Search

The adoption of lean-burn concepts for internal combustion engines working with a homogenous air/fuel charge is under development as a path to simultaneously improve thermal efficiency, fuel consumption, nitric oxides, and carbon monoxide emissions. This technology may lead to a relevant emission of unburned hydrocarbons (uHC) compared to a stoichiometric engine. The uHC sources are various and the relative importance varies according to fuel characteristics, engine operating point, and some geometrical details of the combustion chamber. This concern becomes even more relevant in the case of engines supplied with natural gas since the methane has a global warming potential much greater than the other major pollutant emissions. In this work, a simulation model describing the main mechanisms for uHC formation is proposed. The model describes uHC production from crevices and flame wall quenching, also considering the post-oxidation. The uHC model is implemented in commercial software (GT-Power) under the form of “user routine”. It is validated with reference to two large bore engines, whose bores are 31 and 46 cm (engines named accordingly W31 and W46). Both engines are fueled with natural gas and operated with lean mixtures (λ > 2), but with different ignition modalities (pre-chamber device or dual fuel mode). The engines under study are preliminarily schematized in the 1D simulation tool. The consistency of 1D engine schematizations is verified against the experimental data of BMEP, air flow rate, and turbocharger rotational speed over a load sweep. Then, the uHC model is validated against the engine-out measurements. The averaged uHC predictions highlight an average error of 7% and 10 % for W31 and W46 engines, respectively. The uHC model reliability is evidenced by the lack of need for a case-dependent adjustment of its tuning constants, also in presence of relevant variations of both engine load and ring pack design.

An innovative steam reformer for hydrogen production at temperatures lower than 550 °C has been developed in the EU project CoMETHy (Compact Multifuel-Energy To Hydrogen converter). The steam reforming process has been specifically tailored and re-designed to be combined with Concentrating Solar plants using “solar salts”: a low-temperature steam reforming reactor was developed, operating at temperatures up to 550 °C, much lower than the traditional process (usually > 850 °C). This result was obtained after extensive research, going from the development of basic components (catalysts and membranes) to their integration in an innovative membrane reformer heated with molten salts, where both hydrogen production and purification occur in a single stage. The reduction of process temperatures is achieved by applying advanced catalyst systems and hydrogen selective Pd-based membranes. Process heat is supplied by using a low-cost and environmentally friendly binary NaNO3/KNO3 liquid mixture (60/40 w/w) as heat transfer fluid; such mixture is commonly used for the same purpose in the concentrating solar industry, so that the process can easily be coupled with concentrating solar power (CSP) plants for the supply of renewable process heat. This paper deals with the successful operation and validation of a pilot scale reactor with a nominal capacity of 2 Nm3/h of pure hydrogen from methane. The plant was operated with molten salt circulation for about 700 h, while continuous operation of the reactor was achieved for about 150 h with several switches of operating conditions such as molten salts inlet temperature, sweep steam flow rate and steam-to-carbon feed ratio. The results obtained show that the membrane reformer allows to achieve twice as high a conversion compared to a conventional reformer operating at thermodynamic equilibrium under the same conditions considered in this paper. A highly pure hydrogen permeate stream was obtained (>99.8%), while the outlet retentate stream had low CO concentration (

Hybridization of CSP plants with alternative energy sources (fuels) represents a means to improve flexibility of operation, power dispatchability and utilization factor of the plant. New generation CSP plants make use of molten salts as Heat Transfer Fluid (HTF) besides Thermal Energy Storage (TES) medium. Therefore, proper interfaces should be developed to effectively transfer the heat from the back-up source to the molten salt. This paper presents the results obtained in the experimental validation of an innovative gas-fueled Molten Salt Heater (MSH) prototype. The objective of this research is to validate the MSH design, where the specific properties of molten salts (compared to other HTFs, e.g., thermal oils) have to be taken into account. The developed reduced-scale MSH (90 kW thermal) consists of a heat exchanger with the molten salt flowing inside finned tubes cross-flowed with the hot flue gas generated in an upstream combustion chamber. LPG or a biogas-like mixture has been used as gas fuel. Experimental results have been obtained with two different molten salt mixtures: the “solar salt” binary mixture (NaNO3/KNO3, 60/40%w) typically used in CSP applications (up to 565 °C) and the ternary mixture known as Hitec XL® containing sodium/potassium/calcium nitrates (NaNO3/KNO3/Ca(NO3)2, 15/43/42%w) characterized by lower freezing temperatures. Experimental tests have been carried out changing some operative parameters like the flow rate of the molten salt (0.45–0.94 kg/s), the inlet temperatures of the molten salt (303–445 °C) and of the hot gas (596–632 °C). For both molten salt mixtures, it was demonstrated that heat transfer correlations based on the Dittus-Boelter equation allow to predict experimental results with

