CO Emission and Combustion Dynamics Near Lean-Blowout in Gas Turbine Engines

Abstract

Lean-Blowout (LBO) is a phenomenon that occurs in both land-based premixed and propulsion liquid-fuelled gas turbine engines when the effective equivalence ratio is reduced close to the lean flammability limit. Small perturbations in the flame or flow can result in local quenching that can subsequently lead to total extinction (LBO). Prediction of pollutant emission (e.g., CO) and combustion dynamics near LBO is very complicated since physics at many interacting scales have to be resolved. Here, LES studies of both premixed and liquid-fuelled gas turbine engines are reported using a subgrid linear-eddy mixing (LEM) model. In the premixed study, comparison is made with a thin-flame model and it is shown that the flame length can be changed by adjusting the parameters in this model, whereas the flame length is actually predicted in the LEMLES approach. Results of spray combustion in a full-scale liquid-fuelled gas turbine are also discussed for startup and full power operations. It is shown that the LEMLES is able to anchor the flame at the proper location without requiring any model adjustment.