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International audience; Liquid-liquid dispersion process is experimentally investigated to manufacture oil-inwater emulsion working at high flowrates in the cross-slot type of microfluidics. Two types of the cross layouts, namely symmetric and asymmetric configuration, are compared via characterizing the droplet size and size distribution. Because of the higher shear stress and more intensified interaction, the symmetric geometry of the cross-slot is beneficial to produce less amounts of large droplets and dispersing the oil phase more uniformly at the same hydrodynamic conditions, especially in the low range of Re tested in this study. As the flowrates is enhanced, the disparity between them is diminished due to the fact that the instability inside the channel reaches a high level. The detrimental effect of the symmetric configuration is that energy required to burst the dispersed streams is relatively a little higher than with asymmetric one.

The transformations thermally induced in emulsion 70/30 w/w diesel oil/pyrolysis oil droplets of 82?m have been studied. This was possible by thanks to the application of the Generalized Scattering Imaging laser technique for determining simultaneously size and optical properties of emulsion droplets. Arrays of calibrated droplets of emulsion were injected in pre-heated air flow inside a tubular reactor. Four thermal regimes were analyzed: room temperature, 150°C, 250°C and 350°C. For comparison, droplets of the same diesel oil used to form the emulsion were studied in identical experimental conditions. During heating, the emulsion droplets suffer progressive depletion of the diesel oil phase. The pyrolysis oil, dispersed in the diesel oil matrix in the form of microdroplets 2?m sized, undergoes partial evaporation, liquid phase pyrolysis and polymerization. The formation of heavier compounds in the pyrolysis oil microdroplets was inferred by measuring the increase of absorption of the droplets. Due to the depletion of the diesel oil matrix, the concentration of pyrolysis oil microdroplets increases with the temperature. At 350°C almost the totality of diesel oil is evaporated and the pyrolysis oil microdroplets dispersed in an emulsion droplet coalesce to form one single droplet. These residual droplets showed a very narrow size distribution and absorption greater than the original PO in agreement with the fact that they represent the outcome of combined evaporation, liquid phase pyrolysis and polymerization of the pyrolysis oil. Sample of residual droplets were also captured at the exit of the reactor and analyzed by means of optical microscopy. The microscope analysis was consistent with the laser diagnostic results.

Fast biomass pyrolysis is an effective and promising process for high bio-oil yields, and represents one of the front-end technologies to provide alternative, sustainable fuels as a replacement of conventional, fossil-based ones. In this work, the effect of droplet initial diameter on the evaporation and ignition of droplets of crude fast pyrolysis bio-oil (FPBO) and FPBO/ethanol blend (50% vol) at ambient pressure is discussed. The experimental tests were carried out in a closed single droplet combustion chamber equipped with optical accesses, using droplets with a diameter in the range of 0.9–1.4 mm. The collected experimental data show a significant effect of droplet diameter and initial fuel composition on the evaporation and combustion of the droplets. At the same time, 1-dimensional modeling of the evaporation and ignition of different droplets of crude FPBO and its blend with ethanol is performed to understand the complex physical and chemical effects. To this purpose, an 8-component surrogate was adopted, and a skeletal mechanism (170 species and 2659 reactions) was obtained through an established methodology. The comparison of numerical and experimental results shows that the model is able to capture the main features related to the heating phase of the droplet and the effect of fuel composition on droplet temperature and evaporation, particularly the increased reactivity following ethanol addition and the variation of diameter with time. Also, a sensitivity analysis highlighted the reactions controlling the autoignition of the droplets in the different conditions. It was found that the autoignition of pure FPBO droplets is governed by dimethyl furane (DMF), because of its high volatility and in spite of not being the most abundant species. On the other side, ethanol chemistry drives the gas-phase ignition in the case of the blended (50/50 v/v) mixtures, due to its higher volatility and reactivity.

International audience; The Liquid–liquid dispersion process is experimentally investigated to manufacture oil-in-water emulsion working at high flowrates in the cross-slot type of microfluidics. Two cross layouts, namely symmetric and asymmetric configurations, are compared via characterizing the droplet size and size distribution. Automated granulometry is implemented on the images taken by microscopy observations of the emulsion samples. High-speed shadow photography is carried out to discover the continuous- and dispersed-phase flow interactions in the vicinity of the collision region. The results show that the designed microsystems present great potential in terms of fabricating fine oil droplets distributed in the final emulsion. The arithmetic averaged diameter is less than 10 μm at all tested flow conditions and the minimum mean diameter reaches 3.9 μm at the highest energy consumption case. Because of the higher shear stress and more intensified interaction, the symmetric geometry of the cross-slot is beneficial to create fewer amounts of large droplets and dispersing the oil phase more uniformly at the same hydrodynamic conditions, especially in the low Reynolds flow case in this study. As the flowrate is enhanced, the disparity between them is diminished due to the instability inside the channel reaching a high level. The mean drop diameter for both systems is capable to be scaled with the emulsion velocity-based Weber number. The detrimental effect of the symmetric configuration is that the energy required to burst the dispersed streams is relatively a little higher than with asymmetric one.

Experimental study on drop breakage is carried out in the microchannels utilizing head-on impingement configuration by observing a single drop breakup process. In this study, the breakage of oil drops with a diameter ranging from 30 to 200 mu m is investigated in the vicinity of flows impingement region by using high-speed photography at varied flow rate conditions. The most prominent phenomenon of the single drop breakup in the two streams impinging flow field is that the drop tends to break into multiple fragments. The breakage time and the number of daughter drops in the resulting population are statistically analysed and found to be highly dependent on the mother drop size and energy dissipation rate. Two different micro-system geometries, the 600-600 system and the 600-300 system, are compared to evaluate the advantages and disadvantages of swirl flow developed due to the off-axis layout of inlet channels in the 600-300 system. The results show that swirl flow establishes a low-pressure area acting as the dead zone, where a drop can be trapped and then drastically stretched to breakup. Compared with the 600-600 system, the detrimental effect of swirl flow inside the 600-300 system on increasing the breakage time can be offset by a much greater amount of daughter drops generated. In general, the 600-300 system performs more effectively than the 600-600 system because of the less isotropic flow feature. And this superiority is more distinct when the energy dissipation rate is higher.

