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Abstract With the push to curb dangerous atmospheric pollutant production, energy generation technologies that reduce green-house gas emissions, while still providing adequate electrical supply, are of high importance. With major energy infrastructure already in place, developing enhanced pollutant-reducing combustor systems for micro gas turbines (MGTs), that can utilize low calorific fuels from renewable resources, is a major goal. The current work focuses on the experimental testing of an optimized two-stage combustor designed to operate with various fuel types, including natural gas and syngas produced via biomass gasification. Atmospheric experimental tests were performed and the results indicate larger flame lift-off heights and slightly higher CO gas emissions levels, while displaying lower NOx gas emissions levels for all thermal loads and air-to-fuel equivalence ratios tested, compared to that of the previous combustor designs. Additionally, steady-state computational fluid dynamics (CFD) simulations were conducted and the results are in general good agreement with the experimental data. Overall, the results indicate high fuel flexibility of the combustor, as well as the ability to comply with the NOx emissions limits for a larger range of operating points, compared to that of the previously tested combustors.

Abstract With hydrogen becoming more and more important as energy carrier, there is a need for high capacity storage technologies preferably operating at low pressures. Chemical storage in metal hydrides is promising for that purpose, but they require thermal management for hydrogen release and storage, respectively. To overcome this challenge, it is beneficial to store the heat needed for hydrogen release during hydrogen storage in the storage system keeping the additional effort to provide that heat low. In this work, the experimental proof of concept of an adiabatic storage reactor is presented. Magnesium hydride and magnesium hydroxide have been used for hydrogen storage and thermochemical heat storage, respectively. A prototype reactor has been developed and experimentally investigated. It was found that the operating temperature of the materials can be adjusted with the gas pressure in a way to establish a temperature gradient from the MgH2 to the Mg(OH)2 and vice versa. Hydrogen storage and release is enhanced by the thermochemical heating/cooling. A pressure of 9 bar is sufficient to store hydrogen with a capacity of 20.8 gH2 L-1 based on the two materials only, without the steel vessel or insulation. In the heat storage compartment, 300 °C have been reached at 9.75 bar during heat release which is high enough to drive the MgH2 dehydrogenation.

Optical system design has a significant impact on solar power plant efficiency. It can be advantageous to be able to very precisely adapt mirror shapes in order to improve energy yield. In this article it is investigated whether it is feasible to use non-uniform rational Beziers splines (NURBS) to describe mirrors. Algorithms and equations to evaluate optical performance by ray tracing are lined out. A parameterization scheme is given that reduces the degrees of freedom to a level suitable for automatic processing. To prove feasibility, a secondary reflector based on a NURBS surface and a compound parabolic concentrator (CPC) are designed for a specific test application and compared to each other. It is found that the suggested design method is feasible on contemporary personal computers and that the NURBS based surface performs well compared to the CPC.

Abstract We examine the balancing of economic and environmental goals in long-term airline fleet planning. A multi-objective linear programming model optimizes fleet composition, fleet development, and fleet employment for a 10-year planning horizon. Model inputs include flight plan data, operational, technical, and cost parameters, existing fleet aircraft, and the availability of new, more efficient aircraft. The model determines trade-offs between an economically and an environmentally optimal fleet plan depending on user-defined weightings. Varying these weightings provides alternative Pareto-optimal fleet plans. An example for a major European airline shows that it would have to deviate by approximately 3% from its economic optimum to achieve a 6% improvement in the environmental goal. The study provides insights for policy makers when setting environmental targets for airlines and developing mechanisms to encourage environmental commitment.

Abstract In Germany renewable energies in the heat market are promoted by the Renewable Energies Heat Act (EEWarmeG) and by government grants. Ultimately, these two instruments are not only about short-term market success, but rather about the perspectives of climate protection and resource conservation. The focus of this report is therefore on the long-term significance of the current design of government grants and EEWarmeG. We will introduce and discuss the quantitative goals and structural changes strived for as well as – on a slightly shorter time horizon – the quality assurance regulations which must accompany the steady and stable growth of renewable energies. In the process, we will elaborate in particular on heat pumps, which have recently been added to the government support programme, along with solar collectors. Some explanations regarding the structural relationships between EEWarmeG and government grants round off this contribution.

Abstract A detailed computational model of a direct-flame solid oxide fuel cell (DFFC) is presented. The DFFC is based on a fuel-rich methane–air flame stabilized on a flat-flame burner and coupled to a solid oxide fuel cell (SOFC). The model consists of an elementary kinetic description of the premixed methane–air flame, a stagnation-point flow description of the coupled heat and mass transport within the gas phase, an elementary kinetic description of the electrochemistry, as well as heat, mass and charge transport within the SOFC. Simulated current–voltage characteristics show excellent agreement with experimental data published earlier (Kronemayer et al., 2007 [10] ). The model-based analysis of loss processes reveals that ohmic resistance in the current collection wires dominates polarization losses, while electronic loss currents in the mixed conducting electrolyte have only little influence on the polarized cell. The model was used to propose an optimized cell design. Based on this analysis, power densities of above 200 mW cm −2 can be expected.

