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Abstract To ensure long-term availability of mobility and to keep the effects of humanity on global climate limited, politics, research, and industry currently search for ways to reduce greenhouse gas (GHG) emissions caused by it. A potential reduction could be achieved by transitioning towards more efficient transport modes, optimally powered by renewable energy. Based on mobility (commutes), population, and weather data from Switzerland, we present a model to compute energy savings due to a (hypothetical) widespread deployment of electric bicycles. In different scenarios, we analyze the dependence of the commuting energy demand on users’ preferences about when to take the bike, such as an aversion to biking on cold and rainy days. Our study shows that GHG emission reductions of up to approx. 10% of the total emissions from diesel and gasoline are possible. In combination with a widespread deployment of electric vehicles, further savings of up to 17.5% could be achieved. In particular, the willingness to drive longer commutes by e-bike influences the potential GHG emission reductions, followed by the willingness to use the bicycle at temperatures below 10°C. Using these results, we identify the spatial energy and greenhouse gas savings potential and thus regions that are particularly suited for e-bike use. The identification of regions with high saving potentials allows for targeted marketing, transition-supporting incentives, or infrastructural changes to maximize the reduction of emissions.

A hybrid-twin for gas-bearing supported, high-speed turbocompressor is suggested to be an aide to increase the operational reliability and to provide valuable insights to improve its design. The bearing clearances of a few micrometers imply that excessive thermal or mechanical deformations can result in machine failure due to mechanical seizure or rotor-dynamic instabilities. The high centrifugal forces and thermal gradients may induce material fracture or the lift-off of press-fitted assemblies. The mentioned phenomena and interactions depend strongly on the operating conditions and imply a risk of hitting critical operating zones potentially unscreened during the design phase. The developed twin asset involves 1D multi-domain models that are accurate enough to provide useful information regarding the most critical interactions and are computationally viable for real-time applications suggesting a run-to-real time ratio of 2 per cent. A case study in which a turbocompressor touchdown is analyzed a posteriori using the twin asset to highlight the possible insights to be gained by using the virtual twin to predict data that cannot be readily measured such as the thrust bearing axial clearance under the impeller thrust force. Finally, the generation of signals by the twin asset providing a degree of redundancy with sensor values is highlighted as an opportunity to increase confidence in monitoring tasks, paving the way to extension into control strategies.

In this article is presented the preliminary evaluation of the performance of radiation transmission of glass block, used in support of photovoltaic cells, investigating different internal surface points of the block, which are subject to different shading during daylight hours. The aim is to establish how the edging setting, the only opaque element, can reduce the amount of light radiation during the day, introducing in this way a reduction of efficiency of the entire generation system. The generation system can be based on traditional photovoltaic cells or on the most suitable dye sensitized solar cells. An experimental measurement setup employing a microprocessor-based instrument has been created and a set of measures have been carried out. The measures prove that the shading effect at different irradiation angles do not affect significantly the lighting over the PV cell.

Abstract A new photosensitizer, unsymmetrical alkoxy zinc phthalocyanine based on ‘push–pull’ concept, has been synthesized and fully characterized by CHN, MALDI-TOF, UV–Vis, fluorescence spectroscopies and cyclic voltammetry. The new phthalocyanine photosensitizer has eight alkoxy and two carboxyl groups that act as electron releasing (push) and withdrawing (pull), respectively. Moreover, the alkoxy groups increase the solubility of the new photosensitizer in common organic solvents, and the two carboxyl groups serve to graft on to nanocrystalline TiO2. The new photosensitizer was tested in dye-sensitized solar cells and its performance was compared with PCH001.

Abstract The catalytic effect on the photoelectrochemical behaviour of p-type silicon surfaces, due to thin ruthenium dioxide films, was investigated. Film deposition was by reactive rf sputtering. There was a drastic anodic displacement of the onset potential for the hydrogen evolution reaction in 2 M HCl, and an analogous displacement in the photoresponse onset potential in an electrolyte containing the ferrous/ferric redox couple. There was also a stabilising effect due to the ruthenium dioxide coating. The results are interpreted on a MIS model. A solar cell conversion efficiency of 5.1% was obtained in the V2+/V3+ redox electrolyte.

