Numerical Prediction of Flame Lift Off and NO Emissions for Hydrogen Air Flames

Abstract Fossil fuel-based gas turbine engines contribute significantly to carbon dioxide (CO2) emissions, which can adversely impact the environment. Next-generation of gas turbine engine designs attempt to reduce CO2 emissions by improving the overall engine efficiency or via alternative fuels. Hydrogen is one of the promising alternative fuels due to its inherent zero-carbon nature. Due to relatively high reactivity and diffusivity of hydrogen the flame lift-off prediction is critical for hydrogen injector design. Further, hydrogen combustion is prone to comparatively higher nitrogen oxide (NO) emissions and requires a thorough understanding of the mechanism to meet emission regulations. In this study, we perform two distinct numerical simulations, a diluted lifted hydrogen flame (Cabra et al., 2002) and a pure hydrogen flame (Barlow and Carter, 1992). Time-resolved Large Eddy Simulations (LES) using Laminar Finite Rate (LFR) and Flamelet Generated Manifold (FGM) combustion models are discussed. The predicted lift off characteristics using an FGM manifold generated using premixed flamelets show close agreement with the experiment, whereas other models failed to predict. The lifted flame characteristics indicated premixed mode combustion behavior in the lift-off region and diffusion mode combustion behavior in the downstream of the flame lift off region. For the pure hydrogen flame simulation NO concentrations are predicted using both FGM and LFR model. The NO concentration solutions obtained from the LFR combustion model qualitatively agreed with the experimental measurements.