Nonpremixed swirl-type tubular flames were described recently both experimentally and theoretically. In that new configuration liquid fuel flows inwardly through a porous tube and vaporizes becoming the fuel source for the chemical reaction with the swirling air coming from the bottom inlet of the burner. The permeable walls prevent from optical access to the combustion chamber and only the flame structure produced above the burner rim can be evaluated. Observations of the external flame along with measurements of external combustor wall temperatures provide valuable information on the system stability. However, further evaluation of the tubular flame anchored in the combustion chamber is not possible with the diagnostic tools available. In order to allow flame visualization, and consequently, future studies on the structure of nonpremixed swirl-type tubular flames, a new configuration is proposed and evaluated experimentally. The outer permeable cylinder is replaced by an impermeable translucent tube, and a porous cylinder, from where liquid fuel is injected, is positioned at the axis of the burner. The combustion chamber consists of the annular space between the inner (porous) and the outer (impermeable and translucent) tubes instead of a circular cross section from the original nonpremixed swirl-type tubular flame burner. Experimental results show the feasibility of the proposed configuration as well as how the system stability and the characteristics of external flame compare to the conventional nonpremixed swirl-type tubular flame. The transparent outer wall allows the evaluation of the anchoring mechanisms and the overall structure of the tubular flame produced in the combustion chamber.
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