Thermal oils are nowadays largely employed as heat transfer fluids or cooling media in industrial and energy production plants. However, despite their widespread use, very few data are currently available about their chemical stability and possible composition changes in function of the operating temperatures, which are of crucial importance to evaluate the lifetime of these materials in real conditions. In the present work, a commercial terphenyl-based oil was investigated with respect to its thermal stability, performing ageing tests followed by a complete post-characterization analysis. To this purpose, a dedicated experimental set-up was designed and constructed to study the degradation processes, with a qualitatively and quantitatively analysis of the released gases and condensable products, together with a post-ageing characterization of the oil thermo-physical properties. The results show that the main decomposition mechanism involves the loss of hydrogen atoms, followed by partial polymerization processes, which explain the increase in dynamic viscosity and the decrease in volatility observed for the thermally stressed materials. Finally, the decomposition kinetic constants were estimated, obtaining a value of about 100 kJ/mol for the activation energy, which is in good agreement with the data available in the scientific literature.

High- and low-density polyethylene (HDPE and LDPE) and polypropylene (PP) are the most common polymers among plastic waste as they have multiple commercial applications. This study focused on thermal degradation characteristics and kinetic of a plastic mixture with a composition of 92.5 wt% LDPE and 7.5% PP. Thermal decomposition characteristics of the plastic mixture was analysed through thermo-gravimetric analysis (TGA). The overall kinetic of the process was studied using the modified Coats−Redfern method and the Ozawa-Flynn-Wall (OFW) method. The apparent activation energy (E) and pre-exponential factor (A) obtained were 316.0 kJ/mol; 8.09E+21 min−1 and 311.5 kJ/mol; 4.35E+21 min−1, respectively. Slow pyrolysis of the analysed mixture was carried out in a semi-batch reactor under atmospheric pressure and nitrogen atmosphere and three different pyrolysis temperatures were investigated: 420 °C, 450 °C and 500 °C. H2, CH4, C2H4, C2H6 and C3H8 were the main components of the gas phase. Liquid (oil/wax phase) yields increased with increasing operative temperature from 42% at 420 °C to 62% at 500 °C. On the other hand, solid phase showed a specular behaviour compared to the oil/wax phase, decreasing from 21% to 5% in the considered temperature range. On the contrary, gas phase did not change much with pyrolysis temperature, with a decrease from 37% at 420 °C to 34% at 500 °C. Products’ energy yields were also estimated at 420 °C. They ranged from 7.4% to 37.8% and 43.0% for solid, gas and oil fraction, respectively. Oil fraction collected from pyrolysis at 420 °C was also characterized.

Selective laser technology is an additive technology that can allow for the manufacture of cellular structures using different types of metallic powder with complex applications in industries such as aerospace, automotive and medical implant industries. This paper presents the effect of climate and mechanical stresses on some honeycomb cellular cores, used in sandwich structures made of 316L stainless steel powder by applying the selective laser melting technology. The honeycomb cellular cores have undergone the microhardness testing and the resulting variation obtained from the analyzed samples was 225 ± 15 HV0.3. The compressive strength and the modulus of elasticity of the cellular structures were determined for flatwise and edgewise compressive stresses. Also, the cellular structures were subjected to accelerated corrosion tests in order to determine their mean life in application use conditions similar to those near seas and oceans. Also, a microstructural evaluation of salt deposits was carried out on the cellular structures subjected to accelerated corrosion tests using a salt spray test chamber. © 2017 Transactions of Famena. All Rights Reserved.

One of the main parameters affecting autotrophic algae cultures is photon absorption distribution inside the photobioreactor. This clearly depends on the geometry of both the radiation source and the photobioreactor, as well as on algae suspension optical properties. In this work the local volumetric rate of photon absorption LVRPA in a cross-section of a horizontal-pipe photobioreactor was investigated by means of simplified Monte Carlo simulations. In particular, the fate of a number of photons perpendicularly hitting the photobioreactor circular section was simulated in relation to different values of algae concentration. The model takes into account refraction/reflection phenomena at the air/photobioreactor-wall interface. Simulation results show that radiation distribution inside the photobioreactor is quite strongly affected by reflection/refraction at the air-reactor interface. In particular, dark zones (not revealed when neglecting reflection/refraction phenomena) are observed in conjunction with unexpected radiation intensification in other zones. These phenomena are bound to affect photobioreactor performance and should therefore be considered if effective photobioreactor models are sought. This article is protected by copyright. All rights reserved

