BUOYANCY EFFECTS ON THE FORCED CONVECTION ALONG VERTICALLY MOVING SURFACES

The buoyancy effects on the laminar boundary layer heat transfer from vertically moving flat plate and cylinder are studied by a coordinate perturbation method for the cases of prescribed surface temperature and prescribed wall heat flux. Universal expressions are given to show the temperature distributions and the increase of heat transfer rate with the increase of the buoyancy force parameter.     

Hydrogen Lean-DeNOx as an Alternative to the Ammonia and Hydrocarbon Selective Catalytic Reduction (SCR)

The present article consists a critical up-to-date review of the research conducted so far on the selective catalytic reduction of NO_x with hydrogen under lean-burn conditions as an alternative technology to the existing NH₃- and HC-SCR. Noble Metal based catalysts are described in detail with emphasis on the analysis of the various reaction mechanisms that have been put forward in the literature. The influence of the nature of the support chemical composition and the preparation method and structure of the catalysts on the reaction mechanism is also discussed. Finally, the effects of various reaction parameters on the catalysts activity, selectivity and stability with reaction time are discussed in detail.     

Schnelle optische Tomographie zum Nachweis von OH*‐Verteilungen in Flammen

A recently developed and patented fast tomographic reconstruction system has been applied to detect two‐dimensional distributions of the OH* chemiluminescence in laminar and turbulent flames. This could be achieved by the arrangement at exposure times down to 100 – 200 μs at a spatial resolution of < 1 – 2 mm, even though the concentration of OH* in flames is in the order of some ppb and, therefore, extremely small. Among other things the results provide important information regarding the determination of the heat release rate in flames to predict unstable operating points of gas turbines.     

A numerical study of vortex interactions with flames developing from ignition kernels in lean methane/air mixtures

In this work, the outcomes of interactions of counter-rotating vortex pairs with developing ignition kernels are studied. The conditions are selected to represent those in a lean-burn natural-gas engine with hot-jet ignition. The evolution of flame surface area during kernel–vortex interaction is quantitatively and qualitatively examined. It is observed that flame development is accelerated and the net flame surface area growth rate, i.e. heat release rate, increased with increasing vortex velocity. In general, increasing the vortex length scale increases the surface growth rate, i.e. increases heat release rates, but for small length scales, i.e. when the ratio of vortex length scale to kernel diameter is small, high flame curvature induced during the interaction leads to flame weakening and slower growth rates. When the vortex velocity is high relative to the flame speed and the length scale is comparable to the kernel diameter, the vortex breaks through the ignition kernel carrying with it hot products of combustion. This accelerates growth of the flame surface area and heat release rates compared to a kernel with no vortex interaction. On decreasing the vortex velocity and increasing the length scale, the wrinkling of the kernel becomes important. This also results in increased surface growth rates and higher heat release rates.     

Cost-effective energy carriers for transport – The role of the energy supply system in a carbon-constrained world

The aim of this study is to examine how the options for producing electricity, fuels, and heat in a carbon-constrained world affect the cost-effectiveness of a range of fuels and propulsion technologies in the transportation sector. GET 7.0, a global energy system model with five end-use sectors, is used for the analysis. We find that an energy system dominated either by solar or by nuclear tends to make biofuels in plug-in hybrids cost-effective. If coal with carbon capture and storage (CCS) dominates the energy system, hydrogen cars, rather than plug-in hybrids tend to become cost-effective. Performing a Monte Carlo simulation, we then show that the general features of our results hold for a wide range of assumptions for the costs of vehicle propulsion technologies (e.g., batteries and fuel cells). However, sufficiently large changes in say the battery costs may overturn the impact of changes in the energy supply system, so that plug-in hybrid vehicles become cost-effective even if coal with CCS dominate the energy supply. We conclude that analyses of future energy carriers and propulsion technologies need to consider developments in the energy supply system.     

Application of response surface methodology to assess the combined effect of operating variables on high-pressure coal gasification for H2-rich gas production

Coal gasification was performed by means of a high-pressure fixed bed gasifier fitted with a solids feeding system in continuous mode, using oxygen and steam as gasifying agents. The main aim of the paper was to assess the combined effects of the operating variables (temperature, oxygen and steam concentrations) on high-pressure coal gasification. To this end a face centered central composite design (FCCCD) based on response surface methodology (RSM) was used. The response variables studied were: H₂, CO and syngas production, H₂/CO ratio, cold gas efficiency (η), and carbon conversion (X). The study was carried out at temperatures of 900, 950 and 1000 °C, using oxygen concentrations of 5, 10 and 15 vol.%, and steam concentrations of 25, 40 and 55 vol.%. The gasification temperature was found to be the most influential variable, with high temperatures leading to an increase in all the response variables studied. An increase in the oxygen content of the gasifying agent led to a decrease in H₂ and CO production, and cold gas efficiency, whilst carbon conversion was favoured. An increase in steam concentration, on the other hand, favoured the production of H₂ and syngas production, whereas CO production underwent a reduction; cold gas efficiency and carbon conversion were observed to increase. Response surface methodology (RSM) revealed the effects of interaction between the operating variables, which would not have been identified by the traditional “one-factor-at-a-time” method. The models developed successfully fitted the experimental results for all the response variables studied.     

