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The reduction of the dioxin levels in the exhausts of today waste-to-energy plants relies on the control of the thermo-fluid-dynamic processes occurring within the combustion chamber, rather than on policies aimed at restricting the amount of chlorine in the waste material to be treated. This is a consequence of the fact that waste-to-energy plants currently receive the bulk of discarded PVC and other chlorine sources that are deliberately burned in order to increase the waste heating value. Indeed, severe law regulations are into force in many industrialised countries, posing constraints on the value of some relevant in-chamber thermo-fluid-dynamic variables, such as temperature and residence time of the gases resulting from the combustion process, whose accurate experimental monitoring is extremely expensive and difficult to achieve. The present work analyses the shortcomings of the methods generally employed in full scale plants for the verification of the temperature and residence time of gases produced during the combustion process, and presents the advantages of using a new procedure developed by authors, based on the numerical simulation of the waste combustion process to optimise monitoring of the quantities of interest. The verification of the developed model, which accounts for both the solid and the gaseous phases, and for the various modes of heat and mass transfer between these phases, is obtained through a comparison with the results of an experimental campaign carried out on a full scale plant in Italy. The temperature distribution in the combustion chamber is calculated considering various waste compositions, and both forced and mixed convection. In fact, it is also shown that neglecting buoyancy effects may lead to appreciable errors.

Abstract Several environment agencies worldwide have identified biofuels as a viable solution to meet the stringent targets imposed by future regulations in terms of on-road transport emissions. In the last decades, petroleum-based gasoline has been increasingly blended with oxygenated fuels, mostly ethanol. Blending ethanol with gasoline has two major effects: an increase of the octane number, thus promoting new scenarios for engine efficiency optimization, and a potential reduction of soot emissions. 3D-CFD simulations represent a powerful tool to optimize the use of ethanol-gasoline blends in internal combustion engines. Since most of the combustion models implemented in 3D-CFD codes are based on the “flamelet assumption”, they require laminar flame speed as an input. Therefore, a thorough understanding of the gasoline-ethanol blend chemical behavior at engine-relevant conditions is crucial. While several laminar flame speed correlations are available in literature for both gasoline and pure ethanol at ambient conditions, none is available, to the extent of authors’ knowledge, to describe laminar flame speed of gasoline-ethanol blends (for different ethanol volume contents) at engine relevant conditions. For this reason, in the present work, laminar flame speed correlations based on 1D detailed chemical kinetics calculations are derived targeting typical full-load engine-like conditions, for different ethanol-gasoline blends. A methodology providing a surrogate able to match crucial properties of a fuel is presented at first and validated against available experimental data. Then, laminar flame speed correlations obtained from 1D chemical kinetics simulations are proposed for each fuel blend surrogate.

Abstract Wood pellets were pyrolyzed using a microwave oven and different microwave power, apparatus set-up and microwave absorbers (none, Fe, and carbon). Pyrolysis was realized in a short time in the presence of Fe or carbon while it was incomplete if the absorber was not present. Furthermore when the absorber was present the shape of the pellets remained unaltered while if the absorber was not employed pellets were disaggregated. Three fractions were collected from each pyrolysis: a gas, a liquid also called bio-oil and a solid called bio-char. The bio-oil contained two phases and they were quantitatively characterized through a GC/MS-FID procedure using an internal standard according to a previously reported method. HPLC/MS, FTIR and 1 H NMR spectroscopy were also employed for characterization of these liquids. Cellulose pyrolysis products were present in the upper phase such as water, acetic acid, furans (such as furfural), carbohydrates and their derivatives. Compounds from pyrolysis of lignin such as phenols and veratric acid were present in the bottom phase. The microwave assisted pyrolysis showed the possibility to efficiently convert wood pellets in different products. The main economical important components may be separated and used as chemicals, natural drugs or pesticides, while the remaining components, the solid and the gas may be used for energy production (solid and bio-oil). Solid may be also used for carbon sequestration.

Digital imaging and spectroscopic techniques, with high temporal and spatial resolution, were applied in order to study the low temperature combustion process. Injection and combustion phases were analysed by digital imaging. Mixing process, autoignition and pollutants formation were investigated by broadband ultraviolet–visible extinction spectroscopy and flame emission measurements. Moreover, fuel distribution and oxidation were studied as well. Liquid fuel and vapour phase, injected around the top dead centre, were analysed. The liquid diesel fuel was observed by extinction measurements when the liquid jet reached the bowl rim and aromatic compounds due to fuel decomposition were identified. On the other side, the vapour fuel was detected about 2° after the injection start and liquid fuel disappeared. Then, radicals and species were detected in the combustion chamber. They are interesting in order to study the chemical kinetics of low temperature combustion process. The chemiluminescence spectra of HCCI combustion appeared as well as several distinct peaks corresponding to the emission from HCO, HCHO, CH, and OH. In particular, this latter was clearly evident during the whole premixed combustion and dominated the process also after the end of the premixed phase of the heat release. Advancing the combustion, bright spots due to not homogeneous charge were detected. They were the source of the very little soot amount detected at the exhaust pipe. Finally, the injection pressure effect on the development of low temperature combustion was analysed.

