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This article presents an analysis of the capacity and the state of health (SoH) of 3-Ah lithium battery cells operating in a real case vibration stress scenario based on drones. An unmanned aerial vehicle (quad-copter) is adopted to acquire real vibration profiles during different phases of flight. First, the possible capacity fade and aging effect on lithium cells are investigated by considering vibrations applied to the radial and longitudinal battery axes with both short-term and long-term (aging) tests. Then, the cruise-flight vibration profiles are applied and characterized. A comparison with standard (no vibrations) cycling aging is also presented and discussed. The experimental results show that no significant effect on capacity fade can be observed between standard and real case vibrating operating conditions.

In this paper, we analyze the electrostatic charge distribution on arbitrarily shaped conductor surfaces. Following a perturbative approach, we derive an approximate analytical formulation of the problem. We start from the known case of a conducting ellipsoid, we adopt a deformed ellipsoidal coordinate system, and we search for the zero-order approximated solution of the problem. We also focus on arbitrary-shaped thin foils, showing that the charge density is divergent on their borders. We then define the applicability range of the proposed approach expressing the contour equation as the Fourier series. Finally, we present a detailed error analysis for several polygonal contours, comparing the analytical results with those obtained via a numerical analysis based on the Finite Element Methods (FEM).

Biomass combustion performance is greatly affected by the particle size distribution, which influences heat and mass transport phenomena. The present work investigates the effect of woodchip size distribution on combustion in a 140 kW underfeed stoker boiler. Three different fuel sizes were prepared, and their combustion performance was measured by monitoring temperatures inside and above the fire pit and the gas composition above the fuel bed. The gas composition was then correlated to the particle mean diameter. Although minor effects could be detected in the temperature and composition of the flue gases, a more uniform spatial distribution of volatiles was observed when employing bigger woodchips. The present results can improve the understanding of the impact of fuel size on the performance of woodchip-fired boilers and can be valuably used for numerical model validation.

Acoustic pyrometry is a widely used technique for contactless temperature measurement. It may be used in several applications, especially when high temperatures and harsh environments are involved. For instance, it has been applied to measure the temperature distribution at gas turbine outlet. This technique is based on the measurement of the time of flight of an acoustic wave through a medium. If multiple emitter-receiver couples are used, using a computational procedure a reconstruction of a temperature map is possible. On the other hand, a full assessment of the robustness of this technique to potential errors in TOF estimation is still missing. In this study, the impact of an inaccuracy in TOF estimation on the reconstruction of a correct temperature map is investigated by means of a statistical approach. As a general result, it was found that when the TOF was measured without inaccuracies, temperature estimation errors may be lowered by simply increasing the number of cells in which the estimation is performed. However, when the estimation of the TOF is affected by errors, an optimal configuration exists that minimize the temperature estimation errors.

Natural draft wood log stoves for residential bioheat production are very popular due to the low fuel costs, the ecological aspect of a renewable energy source and the visual appeal of the flame. However, they have rather high pollutant emissions, specially of unburnt products. The description of large wood logs conversion in stoves needs to be improved to allow a process optimization which can reduce these emissions. The transient conversion of a single wood log in a stove is experimentally investigated with test runs quenching the log after defined time intervals and measuring the flue gas composition and temperatures in the log and stove. The experiments have been described with a volumetric single particle model, which predicts with good accuracy the log conversion until a time of around 30 min, when pyrolysis is almost ending. At that point, log fragmentation takes place and smaller fragments are detached from the log falling onto the bed of embers. Despite the increase in external surface area, char oxidation takes place at a moderate rate. This last stage of wood log conversion in a stove is the most challenging to model. Finally, preliminary recommendations are provided for reducing CO emissions in wood log stoves.

Biomass is a suitable energy source to reduce the carbon footprint and increase the use of renewable energy. However, the biomass exploitation is still slowed by many technical issues. In most practical applications, such as gasification or combustion devices, it is important to predict the fuel physical behavior in order to determine the emissions and heat release profile as well as for modeling and design purposes. Within this paper, the study of the dimensional evolution of a biomass fuel (beech wood) in pyrolysis and combustion processes were carried out with the use of the image analysis tool. Sizes from 15 mm to 300 mm characteristic length range were employed in the experiments and the collected data were related to the mass loss and temperature evolution of the biomass particle. It was found that for all the fuel sizes employed a similar volume reduction (60%–66%) was obtained at the end of pyrolysis. However, for the small particles with minor intra-particle gradients shrinkage took place mainly at the end of conversion, while for bigger particles the size variation patter was more linear. Furthermore, swelling was detected in the pyrolysis experiments, and it was higher for a bigger particle size, while cracking and fragmentation phenomena was observed for large wood logs combustion in the stove.