International audience; Biofuels in the form of water-in-oil (W/O) emulsions are a promising substitution for hydrocarbon fuels, mainly thanks to the micro-explosion phenomenon that occurs under strong heating. Micro-explosion is the atomization of a W/O emulsion drop into daughter droplets because of the water embedded droplets phase change. This atomization leads to the reduction of pollutants and unburnt hydrocarbons emissions. However, micro-explosion is not a systematic phenomenon: indeed, for some cases the water phase change is weak and leads to a partial atomization, called "Puffing". This paper relates a novel approach to better understand the occurrence of micro-explosion. It consists on the identification of the drop triggering the atomization, called the trigger drop, and measure its properties (temperature, size and position within the emulsion drop) thanks to non-intrusive optical diagnostics. Two colors laser induced fluorescence (LIF2C) is the main method used in this work for temperatures. These temperature measurements showed promising results of both quantitative and qualitative aspects. After the calibration steps and the method validation, it is applied for the temperature measurements of water droplets embedded in oil with the maximum temperature recorded around 130°C. Using these measurements methods, a correlation is found between quality of atomization (either micro-explosion or puffing) and the properties of the trigger drop (temperature, size and position). When one of these parameters is not optimal, it can indeed be compensated by the others.

The paper is focused on coupling a small-scale power plant, based on a micro gas turbine (mGT) and a bottoming Organic Rankine Cycle (ORC), with a biomass gasifier. The aim of this study is to define the optimal strategies to maximize the benefits related to distributed generation and to promote the organic solid waste gasification, in terms of energy efficiency and renewable sources exploitation. In particular, they were investigated the energetic performances of the system when the micro gas turbine was fed with several fuel blends, made by specific volume concentration of syngas and biogas. The low heating value of both considered fuels implies the necessity of operating the mGT in peculiar conditions as determined by the performance maps of compressor and turbine. Then, the thermodynamic analyses of the whole energy system have been carried out to evaluate the performance for each fuel. The high hydrogen content of syngas and the different thermodynamic properties of the studied fuel blends required a deeper investigation of the combustion process. In order to analyze the combustion stability and the fluid dynamic aspects, an accurate investigation of combustion chamber has been performed through a CFD solver. Finally, a comparison of the plant performances for each fuel blend have been reported, along with opportunities and critical aspects related to power plant integration.

International audience; Liquid-liquid dispersion by head-on impingement in a cross-slot microfluidic device to form oil-in-water emulsion is experimentally investigated at broad range of flow rate conditions. Reynolds number based on the continuous aqueous phase flow is changed from 1000 to 7000 and the oil dispersed volume fraction varies between 3% and 30%. The flow patterns are observed in the vicinity of impinging region to characterize the effect of Reynolds number and oil volume fraction on the water-oil interaction and thus emulsification process. Based on the measured droplet size and size distribution, two geometries are compared, aimed at evaluating the advantages and disadvantages of swirl flow in the collision region for producing high quality emulsion. One configuration, "600-600", corresponds to inlet channels of identical size (600 μm×600 μm), while the other one, "600-300", has a smaller channel for dispersed phase which is off-axis with the water channel. The results show that flow characteristics during dispersing process are significantly different for viscous and turbulent conditions. Dominated by Reynolds number, the flow patterns are classified into three regimes. The more turbulent the flow is, the finer and more monodispersed droplets will be in the o/w emulsion. In the medium Reynolds number regime, characteristics of flow are closer to laminar flow using higher oil volume fraction, compared to small oil volume content. It is particularly evident with 600-300 system because of lowering velocity gradient between two phase streams. Based on results of drop mean diameter and polydispersity index, 600-300 system which generates swirl flow structure only exhibits a superior performance, compared to the conventional equal-size geometry, at relatively higher Reynolds number.

The use of biogas in micro gas turbines (MGTs) generally requires invasive structural modifications to fuel compression units, control valves and combustor. Costs associated with the modifications significantly reduce the benefits of a rational and sustainable exploitation of energy resources of lower value as the biogas. In order to overcome this aspect, in a recent paper the authors proposed a dual fuel approach, identifying a structurally non-invasive and cost-effective technical solution to increase the CO2 concentration in the fuel and to extend the operation domain of the MGT when low calorific value fuels are used. In that study, it has been evaluated, implemented and tested an innovative management strategy of fuel feeding and combustion. Experimental preliminary tests validated the idea of a new supply strategy for exceeding the current limits of biogas exploitation as MGT fuel. With this approach the MGT operating domain has been extended, increasing more than twice the CO2 concentration limit than experimentally validated limit available in literature. In this study the authors present a more extensive investigation concerning the energetic performance and the environmental impact of a 100 kWe MGT Turbec T100 when fuelled with a mixture of natural gas and carbon dioxide (synthesis biogas) in the dual fuel approach, by varying CO2 concentration in the fuel at part load condition. The data acquired by an extensive experimental campaign, in terms of thermodynamic parameters and gaseous exhaust emissions, are presented and compared with the results of numerical simulations. A 3D CFD analysis of the combustion process is also presented. Initial and boundary conditions of the numerical approach were obtained from a previous validated 0D thermodynamic matching model. The synergistic activity between numerical modeling and experimental work allows to analyze and explain the overall behavior of the micro gas turbine in the dual fuel mode with biogas fuel. The study shows that the micro gas turbine can stably operate in a dual fuel mode until the CO2 content rises above 25%.