Abstract Solar thermal parabolic trough collectors can be used to provide heat for desalination, cooling and electricity generation. The set-up and some intermediate results of a measurement campaign for the evaluation of a parabolic trough collector — the Solitem PTC1800 — are presented. Optical tests of the concentrator were used to determine the intercept factor, allowing to give recommendations for optical improvements. Thermal testing up to 200°C with pressurised water showed low radiative and convective losses.

Abstract The potential of dimethyl ether (DME) and dimethoxymethane (DMM), representatives of the attractive oxymethylene ether (OME) alternative fuel family, are explored here as reactivity enhancers for methane-fueled polygeneration processes. Typically, such processes that can flexibly generate power, heat, or chemicals, operate under fuel-rich conditions in gas turbines or internal combustion engines. To provide a consistent basis for the underlying reaction mechanisms, it is recognized that speciation data for the DME/CH4 fuel combination are available for such conditions while such information for the DMM/CH4 system is largely lacking. In addition, it should be noted that a detailed speciation study in flames, i.e., combustion systems involving chemistry and transport processes over a large temperature range, is still missing in spite of the potential of such systems to provide extended species information. In a systematic approach using speciation with electron ionization molecular-beam mass spectrometry (EI-MBMS), we thus report, as a first step, investigation of six fuel-rich premixed flames of DME and DMM and their blends with methane with special attention on interesting chemicals. Secondly, a comprehensive but compact DME/DMM/CH4 model (PolyMech2.1) is developed based on these data. This model is then examined against available experimental data under conditions from various facilities, focusing preferentially on elevated pressure and fuel-rich conditions. Comparison with existing literature models is also included in this evaluation. Thirdly, an analysis is given on this basis, via the extensively tested PolyMech2.1 model, for assumed polygeneration conditions in a homogeneous charge compression ignition (HCCI) engine environment. The main interest of this model-assisted exploration is to evaluate whether addition of DME or DMM in a polygeneration process can lead to potentially useful conditions for the production of syngas or other chemicals, along with work and heat. The flame results show that high syngas yields, i.e., up to ∼78% for CO and ∼35% for H2, can be obtained in their burnt gases. From the large number of intermediates detected, predominantly acetylene, ethylene, ethane, and formaldehyde show yields of 2.1−4.4% (C2 hydrocarbons) and 3.4−8.7% (CH2O), respectively. Also, methanol and methyl formate show comparably high yields of up to 0.6−6.7% in the flames with DMM, which is 1–2 orders of magnitude higher than in those with DME as the additive. In the modeling-assisted exploration of the engine process, the PolyMech2.1 model is seen to perform at significantly reduced computational costs compared to a recently validated model without sacrificing the prediction performance. Promising conditions for the assumed polygeneration process using fuel combinations in the DME/DMM/CH4 system are identified with attractive syngas yields of up to 77% together with work and heat output at exergetic efficiencies of up to 89% with DME.

Abstract Cascaded ThermoChemical Storage (CTCS) of solar energy is a concept targeted to increase the volumetric energy storage density and address the thermocline temperature distribution inside regenerative sensible-only storage systems. CTCS involves the use of cascades consisting of different thermochemical systems, distributed in a rational pattern inside the storage module tailored to their thermochemical characteristics and to the local heat transfer medium temperature. In the case of air-operated Solar Thermal Power Plants such cascades can consist of porous structures incorporating different redox pair oxide materials that can come in direct contact with the air stream used as heat transfer fluid and operate as compact, hybrid sensible-thermochemical storage modules in series. Having previously identified the Co3O4/CoO and Mn2O3/Mn3O4 redox pairs as the most promising single-oxide systems for solar energy thermochemical storage, lab-scale (∅ 25 mm), Co3O4- and Mn2O3-coated, porous cordierite honeycombs and foams were prepared and tested with respect to their thermochemical characteristics in one- and two-oxides cascaded configurations employing redox oxide quantities in the range 15–150 g. For such Co3O4-loaded cascades thermochemical storage was clearly demonstrated as heat uptake/release at constant temperature under proper testing conditions. Besides, the additive effect of thermochemical on sensible storage within the same storage volume was visualized. The operating conditions of cascades including both Co3O4 and Mn2O3 were dictated by the redox behaviour of the Mn2O3/Mn3O4 pair. Under proper conditions, such two-oxides-cascades could undergo cyclic reduction-oxidation and operate in complementary temperature ranges during oxidation; however the thermal effects of only the CoO oxidation reaction could be materialized into temperature rise of the air stream exiting the cascade.