In the current work, electrochemical impedance spectroscopy is applied to lithium batteries with different power size, shape and technology in order to monitor the state of health of the cells. The employed approach shows that the frequency analysis can provide the aging state evaluation. This is particularly evident for a narrow frequency range, and even a single frequency readout can be exploited to quickly and reliably evaluate the state of health of the cell. Therefore, the presented method results promising for many practical applications, such as for battery management strategies and cell monitoring purposes.

Carbon fiber reinforced polymers (CFRPs) are particularly suitable for aerospace applications due to their specific mechanical properties. During their service life, these materials can suffer damage, sometimes difficult to detect, which may compromise their mechanical performances. The variation of the electrical properties of CFRPs is one of the strategies that can be used to monitor such damage. However, multiple variables contribute to this variation. This paper presents a preliminary analysis of the electrical impedance dependence on temperature and on damages outbreaks. The measurements are performed in controlled environment on a wide range of temperature and frequency. In some cases, the measured data show an impedance change due to the damage presence, which is of similar entity with respect to the variations caused by temperature. This may lead to misleading interpretations of impedance measurements in the absence of additional information. Hence the need of a proper temperature monitoring to possibly use electrical impedance spectroscopy analysis is required to unequivocally determine the health status of CFRPs.

In this article, we present a novel measurement method to estimate the current distribution in electromagnetic rail launchers. A loop array is magnetically coupled with the railgun to reconstruct the current barycenter position, from which we can argue on the current distribution through the rail cross section. After describing the adopted measurement procedure, we present the results of an experimental analysis performed using the NGL60 rail launcher at the laboratories of the French-German Research Institute of Saint-Louis (ISL). We also compare the experimental results with finite-element simulations, and we show the agreement during the current pulse transient. Finally, we provide a measurement uncertainty analysis performed using Monte Carlo method.

In this paper we present an analysis of temperature response of a 100 µm hysteretic wire exploiting a time domain readout. The ferromagnetic wire is composed of 80% Co-Fe, 20% Si, B. The study here conducted investigates the effect of temperature in the microwire with an output measured as time response, which represents an intriguing method to convert the target quantity. The experiments have been accomplished by using a MuMetal® electromagnetic shield with controlled temperature and an acquisition system to process the output. Results here reported evince the suitability of the proposed method which arouses interest for several interesting applications.

In recent years, biofuels have been attracting more attention, especially in Europe, due to the new regulations concerning the improvement of renewables in fuel composition. The acid-catalysed alcoholysis reaction of the cellulosic fraction of raw and pre-treated lignocellulosic biomasses, using n-Butanol (n-BuOH) and diluted inorganic acid as homogeneous catalyst, produces a mixture mainly composed by Butyl Levulinate (BL) from cellulose, Dibutyl ether (DBE) from n-BuOH etherification and unreacted n-BuOH. This last can be then separated and recycled, so increasing the sustainability of the whole process. BL is directly obtained from cellulosic fraction of not edible biomass and represents a promising advanced biofuel. Therefore, in the different types of blends containing the main products obtainable from the one-pot alcoholysis of lignocellulosic biomasses, BL represents the effective renewable component of the fuel. In this work, different blends of BL/DBE mixed with Diesel fuel were tested in a small single-cylinder air-cooled Diesel engine with direct injection. Data concerning the measurement of pollutant emission, engine performance and combustion characteristics are reported. Results have been compared with those obtained fuelling the engine with a conventional Diesel fuel. The mixtures were prepared by using commercial reactants, characterized by compositions analogous to those of the reaction mixtures. The obtained results evidenced the potentiality of these novel blending mixtures to reduce the emissions of particulate without any increasing of NOx emission or changing in engine power and efficiency.

Acoustic pyrometry is an interesting technique that may find several useful applications in turbomachinery. It is well known that the speed of sound in a medium is directly related to its temperature. Acoustic pyrometry estimates the temperature of a gas by considering the time of flight of an acoustic wave moving through it. If one acoustic emitter-receiver couple is used, only the average temperature along the acoustic path can be determined. If multiple emitter-receiver couples laying on the same plane are used, a reconstruction of the temperature map in the section is possible. In this last case, the analysis is based on the fact that the temperature of each sub portion of the section affects the time of flight of all the acoustic paths travelling across it. Many parameters affect the accuracy of the measurement. They are mainly related to the physic of the sound propagation in a medium, the accuracy of the instrumentation used, the interaction between the acoustic wave and the flow velocity and the hardware set-up. In this study, the impact of the measurement set up of an acoustic pyrometry for the measurement of the exhaust gas temperature in a gas turbine was investigated to determine the optimal solution in terms of accuracy and robustness to uncertainties.

