A numerical study on the flame structure and stability of non-premixed methane-air and methane-oxygen turbulent tubular flame

Recently, tubular flames are considered due to their advantageous in geometry of the flame. The major importance of tubular flame is its uniform temperature distribution. Therefore, it may reduce thermal fluctuations along the combustion chamber. In this paper, a non-premixed tubular flame is simulated numerically under various operational conditions. A solver is developed in openFOAM and numerical results are validated against the experimental measurements. Also, temperature distribution and concentration of major species of the flame in the middle of the burner are investigated and compared using global and DRM22 as chemical kinetics. In addition, stability of the flame in air presence as oxidizer has been studied. Results show that by increasing oxygen mole fraction in oxidizer, the equivalence ratio of the steady tubular flame region decreases and the flame will be established uniformly in equivalence ratio near the extinction limit. If pure oxygen is used as oxidizer, flame temperature will be increase strongly and tubular flame can be stable for equivalence ratio between 0.1 and 0.2. Thereupon carbon dioxide from the flue gases is added to the oxidizer to control the flame temperature changes. Establishment of steady tubular flame in presence of carbon dioxide is simulated too. Results show that by decreasing oxygen mole fraction, the equivalence ratio of the steady tubular flame region increases and the stability zone becomes wider