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International audience; Aerospace industry needs accurate coating thickness measurement as well as adhesion testing for preventing the corrosion of wear of metal substrates. Recently, a constant attention is focused towards the potentialities offered by non-invasive sensing techniques and their technological advancements. This communication deals with time of flight THz imaging, enhanced by a noise filtering procedure based on the Singular Value Decomposition of the data matrix. In this work, THz imaging is exploited to analyse painted steel samples in order to detect paint coating layers and provide images of them and of the interface between the coating layer and the steel substrate.

Molecules constituting nascent soot particles have been analyzed by two-step laser desorption laser ionization mass spectrometry. Three samples have been collected from a slightly sooting ethylene/air premixed flame with the aim to investigate soot composition in the transition from nucleated to just-grown soot particles. Sampling locations have been selected based on the evolution of the particle size distribution along the flame axis. The mass spectrometric results point to a strong evolution of the molecular composition. Just-nucleated soot is rich in polycyclic aromatic hydrocarbons (PAHs) dominated by medium sizes from 18 to 40 carbon atoms but containing sizes as large as 90 carbon atoms. Most abundant PAHs are in the form of peri-condensed structures. The presence of a large fraction of odd numbered carbon species shows that pentagonal cycles are a common feature of the detected population. Increasing the distance from the burner outlet, i.e., the particle residence time in flame, leads to an evolution of the chemical composition of this population with a major contribution of carbon clusters including also fullerenes up to about 160 carbon atoms. Our data support a scenario in which large PAHs containing pentagonal rings evolve very efficiently upon thermal processing by a series of dehydrogenation and isomerization processes to form fullerenes. This chemistry happens in the early steps of soot growth showing that carbonization is already active at this stage. © 2020 The Authors. Published by Elsevier Inc. on behalf of The Combustion Institute. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)

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.

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.

International audience; In Heritage Science, the evaluation of stone consolidation treatments by investigating the nature of in situ newly formed products and their penetration depth within the consolidated matrix is a grand challenge. A number of analytical methods have been proposed, but, currently, most of them are not able to supply a full overview of the spatial, structural and compositional information of the newly formed crystalline and amorphous phases with a submicrometric lateral resolution. Here, we examined, the capabilities of synchrotron radiation (SR)-based two-dimensional X-ray absorption near-edge structure (2D-XANES) spectroscopy at Ca K-edge for determining the structural and compositional properties of the compounds formed after the application of a calcium acetoacetate-based consolidant on a porous carbonatic stone (limestone) and for investigating their stratigraphic distribution at the submicrometric scale length. We evaluated advantages and drawbacks of three Ca K-edge 2D-XANES-based approaches: (i) transmission mode full-field-XANES (FF-XANES) imaging; (ii) micro-X-ray fluorescence (μ-XRF) mapping above the Ca K-edge combined with the acquisition of XRF mode μ-XANES spectra at a limited number of spots; (iii) full-spectral µ-XANES (FS µ-XANES) mapping in XRF mode and its variant called selectively induced X-ray emission spectroscopy (SIXES) mapping. Overall, Ca K-edge 2D-XANES spectroscopy provided accurate qualitative and semi-quantitative information on the newly formed calcium carbonates (i.e., amorphous calcium carbonate, vaterite and calcite) and their stratigraphic distribution at the submicrometric scale, thus opening a new scenario to study the carbonatation process of calcium-based consolidants in limestones. Stone consolidation is a major challenge for protection of buildings and stone artefacts from weathering and decay, which usually lead to decohesion of the structural elements of the material. Over the last decades, thanks to the progress in material science and nanotechnology, a wide range of novel materials has been developed, with the aim of re-establishing adhesion, cohesion and stability of the damaged stone as well as to improve efficacy and durability of the treatment 1,2. The effectiveness of a consolidation treatment depends on different aspects, including penetration depth, reaction kinetics and mechanism of formation of the final products, and physical chemical properties of the consolidant phase in the stone matrix. In consideration of that, tailored analytical tools and methodologies have been developed to characterize newly synthesized consolidation products and to understand the chemistry behind their performances. Although open

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).

This paper presents advances in the realization of a head phantom dedicated to the test of a microwave imaging system in order to assess its performances in a realistic laboratory controlled configuration before a possible clinical application to brain stroke monitoring. The phantom is based upon a rigid 3D-printed structure that delineates several cavities which can be filled up with different biological tissue mimicking liquid mixtures. The phantom structure and the composition of the tissue mimicking mixtures are detailed and, then, some effects of the differences in dielectric properties between the phantom and a real head on the electric field distribution within the phantom are analyzed through numerical simulations.

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.

