Flame stability limits of low swirl burner − Effect of fuel composition and burner geometry

The stability of turbulent non-premixed biogas flame was studied experimentally by varying the fuel composition (i.e., changing the carbon dioxide content in the fuel, which is mainly composed of CH4 and CO2) and altering the fuel nozzle geometry. The fuel was discharged through a central nozzle surrounded by a co-axial airflow passing through a low-swirl (25°-angle vanes) generator. The results revealed that the biogas flame stability limits are highly sensitive to fuel composition in that a small increase in carbon dioxide content can lead to a significant shrinkage in the flame stability operating conditions. On the other hand, the results showed that the fuel jet momentum (fuel nozzle geometry) plays a key role in reducing the dependency of the stability of swirling non-premixed flame on fuel composition. The experimental data with varying both the fuel composition and fuel nozzle geometry was used to develop semi-empirical non-dimensional correlations capable of describing both the lower and upper flame stability limits of both biogas and methane fuel. The validity of these correlations was extended to include both non-premixed and premixed swirling flames.