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

• Water-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.

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.