This paper investigates the Lithium battery behavior and possible aging effects in presence of current ripple during the operation. In the context of a research funded project aimed at increasing the safety level of Lithium batteries for the naval propulsion, we present the results of an experimental analysis aimed at investigating the effect of current ripple on cell performances. An ad-hoc experimental setup is developed to test the batteries and the effect of current ripple on battery capacity and cell aging is discussed throughout the paper.

The increment in the world energy consumption and the necessity for a sustainable industrial production, indicate that renewable resources may be key actors for future development. In this scenario, biomass appears fundamental for the smooth transition from fossil fuels to lower carbon footprint technologies, and as a moderator agent within the renewable market. The small size biomass combustion application appears as suitable for smart grid and distributed generation applications, but it is necessary to improve the design tools capabilities and the experimental knowledge of these systems. The present work aims at investigating the thermal behaviour of a 140 kW fixed-bed boiler sited at the Biomass to Energy Research Centre (CRIBE) of the University of Pisa and fed with woodchips. Experimental activities were conducted in order to acquire thermal and chemical data. Moreover, a computational fluid dynamic model was developed and validated. Attention was paid to the fixed bed analysis, and the results showed a good model prediction capability, with respect to the reduced computational demand required.

The world energy demand growth is more and more supplied by renewable energy sources. In this scenario, biomass has a key role in both heat and power generation. Particularly, biomass combustion can be used in small size micro and distributed generation systems, or in smart grids together with wind and solar energy where a programmable energy source is necessary to keep the electric grid stable. In this paper, a small size 140 kWth biomass fixed bed boiler of the University of Pisa, located at the Biomass to Energy Inter-University Research Centre (CRIBE), was studied experimentally to characterize the biomass combustion process. Emissions of NOx, O2, CO2 and CO, together with the temperature data, were measured in the flue gases. Moreover, the spatial distribution of volatile products from the fixed bed surface, such as H2, CO, CO2, CH4, C2H6, C2H4, C2H2, together with temperature data, was studied in the early combustion stage. The parametric variation of the feed air flow and its effect on the emissions and performances was also investigated. The results indicate that the primary air mainly affects the volatiles distribution on the biomass combustion surface. Therefore, the CO emission was minimized at values of 0.03%vol with an air excess equal to 2 and a 0.06 secondary to primary air mass flow ratio.

Biomass has a key role in the future of the energetic scenario, since it is a programmable renewable energy source which is suitable either to generate power and/or produce heat. This paper deals with biomass combustion processes in small size boilers, which is suited either for large residential buildings, or for small size industrial users. This kind of boilers is different from small pellet stoves and fireplaces and from large utility size boilers. In particular, those small size boilers have been seldom studied in the scientific literature about the combustion kinetics and pollutant formation mechanisms. Hence, the authors present the thermo-chemical data collected from a 140 kWth chipped wood boiler at the University of Pisa. The effect of the air excess and the ratio between and secondary feeding air and primary feeding air mass flow rate, on CO, CO2 and NOx emissions was investigated. Results have shown that the air excess has the main influence on the pollutant produced. A comparison of the measured data with those presented in the literature and the discrepancies with other studies are also discussed.

Acoustic pyrometry is an interesting technique that may find several useful applications in turbomachinery. As the speed of sound is directly related a medium temperature, this measurement technique estimates the temperature of a gas by considering the time of flight of an acoustic wave moving through it. If only an acoustic emitter-receiver couple is used, only the average temperature along the acoustic path can be determined. If multiple emitter-receiver couples laying on the same plane are used, a reconstruction of the temperature map in the section is possible. This estimation is performed by considering that multiple acoustic paths travel across the same sub-portions of the section and, therefore, the temperature of each sub-portion affects the time of flight along several sound paths. Many parameters affect the accuracy of the measurement, and they are related to the physic of the phenomena involved in the measurement, the accuracy of the instrumentation used, the interaction between the acoustic wave and the flow velocity and the hardware set-up. In this study, the impact of some set-up parameters on the accuracy of the measurement was investigated and, in particular, the number of sound emitter-receiver couples and the number of investigation sub-portions in which the section is divided. A reference temperature map has been considered as a benchmark. This study, which is a preliminary investigation on this technique, was useful to assess the capability of this methodology to correctly describe a temperature distribution in an ideal condition. Therefore, it represents a first step in the set-up of an experimental investigation with an acoustic pyrometer..

