Experimental study on laminar lifted flames of pre-vaporized palm oil biodiesel

Abstract

Characteristics of laminar lifted flame of pre-vaporized palm oil biodiesel have been experimentally investigated by varying fuel mole fraction at elevated unburnt gas temperatures. The biodiesel fuel was pre-vaporized and mixed with pre-heated nitrogen at a range of fuel mole fractions of 0.01 – 0.02. The unburnt gas temperature was varied from 500 K to 650 K. The results showed that the increase in jet flow velocity influenced the liftoff of the laminar non-premixed flame. Furthermore, the higher fuel mole fractions and the elevated unburnt gas temperatures led to a reduction in the liftoff height of the flame. Hence, a limited range of conditions, where the lifted flame occurred was determined for a given unburnt gas temperature and fuel mole fraction. At some of the experimental conditions such as 500 K and 550 K, the flames still experienced liftoff even at smaller jet velocities compared to stoichiometric laminar burning velocity of the same mixture. This behavior was believed to associate with the buoyant force produced at the nozzle of the rim, causing secondary entrainment of the mixture flow at relatively low jet flow velocities. The results suggested a correlation between the liftoff height and jet flow velocity, with the inclusion of the stoichiometric laminar burning velocity, regardless of the unburnt gas temperature and fuel mole fraction in the mixture. The adaptation of the buoyancy-induced velocity to the liftoff velocity correlated well with the stoichiometric laminar burning velocity, showing the significance of the buoyant force near the nozzle exit.