Zinc oxide (ZnO) is one of the main functional materials used to realize chemiresistive gas sensors. In addition, ZnO can be grown through many different methods obtaining the widest family of unique morphologies. However, the relationship between the ZnO morphologies and their gas sensing properties needs more detailed investigations, also with the aim to improve the sensor performances. In this work, seven nanoforms (such as leaves, bisphenoids, flowers, needles, etc.) were prepared through simple wet chemical synthesis. Morphological and structural characterizations were performed to figure out their growth mechanisms. Then, the obtained powders were deposited through screen-printing technique to realize thick film gas sensors. The gas sensing behavior was tested toward some traditional target gases and some volatile organic compounds (acetone, acetaldehyde, etc.) and compared with ZnO morphologies. Results showed a direct correlation between the sensors responses and the powders features (morphology and size), which depend on the specific synthesis process. The sensors can be divided in two behavioral classes, following the two main morphology kinds: aggregates of nanocrystals (leaves and bisphenoids), exhibiting best performances versus all tested gases and monocrystal based (stars, needle, long needles, flowers, and prisms).

The proper operation of a fluid power system in terms of efficiency and reliability is directly related to the fluid state; therefore, the monitoring of fluid ageing in real time is fundamental to prevent machine failures. For this aim, an innovative methodology based on fluid vapor analysis through metal oxide (shortened: MOX) gas sensors has been developed. Two apparatuses were designed and realized: (i) a dedicated test bench to fast-age the fluid under controlled conditions; (ii) a laboratory MOX sensor system to test the headspace of the aged fluid samples. To prepare the set of MOX gas sensors suitable to detect the analytes’ concentrations in the fluid headspace, different functional materials were synthesized in the form of nanopowders, characterizing them by electron microscopy and X-ray diffraction. The powders were deposited through screen-printing technology, realizing thick-film gas sensors on which dynamical responses in the presence of the fluid headspace were obtained. It resulted that gas sensors based on solid solution Ti_xSn_1–xO₂ with x = 0.9 and 0.5 offered the best responses toward the fluid headspace with lower response and recovery times. Furthermore, a decrease in the responses (for all sensors) with fluid ageing was observed.

A comparative study is presented on the photoluminescence (PL) response toward molecular oxygen (O₂) in tin dioxide (SnO₂), zinc oxide (ZnO) and titanium dioxide (TiO₂) nanoparticles. The findings show that both PL enhancement and PL quenching can be observed on different materials, arguably depending on the spatial localization of the defects responsible for the PL emission in each different oxide. No significant results are evidenced for SnO₂ nanoparticles. ZnO with red/orange emission shown an O₂-induced PL enhancement, suggesting that the radiative emission involves holes trapped in surface vacancy oxygen centers. While the ZnO results are scientifically interesting, its performances are inferior to the ones shown by TiO₂, which exhibits the most interesting response in terms of sensitivity and versatility of the response. In particular, O₂ concentrations in the range of few percent and in the range of a few tenths of a part per million are both detectable through the same mixed-phase TiO₂ sample, whose rutile phase gives a reversible and fast response to larger (0.4–2%) O₂ concentration while its anatase phase is usable for detection in the 25–75 ppm range. The data for rutile TiO₂ suggest that its surfaces host deeply trapped electrons at large densities, allowing good sensitivities and, more notably, a relatively unsaturated response at large concentrations. Future work is expected to improve the understanding and modeling of the photophysical framework that lies behind the observations.

With the increasing environmental awareness, in many applications, ranging from agriculture to industry and logistics, a wider and wider use of eco-friendly fluids is desirable. Although the chemical and biological aspects related to environmental compatibility have been extensively investigated by industries and researchers for obvious environmental reasons, not much literature is available on the performance of hydraulic components and systems operating with eco-friendly fluids, especially on the possible degradation of performance due to fluid aging. This work is aimed at studying the influence of eco-friendly fluids on the performance of external gear pumps for compact mobile hydraulic power units, which are among the most widespread hydraulic devices in the world, for their cost-effective and flexible construction. Once the experimental set-up is implemented to be well representative of the hydraulic power packs’ typical arrangement, pump performance is investigated. Pump energy performance is obtained in terms of volumetric efficiency and torque efficiency. Alongside the traditional fluid, two types of eco-friendly fluid available in the market are tested. Once the comparison is complete, the investigations are devoted to highlighting the impact of fluid aging on the pump performance. The fluids were aged through 2000 h operation under heavy-duty thermo-mechanical stress on a separate set-up and, afterwards, the pump performance was tested again with aged fluids. The results allow the assessment of the influence of different fluids on pump performance and a comparison of the impact of new versus aged eco-friendly fluids. The eco-friendly fluids exert a significant effect on the pump energy profile. The pump overall efficiency increases, marking an up to 5% improvement, depending on the cases. Fluid aging is found to reduce the pump’s overall performance. This paper addresses the key points defining the pump performance and provides new information on the topic. The results are original and represent a fundamental contribution to define the best practices for energy and maintenance management of hydraulic systems and to foster the deployment of further studies on models and simulation tools to catch the effect of the fluid condition.

Through a study on the Fluid Power innovations in the last years emerged that still few solutions have been successfully implemented for the optimization of the hydraulic circuits. The recent machine electrification offers a potential for investment in energy-saving hydraulic systems to ensure greater performance and higher battery autonomy. From different studies emerged that in the specific field of ICE Off-road Vehicles, only about 10–15% of the available power at fuel level is actually transformed into useful energy for the actuators. Particularly the losses in the Directional Control Valves represent about 35–40% of the hydraulic energy available at the pump level. The traditional Directional Control Valves design solutions, in fact, neglects important opportunities for reducing losses and improving internal regeneration. Especially, energy recovery is rarely applied and in any case by means of important superstructures which considerably increase the costs of the system. This paper presents a new hydraulic architecture: an original Directional Control Valve layout based on a Downstream Compensation approach. In particular, a Flow Sharing system is implemented in this new architecture with the goal to minimize the wasted energy. In fact, this system realizes an important energy recovery from both the inertial loads and the simultaneous use of multiple actuators at different pressure level. The circuit enables recovered energy to be stored in a high-pressure accumulator. The paper presents the simulation results and the energy saving estimation realized through a lumped parameter environment “Amesim Simcenter”. Additionally, the results of experimental activities show the innovative system performance, benefits and physical applicability. This idea is based on concrete objectives and pays particular attention to cost sustainability, industrial manufacturability and system scalability.

The demand for more efficient machines is pushing hydraulic manufacturers to develop a new generation of systems capable of energy saving and recovering. An advanced flow sharing directional control valve with downstream compensation reduces meter-out pressure losses and recovers energy both in combined movements and with overrunning loads. Tests carried out on a prototype on a test bench confirm the proper functioning of the concept and allow tuning its lumped parameters numerical model. A control strategy based on keeping the optimal compensator position allows computing the maximum theoretical recovery. The simulation of a mini-excavator digging cycle shows the energy saving and recovery compared to a standard flow sharing system.