The study evaluated the growth of Desmodesmus communis on column photobioreactor and its thermochemical treatment by catalytic pyrolysis using HZSM-5 zeolite. D. communis showed good results in terms of growth (0.05g L−1 d−1). Analytical pyrolysis of original algae and derived bio-oil mixed with zeolite was used as a screening method in order to gather information on the cracking process. Preparative pyrolysis on bench scale reactor was performed on algae biomass over a zeolite bed at 1:10 ratio (wt/wt). Py-GC–MS of biomass/catalyst mixture showed that the denitrogenation/deoxygenation increased with increasing zeolite load from 1:5 to 1:20 ratio and became significant at 1:10 ratio. The composition observed by analytical pyrolysis was featured by the predominance of alkylated monoaromatic hydrocarbons. The scaling-up to bench scale confirmed the results obtained with analytical pyrolysis in terms of monoaromatic hydrocarbons. However, low yield of catalytic oil (8% by weight) was observed.

International audience; h i g h l i g h t sWater-in-oil emulsion is produced using two micro-channels in series. Droplets size of the dispersed phase reaches 11 µm without surface active agent. A decrease of the average water droplet size by 40% compared to the use of single micro-system. Energy balance is performed. Flow visualization is given.a b s t r a c t Development of alternative fuels and improvement of their combustion is a necessity in a general context of scarcity of fossil energy resources and of environmental pollution. In particular, the use of water dispersed in biofuels is known to improve combustion quality of diesel engine and to reduce pollution in gas emissions. This work aims at contributing in the development of a compact continuous emulsifier that could be used to feed energy systems. In order to fulfil requests such as convenient size of water droplets, absence of surfactant and needed flow rates of biofuel, the association of two micro-systems in series is investigated and compared to the use of a single one. The comparison of the emulsions obtained by the different systems is made in terms of mean size and size distribution of the water droplets in the dispersion, and process energy consumption. In the absence of surfactant, depending on applied flow-rates and water fraction, the use of two micro-systems in series allows to reduce the mean size of droplets by a factor 2 to about 3. Flow phenomena which lead to water phase fragmentation are described thanks to high-speed visualization of the flows in the micro-channels.

A water-in-oil emulsion droplet may undergo a phenomenon called microexplosion when under strong heating. A microexplosion can be defined as the atomization of the continuous phase (i.e., oil) by the dispersed droplets (i.e., water) phase change and the volume expansion that is induced. It is established that microexplosion occurrence is favored by the (partial) coalescence of water droplets before phase change. This process has direct influence on the time evolution of water droplet size. For this purpose, an experimental method based on laser-induced fluorescence is set up. It basically consists of adding a fluorescent dye, fluorescein, which is soluble only in water, and exciting the emulsion drop by a laser sheet during its heating. The goal is to gain a better understanding of microexplosion by measuring the size evolution of dispersed droplets and targeting the water droplet that triggers the atomization of the emulsion drop. The sizing procedure showed promising results. Manual and automatic measurements of the size were compared in order to quantify the average error, which happens to be < 10%. Results show that the size of this trigger droplet is not sufficient in order to determine whether an emulsion drop will undergo optimal atomization.

The heating of two-component droplets and the following explosive breakup of those droplets have been extensively studied over the most recent years. These processes are of high interest, since they can significantly improve the performance of many technologies in fuel ignition, thermal and flame liquid treatment, heat carriers based on flue gases, vapors and water droplets, etc. Research throughout the world involves various schemes of droplet heating and supply (or, less frequently, injection) to heating chambers. The most popular scheme features the introduction of a two-component or multi-component droplet onto a holder into the heating chamber. In this research, we study how holder materials affect the conditions and integral characteristics of droplet heating and explosive breakup: heating time until boiling temperature; minimum temperature sufficient for droplet breakup; number and size of fragments in the resulting droplet aerosol, etc. Experiments involve droplets that are produced from flammable (oil) and non-flammable (water) components with significantly different thermophysical and optical properties, as well as boiling temperature and heat of vaporization. The most popular elements with the scientific community, such as ceramic, steel, aluminum, copper, and phosphorus rods, as well as a nichrome wire, serve as holders. We establish the roles of energy inflow from a holder to a droplet, and energy outflow in the opposite direction. We compare the holder results with a supporting thermocouple, recording the drop temperature under a heat transfer provided at 350°C. Finally, we forecast the conditions that are required for a significant improvement in the performance of thermal and flame water treatment through the explosive breakup of two-component droplets.

When a water-in-oil (W/O) emulsion droplet is heated, a phenomenon called micro-explosion (μ-exp) may occur. Micro-explosion can be defined as the burst of the continuous phase (i.e. oil) by the energy of evaporation of dispersed droplets (i.e. water) and the volume expansion that goes with it. In the paper are presented results that show a strong correlation between size average value (and distribution size) of water droplets and micro-explosion occurrence rate. Emulsion dispersed phase size, when using micro-channel techniques, depends highly on the emulsion composition and the energy provided to the system (Oil flow rate). A (3–18) μm diameter range was measured in the tests discussed in the paper. Micro-explosion occurrence can reach 70% for larger droplet sizes (about 20 μm). It declines to less than 20% for small sizes (between 5 and 10 μm). Influence of other parameters on micro-explosion occurrence like temperature heating or physical properties is also studied. Ohnesorge number seems to be an adequate parameter to study micro-explosion occurrence because of its direct relation with the relevant emulsion properties: droplet size, oil viscosity and interface tension. Micro-explosion rate achieves its maximum rate (60%) for Oh = 0.12, in other words, for emulsion where dispersed droplets move easily (low viscosity) with a great ability to coalesce (larger droplets and no surfactant).

