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Alternative fuels and energy vectors are becoming increasingly important in terms of technical, geopolitical, economic, and environmental aspects. In particular, gaseous fuels and vectors, such as fossil or synthetic natural gas (NG) blended with hydrogen, commonly help provide optimal strategies to reduce global and toxic emissions of internal combustion engines, owing to their adaptability, anti-knock capacity, lower toxicity of pollutants, reduced CO2 emissions, and costeffectiveness. However, diesel engines still represent the reference category among internal combustion engines in terms of maximum thermodynamic efficiency. The possibility offered by dual-fuel (DF) systems to combine the efficiency and performance of diesel engines with the environmental advantages of gaseous fuels has been the subject of extensive investigations. However, the simple replacement of diesel fuel with gaseous fuel does not allow for optimising the engine performance, owing to the high percentage of unburned gaseous fuel, which compromises the potential reduction of CO2; therefore, more complex combustion strategies should be realised. In this study, with the aim of improving the DF combustion process, an experimental investigation was performed to analyse low-temperature combustion (LTC), using NG and two enriched hydrogen-compressed NG blends as primary fuels. The LTC mode was activated by means of a very early advanced pilot injection and carried out in two close steps. The double pilot injection was used to control the energy release rate in the first combustion stage, thereby minimizing the increase of the rate of pressure and allowing the extension of the operation range under LTC. The experimental activity was also focused on analysing the particle emissions, as it is well known that these emissions, together with those of nitrogen oxide, constitute the main pollutants resulting from diesel fuel combustion. The results demonstrated the potential to reduce the unburned fuel, NOx, and particle emissions simultaneously, while maintaining equivalent CO2 emissions to a diesel-only engine. Both the timing and pressure of the pilot injection proved to be critical parameters for optimising the emissions and performance

Internal combustion engines are still the energy conversion units of choice in transport and distributed energy generation. Due to the fuel mix, spark ignition (SI) engines represent a viable solution that features improved fuel flexibility with respect to their compression ignition counterparts. Therefore, manufacturers are continuously trying to increase their performance and reduce emissions through experimental and numerical investigations. A growing trend in engine improvement is the application of simulations on a wider scale in order to contain development costs. Combustion is the most complex part of the working cycle and for SI power units, modeling flame propagation represents an essential feature of predictive numerical investigations. Within this context, the present study was aimed at better understanding the mass transfer between unburned and reacting gas, as well as characteristic reaction time scales within the reaction zone. A OD model with three zones was applied for different engine speed, load, air-fuel ratio and spark timing settings, chosen as representative for mid-road load automotive use. Combined in-cylinder pressure measurements and flame imaging were used for validating the essential concept of fresh charge entrainment and burn-up process. One major conclusion of the work was that there is a definite stratification of chemical species within the burned-reacting gas that can be well captured by the entrainment model. The fact that the calibration coefficients require different values for accurate prediction of the pressure traces during flame propagation, emphasizes the complexity of the combustion process, as well as the limitations of considering flames as laminar even at local scale. The study also identified the scale at which mass transfer takes place as an essential factor for correct turbulent combustion modeling. (C) 2015 Elsevier Ltd. All rights reserved.

In this paper we report the use of the optical technique applied in the cylinder of an optically accessible engine equipped with the latest-generation diesel engine head of a European passenger car. The injection strategy with high percentage of EGR, characteristic of real engine operating point, was adopted. Alternative diesel fuels were used. In particular, rapeseed methyl ester (RME) and gas to liquid (GTL) were selected as representative of 1st and 2nd generation alternative diesel fuels, respectively. Combustion analysis was carried out in the engine combustion chamber by means of 2D spectroscopic measurements from UV to visible. These measurements helped to analyze the chemical and physical events occurring during the mixture preparation and the combustion development. Ultraviolet (UV) digital imaging was also performed and the presence of characteristic radical, like OH, in the various phases of combustion was detected as well. OH spatial distribution and temporal evolution were measured. Two color pyrometry technique was applied in order to measure the soot volume fraction within the combustion chamber. The GTL fuel showed better performance in terms of indicated mean effective pressure (IMEP) with respect to the diesel reference fuel with different effects on particulate matter (PM) and gaseous emissions. It showed the highest in cylinder soot production, while the OH radical had maximum intensity value close to the reference diesel (REF) one. On the other hand, the RME fuel showed a decrease in IMEP that can be adjusted with a little increase of fuel injected quantity, and very low production of soot in the cylinder and PM at the exhaust compared to the diesel reference fuel. Finally, the OH radical had the lowest intensity value.

