CO2 diluted propane/oxygen combustion in a rapidly mixed tubular flame burner

Abstract

Propane/oxygen combustion diluted by CO2 was attempted in a rapidly mixed tubular flame burner to eliminate hazards of flame flash back. The flame structure and stability were systematically examined with oxygen mole fraction varying from ultralow to ultrahigh in the oxidizer. To enhance mixing, a tubular flame burner with a thin inlet was utilized, and in addition, CO2 was added also to the fuel slit as well as the oxidizer slit. The results show that a steady and uniform tubular flame can be obtained from lean to rich when the oxygen mole fraction was no more than 0.50, in which the tubular flame was established at ultralow oxygen mole fraction of 0.18, and the steady flame range in equivalence ratio gradually expanded with increasing oxygen mole fraction. By increasing oxygen mole fraction to 0.60, the tubular flame became non-uniform in structure; above 0.70, the tubular flame at the stoichiometry was not obtained. To obtain stoichiometric combustion at a higher oxygen mole fraction, the width of fuel slit was halved while that of the oxidizer slit was doubled to make the width ratio approach the stoichiometry of propane/oxygen (1/5). However, a tubular flame failed to be established above the oxygen mole fraction of 0.70 owing to flame anchoring at the exit of oxidizer slit. To increase both the fuel and oxidizer injection velocities, the width of oxidizer slit was also reduced, and steady tubular combustion at the stoichiometry was achieved up to oxygen mole fraction of 0.80. In the case of stoichiometric propane/oxygen combustion, a flame was anchored at each exit of slit, resulting in turbulent combustion. For combustion under ultrahigh oxygen mole fractions, a tubular flame was established at the very lean condition, and evolved into turbulent combustion through an oscillation region with increasing the equivalence ratio.