The paper reports the results of an experimental investigation carried out on a prototype optically accessible compression ignition engine fueled with water in diesel emulsion (WiDE) and Diesel only. The effect of WiDE on combustion process evolution and exhaust emissions was investigated through standard engine benchmark and optical diagnostics. 2D chemiluminescent emission measurements centered at 690 nm were carried out during the whole combustion process to discriminate the soot emission from other excited chemical species. The emulsion was produced through a prototype designed microchannels emulsifier that can also work inline. The water concentration was 9.1%v with a small amount (0.2%v) of nonionic surfactant (SPAN80) used to stabilize the emulsion. Tests were performed comparing combustion and exhaust emissions of the reference commercial diesel fuel to the WiDE. For any investigated fuel and operating point, engine tests were carried out changing the injection interval to achieve the same chemical energy as the reference diesel (935 J/str). Compared to Diesel, the WiDE induced an increase in ignition time, enhancing the air/fuel mixing with a simultaneous reduction in both PM and NOx. The digital imaging and 2D chemiluminescence techniques highlighted a reduction in soot formation without significant changes on the soot oxidation rate. The results suggest the use of WiDE as a reliable method to improve NOx-soot trade-off of CI engines.

In this study, research activity concerning the utilization of biogas into a commercial micro gas turbine (MGT) Ansaldo Turbec T100P is presented. The use of biogas in MGT has been already quite explored in literature. However, conflicting and not yet fully comprehensive results highlight the need for further scientific investigations. Although several authors have demonstrated, through numerical studies, the possibility of using biogas with amounts of CO2 up to 40–50% in volume in commercial MGT, experimental evidences of this condition are not yet present in literature. In fact, the CO2 concentration limit experimentally validated in literature, after which phenomena of detachment and instability of the flame happen, is considerably lower (∼12%). The utilization of biogas in micro gas turbines generally requires structural adaptations, often invasive and expensive, to the fuel compression unit and control valves. Not infrequently a partial redesign of the combustor is often necessary. Costs associated with the modifications significantly reduce the benefits of a rational and sustainable exploitation of energy resources of lower value as the biogas. Aim of this activity is to overcome these issues, by identifying a non-invasive and cost-effective technical solution to increase the CO2 concentration in the fuel and to extend the operation domain when low calorific value fuels are used. It has been studied, implemented and tested an innovative management strategy of fuel feeding and combustion. Experimental layout and preliminary results of this novel approach are shown and discussed.

Lorsqu'une goutte d'émulsion eau/huile (E/H) est portée à haute température, un phénomène thermique appelé « micro-explosion » peut avoir lieu. Ce phénomène peut être défini comme l'atomisation de la phase continue (ici l'huile) par l'énergie dégagée par la vaporisation de la phase dispersée (ici l'eau). Cependant, cette énergie n'est parfois pas suffisante pour atomiser la phase continue : ce phénomène est alors connu sous le nom de « puffing », que l'on pourrait définir comme étant une micro-explosion « partielle ». Nous proposons ainsi d'étudier l'influence de certains paramètres physiques sur l'occurrence de la micro-explosion et de visualiser les phénomènes physiques internes à la goutte avant son explosion

Water in diesel emulsion (WiDE) is a viable solution for lowering both NOx and Soot emissions from compression ignition (CI) engines. In this paper, the effect of WiDE on the combustion process and exhaust emissions of a prototype optically accessible CI engine was investigated through conventional in-cylinder pressure measurements and optical diagnostics. The emulsion (9.1%v of water) was produced through a prototype designed microchannels emulsifier with a small amount of nonionic surfactant. Commercial diesel was set as reference fuel and compared to WiDE. The start of injection (SOI) was swept from 8 to 23 CAD BTDC. For diesel fuel, the injected mass and injection pressure were representative of a medium load regime, WiDE injection interval was adjusted to keep constant the energy content. Compared to Diesel, WiDE induced an increase in ignition time, enhancing the air/fuel mixing with a simultaneous reduction in PM and NOx. 2D chemiluminescent emission measurements highlighted a reduction in soot formation using WiDE, without significant changes in soot oxidation rate.

"Micro-explosion" is a thermal phenomenon that can happen when an emulsion droplet is heated, at one condition: The two non-miscible fluids (for our case water and n-tetradecane) must have different boiling points. In this case, the dispersed phase (water) reaches its saturation temperature faster than oil, resulting in a sudden phase change that leads to a volumetric expansion and thus, the atomization of the continuous phase (n-tetradecane). However, micro-explosion is not a systematic process and other phenomena like "puffing" (partial micro-explosion) can take place. It appears that micro-explosion occurrence is strongly related to physical properties of the fluids, but mostly to the size distribution of the water dispersed droplets. For this reason, two optical diagnostic technics have been developed. The first one consists on the observation of an emulsion droplet at 500°C thanks to a CCD at high frequency (2000-3000 Hz). The second one consists on adding a fluorescent dye, Fluorescein, that is soluble only in water. The emulsion droplet is then heated in the same conditions, and excited by a continuous laser plane sheet. The emitted light is filtered before being recorded by the CCD camera. Thanks to these two technics, we are able to record the evolution of the size distribution of water droplets and identify the optimal ones for a higher micro-explosion occurrence, study the motion of the dispersed droplets and other phenomenon like dynamics of the coalescence of dispersed droplets.

Combustion of water in oil μ -emulsions is still considered as a useful technology for the energy conversion of waste oil. One of the most relevant advantages is related to the phenomenon of micro-explosion ( μ – e ) that produces the secondary atomization of the oil. Several experimental approaches have been proposed in the last years with the aim to characterize the μ – e effect under different conditions. In this paper, an experimental comparison between the two useful approaches is presented. The results obtained with the technique of the Suspended droplet will be related to data present in the literature, obtained through the Leidenfrost technique . Quantitative thermal results such as the μ – e temperature and the fall temperature after μ – e show the most important differences. The important role played by the separation process as coalescence and creaming in both approaches is also discussed.

