Influence of turbulence on the dynamic behaviour of premixed flames

Abstract

Environmental compatibility requires low emission burners for gas turbine power plants as well as for jet engines. In the past significant progress has been made developing low NOx and CO burners by introducing lean premixed techniques. Unfortunately these burners often have a more pronounced tendency than conventional burner designs to produce combustion driven oscillations. The oscillations may be excited to such an extent that strong pulsation may possibly occur; this is associated with a risk of engine failure and higher NOx emissions. In order to describe the acoustical behaviour of the complete burner system the determination of the transfer function of the flame itself is crucial. Using a new method which was presented by Bohn, Deutsch and Krüger (1996) and Bohn, Li, Krüger and Matouschek (1997), the dynamic flame behaviour can be predicted by means of a full Navier-Stokes-simulation of the complex combustion process for the steady-state as well as for the transient situation. This method has been successfully used by the authors to obtain the frequency response of turbulent diffusion flames and laminar premixed flames. For the application in modem gas turbines the influence of turbulence on the dynamic behaviour of premixed flames is of big interest. Therefore, this paper presents numerical studies of a turbulent premixed flame configuration for which experimental data is available in the literature. Two different combustion models have been used for the steady-state as well as for the transient calculations. With the improved model, which takes into account the chemical kinetics and the interaction between turbulence and kinetics, good agreement has been found for the steady-state results and for the frequency response of the flame.