International audience; The influence of the main process parameters on the oscillatory behavior of methane oxidation was analyzed in conditions relevant for low-temperature combustion processes. The investigation was performed by means of direct comparisons between experimental measurements realized in two jet-stirred flow reactors used at atmospheric pressure. With the operating conditions of the two systems coupled, wide ranges of the inlet temperature (790–1225 K), equivalence ratio (0.5 < Φ < 1.5), methane mole fraction (XCH4 from 0.01 to 0.05), bath gases (i.e., He, N2, CO2, or H2O) and different overall mixture dilution levels were exploited in relation to the identification of oscillatory regimes. Although the reference systems mainly differ in thermal conditions (i.e., heat exchange to the surroundings), temperature measurements suggested that the oscillatory phenomena occurred when the system working temperature accessed a well-identifiable temperature range. Experimental results were simulated by means of a detailed kinetic scheme and commercial codes developed for complex chemistry processes. Simulations were also extended considering systems with different heat losses to the surroundings, thus passing from adiabatic to isothermal systems. Results highlighted the kinetic nature of the dynamic behavior. Because predictions were consistent with experimental tests, further numerical analyses were realized to identify the kinetics responsible for the establishment of oscillatory phenomena. Temperature oscillations were predicted for a significant reactor working temperature range, where oxidation and recombination kinetic routes, involving carbon C1–2 species as well as reactions of the H2/O2 sub-scheme, become competitive, thus boosting limit cycle behaviors. Oscillatory phenomena cease when the system working temperatures exceed characteristic threshold values with the promotion of faster oxidation routes that diminish the inhibiting effects of recombination reactions.

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.

The newly developed hybridization approach for thermoplastic composites, based on the gradation of the interlaminar interface strength (IGIS design), was used to prepare polypropylene/glass fibre composites by properly alternating layers of reinforcing fabric with compatibilized and not compatibilized polymeric films. Maleated polypropylene was used to improve the matrix/fibre interface strength. The flexural and low-velocity impact characterizations showed that the use of the coupling agent improved the quasi-static flexural properties through the strengthening of the matrix/fibre interface, but considerably lowered the low velocity impact resistance of the laminate. The use of the IGIS design, which grades the interface strength through the laminate thickness, enabled the fabrication of composites with a favourable combination of flexural properties and impact resistance and proved to be effective in better preserving the integrity of the fibres. The damage after impact has been assessed by means of micro computed tomography, which elucidated the improving effect of the matrix hybridization on the impact resistance, and acoustic emission analysis, which allowed the identification of the mechanisms responsible for impact energy absorption. The role played by the matrix hybridization sequence was pointed out along with the effective role of IGIS design in the overall mechanical performance of laminates. (C) 2017 Elsevier Ltd. All rights reserved.

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.

International audience

Simultaneous small-angle and wide-angle X-ray scattering (SAXS and WAXS) were used to measure several properties of the nanoparticles and soot being produced and undergoing condensation and phase changes below a stabilizing cooling plate inserted in an ethylene diffusion flame. From the SAXS data several distinct size modes appeared showing interdependent changes in the size, shape/morphology, and concentrations over the time of the experiment. The WAXS data contained information on the internal atomic-level structure of the nanoparticles and soot. They also provided important information on the onset and evolution of the condensation of particles onto the plate and the graphitization process. The concentrations of particles were determined quantitatively from the SAXS data. A very important result was the strong increase for sizes smaller than 100 angstrom, which increased drastically to very high values with number concentrations orders of magnitude higher than normally reported from flames. The results and methods applied are of interest for future studies of dynamics related to condensation and material synthesis of carbon- and non-carbon based nanoparticles in the gas phase and during deposition on surfaces. (C) 2012 Elsevier Ltd. All rights reserved. (Less)

International audience; Small-angle X-ray scattering (SAXS) has been used to examine the growth of soot primary particles (15-20 nm) and aggregates of primaries (>30 nm) formed in an ethylene flame doped with ferrocene. It is found that, early in the flame, the size of the primary particles formed when ferrocene is added tracks that for an undoped flame. Higher up (at height z above the burner greater than 18 mm), both primary and aggregate sizes are significantly smaller with ferrocene doping compared to the undoped flame. Within experimental error, the number densities of primary (N1) particles in the ferrocene flame are about the same as for the pure ethylene flame at low heights and higher (factor of 10) at larger heights (above 18 mm). On the other hand, the number concentration of aggregate particles (N2) in the doped flame is always greater than in the pure ethylene flame regardless of the height but with drops and increases in the ferrocene-doped flame case that can be correlated with corresponding increases and decreases in aggregate size. SAXS data at sufficiently long residence times in the flame show, through the value of the Porod exponent, that the particle surfaces of primaries and aggregates are much rougher in the doped versus undoped flame, which we interpret as being the effect of iron oxide inclusion that produces enhanced oxidation inside the soot material.

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.

International audience; Small Angle X-ray Scattering (SAXS) measurements have been performed on a partially pre-mixed ethylene-air flame with and without the introduction of a water aerosol for the same flame height. Our measurements are sensitive to particles with radii in the range of 6-78 nm. It is found that water addition leads to soot suppression below the detection limit at low heights along the flame centerline (

International audience; The size distribution of soot nanoparticles in an ethylene flame has been mapped in an in situ small angle x-ray scattering measurement at the European Synchrotron Radiation Facility. It has been seen that an abrupt size distribution change occurs at about a third of the flame's visible height and this is believed to be due to the oxidation and dehydrogenation of the particles.