The paper reports the experimental results concerning emissions from 30 kWe commercial micro gas turbine feed with blends of straight vegetable oil with fossil fuel. Both gaseous and particulate emissions were measured at full and partial load for blends 10% v/v and 20% v/v of rapeseed and sunflower oils with JET A1 kerosene. The variations of nitric oxide and carbon monoxide emissions were taken into account to evaluate the combustor behavior at different loads and blends. The effects of the fuel composition on the variations, in terms of concentrations and dimensions, of ultrafine – particulate matter were also evaluated. NOx and CO emissions are practically insensitive to the composition of the fuel being the differences within the experimental uncertainty of the instrumentation. This demonstrates a similar overall combustion at both partial and full load for the five fuels used (Jet A1 and four SVO blends). On the contrary, particle matter emission is three times for blends of rapeseed oil and more than fifty times greater for blends of sunflower oil with respect to pure Jet A1. The differences are ascribed to the chemical structure of the vegetable oil tested.

A detailed analysis on the evaporation of acetic acid and ethylene glycol droplets is performed experimentally and numerically. The isolated droplet is positioned in a combustion chamber, suspended on a thermocouple and evaporated in buoyancy driven convection, following the thermal history throughout the droplet lifetime. The experiments provide quantitative and qualitative data on the evaporation physics of acetic acid, ethylene glycol and their mixture. The data are then modeled adopting the multiphase CFD code DropletSMOKE++ , describing the flow field around the droplet, the heating rate and the evaporation process. The main novelty introduced in this work is a multiregion approach to describe the solid fiber, which allows to model the conjugate heat transfer with the liquid and the gas phase, as well as its impact on the droplet evaporation. DropletSMOKE++ results show a good agreement with the experimental data, regarding both the diameter decay and the liquid temperature, whose internal distribution in the liquid is shown to be highly affected by the heat flux from the fiber (which can contribute up to 30–40% in the total heat flux on the droplet). The effect of the thermocouple on the evaporation rate has been highlighted simulating the same experiments considering the solid as adiabatic, showing in this case a large underprediction of the vaporization rate and confirming the need of a detailed model for the fiber to correctly predict the vaporization phenomenon. The mixture evaporation has been investigated, emphasizing the importance of adopting a detailed thermodynamic model (which includes activity coefficients) and the impact of the mixture non-ideality on the evaporation process. The mixture also exhibits preferential vaporization, facilitated by the internal convection in the liquid phase.

The off design behavior of a 100kW Turbec T100P micro gas turbine fuelled with methane is analyzed in the paper. The work is focused on the analysis of combustion efficiency, overall performance and gaseous emissions at different loads. A critical comparison between experimental data and results of a 3D CFD analysis of the combustor is discussed. The RANS RSM turbulence model is used in the numerical computations. The Zeldovich mechanism for NO formation evaluation is coupled to a methane-oxygen multistep chemical kinetic mechanism for predicting the concentration of O2, CO2, CO and NO at the exhaust. The experimental campaign showed no sensible variations in NOxemissions by varying MGT load; otherwise a great CO increasing is highlighted by load decreasing. The results of numerical analysis are in good agreement with experimental data as concerns CO emissions, while overestimate NO production in the diffusive flame region at 50% load.

The emulsification is well known for being considered as a solution for improving biodiesel combustion. In this extent, the size of the dispersed droplets is crucial to favour micro-explosions and optimising the combustion. The present mini-channel operates liquid/liquid dispersion at higher flow rates than with usual implementations of minichannels and micro-channels. Due to this particular condition of functioning, the flow enhanced in the mini channel is classified as a high-speed emulsifying one. In this study, the dispersion of water into sunflower oil as a water-in-oil (w/o) emulsion is tested. In such an in-line process, high-shear implies higher velocities at smaller scales, making an optical visualisation difficult. But the light scattering technique enables to detect micro-scaled droplets, at the required high velocities. The proper design and exploitation of a focalised laser beam through a transparent, hydrophobic mini-channel is explained. A focalised laser beam is crossing the mini-channel, dealing with the scattering cross sections of the water droplets. The measurement of the collected beam is successfully matched to the geometrical properties of the emulsion (water fraction and size of inner droplets) through the classical light scattering theoretical basement. The calibration of the collected laser light technique obtained in the straight mini-channel is followed by measurements approaching the high shear rate zone of the cross-flowing mini-channel

Lipase is an enzyme that finds application in biodiesel production and for detection of esters and triglycerides in biosensors. Matrix Assisted Pulsed Laser Evaporation (MAPLE), a technique derived from Pulsed Laser Deposition (PLD) for deposition of undamaged biomolecules or polymers, is characterized by the use of a frozen target obtained from a solution/suspension of the guest material (to be deposited) in a volatile matrix (solvent). The presence of the solvent avoids or at least reduces the potential damage of guest molecules by laser radiation but only the guest material reaches the substrate in an essentially solvent-free deposition. MAPLE can be used for enzymes immobilization, essential for industrial application, allowing the development of continuous processes, an easier separation of products, the reuse of the catalyst and, in some cases, enhancing enzyme properties (pH, temperature stability, etc.) and catalytic activity in non-aqueous media. Here we show that MAPLE technique can be used to deposit undamaged lipase and that the complex structure (due to droplets generated during extraction from target) of the deposited material can be controlled by changing the laser beam fluence.