The experiment determined the technical and financial efficiency of five storage techniques, specifically designed for SRF poplar chips stored at the farm site in small (20 m3) piles. The treatments on test were: uncovered storage, storage under a temporary roof structure, cover under a semi-permeable fleece sheet, cover under two types of plastic sheet (i.e. white and black). Each treatment was replicated 3 times. Researchers monitored temperature and moisture content trends inside the piles, and determined dry matter losses at the end of the 170 days storage period. In general, piles under plastic cover presented opposite trends compared to all other piles. They acquired moisture rather than losing it, and showed gradual temperature trends instead of a typical peak-and-drop behaviour. Dry matter losses varied from 5.1% to 9.8%, and were highest for the uncovered treatment, and lowest for the plastic cover treatment. Under the conditions of north-western Italy, uncovered storage was a cost-effective option. Protecting the piles with some cover incurred more cost than it saved, resulting in a higher storage cost per unit energy. Although more expensive, sheltering the piles under a simple roof structure offered the benefit of a higher reduction of moisture content, which may turn the chips into a higher quality fuel. Of course, these results were closely related to the Southern European climate, and the specific year of the test. Occasional wetter years may overturn these results. © 2013 Elsevier Ltd. All rights reserved.

Abstract The effect of pre-oxidation on the porosity evolution in heavy-oil fly ash subjected to activation with CO 2 has been investigated. After preliminary acid leaching, used to reduce the mineral matter content, the leached fly ash has been oxidised in air at 250 °C for 36 h. Pyrolysis was conducted on the unoxidised and oxidised leached fly ash at 900 °C for 2 h and the resultant chars were activated with CO 2 at 900 °C for different times. The activated samples have been characterised as regards the surface area and the pore volume. The pre-oxidation enhances the porosity development mainly in terms of mesoporosity leading to obtain activated products with higher surface area (about 270 m 2 /g at a 40% burn-off).

The paper explores changes in reactivity and chemico-physical characteristics of char and tar produced by severe heat treatment of lignite in both inert atmospheres, and CO2 rich atmospheres. The role of mineral matter, in particular metal oxides, in catalysing chemical and physical transformations is also addressed. A Rhenish Lignite from the Garzweiler mine was studied and compared with: a) mineral-free synthetic carbon (HTC), obtained from cellulose; b) a synthetic carbon doped with iron oxide (Fe2O3). A heated strip reactor (HSR) was employed at temperatures of 1300 and 1800 °C in N2 and CO2 atmospheres. Liquid and solid products (tar and char) were analysed and compared. Tar composition was evaluated by extraction and gas chromatography-mass spectrometry, whereas the solid carbonaceous material produced by pyrolysis, mainly composed of char, was characterized regarding its thermal behaviour by thermogravimetric analysis and its structure by Raman spectroscopy and scanning electron microscopy. Results show that iron oxide exerts a catalytic influence on both pyrolysis and char oxidation. Upon severe heat treatment, it reduces char reactivity promoting graphitization and structural ordering. The overall effect on char reactivity is therefore not easy to predict.

In the aim of reducing CO2 emissions and fuel consumption, the improvement of the diesel engine performance is based on the optimization of the whole combustion system efficiency. The focus of new technological solutions is devoted to the optimization of thermodynamic efficiency especially in terms of reduction of losses of heat exchange. In this context, it is required a continuous development of the engine combustion system, first of all the injection system and in particular the nozzle design. To this reason in the present paper a new concept of an open nozzle spray was investigated as a possible solution for application on diesel engines. The study concerns some experimental and numerical activities on a prototype of an open nozzle. An external supplier provided the prototypal version of the injector, with a dedicated piezoelectric actuation system, and with an appropriate choice of geometrical design parameters. The characteristics of nozzle open spray concept (in terms of spray penetration and diffusion) were evaluated in a constant volume combustion bomb and validated by numerical simulations with the OpenFOAM libraries in the lib-ICE version of the code. The considered injector configuration is proved to be a promising solution for the realization of a high-pressure diesel cone spray. It was assessed that spray atomization and penetration are sensible to the injection control parameters, in particular to the injection pressure level, and to the HV (stationary level of the voltage command at the actuator). This could mean, in a certain sense, the possibility to graduate injection control parameters in order to assure an appropriate control of spray penetration and atomization levels in a dedicated engine combustion chamber. The numerical results show that the adopted setup of spray sub-models, well assessed in previous work in capturing the whole spray behavior for high pressure MHN injectors, indicates a quite good prevision of the radial tip penetration (TP) but a sensible overestimation of axial TP over all the injection event. CFD simulation describes a rapid breakup process immediately after the fuel discharge providing a finely atomized spray along the whole circumference