Synergistic combustion of droplets of ethanol, diesel and biodiesel mixtures

Freely-falling droplets of ethanol, diesel, (castor oil) biodiesel, and their mixtures were experimentally examined in a high-temperature combustion chamber. The combustion characteristics including the burning rate, microexplosion, and sooting propensity are reported. Results show that adding biodiesel to diesel significantly reduces the extent of soot formation and slightly reduces the burning rate. In addition, higher soot production of methyl stearate than castor oil biodiesel is observed suggesting strong oxidation propensity of the OH function group in castor oil biodiesel. Furthermore, by adding ethanol to diesel and biodiesel, microexplosion is observed, with the biodiesel/ethanol mixtures exhibiting stronger propensity, leading to significantly reduced gasification time and extent of soot formation. The burning of these mixtures occurs in a three-staged, liquid-phase diffusion-limited manner previously observed for distinct bi-component droplets with highly disparate volatilities.