The paper deals with the development of a dynamic model of a commercial 100 kW Micro Gas Turbine (MGT) fuelled with mixtures of standard (i.e. natural gas or methane) and alternative fuels (i.e. hydrogen). The model consists of a first-order differential equation (ODE) describing the dominant dynamics of the MGT imposed by its own control system during production electrical power. The differential equation is coupled to a set of nonlinear maps derived numerically from a detailed 0D thermodynamic matching model of the MGT evaluated over a wide range of operating conditions (i.e. mechanical power, fraction of hydrogen and ambient temperature). The efficiency of the electrical machine with power inverter and power absorbed by auxiliary devices is also taken into account. The resulting model is experimentally validated for a sequence of power step responses of the MGT at different ambient conditions and with different fuel mixtures. The model is suited for simulation and control of hybrid energy grids (HEGs) which rely on advanced use of MGT and hydrogen as energy carrier. In this regard, the MGT model is used in the simulation of an HEG based on an appropriate mix of renewable (non-programmable) and non-renewable (programmable) energy sources with hydrogen storage and its reuse in the MGT. Here, the MGT is used as a programmable energy vector for compensating the deficits of renewable energies (such as solar and wind) with respect to user demand, while excess renewable energy is used to produce hydrogen via electrolysis of water. The simulated HEG comprises a solar PhotoVoltaic (PV) plant (300 kW), an MGT (100 kW) fuelled with natural gas and hydrogen blends, a water electrolyzer (WE) system (8 bar, 56 Nm3/h), a hydrogen tank (54 m3), and an Energy Management Control System (EMCS).

Spirulina ( Arthrospira platensis) was cultivated in a 70 L indoor vertical photobioreactor and harvested at concentrations of 1.0 g L −1 dry biomass. Lyophilised algal biomass was pyrolysed at 500 °C under nitrogen and vapours were passed over pelletised HZSM5- zeolite (SiO 2 /Al 2 O 3 38). An organic fraction (bio-oil) overlaying an aqueous phase was obtained by cold trapping, while non-condensed bio-oil components (XAD fraction) were adsorbed onto a poly(styrene— co -divinylbenzene) resin. About 20% of the original algal carbon was converted into inorganic carbon in the aqueous (HCO 3 − /CO 3 2− ) and gas phase (composed of 70% CO 2 , 20% CO). Most of spirulina carbon ended up in char (30%) and coke (30%). Bio-oil and XAD fraction represented approximately 10% mass, 20% carbon and 20% energy of algal biomass. Bio-oil composition was dominated by alkylated monoaromatic hydrocarbons, with benzene concentrations below 10 g kg −1 . Large part of original nitrogen was dissolved in the aqueous phase (40%) and incorporated into char/coke (37%). A minor fraction (6%) of nitrogen ended up in bio-oil in the form of indoles, pyrroles, carbazoles, anilines. While deoxygenation was effective, denitrogenation was incomplete and probably counteracted by zeolite ammonisation. Microcombustion experiments showed that the bio-oil burnt efficiently, but with a sooting flame, and a tendency to form small solid carbonaceous residues probably associated with the presence of heavy compounds.

Relazione tecnico-scientifica sulle attività del progetto di ricerca finanziato nell'ambito dell'Accordo di Programma (AdP) CNR-MISE. Area prioritaria d'intervento: RAZIONALIZZAZIONE E RISPARMIO NELL'USO DELL'ENERGIA ELETTRICA. Tema: RISPARMIO DI ENERGIA ELETTRICA NEI SETTORI: CIVILE, INDUSTRIALE E SERVIZI. Progetto: "Bioenergia Efficiente". Linea di attività L2: Risparmio di energia elettrica attraverso l'ottimizzazione di schemi energetici e lo sviluppo di tecnologie di conversione innovative. WP 1: Risparmio di energia elettrica attraverso l'ottimizzazione di schemi energetici. Report Attività: PAR 2013 - 2014.

Lipases (triacylglycerol ester hydrolases) are enzymes used in several industrial applications. Enzymes immobilization can be used to address key issues limiting widespread application at industrial level. Immobilization efficiency is related to the ability to preserve the native conformation of the enzyme. MAPLE (Matrix Assisted Pulsed Laser Evaporation) technique, a laser deposition procedure for treating organic/polymeric/biomaterials, was applied for the deposition of lipase enzyme in an ice matrix, using near infrared laser radiation. Microscopy analysis showed that the deposition occurred in micrometric and submicrometric clusters with a wide size distribution. AFM imaging showed that inter-cluster regions are uniformly covered with smaller aggregates of nanometric size. Fourier transform infrared spectroscopy was used for both recognizing the deposited material and analyzing its secondary structure. Results showed that the protein underwent reversible self-association during the deposition process. Actually, preliminary tests of MAPLE deposited lipase used for soybean oil transesterification with isopropyl alcohol followed by gas chromatography–mass spectrometry gave results consistent with undamaged deposition of lipase.

Relazione tecnico-scientifica sulle attività del progetto di ricerca finanziato nell'ambito dell'Accordo di Programma (AdP) CNR-MISE. Gruppo tematico: AREA C "Razionalizzazione e risparmio nell'uso dell'energia elettrica", Sub C1: "Risparmio dell'energia elettrica nei settori civile, industria e servizi". Progetto: "Risparmio di Energia Elettrica attraverso l'uso efficiente di tecnologie innovative". Linea Progettuale 1: "Risparmio di energia elettrica nel settore industriale/civile". WP 1.1: "Risparmio di energia elettrica attraverso l'ottimizzazione di schemi energetici". Report Attività: PAR 2012.

