts. Among investigated surfaces, Cu_ML/WC(0001) and Rh_ML/WC(0001) are identified as promising HER electrocatalysts with (i) HER exchange current density matching the one of Pt and (ii) stability in electrochemical environment under HER conditions. Provided results point to a general conclusion that Pt might not be necessary for efficient catalysis of hydrogen electrode reactions – superior catalysts can be obtained by rational design approach with suitable choice of overlayer/support system not involving Pt at all.     

Effect of substituting elements on hydrogen uptake for Pd–Rh–H and Pd–Ag–H systems evaluated by magnetic susceptibility measurement

The magnetic susceptibility and the pressure-composition isotherm were measured simultaneously for Pd–Rh–H and Pd–Ag–H systems in order to clarify the effect of Rh or Ag substitution on the hydrogen uptake from viewpoint of the electronic band structure. The magnetic susceptibility of all Pd binary alloys prepared decreased monotonically with increasing hydrogen content. At high hydrogen contents, the magnetic susceptibility became approximately zero for Pd–Rh–H and Pd–Ag–H system, and the hydrogen content at which the magnetic susceptibility gives zero corresponded with the terminal of the plateau region in the isotherm curve. The results indicated that the magnetic susceptibility of hydride phase was almost zero for all Pd binary alloys. On the basis of the band structure of Pd metal, we concluded that atom substitution only affected shift of the energy at Fermi level, and the amount of the hydrogen uptake was dominated by the number of unoccupied d-band in the alloys.     

The effects of plasma treatment on electrochemical activity of Co–W–B catalyst for hydrogen production by hydrolysis of NaBH4

A plasma treatment of Co–W–B catalyst increases the rate of hydrogen generation from the hydrolysis of NaBH₄. The catalytic properties of Co–W–B prepared in the presence of plasma have been investigated as a function of NaBH₄ concentration, NaOH concentration, temperature, plasma applying time, catalyst amount and plasma gases. The Co–W–B catalyst prepared with cold plasma effect hydrolysis in only 12 min, where as the Co–W–B catalyst prepared in known method with no plasma treatment in 23 min. The activation energy for first-order reaction is found to be 29.12 kJ mol⁻¹.     

The status of conventional world oil reserves—Hype or cause for concern?

The status of world oil reserves is a contentious issue, polarised between advocates of peak oil who believe production will soon decline, and major oil companies that say there is enough oil to last for decades.     

The metal–carbon–fluorine system for improving hydrogen storage by using metal and fluorine with different levels of electronegativity

In order to improve the capacity of hydrogen storage using activated carbon nanofibers, metal and fluorine were introduced into the activated carbon nanofibers by electrospinning, heat treatment, and direct fluorination. The pore structure of the samples was developed by the KOH activation process and investigated using nitrogen isotherms and micropore size distribution. The specific surface area and total pore volume approached 2800 m²/g and 2.7 cc/g, respectively. Because of the electronegativity gap between the two elements (metal and fluorine), the electron of a hydrogen molecule can be attracted to one side. This reaction effectively guides the hydrogen molecule into the carbon nanofibers. The amount of hydrogen storage was dramatically increased in this metal–carbon–fluorine system; hydrogen content was as high as 3.2 wt%.     

The effect of the absence of Ni,Co, and Ni–Co catalyst pretreatment on catalytic activity for hydrogen production via oxidative steam reforming of ethanol

This article presents a study of the catalytic performance of Ni, Co, and Ni–Co–Mg–Al mixed oxides obtained from hydrotalcite precursors for the oxidative steam reforming of ethanol (OSRE) when no pretreatment (pre-reduction) is accomplished. Two catalysts (a Ni-based monometallic and an equimolar Ni–Co-based catalyst) achieve in situ reduction over shorter time periods compared with the other bimetallic catalysts and also, exhibit the best catalytic activity. On the contrary, the monometallic Co catalyst did not exhibit good catalytic performance, likely because of the existence of resistant spinel phases to soft reduction processes and/or to the re-oxidation of Co. The equimolar presence of Ni and Co generates a synergistic effect evidenced by the increase in the reducibility, basicity, and mobility of electrophilic oxygen species of the solid. The results yield important information for better understanding the catalytic system under study.     

The fixed dome digester: An appropriate design for the context of Sub-Sahara Africa?

The fixed dome digester design is the most deployed small scale biogas technology in sub-Sahara Africa (SSA). This design is deployed on mono-feedstock-wet anaerobic digestion (WAD) principle. Little or nothing has been reported in the literature on the sustainability in terms of the actual field operation and performance of this design within the SSA context. This study aims at bridging this gap and bringing additional insights to the scientific literature by investigating the sustainability of the Nepali–type fixed dome digester within the context of rural Cameroon. The investigations were evaluated in terms of operating parameters, biogas production, production rate and productivity of the digester. In addition the local investment cost of the design was analyzed. The design was operated on multiple-locally-available feedstock mixed with water at an average of 3:1 ratio resulting in a higher than design TS of 16%. The design, thus was operated towards the dry anaerobic digestion principle, highlighting insufficient mono-feedstock and water scarcity for a sustainable operation of the design within the context of rural SSA. The average biogas production was 1.2 m³_biogas/day, giving average volumetric production rate of 0.16 m³_biogas/m³_digester day⁻¹ and yields of 0.18 m³_biogas/kg VS respectively. This low performance compared with the potential mesophilic biogas production rate of 0.27 m³_biogas/m³_digester day⁻¹ could be linked to insufficient mixing of digester content and low operating temperatures. Gas storage facility (dome), skilled labour and cement made significant contributions to the investment cost of the digester. The Levelized cost of Energy from the digester was less than 1 € cents/MJ.     