In the present paper design, realization and testing of a novel small scale adsorption refrigerator prototype based on activated carbon/ethanol working pair is described. Firstly, experimental activity has been carried out for identification of the best performing activated carbon available on the market, through the evaluation of the achievable thermodynamic performance both under air conditioning and refrigeration conditions. Once identified the best performing activated carbon, the design of the adsorber was developed by experimental dynamic performance analysis, carried out by means of the Gravimetric-Large Temperature Jump (G-LTJ) apparatus available at CNR ITAE lab. Finally, the whole 0.5 kW refrigerator prototype was designed and built. First experimental results both under reference air conditioning and refrigeration cycles have been reported, to check the achievable performance. High Specific Cooling Powers (SCPs), 95 W/kg and 50 W/kg, for air conditioning and refrigeration respectively, were obtained, while the COP ranged between 0.09 and 0.11, thus showing an improvement of the current state of the art.

Chemical storage in suitable energy carriers is a requirement for any renewable source-based energy supply system. In this framework, owing to its very high hydrogen density and long established production processes, ammonia appears to be a very promising carrier. Furthermore, it is not necessary to use hydrogen extraction processes because ammonia can be directly used as a fuel in combustion systems. Nevertheless, there is a notable gap between the rising interest in ammonia-based power technologies and the actual knowledge and understanding of the physical and chemical underpinnings of its reactivity features. In particular, the viability of ammonia as an energy vector relies on the global process conversion efficiency, including the possibility of obtaining the required power levels at consumption points with minimal environmental impact. Therefore, this study is aimed at bridging the gap between the fundamental research and the development and implementation of ammonia-fueled combustion technologies in the context of eco-friendly, safe, and sustainable energy systems. The combination of high preheating and dilution levels, which are realized by means of a strong internal recirculation, leads to a very peculiar combustion regime. The potential of this oxidation mode, as realized in a cyclonic flow burner, to achieve stable ammonia combustion is explored to determine the influence of the operational parameters. The dependence of the process stability and NO emissions on the equivalence ratio, inlet preheating level, and thermal load of the inflow mixture was studied by monitoring the temperatures and species concentrations to identify the optimal burner operating conditions.

Artículos en revistas A major aim of Capacity Remuneration Mechanisms (CRMs) is to lead the power system expansion towards the level of security of supply that the regulator considers adequate. When introducing a capacity mechanism, therefore, regulators must ensure that the resulting mix will actually provide the firmness pursued, in such a way that both the generation and the demand resources awarded with the capacity remuneration actually perform as expected when the system needs them. In order to achieve this goal, some experts stressed the importance of including performance incentives in the CRM design. However, first capacity mechanisms (implemented mainly in the American continent) did not pay enough attention to this aspect. Two decades of operation have evidenced the need for performance incentives and these instruments are, at this writing, at the centre of the regulatory discussion. On the basis of a model analysis, this article demonstrates how the introduction of properly designed explicit penalty schemes for under-delivery can positively impact the CRM outcomes, providing resources with effective incentives to maximise their reliability, discriminating against non-firm generation units, and therefore increasing the effectiveness of the mechanism in achieving its objectives. info:eu-repo/semantics/publishedVersion

The valorization of typical household food waste (HFW) produced at municipality level was studied for the production of electricity in a microbial fuel cell (MFC) from its extract, and methane, through anaerobic digestion of the solid extraction residue. HFW, after heat drying and shredding, was subjected to extraction using warm water, which resulted in a liquid fraction (extract) and a solid residue. The rich in soluble chemical oxygen demand extract was used for electricity production in a four air- cathodes single chamber MFC, operating under different organic loading rates, while the solid residue from the extraction process was used as substrate for methane production in biochemical methane potential experiments. On the basis of the energy outputs estimated for the optimum operational conditions of both aforementioned processes, it can be concluded that the exploitation of dried HFW is quite appealing as it leads to promising energy recovery.

The acceptability, energy consumption, and environmental benefits of electric vehicles are highly dependent on travel patterns. With increasing ride-hailing popularity in mega-cities, urban mobility patterns are greatly changing; therefore, an investigation of the extent to which electric vehicles would satisfy the needs of ride-hailing drivers becomes important to support sustainable urban growth. A first step in this direction is reported here. GPS-trajectories of 144,867 drivers over 104 million km in Beijing were used to quantify the potential acceptability, energy consumption, and costs of ride-hailing electric vehicle fleets. Average daily travel distance and travel time for ride-hailing drivers was determined to be 129.4 km and 5.7 h; these values are substantially larger than those for household drivers (40.0 km and 1.5 h). Assuming slow level-1 (1.8 KW) or moderate level-2 (7.2 KW) charging is available at all home parking locations, battery electric vehicles with 200 km all electric range (BEV200) could be used by up to 47% or 78% of ride-hailing drivers and electrify up to 20% or 55% of total distance driven by the ride-hailing fleet. With level-2 charging available at home, work, and public parking, the acceptance ceiling increases to up to 91% of drivers and 80% of distance. Our study suggests that long range BEVs and widespread level-2 charging infrastructure are needed for large-scale electrification of ride-hailing mobility in Beijing. The marginal benefits of increased all electric range, effects on charging infrastructure distribution, and payback times are also presented and discussed. Given the observed heterogeneity of ride-hailing vehicle travel, our study outlines the importance of individual-level analysis to understand the electrification potential and future benefits of electric vehicles in the era of shared smart transportation.