Experimental Evaluation of a Premixed Swirl-Stabilized Gas Burner with a Focus on Mixture Stratification

The present work reports an experimental evaluation of the flame stabilization, structure and pollutant emissions for a swirl-stabilized premixed burner at atmospheric conditions. The burner has been designed to accommodate two inlet streams, namely a swirling air and a non-swirling fuel-air mixture, which are fed into a mixing chamber. By modifying the air mass distribution between the swirling and non-swirling streams, the burner can produce different swirl numbers at the chamber, as well as different fuel-air mixture stratification. A central tube acts as a bluff body to help stabilize the flame. Experimental diagnostics include high speed flame visualization in terms of OH* chemiluminescence, and NOx pollutant at the burner outlet. The study has been carried out using both hydrogen and methane as fuels. A sweep of conditions has been carried out to identify the lean blow-off limit over the burner operational map. Results for methane indicate that the lean blow-off limit is strongly affected by the air distribution between the swirling and non-swirling parts. In contrast, air distribution has a more significant effect on NOx emissions for hydrogen. Different flame shapes are analyzed over the operational map, where strong differences in lift-off, flame width, and reaction zone chemiluminescence have been identified.