This paper discusses the influence of time horizon on dynamic optimization of small-size wastewater treatment plants alternating aerobic and anoxic processes. The optimization problem consists in determining the aeration policy (air-on and air-off periods) that minimizes the energy dissipated by the aeration system subject to both effluent and operating constraints. Optimization over short time horizons is first considered and reductions of the energy consumption up to 30% are obtained with respect to the usual operating mode of the process. But the application of such aeration strategies eventually results in a biomass wash-out when applied over long time periods. Here, it is shown that long time horizon optimized policies guarantee a durable functioning of the treatment plant. The resulting energy consumption savings are however lower (up to 15%), but are still important.

Abstract The Kramers Kronig (KK) relations are applied to locally resolved impedance data as obtained from a simple, analytic ‘down the channel’ impedance model of a polymer electrolyte fuel cell (PEFC) air cathode. It is shown that the transport and superposition of oxygen concentration oscillations in gas flow direction can lead to non-causal local cell impedance spectra, while the calculated local cell admittance always fulfills the KK relations. This is explained by the homogeneous distribution of the ac perturbation voltage over the electrode area due to the high electrical conductivity of the bipolar plates. Hence, the KK relations must be applied to the locally resolved admittance data of PEFCs to check if the measured spectra can be a physical response of the system.

Abstract Knowledge of flame responses to acoustic perturbations is of utmost importance to predict thermoacoustic instabilities in gas turbine combustors. However, measuring transfer functions linking acoustic quantities upstream and downstream of flames is very challenging in practical systems and these measurements can significantly deviate from state-of-the-art models. Moreover, there is a lack of studies investigating the effect of hydrogen enrichment on the response of natural gas (NG) flames. In this work, measurements of flame transfer matrices (FTM) of turbulent H2/NG flames in an atmospheric combustor featuring an axial swirler burner have been performed, allowing us to unravel the transition between FTM in fully premixed (FP) and in technically premixed (TP) conditions. Furthermore, imaging of OH* chemiluminescence and OH-Planar Laser Induced Fluorescence are obtained for characterizing the topology of the flame for varying H2 fraction and mixing conditions. Transfer matrices are measured using the multi-microphone method for H2 fractions ranging from 12% to 43% in power. Afterwards, the flame transfer functions (FTF), which linearly relate the coherent fluctuations of the heat release rate to the acoustic velocity oscillations, are obtained from the FTM by using the Rankine-Hugoniot jump conditions across the flame. Using the OH* chemiluminescence intensity as a surrogate for the heat release rate, the FTF based on this optical measurement is also extracted and compared to the one exclusively obtained with the multi-microphone method. As expected, the two different methods are in very good agreement for the FP case and significantly differ for the TP case. Indeed, chemiluminescence fluctuations cannot be directly linked to heat release rate fluctuations when the acoustic forcing induces equivalence ratio fluctuations at the flame, making the optical method unusable for TP configurations. We also show that the two methods agree in the high end of the explored excitation frequency range and we provide an explanation to this intriguing finding. Moreover, we investigate the sensitivity of the FTM measurement to the estimate of the speed of sound in the rig in FP conditions. Finally, the measured FTFs are fitted with FTF models based on multiple distributed time delays. This allows us to explain the frequency dependence and the hydrogen fraction dependence of the gain and the phase in FP and TP conditions.

The homogeneous ignition of lean methane-air mixtures was investigated numerically and experimentally in a laminar plane channel flow configuration established by two externally heated catalytically active (Pt-coated) ceramic plates, 250 mm long by 100 mm wide, place 7 mm apart. Preheated fuel-air mixtures with equivalence ratios of 0.31 and 0.37 and uniform velocities of 1 and 2 m/s were examined, resulting in incoming Reynolds numbers ranging from 190 to 380. Planar laser-induced fluorescence (PLIF) was used to map the OH concentration field along the streamwise direction and thermocouples to monitor both catalyst plate temperatures. The numerical predictions included a two-dimensional elliptic model with detailed heterogeneous and homogeneous chemical reactions. The homogeneous ignition location strongly depends on the incoming velocity and mildly on the equivalence ratio. Following homogeneous ignition, a very stable V-shaped flame is formed in all cases. Measured and predicted flame sweep angles, OH levels, and the post-flame OH relaxation are in good agreement with each other, while the homogeneous ignition distance is predicted within 9% in all cases. The homogeneous ignition location is shown to be better identified with changes of averaged (over the channel cross section) quantities rather than with changes in local wall gradients. The overall model performance suggests that the employed surface scheme is capable of capturing the coupling between surface and gaseous chemistries leading to homogeneous ignition. Experiments and predictions were also carried out with noncatalytic plates. The resulting flame is unstable and asymmetric, clearly showing the stability advantages of catalytically assisted combustion.