The formation of water-in-oil disperse flows is investigated in a microfluidic device. The liquid–liquid flow mainly differs from these presented in the existing literature in its high capillary number (between 3 and 14). The pressure-driven high flow rate, the viscous oily continuous phase, and the head-on impinging flow contribute to oppose a maximal shear force to the interfacial tension. Interfacial tension effects are significant at scales smaller than the capillary length within microfluidic devices, but not dominant in the present work. Moreover, the impinging channel is designed to deliver a low water fraction. As a result, the obtained water-in-oil emulsion is finely dispersed. A channel geometry is selected among three different items, with a physical explanation of its observed finer emulsification. In comparison with experimental data, two complementary approaches are used to model the Ohnesorge number from fluids and flow parameters. Finally, an in situ optical diagnostic using polarized laser light provides a precise knowledge of the emulsifying area and the overall flow pattern within the microchannel.

Development of alternative fuels and improvement of their combustion is a necessity in a general context of scarcity of fossil energy resources and of environmental pollution. In particular, the use of water dispersed in biofuels is known to improve combustion quality of diesel engine and to reduce pollution in gas emissions. This work aims at contributing in the development of a compact continuous emulsifier that could be used to feed energy systems. In order to fulfil requests such as convenient size of water droplets, absence of surfactant and needed flow rates of biofuel, the association of two micro-systems in series is investigated and compared to the use of a single one. The comparison of the emulsions obtained by the different systems is made in terms of mean size and size distribution of the water droplets in the dispersion, and process energy consumption. In the absence of surfactant, depending on applied flow-rates and water fraction, the use of two micro-systems in series allows to reduce the mean size of droplets by a factor 2 to about 3. Flow phenomena which lead to water phase fragmentation are described thanks to high-speed visualization of the flows in the micro-channels.

Aim of the paper is to evaluate the potentialities and critical issues of the micro-gas turbine Turbec T100 properly modified in order to be powered by liquid fuels. The main difference with respect to the version designed for gaseous fuels concerns the combustor, namely the combustion chamber and the fuel injection system. The numerical study was carried out using both a 0D matching analysis and a 3D CFD analysis of the combustor. The thermodynamic model, coupled with the operating maps of rotating components, was calibrated using the experimental data collected during operation of the micro-gas turbine with gaseous fuel. The operative parameters computed through the 0D model have been utilized to simulate the behavior of micro-gas turbine fed by liquid fuels, thus obtaining the initial and boundary conditions to be used in the CFD analysis. The combustion process of liquid fuels is analyzed; the main differences at varying loads are discussed in terms of temperature and velocity profiles of the air flows inside the combustion chamber and mean values of turbine inlet temperature and exhaust gaseous concentration. A preliminary study concerning the characteristics of the injection system is also reported.

Green Air is a project held in joint venture between the Italian Space Agency (ASI) and AGT Engineering, an Italian small company specialized in technology transfer, to develop two scientific experiments on board the ISS: ICE - Italian Combustion Experiment, in partnership with the National Research Council of Italy (CNR) Istituto Motori; and Diapason in partnership with DTM, an Italian SME. The two experiments were carried out with the help of the Italian astronaut Luca Parmitano during the "Volare" mission, increment 36/37 (May-November 2013). Green Air is the first public private partnership (PPP) project between ASI and an Italian SME for the use of the ISS equipment and services. By this project ASI (in partnership with NASA), AGT and its partners shared the access on board the ISS and its facilities, the astronauts' skills and time and the scientific knowledge to carry out the experiments. ICE is the study of the evaporation and combustion regimes of second and third generation biofuels and fundamental biofuel surrogates. The combustion of droplets in microgravity (taking place into the NASA Combustion Integrated Rack) allows to study the combustion processes in perfect spherical symmetry, which means ideal conditions for combustion. Thanks to this experiment it is possible to produce a library of data which are then used to model and optimize the combustion of next generation fuels in earth-working engines and combustion chambers. Diapason is a simple portable and light instrument, developed by DTM, able to analyze the particles contained in the air. It can capture nanoparticles from 10 to 1000 nanometers into a cartridge that can be removed and analyzed by an analytical instrument. Diapason was placed and switched on in 5 different locations within the ISS in order to measure the air quality on the ISS and to tune the instrument in the ideal conditions for the subsequent use on the Earth. In addition to the air quality checks, AGT and DTM have identified the collection and identification of some types of virus and bacteria in the air as a possible development, extending the Diapason use to hospitals surgery rooms and special environments. The Green Air team is working into the analysis of the scientific results coming from the experiments with the aim of targeting new applications and their related markets. The paper will describe how the scientific outputs are being turned into their applications and will include recommendations for further policy implementation mechanisms on the Aerospace PPPs.

In recent years an increasing interest is focused on the study of micro gas turbines (MGT) behavior at part load by varying fuel, in order to determine their versatility. The interest in using MGT is related to the possibility of feeding with a wide range of fuels and to realize efficient cogenerative cycles by recovering heat from exhaust gases at higher temperatures. In this context, the studies on micro gas turbines are focused on the analysis of the machine versatility and flexibility, when operating conditions and fuels are significantly varied. In line of principle, in case of gaseous fuels with similar Wobbe Index no modifications to the combustion chamber should be required. The adoption of fuels whose properties differ greatly from those of design can require relevant modifications of the combustor, besides the proper adaptation of the feeding system. Thus, at low loads or low calorific value fuels, the combustor becomes a critical component of the entire MGT, as regards stability and emissions of the combustion process. Focus of the paper is a 3D CFD analysis of the combustor behavior of a Turbec T100P fueled at different loads and fuels. Differences between combustors designed for natural gas and liquid fuels are also highlighted. In case of natural gas, inlet combustor temperature and pressure were taken from experimental data; in case of different fuels, such data were inferred by using a thermodynamic model which takes into account rotating components behavior through operating maps of compressor and turbine. Specific aim of the work is to underline potentialities and critical issues of the combustor under study in case of adoption of fuels far from the design one and to suggest possible solutions.Copyright © 2015 by ASME

