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Technologies for direct injection of fuel in compression ignition engines are in continuous development. One of the most investigated components of this system is the injector; in particular, main attention is given to the nozzle characteristics as hole diameter, number, internal shape, and opening angle. The reduction of nozzle hole diameter seems the simplest way to increase the average fuel velocity and to promote the atomization process. On the other hand, the number of holes must increase to keep the desired mass flow rate. On this basis, a new logic has been applied for the development of the next generation of injectors. The tendency to increase the nozzle number and to reduce the diameter has led to the replacement of the nozzle with a circular plate that moves vertically. The plate motion allows to obtain an annulus area for the delivery of the fuel on 360 degrees; while the plate lift permits to vary the atomization level of the spray. The experimental activities have been performed on a single-cylinder metal engine in order to evaluate the new injector concept functionality in typical engine working conditions. Then a deeper investigation of injector the characteristics has been performed in an optical single-cylinder diesel engine via high speed digital imaging in order to catch information on its operation. The results have shown a good response of the injector fuel delivery control but penalties in terms of emissions and efficiency compared to multihole nozzles. Images of the injection process showed that the fuel assumed an asymmetric shape at the exit of the injector affecting the mixing quality and, then, the combustion efficiency.

Technologies for direct injection of fuel in compression ignition engines are in continuous development. One of the most investigated components of this system is the injector; in particular, main attention is given to the nozzle characteristics as hole diameter, number, internal shape, and opening angle. The reduction of nozzle hole diameter seems the simplest way to increase the average fuel velocity and to promote the atomization process. On the other hand, the number of holes must increase to keep the desired mass flow rate. On this basis, a new logic has been applied for the development of the next generation of injectors. The tendency to increase the nozzle number and to reduce the diameter has led to the replacement of the nozzle with a circular plate that moves vertically. The plate motion allows to obtain an annulus area for the delivery of the fuel on 360 degrees; while the plate lift permits to vary the atomization level of the spray. The experimental activities have been performed on a single-cylinder metal engine in order to evaluate the new injector concept functionality in typical engine working conditions. Then a deeper investigation of injector the characteristics has been performed in an optical single-cylinder diesel engine via high speed digital imaging in order to catch information on its operation. The results have shown a good response of the injector fuel delivery control but penalties in terms of emissions and efficiency compared to multihole nozzles. Images of the injection process showed that the fuel assumed an asymmetric shape at the exit of the injector affecting the mixing quality and, then, the combustion efficiency.

As of mid-2017, there were ~7500 metric tons of mass in orbit around the Earth, of which about 95% concentrated in almost 6700 intact spacecraft and orbital stages. Among them, nearly 80% were abandoned and more than 90% could not be maneuvered. The intact objects abandoned in LEO above ~650 km, i.e. with a typical residual lifetime of more than 25 years, represent the main potential mass reservoir for the generation of new detrimental orbital debris in case of mutual collisions with the existing debris environment. A practicable strategy to assess the latent long-term environmental impact of an orbiting object is to devise a ranking scheme based on simplified and reasonable inferences. Several ranking schemes have been proposed by different authors during the last decade. Various "criticality indexes" have been devised by us (at ISTI-CNR) in the last few years, and they have been applied to evaluate the environmental impact of many families of rocket bodies and selected spacecraft. A couple of the most complete indexes formulated by us are herein applied to assess the potential criticality of the most massive objects abandoned in LEO.

As of mid-2017, there were ~7500 metric tons of mass in orbit around the Earth, of which about 95% concentrated in almost 6700 intact spacecraft and orbital stages. Among them, nearly 80% were abandoned and more than 90% could not be maneuvered. The intact objects abandoned in LEO above ~650 km, i.e. with a typical residual lifetime of more than 25 years, represent the main potential mass reservoir for the generation of new detrimental orbital debris in case of mutual collisions with the existing debris environment. A practicable strategy to assess the latent long-term environmental impact of an orbiting object is to devise a ranking scheme based on simplified and reasonable inferences. Several ranking schemes have been proposed by different authors during the last decade. Various "criticality indexes" have been devised by us (at ISTI-CNR) in the last few years, and they have been applied to evaluate the environmental impact of many families of rocket bodies and selected spacecraft. A couple of the most complete indexes formulated by us are herein applied to assess the potential criticality of the most massive objects abandoned in LEO.

