ABSTRACT
The aim of this study is to find a reduced mechanism that accurately represents chemical kinetics for lean hydrogen combustion at elevated pressures as present in a typical gas turbine combustor. Calculations of auto-ignition, extinction, and laminar premixed flames are used to identify the most relevant species and reactions, and to compare the results of several reduced mechanisms with those of a detailed reaction mechanism. The investigations show that the species OH and H are generally the radicals with the highest concentrations, followed by the O radical. However, the accumulation of the radical pool in auto-ignition is dominated by HO₂ for temperatures above and by H2O2 below the crossover temperature. The influence of H2O2 reactions is negligible for laminar flames and extinction, but becomes significant for auto-ignition. At least a11 elementary reactions are necessary for a satisfactory prediction of the processes of ignition, extinction, and laminar flame propagation under gas turbine conditions. A 4-step reduced mechanism using steady-state approximations for HO2 and H2O2 yields good results for laminar flame speed and extinction limits, but fails to predict ignition delay at low temperatures. A further reduction to three steps using a steady-state approximation for O leads to significant errors in the prediction of the laminar flame speed and extinction limit.