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Chemical looping combustion allows a simple separation of CO2 during the combustion of fossil fuels, thanks to the use of regenerable oxygen carriers. In this work, novel materials containing manganese and iron/manganese oxides have been developed via geopolymerization, and characterized in thermogravimetric apparatus and fixed bed reactor. The materials demonstrated suitable characteristics for chemical looping combustion (CLC). The tests conducted in the temperature range 800-900 °C revealed the good performance of the developed oxygen carriers, which also exhibited the ability to release O2 in inert conditions. Efficiencies in CO conversion up to 99% were achieved, as well as some synergies between Fe and Mn oxides gave a beneficial effect toward the oxygen yield. X-ray diffraction analyses of the samples confirmed the effective reduction/oxidation behavior of the materials, as well as the morphological characterization did not reveal dramatic changes of the internal microstructure up to 900 °C

Potential improvement on exhaust emissions, biodegradability and the possibility to reduce dependence on fossil fuel resources has led to an increasing interest on the use of biofuels for transport application. In this work, the analysis of the spray behaviour of first and second generation biodiesel in a Euro 5, common rail transparent diesel engine has been performed. GTL, SME and RME fuels have been used in blends at 100% and 50% in volume; while reference fuel consisted of commercial diesel. Two engine operating conditions of the NEDC have been selected: 1500 rpm at 2 bar of brake mean effective pressure (BMEP) and 2000 rpm at 5 bar BMEP. The injection process has been accurately studied, and the influence of the combustion process on the spray behaviour has been taken into account. Typical jets parameters such as penetration and cone angles have been detected and a comparison with theoretical models of Hiroyasu and Siebers has been performed. A new correlation for the forecasting of the jet penetration has been obtained starting from Hiroyasu equations. An image-based method has been applied for the identification of the phenomena that control the spray behaviour during its evolution in the combustion chamber. First generation biodiesels, pure and blends, show longer penetration with respect to the reference fuel at both the engine speed analysed. Moreover, they penetrate for a longer time in the combustion chamber, because of the longer energizing time set, so impingement phenomena can be observed. On the other hand, the second generation biodiesels penetrate less than reference one, due to its lower density, but also because the combustion of the pilot injection causes an increase of pressure that obstructs the penetration in the combustion chamber. Finally, a good agreement between the breakup times computed by means of the Hiroyasu and Siebers correlations and the ones from the experimental data has been found.

The performance of entrained-flow gasifiers of solid fuels is critically affected by the complex gas-solid multiphase flow patterns and near-wall segregation of char/ash particles. The impact-deposition-rebound dynamical patterns of particles, as they approach and collide onto the walls, control the establishment of near-wall segregated phases. A detailed micromechanical analysis of char/ash particles interaction with a surface is considered to characterize ash deposition onto the walls and adhesion and inelastic rebound of char particles. The effect of the residual carbon content within the particles, from char after devolatilization to ash particles, as well as the influence of the impact velocity, have been investigated for different fuels. The experimental outcomes have been used to derive closure equations describing the behaviour of char/ash particles after the collision with the wall, in terms of deposition and inelastic rebound. It has been highlighted that impact velocity and carbon conversion do affect the deposition tendency of char and ash particles, while the inelastic rebound is mainly influenced by the mechanical properties of the bulk of the particles, which are closely dependent on the particle structure developed during the gasification process.

Natural gas is recognized as a valid alternative to conventional fuels for internal combustion engines, thanks to its characteristics of low environmental impact and considerable natural reserves. In a Dual Fuel (DF) NG/Diesel configuration, NG offers interesting possibilities in terms of nitrogen oxides and soot emissions abatement, with reduced CO2 levels. Despite a proven feasibility of the DF concept for heavy duty engines, its applicability to light duty engines still clashes with several issues, especially the high unburned hydrocarbons emission. The present activity was devoted to assess the potentiality of an optimized DF engine calibration, to minimize GHGs emissions. A first experimental campaign on an automotive Diesel engine, equipped with an advanced combustion control, illustrated the effects of crucial control parameters on DF combustion. Hence, an optimization procedure permitted to identify the optimal set of control parameters. Finally, experiments in steady state and transient conditions allowed quantifying the THC and CO2 emissions reductions achievable moving from a starting DF engine map to the optimized calibration. The investigations highlighted that an adequate engine recalibration can offer a CO2 saving of about 12%, compared to the standard Diesel configuration, whereas the detrimental effect in terms of THC emissions could not be fully eliminated. Nevertheless, compared to a non-recalibrated DF map, the engine parameters optimization allowed achieving a THCs reduction of roughly 50%. Reported results could provide valuable information on behavior tendencies of a DF engine, useful for the development of dedicated engine technologies for DF combustion systems

A laminar drop tube reactor (DTR) was used to perform fast pyrolysis of walnut shells, a ligno-cellulosic biomass sample, in nitrogen and carbon dioxide atmospheres. The DTR reached the temperature of 1300 degrees C and the heating rate of 10(4)-10(5) degrees C/s. Char samples collected at different residence times along the reactor were characterized by ultimate and proximate analysis and by SEM. Char combustion reactivity was then measured by non-isothermal thermogravimetric analysis (TGA) in air. The analyses show that at residence times of 66 ms pyrolysis in N-2 is not complete, whereas it is complete in CO2. For residence times of 115 ms the differences between samples produced in N-2 and CO2 atmospheres level off.

An experimental study has been performed for identifying the role of injector nozzle hole convergence and cavitation in diesel engine combustion and pollutant emissions. For doing so, five nozzles were tested under different operating and experimental conditions. The critical cavitation number of each nozzle was analyzed. With this value, an estimation of the mixing process at different conditions obtained. This data is used to explain the combustion results which are analyzed in terms of the apparent combustion time, rate of heat release, in-cylinder pressures, adiabatic temperatures and soot and NO, emissions. Special emphasis is put in developing an expression to explicitly link the mixing process and the injection rate with the rate of heat release. The results show that the fuel-air mixing process can be improved by the use of both convergent and cavitating nozzles, thus lowering the soot emissions. The NO, production, being dependent of the injection rate and the mixing process, does not necessarily increase with the use of more convergent nozzles. (c) 2007 Elsevier Ltd. All rights reserved.

The paper describes an experimental study aimed to characterize the impact of the dual-fuel ethanol-diesel combustion system on size, number and chemical characteristics of the emitted carbonaceous particles. The tests were conducted on a single cylinder research engine provided with a modern architecture and properly modified in a dual-fuel (DF) configuration. In particular, the experimental campaign was aimed to evaluate in detail the effect of the use of the ethanol as port injected fuel in diesel engine on the size distribution function, morphology, reactivity and chemical features of the exhaust emitted soot particles. The engine tests were chosen properly in order to represent actual working conditions of an automotive light-duty diesel engine. The morphological and chemical features of soot particles were studied in dependence of the ethanol-diesel substitution rate by analyzing the soot collected at the engine exhaust. Results indicated a significant effect of ethanol fumigation on the concentration of the emitted particles but not on the average size, as well as, a negligible impact of ethanol premixed charge on the soot nanostructural features.