Abstract Purpose of Review What does recent work say about how changes in convective organization could lead to changes in extreme precipitation? Recent Findings Changing convective organization is one mechanism that could explain variation in extreme precipitation increase through dynamics. In models, the effects of convective self-aggregation on extreme precipitation are sensitive to parameterization, among other factors. In both models and observations, whether or not convective organization influences extreme precipitation is sensitive to the time and space scales analyzed, affecting extreme precipitation on some scales but not others. While trends in observations in convective organization associated with mean precipitation have been identified, it has not yet been established whether these trends are robust or relevant for events associated with extreme precipitation. Summary Recent work has documented a somewhat view of how changes in convective organization could affect extreme precipitation with warming, and it remains unclear whether or not they do.

Abstract Purpose of Review What does recent work say about how changes in convective organization could lead to changes in extreme precipitation? Recent Findings Changing convective organization is one mechanism that could explain variation in extreme precipitation increase through dynamics. In models, the effects of convective self-aggregation on extreme precipitation are sensitive to parameterization, among other factors. In both models and observations, whether or not convective organization influences extreme precipitation is sensitive to the time and space scales analyzed, affecting extreme precipitation on some scales but not others. While trends in observations in convective organization associated with mean precipitation have been identified, it has not yet been established whether these trends are robust or relevant for events associated with extreme precipitation. Summary Recent work has documented a somewhat view of how changes in convective organization could affect extreme precipitation with warming, and it remains unclear whether or not they do.

The production of synthetic methane using CO from flue gases and green hydrogen appears to be a promising way to combine the concepts of renewable energy, chemical storage, and utilization of CO. Recently, a new reactor configuration for catalytic methanation has been proposed, integrating sorption-enhanced methanation and chemical looping in interconnected fluidized bed systems. This configuration would ensure high methane yields while keeping good temperature control and low operating pressure. In this work, such novel system layout for the catalytic production of methane was combined with a calcium looping unit for CO capture from flue gases of a coal-fired power plant, and with a water electrolyzer sustained by renewable energy. The integrated layout offers a series of advantages deriving from the integration of different mass and energy flows of the different sections of the plant. The performance of this latter was assessed in terms of construction and production costs, as well as from an environmental point of view: a life cycle assessment was carried out to quantify the environmental impact of all process units. Results of the techno-economic analysis indicated that the production cost of methane is higher than that of natural gas (0.66 vs 0.17 EUR/Nm), but lower than that of biomethane (1 EUR/Nm). The largest impact on such costs comes from the PEM electrolyzer. The LCA analysis showed that the environmental performance is better in some categories and worse in others with respect to traditional scenarios. Again, the PEM electrolyzer appears to account for most of the environmental impacts of the process.

The production of synthetic methane using CO from flue gases and green hydrogen appears to be a promising way to combine the concepts of renewable energy, chemical storage, and utilization of CO. Recently, a new reactor configuration for catalytic methanation has been proposed, integrating sorption-enhanced methanation and chemical looping in interconnected fluidized bed systems. This configuration would ensure high methane yields while keeping good temperature control and low operating pressure. In this work, such novel system layout for the catalytic production of methane was combined with a calcium looping unit for CO capture from flue gases of a coal-fired power plant, and with a water electrolyzer sustained by renewable energy. The integrated layout offers a series of advantages deriving from the integration of different mass and energy flows of the different sections of the plant. The performance of this latter was assessed in terms of construction and production costs, as well as from an environmental point of view: a life cycle assessment was carried out to quantify the environmental impact of all process units. Results of the techno-economic analysis indicated that the production cost of methane is higher than that of natural gas (0.66 vs 0.17 EUR/Nm), but lower than that of biomethane (1 EUR/Nm). The largest impact on such costs comes from the PEM electrolyzer. The LCA analysis showed that the environmental performance is better in some categories and worse in others with respect to traditional scenarios. Again, the PEM electrolyzer appears to account for most of the environmental impacts of the process.