Etude de la micro-explosion de biocarburants émulsionnés sous différents schémas de chauffage radiatifs

National audienceLa micro-explosion, où seconde atomisation, se produit au sein d’une goutte d’émulsion d’eau dans l’huile, lorsque la phase dispersée atteint la température de saturation. S’en suit alors un changement d’état soudain de la phase aqueuse au sein de la couche huileuse environnante, toujours à l’état liquide, résultant en une fragmentation de cette dernière en un nuage de fines gouttes appelées « gouttes filles ». Ce phénomène, appelé micro-explosion, permet d’obtenir une combustion de meilleure qualité de part une surface totale de combustible en contact avec l’air plus grande dans le cas d’un nuage de fines gouttes par rapport à celui d’une goutte simple.Il a été observé expérimentalement, que le comportement des gouttes d’eau dispersées durant le chauffage précédent la micro-explosion avait un impact significatif sur la qualité de celle-ci. En effet, lorsque sujettes à des mouvements de convection interne (de par l’hétérogénéité du champ de température au sein de l’émulsion), les gouttes d’eau ont tendance à se regrouper en partie basse de la goutte d’émulsion, puis à fusionner (phénomène de coalescence), en des gouttes de taille plus grande. Ce phénomène est accentué par la perte du pouvoir stabilisant du surfactant avec la température. Cette coalescence de petites gouttes en des gouttes de tailles plus grandes semble permettre d’obtenir une micro-explosion plus forte, de par l’énergie plus grande libérée lors du changement de phase.L’étude présentée se propose de mesurer l’influence du chauffage radiatif sur le phénomène de micro-explosion, ainsi que l’importance de la convection interne au sein de la goutte d’émulsion pouvant résulter en la coalescence de la phase dispersée. Pour se faire, la goutte d’émulsion est chauffée à l’aide de deux panneaux radiatifs dont la température de surface est contrôlée et peut-être variée entre 300 et 700°C. L’expérience est filmée à l’aide d’une caméra rapide permettant d’étudier le comportement de l’émulsion durant sa phase de montée en température ainsi que les mouvements des gouttelettes d’eau. L’influence de la distance des panneaux à la goutte ainsi que de la puissance de chauffe est étudiée (délai avant la micro-explosion, puissance radiative reçue…). Différents positionnements des panneaux sont utilisés, afin d’accentuer où de bloquer les mouvements de convection naturelle, et ainsi de mesurer la prépondérance (ou non) de la coalescence de la phase dispersée sur la micro-explosion. Cette étude a pour but de mieux comprendre le comportement des systèmes diphasiques que représentent les émulsions afin d’optimiser les différents paramètres permettant de maximiser la probabilité d’occurrence de la micro-explosion et sa qualité

Optical diagnostics for W/O emulsification within impinging flow and right angle mini-channel

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-channe

Experimental study of the water in oil emulsions features by differential scanning calorimetry analysis

International audienc

Study of two impinging flow microsystems arranged in series. Application to emulsified biofuel production

International audienceDevelopment 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

Performance and Emissions of a Spark Ignition Engine Fueled with Water-in-Gasoline Emulsion Produced through Micro-Channels Emulsification

International audienceThis paper presents an experimental study investigating the effects of water-in-gasoline emulsion (WiGE) on the performance and emissions of a turbocharged PFI spark-ignition engine. The emulsions were produced through a micro-channels emulsifier, potentially capable to work inline, without addition of surfactants. Measurements were performed at a 3000 rpm speed and net Indicated Mean Effective Pressure (IMEP) of 16 bar: the engine point representative of commercial ECU map was chosen as reference. In this condition, the engine, fueled with gasoline, runs overfueled (λ = 0.9) to preserve the integrity of the turbocharger from excessive temperature, and the spark timing corresponds to the knock limit. Starting from the reference point, two different water contents in emulsion were tested, 10% and 20% by volume, respectively. For each selected emulsion, at λ = 0.9, the spark timing was advanced from the reference point value to the new knock limit, controlling the IMEP at a constant level. Further, the cooling effect of water evaporation in WiGE allowed it to work at stoichiometric condition, with evident benefits on the fuel economy. Main outcomes highlight fuel consumption improvements of about 7% under stoichiometric mixture and optimized spark timing, while avoiding an excessive increase in turbine thermal stress. Emulsions induce a slight worsening in the HC emissions, arising from the relative impact on combustion development. On the other hand, at stoichiometric condition, HC and CO emissions drop with a corresponding increase in NO

Photobioreactor cultivation and catalytic pyrolysis of the microalga Desmodesmus communis (Chlorophyceae) for hydrocarbons production by HZSM-5 zeolite cracking

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