The performance of a micro gas turbine in terms of global efficiency and exhaust emissions at different loads and methane-hydrogen blends has been experimentally studied. The load was varied from full load down to half load. A critical comparison between experimental data and results of the 3D CFD analysis of the combustor is discussed in order to study the effects of part load operation. Additional objective of the present study is to extend the numerical analysis of the combustor in order to describe the influence of a wider range of hydrogen concentrations in the fuel gas mixture. Numerical simulations were performed through the commercial code ANSYS CFX 14.5. Turbulence model adopted was the RSM RANS model, which ensures a good evaluation of effects of swirled turbulent flows in the combustion chamber. The oxidation of methane is simulated by using multistep kinetics models. They assure a better reproduction of CO emissions with load. Boundary and initial conditions were defined by using experimental data, when available, and results of numerical matching analysis, which assumes importance in case of absence of specific measurements at combustor inlet. Discussion of results is mainly focused on the variation in terms of exhaust gaseous emissions and temperature distributions in the combustor by varying load and fuel. A numerical evaluation of the MGT combustor behavior in critical conditions is also presented.Copyright © 2014 by ASME

The micro-explosion phenomenon is involved in emulsified fuel droplets placed in a hot atmosphere, such as spray combustion. Droplets of water-in-sunflower oil emulsion are used, since they are representative of a class of emulsions used in practical applications of biofuels. Once the micro-explosion is triggered after a short delay, the rapid (

The combustion features of water-in-diesel fuel emulsions were studied in a single drop combustion chamber by means of high speed shadowgraphs, suspending emulsion drops to a thermocouple in order to follow their thermal history. Several emulsions were prepared by varying the internal parameters that affect their stability, such as water volume fraction, water particle size distribution and the amount of surfactant. It was found that the emulsion internal parameter which have influence on emulsion stability (water volume fraction and size distribution, quantity of surfactant) also influence the tendency towards micro-explosion.

An extensional flow involving water-in-oil emulsification is created in an impinging micro-channel. A focalised beam of laser light is polarised in the direction of the channel, and its amount of collected light through the emulsion is measured. Polarised light is expected to be more interacting with stretched and elongated droplets. The obtained mappings of four different flow patterns confirm the observations of Segre and Silbergerg in suspensions across micro-channels.

The micro-explosion phenomenon consists in the explosive vaporization of water droplets inside a droplet of water-in-oil emulsion. It is used in the combustion of emulsified fuels. The distribution of temperature and thermal energy of the "daughter-droplets" issued from a micro-explosion remains unknown so far. The difficulty of such an investigation is their small size and fast velocity, for an on-the-fly characterization. The present investigation explains an experimental facility designed to record the temperature field on a thermally thin plate, when impacted by the droplets issued from a micro-explosion. The distribution of maximum temperatures at impact is shown, on a representative sample of droplets. A complete calculation is exposed, that enables to obtain the thermal energy of droplets from the unsteady temperature field on the plate.

The burning of water in oil emulsions is considered as an effective alternative to bring out waste oil because of a significant reduction in carbon monoxide, nitrogen oxides and particulates in the exhaust. These advantages have different origins, an important contribution is provided by the phenomenon of micro-explosion. In this work, the influence of the size of the dispersed water droplets in the micro-explosion phenomenon is studied by the hot plate technique. The variation of the temperature and the evolution of the phenomenon have been investigated using a synchronized thermocouple/high speed imaging system. Three emulsions with the same amount of water (30% mass ) but with different distribution of the size of the dispersed water droplets have been tested. The results show that the size distribution of the dispersed water droplets plays an important role in the phenomenon of micro-explosion. Moreover, some internal phenomenon as the separation process between water and oil seems to affect significantly the phenomenon.

The aim of this paper is to perform an accurate analysis of the evaporation of single component and binary mixture fuels sprays in a hot weakly turbulent pipe flow by means of experimental measurement and numerical simulation. This gives a deeper insight into the relationship between fuel composition and spray evaporation. The turbulence intensity in the test section is equal to 10%, and the integral length scale is three orders of magnitude larger than the droplet size while the turbulence microscale (Kolmogorov scales) is of same order as the droplet diameter. The spray produced by means of a calibrated droplet generator was injected in a gas flow electrically preheated. N-nonane, isopropanol, and their mixtures were used in the tests. The generalized scattering imaging technique was applied to simultaneously determine size, velocity, and spatial location of the droplets carried by the turbulent flow in the quartz tube. The spray evaporation was computed using a Lagrangian particle solver coupled to a gas-phase solver. Computations of spray mean diameter and droplet size distributions at different locations along the pipe compare very favorably with the measurement results. This combined research tool enabled further investigation concerning the influencing parameters upon the evaporation process such as the turbulence, droplet internal mixing, and liquid-phase thermophysical properties.

The emulsification is well known for being considered as a solution for improving biodiesel combustion. In this extent, the size of the dispersed droplets is crucial to favour micro-explosions and optimising the combustion. The present mini-channel operates liquid/liquid dispersion at higher flow rates than with usual implementations of mini-channels and micro-channels. Due to this particular condition of functioning, the flow enhanced in the mini channel is classified as a high-speed emulsifying one. In this study, the dispersion of water into sunflower oil as a water-in-oil (w/o) emulsion is tested. In such an in-line process, high-shear implies higher velocities at smaller scales, making an optical visualisation difficult. But the Extinction technique enables to detect m-scaled droplets, at the required high velocities. The proper design and exploitation of a focalised laser beam through a transparent, hydrophobic mini-channel is explained. A focalised laser beam is crossing the mini-channel, dealing with the scattering cross sections of the water droplets. The measurement of the collected beam is successfully matched to the geometrical properties of the emulsion (water fraction and size of inner droplets) through the classical Extinction theoretical basement. The calibration of the Extinction technique obtained in the straight mini-channel is followed by measurements approaching the high shear rate, emulsifying zone of the cross-flowing mini-channel.