Numerical investigation of non-premixed and premixed rotational tubular flame: a study of flame structure and instability

Tubular flames are considered due to their advantages in the geometry of the flame. The major importance of tubular flame which makes it different from other flames is its uniform temperature distribution. Therefore, it reduces the possibility of the formation of thermal fluctuations and hot spots along the furnaces. In this paper, high-speed, non-premixed and premixed tubular flames are numerically investigated using computational fluid dynamics under various operational conditions. Methane/air and CO2-diluted methane/oxygen combustions are considered in both non-premixed and premixed modes. k-omega SST model, eddy dissipation concept combustion model, and P1 radiation model have been used as numerical models. Numerical results are validated against available experimental measurements in the non-premixed tubular flame using DRM22 kinetic mechanism for methane/air combustions and GRI-Mech 3.0 for methane/oxygen mixtures. The structure of the tubular flame in the combustion chamber and stability limits of tubular flame in terms of operating conditions have been studied in the present paper. Results show that premixed tubular flames establish more uniform radial temperature distribution and wider stable flame operating conditions. In addition, diluted methane/oxygen tubular flames have been shown broader stable condition limits than methane/air flames.