Experimental Studies on Burning Characteristics of Methanol, Diesel, and Sunflower Biodiesel Fuels

The combustion of liquid fuel droplets provides fundamental information that is relevant to spray combustion. A porous sphere setup has been used to investigate non-premixed combustion experimentally with three different liquid fuels, viz. methanol, diesel, and biodiesel (sunflower oil methyl ester). Experiments have been performed at atmospheric pressure with spheres of different diameters and over a range of free stream air velocities, resulting in different types of flames from envelope flame to wake flame. The measured mass burning rates are compared with the predictions from a theoretical model developed for envelope flames considering mixed convective transport. The model predictions are first validated for methanol and subsequently the model is applied for the other two fuels to evaluate their transfer numbers from the experimental mass burning rate data. A power law variation of nondimensional mass burning rate with effective Reynolds number (with contributions of forced and natural convection) is proposed for each of the fuels irrespective of sphere size and air velocity. The transition air velocities (from envelope to wake flames) for different fuels and the change in mass burning rate on transition are measured.