We present the localized in situ formation of Pd and Pt nanoparticles embedded in chitosan solid films. This is achieved by the photo-induced reduction of metallic precursors, previously incorporated in chitosan films, through controlled UV pulsed laser irradiation. Interestingly, at high number of laser pulses, Pd and Pt follow different formation pathways, contrary to their common photoreduction mechanism occurring at low irradiation pulses. Specifically, in the case of the Pd, a photofragmentation process takes place fracturing the previously formed nanoparticles into smaller ones; whereas in the case of Pt, the prolonged irradiation promotes the nanoparticles agglomeration. The combination of both precursors in a binary solid system results in the combined formation of both Pd and Pt nanoparticles in the polymer film upon laser irradiation. The herein reported approach is an efficient and precise tool to generate size- and density-controlled Pd and Pt nanoparticles in desired areas of polymeric films, rendering this method a potential candidate for the fabrication of flexible polymeric devices for gas-sensing or electro-catalysis applications. Graphical Abstract: Schematic representation of Pd, Pt and Pd–Pt combined NPs formation mechanisms under pulsed laser irradiation [Figure not available: see fulltext.]

Silica aerogel (SA) was loaded with nimesulide, a drug model compound, to demonstrate the potentiality of adsorption processes based on the usage of supercritical carbon dioxide to treat poorly water-soluble drugs, forming new kinds of drug delivery systems. Adsorption isotherms and kinetics were measured and described by models. The effect of pressure, temperature and solution concentration on loaded SA were also studied. Modelling of kinetic data showed that the sorption process was best described by a pseudo-second-order model. The adsorption isotherm data were best fitted by the Freundlich isotherm. The drug/SA composites were characterized using scanning electron microscopy, X-ray microanalysis, and FT-IR. Release kinetics of the adsorbed drug were also evaluated by in vitro dissolution tests. Results showed that nimesulide can be uniformly dispersed into the aerogel and that the release rate of nimesulide from the composite, constituted by drug and silica aerogel, is much faster than that of the crystalline drug. © 2011 The Institution of Chemical Engineers.

The dispersion polymerization of methyl methacrylate in dense carbon dioxide, initiated by γ-rays, utilizing different polysiloxanes as polymeric stabilizers, was investigated. The progress of the reaction, as a function of the irradiation dose, was also studied and the occurrence of a gel effect has been detected. For comparison, the dispersion polymerization has been carried out in supercritical conditions ( T =65°C and 38 MPa) in the presence of 2,2′-azobis(isobutyronitrile) (AIBN) as initiator. High molecular weight polymer (M w > 1000 kg/mol) with narrow molecular weight distribution has been obtained both with γ-rays and AIBN. The electron scanning micrographs show that regular spherical particles (average diameter ca. 2.5 μm) with narrow particle size distribution have been obtained through the dispersion polymerization mechanism in CO 2 .

Supercritical adsorption coupled with the high adsorption capacity of silica aerogel allows the preparation of a new kind of delivery systems of poor water soluble drugs. In order to overcome drawbacks of conventional techniques where the use of liquid solvents can cause the fracture of aerogel porous structure, in this work a new adsorption process of drugs from a supercritical mixture is proposed. Adsorption takes place from a fluid solution of the drug in supercritical CO2and ethanol as cosolvent. A fixed bed adsorption plant has been developed to allow fast mixing of fluid phase and effective contact in the adsorption column. The use of ethanol as cosolvent allows to overcome the limitation of supercritical adsorption due to low solubility of many drugs in supercritical CO2. Adsorption isotherms were measured for one-model substance, nimesulide, at 40°C, and breakthrough curve was experimentally obtained. The drug loading of the drug into silica aerogel was up to 9 wt%. The drug composite was characterized using scanning electron microscopy, and release kinetics of the adsorbed drug were also evaluated by in vitro dissolution tests. The dissolution of nimesulide from loaded aerogel is much faster than dissolution of crystalline nimesulide. Around 80% of nimesulide dissolves from the aerogel within 6 minutes, whereas dissolving 80% of the crystalline drug takes about 90 min.