Energy sector sustainability is one of the main concerns in the recent years. Biomass, in form of woodchips, is interesting for direct combustion in external combustion cycles (e.g. supercritical CO2 Brayton cycles) due to the opportunity of using low quality and low environmental impact fuels. In this study, a direct combustion system working with biomass woodchips is investigated by means of an image analysis technique. The system is made up by a screw conveyor and a fixed bed, where the woodchips are processed. The analysed device operates in cold-condition, and woodchips are partially coloured according to their dimensional class to be traced once these reached the bed surface. A proper algorithm was developed to identify the particles size, define and detect macroparticles centres, and evaluate the main particles motion pattern by comparing the centre positions during time. The results were particularly useful to understand potential inefficiencies of the combustion system due to an uneven woodchips distribution. In addition, the results achieved with the proposed test rig and the adopted methodology can also be used to validate results from Discrete Element Modelling (DEM) simulations.

During the last decades, the increase of the world energy consumption promoted the renewable resource development and use. Together with wind, solar and hydro energy, biomasses play a key role in the reduction of the industrial environmental impact; moreover, the biomass combustion systems are very attractive for micro-generation purpose. In this paper, experimental tests on a 140kW small size fixed bed biomass boiler were carried out. The main goal was to study the thermal behavior and some chemical products, such as CO, CO2, Methane and Ethylene, from the combusting fixed bed of the system. In fact, despite the wide amount of literature for the laboratory scale systems, the commercial scale boilers have been seldom studied by the experimental point of view. The data were obtained by varying the operational parameters of the boiler, that are the air excess and the secondary to primary air feeding ratio. Furthermore, the collected data were analyzed and the relationship between the thermal-chemical data and the control variables was discussed.

In the last decades, the energy market increased its interest towards the smart grids and electrically isolated systems. These systems utilize small size power generators in which volumetric expanders may be employed for a wide range of operative conditions, because of their robustness and reliability. In this work a study on a volumetric expander based on the Wankel mechanism was carried out. The aim of this study was to develop a lumped parameters numerical model able to predict the brake effective torque and working fluid consumption of the expander. This model was validated by comparison with experimental results obtained using steam as working fluid. This model allowed to trace the trends of mechanical and thermal losses versus rotating speed and inlet pressure. The experimental results encouraged the need for a further development of this expander, and showed the capability of the numerical model to predict the effective performances of the device.

This article deals with the measurement of current distribution through the rail cross section of an electromagnetic rail launcher. A measurement approach based on a loop system magnetically coupled to the launcher that is placed along the rails is proposed. The estimation of the current distribution in the rail, following the basic rules of the partial-inductance method, is discussed in this article. To test the proposed method, an experimental analysis on an “ad-hoc” -developed multiconductor rail prototype supplied by a high-voltage capacitor bank is presented. The experimental results obtained by the proposed method were compared with the direct-current measurements achieved by a set of Rogowski coils showing good agreement for different current values.

In this paper we present a characterization of a ferromagnetic microwire having a diameter of about 100 μm and a composition of CoFeSiB as 80% Co-Fe, 20% Si, B. We experimentally analyze the influence of the temperature and excitation frequencies on the hysteresis loop of the material. In particular, results and discussion about how the temperature can affect the magnetic characteristic of the material are provided. All measurements have been performed under controlled conditions. A suitable setup has been conceived, realized and an experimental campaign with the characterization of the microwire has been accomplished obtaining very promising results.

In the recent years the progressive decrease in fossil petroleum resources and gradual deprivation of the environment have attracted increasing interest towards the use of biomass as renewable carbon source for the production of chemicals and transportation fuels. In particular, lignocellulosic biomass represents an abundant and inexpensive renewable resource with high carbon sequestration ability and non-polluting. In this paper, the valorisation of mixtures made of n-butanol (n-BuOH), butyl levulinate (BL) and dibutyl ether (DBE), in different percentages, as additive fuel for compression ignition (CI) internal combustion engine (ICE) was studied. These mixtures can be directly obtained from the catalytic alcoholysis reaction of the cellulosic fraction of raw and pre-treated lignocellulosic biomasses. Moreover, the possibility to recycle and reutilize the excess alcohol (n-Butanol), during the catalytic alcoholysis reaction, has been considered since it represents an opportunity to reduce the overall costs of the process. Therefore, a blend constituted only by BL and DBE has been also tested. The model mixtures were prepared by using commercial reactants, characterized by compositions analogous to those of the reaction mixtures. These model mixtures were tested as blend with Diesel fuel in a CI-ICE with the measurement of pollutant emission and performance. Results have been compared with those obtained fuelling the engine with a commercial Diesel fuel. As a whole, tests results have evidenced the potentiality of these novel blending mixtures to reduce the emissions of particulate without any significant increase in the other pollutants and negligible changes in engine power and efficiency.

