Large Eddy Simulation of Swirling Reacting Flows

Licentiate thesis, 2008

The combustion of fossil fuels remains a key technology as these fuels are the main source of energy in the foreseeable future. Heat released in combustion is often accompanied by emission of undesired soot, CO and NOx pollutants. Environmental concerns have led to stringent emission rules for combustion industry specially for reducing the amount of NOx emissions. This ever increasing demand for clean combustion has led to high interests in lean premixed combustion in recent years as an approach toward reduced NOx emissions by reducing the operating temperature. However, lean blow off limit and the tendency of the dynamic flame to become unstable present technical challenges. Low swirl burner is a rather new and promising design to stabilize lean premixed flames close to their flammability limit. Low swirl burner prototypes have been built at different sizes but the underlying physical processes which govern the operating conditions are not yet well understood. This thesis aims to employ and develop the existing numerical tools to simulate the flow in an experimental low swirl burner. A computational domain including the major components of the burner is adapted to the geometry and Large eddy simulation along with a novel flame capturing combustion model are used to solve the governing equations. The results are then validated against the available experimental data. The inflow boundary condition is investigated and an inlet profile is found which gives the correct boundary conditions. The exact stabilization mechanism of the flame in these burners is not yet understood and is discussed within the scope of the thesis.