Investigation on the conditions leading to the micro-explosion of emulsified fuel droplet using two colors LIF method

Biofuels in the form of water-in-oil (W/O) emulsions are a promising substitution for hydrocarbon fuels, mainlythanks to the micro-explosion phenomenon that occurs under strong heating. Micro-explosion is the atomization of aW/O emulsion drop into daughter droplets because of the water embedded droplets phase change. This atomizationleads to the reduction of pollutants and unburnt hydrocarbons emissions. However, micro-explosion is not a systematicphenomenon: 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. Itconsists 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. Twocolors laser induced fluorescence (LIF2C) is the main method used in this work for temperatures. These temperaturemeasurements showed promising results of both quantitative and qualitative aspects. After the calibration steps andthe method validation, it is applied for the temperature measurements of water droplets embedded in oil with themaximum temperature recorded around 130 °C. Using these measurements methods, a correlation is found betweenquality of atomization (either micro-explosion or puffing) and the properties of the trigger drop (temperature, sizeand position). When one of these parameters is not optimal, it can indeed be compensated by the others.