Variable renewable energy sources are continuously increasing their share in the world energy mix. However, their uncertainty has a deep impact in the electric grid safe operation. One of the most promising solutions to tackle such challenge at a distribution grid level consists of quasi-real-time, peer-to-peer electricity markets. These can use the blockchain to be successfully implemented in a secure and privacy preserving way, making effective use of the increasing intelligence of Internet of Things appliances. Nevertheless, providing blockchain-based solutions compatible with the energy sector is not an easy task. In particular, in order to be compliant with typical electricity costs of the order of some €cents/kWh, blockchain transactions are required to be very cheap. Unfortunately, none of the existing research works took the issue of transaction costs into account. As a result, real-world feasibility of existing solutions is rather to be investigated. In this work, we propose an ad-hoc Ethereum-based consortium blockchain explicitly addressing this issue. Leveraging on this platform, we design a blockchain-based electricity market. The market consists of two-steps. The first (day-ahead) step settles the amounts and prices of the energy traded among peers. The second step is instead quasi-real-time, thus enabling the unexpected excess or lack of electricity to be directly negotiated on a peer-to-peer basis. Negotiations occurs without the need of any intermediary, except for the check of grid physical limits, performed by the distribution system operator. To demonstrate the functionality of the solution, a proof-of-concept has been implemented at the University of Pisa (Italy).

A Computational Fluid Dynamic model of oxy-coal devolatilization experiments in a pilot-scale entrained flow reactor is proposed to gain insight into the thermal histories of the cloud of solid fuel particles and to investigate sources of uncertainties that may affect the analysis of devolatilization. Solid fuel particles experience different paths and are characterized by a temperature which is lower than the reactor nominal one at some of the sampling locations used for investigating devolatilization rates. Indeed, neglecting the quick heating up of the particles by assuming their temperature to be equal to the reactor one for calculating kinetics leads to an underestimation of devolatilization rates. A simple hypothesis on a linear dependence of the particle temperature on residence time through an average heating rate, with residence time and heating rate estimated from the numerical model, was found to largely improve the reliability of devolatilization kinetics even with a simple Single First Order ...

In the recent years, the sustainable energy demand is growing among the civil and industrial sectors. However, the renewable sources present an aleatory behaviour, and the improvement of their reliable and secure employment have received great interest. In this framework, the energy storage devices can be used to smooth the market demand and to increase the control on the energy fluxes over transmission lines. To this aim, devices such as Li-ion batteries are widely used in several application scenarios, such as the transportation sector. Generally speaking, batteries are often classified as high-energy devices and their use for high-power applications is limited. Indeed, for the latter applications, other devices, such as supercapacitors or ultracapacitors, are usually employed. In the present work, the use of 3Ah 18650 Li-Ion batteries is investigated for high-power applications, and a performance analysis during pulsed discharge with current up to 50C is carried out. These experimental conditions are significantly beyond the manufacturer specifications; therefore, an accurate ageing estimation of the cell is required, and a novel internal resistance control method is proposed to monitor the state of health of the device.

Biogas plants are an interesting solution for production of clean energy. Biogas produced in an anaerobic digester can be used locally to produce electric energy in an internal combustion engine or in a micro-gas turbine. A portion of the waste heat is used to keep the digester at a constant temperature which is a necessary condition for a correct operation of the digester. Generally, waste heat overcomes that necessary to keep the digester at the desired temperature and a big portion of this thermal energy is dissipated. Many solutions exist to increase the amount of heat recovered. In this study, the use of an absorption chiller to decrease the inlet temperature of a micro-gas turbine operating with biogas was considered. The advantage of this solution relies in a more stable operation of the micro gas turbine and an increase in the power output. The integration of the absorber chiller in the biogas plant and the effect of the ambient conditions were investigated in detail. The study was based on an existing plant operating near Pisa (Italy). A model of the system has been developed in AMESim and a numerical simulation has been performed. The effects of different temperature profiles, corresponding to different climate conditions, have been investigated both from the energy and economic points of view. The results showed that local climate conditions strongly influence the effectiveness and the profitability of the inlet turbine air cooling technique. In those climates where the temperatures are constantly high over the year, this technique may lead to interesting benefits and profitability.