Auto-ignition and heat release in a gas turbine burner at elevated temeperature

This paper reports on the validation of an advanced model for ignition and heat release of natural gas at elevated pressures and temperatures. The model comprises two sub-models: one for the auto-ignition process and the other to consider heat release. To describe the ignition process efficiently the model uses an intermediate species to represent the evolution of the radical pool. Once the radical pool has reached a critical concentration, the subsequent heat release process starts. Rates for both processes are determined by use of detailed chemistry; hence the model can also take into account effects of higher hydro-carbons without use of a tuning parameter. Turbulence-chemistry interactions are considered with a new Monte-Carlo formulation for the joint probability distribution. This approach is based on the description of the mixture statistics via particle ensembles and not via a function as traditional presumed PDF (Probability Density Function) methods do. The particle ensembles are generated for given means and (co-) variances of mixture fractions in a pre-processing step. To get information about the statistics in the CFD (Computed Fluid Dynamics) simulation, transport equations for means and variances are solved. Since the computation of turbulent mean reaction and heat release rates is performed in a pre-processing step, this approach is very efficient. Experimental results from a full-size burner of an industrial reheat gas turbine at atmospheric pressure was used as data for the model validation. It was found that this approach made possible the calculation of important physical characteristics, e.g. flame position and thickness for a wide range of operating conditions and burner geometries, with satisfying accuracy. Finally, it will be demonstrated how this numerical model is complementary to experimental development procedures and can be used as a burner design tool.