The optimization of Nb loading amount over Cu–Nb–CeO2 catalysts for hydrogen production via the low-temperature water gas shift reaction

The effect of Nb promotion over a Cu–CeO₂ catalyst was investigated in the low-temperature water gas shift reaction. The Nb loading amount was systematically varied from 0 to 5 wt% for the Cu–Nb–CeO₂ catalyst, and the 1 wt% Nb promoted Cu–Nb–CeO₂ catalyst exhibited the highest catalytic performance even at extremely high GHSV of 72,152 h⁻¹. The catalysts were characterized through various techniques such as Brunauer-Emmet-Teller measurements, X-ray diffraction, N₂O-chemisorption, H₂-temperature programmed reduction, X-ray photoelectron spectroscopy, and transmission electron microscopy. It was found that the superior performance of the 1 wt% Nb promoted Cu–Nb–CeO₂ catalyst was due to its enhanced reducibility, high BET surface area, small metallic Cu crystallite size, and high number of oxygen vacancies.     

The effect of Mn substitution for Ni on the structural and electrochemical properties of La0.7Mg0.3Ni2.55−xCo0.45Mnx hydrogen storage electrode alloys

The structures, hydrogen storage property and electrochemical properties of the $\text{La}{}_{0.7}\text{Mg}{}_{0.3}\text{Ni}{}_{\mathrm{2.55-x}}\text{Co}{}_{0.45}\text{Mn}{}_{\mathrm{x}}\text{(x=0.0,0.1,0.2,0.3,0.4,0.5)}$ electrode alloys has been studied systematically. It can be found that, by X-ray powder diffraction, the alloys are all consisted of the (La,Mg)Ni₃ phase and the LaNi₅ phase, and the lattice parameters and cell volumes of both the (La,Mg)Ni₃ phase and the LaNi₅ phase increase with increasing Mn content in alloys. The P–C isotherms curves indicate that the hydrogen storage capacity first increases and then decreases with increasing x, and the equilibrium pressure decreases. The electrochemical measurements show that the maximum discharge capacity increases from $\text{342.6}\text{(x=0.0)}$ to $\text{368.9}\text{mA}\text{h}\text{/}\text{g}\text{(x=0.3)}$ and then decreases to $\text{333.5}\text{mA}\text{h}\text{/}\text{g}\text{(x=0.5)}$. For the discharge current density of $\text{1000}\text{mA}\text{/}\text{g}$, the high rate dischargeability (HRD) of the alloy electrodes increases from 55.8% (x=0.0) to 72.3% (x=0.4) and then decreases to 70.0% (x=0.5). Moreover, according to the electrochemical impedance spectroscopy, linear polarization and anodic polarization measurements, the exchange current density I₀ and the limiting current density I_L of the alloy electrodes also all increase first and then decrease with increasing Mn content in alloys.     

The unbundling regime for electricity utilities in the EU: A case of legislative and regulatory capture?

Theory and empirics suggest that by curbing competition, incumbent electricity companies which used to be, and here are referred to as, Vertically Integrated Utilities (VIUs), can increase their profitability through combined ownership of generation and transmission and/or distribution networks. Because curbing competition is generally believed to be welfare-reducing, EU law requires unbundling (separation) of the VIU networks. However, the EU allows its member states the choice between incomplete (legal) and complete (ownership) unbundling. There is tantalizing anecdotal evidence that VIUs have tried to influence this choice through questionable means of persuasion. Such means of persuasion should be more readily available in countries with a more corrupted political culture. This paper shows that among the old EU member states, countries which are perceived as more corrupt are indeed more likely to apply weaker forms of unbundling. Somewhat surprisingly, we do not obtain a similar finding for the EU member states that acceded in 2004. We provide a conjecture for this observation.     

Sure,but who has the energy? The importance of location for knowledge transfer in the energy sector

Using over 350,000 U.S. patent citations, we test whether knowledge transfers in the energy sector are sensitive to distance, and whether that sensitivity has changed over time. Controlling for self-citation by inventor, assignee and examiner, multivariate regression analysis shows that physical distance is becoming less important for spillovers with time, but differs by energy subsector.     

Are micro-benefits negligible? The implications of the rapid expansion of Solar Home Systems (SHS) in rural Bangladesh for sustainable development

This paper examines the multiple benefits of the adoption of Solar Home Systems (SHS) and discusses the dissemination potential for sustainable rural livelihoods in developing countries. Based on a household survey conducted in rural Bangladesh, we first identify the impact of SHS on the reduction in energy costs and compare purchasing costs. We then examine household lifestyle changes following the adoption of SHS. Finally, we consider several price-reduction scenarios to examine the potential demand for SHS and to evaluate its future dissemination potential. The results of the analysis indicate that households with SHS successfully reduce their consumption of kerosene and dependency on rechargeable batteries, with the cost reductions accounting for some 20–30% of monthly expenditures on SHS. Moreover, most households with SHS can enjoy its benefits, including electric lighting, watching television, and the ease of mobile phone recharging at home. Further, the price reduction can make possible potential demand in more than 60% of households without SHS, while additional price reductions promote the purchase of even larger SHS packages. This study concludes that even though the scale of single SHS is small, the micro-benefits for each household and the dissemination potential are substantial.