Blowoff characteristics of partially premixed flames of prevaporized blends of biofuels and petroleum fuels

Abstract

The laminar partially premixed flames of prevaporized Jet A, canola methyl ester (CME), palm methyl ester (PME), soy methyl ester (SME), and blend flames of Jet A and CME-PME-SME were studied over a range of equivalence ratios of 0.53-0.83 with and without heated coflow. Coflow velocity ranged up to 3.5 m/s. Measurements of blowoff velocities, flame temperature profiles, and flame dimensions were made. The injector was designed to produce a uniform inner flow and had an inner diameter of 12.7 mm. The flames were laminar and blue in color (dominated by homogeneous gas-phase reactions). The temperature profiles in all the flames were similar, with a peak temperature of 1740 K. Inner cone height and outer cone height both increased with equivalence ratio. Lifted flames were obtained at coflow velocity of 3.5 m/s; the liftoff height stayed approximately constant regardless of equivalence ratio. The blowoff velocity increased with equivalence ratio for all the flames; the difference in blowoff velocity of pure biodiesel flames and pure Jet A flames was within experimental uncertainty. The blowoff velocity of the blend flames ranged around the values for the pure fuel flames. A Damköhler number (based on the velocity gradient at the jet boundary and chemical reaction time scale estimated from laminar flame velocity) of 2-8 characterized the blowoff velocity. As the coflow velocity was increased, the blowoff velocity was increased and the differences between the values for the various flames became smaller.