On Predictions of Fuel Effects on Lean Blow Off Limits in a Realistic Gas Turbine Combustor Using Finite Rate Chemistry

Abstract

The demand for aviation propulsion systems with ever higher power requirements, reliability, and reduced emissions has been steadily increasing. Desirable features for next generation high-efficiency gas turbine engines include improvements in combustion efficiency, fuel economy, and stable operation in the fuel lean limit. Despite recent advances, a significant issue facing gas turbine designers is sustaining flame stability during lean operation, which could otherwise lead to global extinction events, or lean blow out (LBO), resulting in a severe loss of operability, particularly at higher altitudes. Flame stabilization is a complex physical and chemical process which is determined by the competing effects of the rates of chemical reactions and rate of turbulence advection-diffusion of species and energy to and from the flame leading to a local ignition and extinction phenomena. The goal of the present study is to perform a high fidelity numerical investigation of the turbulent diffusion flame in a realistic turbine combustor to evaluate the potential to predict the local lean-blow-off dynamics and to gain more insights of the complex physics. A comparative study on LBO characteristics is performed using Finite Rate Chemistry, Large Eddy Simulation and Adaptive Mesh Refinement, for different fuels using a realistic gas turbine combustor. The fuels investigated include a petroleum based fuel and an alternative fuel candidate. The simulation was broken down in two phases: flame stabilization and a subsequent staged ramp-down of fuel flow rate to initiate LBO. It is shown that the simulations successfully predict LBO occurring at different equivalence ratios for the two fuels. Although, the simulations predict LBO occurring at slightly smaller equivalence (fuel-to-air) ratio than the experimental data, the difference between the equivalence ratios of the two fuels at LBO is very close to the experimental observation.