An integrated approach to hydrogen economy in Sicilian islands

CNR–ITAE is developing several hydrogen and fuel cell demonstration and research projects, each intended to be part of a larger strategy for hydrogen communities settling in small Sicilian islands. These projects involve vehicle design, hydrogen production from renewable energy sources and methane, as well as implementation strategies to develop a hydrogen and renewable energy economy. These zero emission lightweight vehicles feature regenerative braking and advanced power electronics to increase efficiency. Moreover, to achieve a very easy-to-use technology, a very simple interface between driver and the system is under development, including fault-recovery strategies and GPS positioning for car-rental fleets. Also marine applications have been included, with tests on PEFC applied on passenger ships and luxury yacht as power system for on-board loads. In marine application, it is under study also an electrolysis hydrogen generator system using seawater as hydrogen carrier. For stationary and automotive applications, the project includes a hydrogen refuelling station powered by renewable energy (wind or/and solar) and test on fuel processors fed with methane, in order to make the power generation self-sufficient, as well as to test the technology and increase public awareness toward clean energy sources.     

Hydrogen generation from noncatalytic hydrolysis of LiBH4/NH3BH3 mixture for fuel cell applications

Ammonia borane (NH₃BH₃) and lithium borohydride (LiBH₄) are promising hydrides as they contain 19.6 wt.% and 18.5 wt.% hydrogen respectively. However, hydrolysis of NH₃BH₃ needs catalysts or high temperature to initiate the release of hydrogen. On the other hand, hydrolysis of LiBH₄ is incomplete, because the agglomeration of LiBH₄ and its products limits its full utilization. In the present work, hydrolysis performance of LiBH₄/NH₃BH₃ mixture was investigated. The results show that LiBH₄/NH₃BH₃ mixture can fully release its theoretical amount of hydrogen at room temperature without catalysts. In the presence of LiBH₄, NH₃BH₃ can be fully hydrolyzed at room temperature. In return, in the presence of NH₃BH₃, the agglomeration can be avoided resulting in a complete hydrolysis process. Our results indicate that the improvements are attributed to the intermolecular electron migration between LiBH₄ and NH₃BH₃, which changes the reactivity of these compounds. Hydrolytic heat of LiBH₄ also contributes to the promoted hydrolysis of NH₃BH₃. Our results present a novel strategy for noncatalytic hydrolysis of NH₃BH₃ and LiBH₄ for proton exchange membrane fuel cell applications.     

Commercial activated carbon for the catalytic production of hydrogen via the sulfur-Iodine thermochemical water splitting cycle

Eight commercial activated carbon catalysts were examined for their catalytic activity to decompose hydroiodic acid (HI) to produce hydrogen; a key reaction in the sulfur-iodine (S-I) thermochemical water splitting cycle. Activity was examined under a temperature ramp from 473 to 773 K. No statistically significant correlation was found between the measured catalyst sample properties and catalytic activity. Four of the eight samples were examined for one week of continuous operation at 723 K. All samples appeared to be stable over the period of examination.     

Ru incorporated Ni-MCM-41 mesoporous catalysts for dry reforming of methane: Effects of Mg addition, feed composition and temperature

Nickel incorporated MCM-41-like mesoporous materials, which were synthesized following a one-pot hydrothermal route, were promoted by Ru and Mg in order to improve their catalytic performances for dry reforming of methane. In this study, Ni-MCM-41 based catalysts (with a Ni/Si molar ratio of 0.2), containing different amounts of Ru (0.5-3.0 wt%) and Mg (1 and 5 wt%) were prepared by using sequential impregnation of Ru and Mg into Ni-MCM-41. Dry reforming of methane was studied in a tubular flow reactor in the temperature range of 500-600 °C with different CH₄/CO₂ ratios in the feed stream. Quite high hydrogen yield values and improved stability of these catalysts indicated the promoting effects of Ru for the Ni-MCM-41 type catalysts. Ru incorporation (1.0% Ru) was shown to improve H₂ yields. Mg impregnation into 1.0Ru@Ni-MCM-41 improved catalytic performance by increasing CH₄ conversion and decreasing the contribution of reverse water gas shift reaction, especially at initial times (first 60 min). Coke formation by decomposition of CH₄ contributed to the hydrogen selectivity, but did not cause significant change in catalytic performance, especially at longer reaction times.