In this work, results from a study on bolted joints made of unidirectional, quasi isotropic Carbon Fiber Reinforced Polymer (CFRP) composites, subjected to tensile loads, are reported. CFRP composite materials are widely used in the mechanical industry, such as that of aerospace, where requirements of weight reduction and structural high performances are very compelling. Composite materials generally present a high resistance to fatigue and corrosion; however, the presence of joints produces the major problems and a poor design of joints leads to a drastic reduction of the reliability of structures made of these materials. A hybrid bolted joint involving a metal plate, made of aluminum alloy, and a CFRP composite plate has been considered; the plates are held together by a titanium bolt. Experimental results from literature are compared with those obtained through a numerical analysis developed with Abaqus code. Once the CFRP composite has been analyzed and the numerical model validated through numerical-experimental correlations, other possible configurations have been numerically analyzed in order to ensure the highest strength of the examined hybrid joint. Afterwards the effects of bolt-hole clearance on the stiffness and strength of the same joint have been investigated. © (2012) Trans Tech Publications.

In this work we present hybrid organic/inorganic structures that can exhibit reversible surface wettability, altered in a controllable manner. In particular, we use the method of photo-patterning to produce polymeric SU-8 pillars of specific geometries, onto which we subsequently deposit colloidal TiO2 nanorods. In this way, we combine the microroughness of the polymeric pillars with the nanoroughness of the nanorod-coating to create highly hydrophobic surfaces. The hydrophobicity of these systems can be changed reversibly into hydrophilicity upon irradiation of the hybrid structures with pulsed UV laser light. This behaviour is due to the well-known property of TiO2, that becomes superhydrophilic upon UV light irradiation. This property is reversible and we monitor the recovery of our hybrid polymeric/inorganic-nanorods structures to their initial hydrophobic character upon dark storage and heating. The wetting behaviour has been modelled and analysed according to the surface geometry. The direct implementation of such structures into microfluidics devices is demonstrated. Copyright © 2010 Inderscience Enterprises Ltd.

Supercritical antisolvent micronization has been the subject of many works aimed at the production of precipitates with controlled particle size and morphology. Several morphologies have been observed; but, the production of spherical micrometric particles has been the major objective of most of the studies performed. Therefore, in this work, literature data analysis on spherical and related morphologies has been performed. The ranges of process conditions at which spherical microparticles have been obtained have been listed and discussed. A possible formation mechanism is proposed that is based on the competition between jet break-up and liquid surface tension vanishing characteristic times. If surface tension disappears before the jet break-up, nanoparticles formation by “gas to particle” precipitation is observed; if atomization develops first, micrometric droplets drying and spherical micrometric particles formation is the prevailing process. Modifications of the morphology of spherical particles can be explained by the further evolution of the solid material by superimposition of fast crystallization kinetics that can produce rough surfaces, nanocrystalline surfaces, spherical geometry collapse.

Supercritical antisolvent (SAS) micronization has been used to obtain nanoparticles and micro-particles of several kinds of materials. Sometimes hollow expanded micro-particles have also been obtained. This work is focused on the analysis of this last morphology. We organized literature data and our previous experiments and we added new experiments on previously tested compounds and on compounds never tested before. As a result, expanded micro-particles using several compounds belonging to different categories and precipitated from different solvents in laboratory and pilot scale plants were obtained with diameters between about 10 and 180 μm. They also showed different sub-structures: uniform or nanostructured surface or constituted by microcrystals. Also expanded micro-particles of coprecipitates were obtained. To explain all the available experimental evidences, we propose a mechanism of hollow expanded micro-particles formation, based on thermodynamic and mass transfer interactions.

The structure-function relationship understanding of a nanomaterial requires an accurate map of its shape, strain and surface/interface structure. Electron diffractive imaging (EDI) has recently proved to be a powerful method to image shape and internal structure of Au [1] and CdS [2] nanocrystals of few nm diameters with a spatial resolution of 80-100 pm. A synergic use of measured diffraction patterns and phase retrieval techniques allowed to bypass the need for imaging lenses, avoiding the resolution limits associated to their aberrations. We here phase-retrieved electron diffractive HRTEM images of individual TiO2 nanocrystals at 70 pm resolution, even exposing the specimen to a low electron dose [3]. For the first time, while retrieving the detailed crystal structure of the oxide nanomaterial, O atomic columns were visualized in the coupled EDI-HRTEM experiment without the need for any lens aberration corrector [4]. In addition, our approach allowed us to reveal subtle deviation of the nanocrystal unit cell structure from the bulk counterpart. These highlithing results demonstrate EDI-HRTEM as a unique tool to study the actual atomic structure of nanomaterials with an unprecedented level of accuracy and sensitivity to light atomic elements. In principle, the resolution is only diffraction and dose limited (dependent on wavelength, detector aperture size and exposure time), giving to EDI-HRTEM the potential to achieve record sub-atomic resolutions and promising numerous applicationsin life and materials sciences.