Numerical investigation of lean blow-out of kerosene spray flames with detailed chemical models

© 2019 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. Extinction and lean blow-off (LBO) phenomena of different kerosene blends have been modelled with Conditional Moment Closure (CMC), and analysed in both laminar counterflow diffusion and Large Eddy Simulation (LES) bluff-body swirling spray flame contexts, aiming to validate the LES-CMC approach in capturing local extinction in turbulent spray flames as well as to explore different burning behaviours between various types of jet fuels. Two fundamentally different chemical mechanisms have been studied— the first being the Dagaut surrogate mechanism modelling Jet A-1. The second is the lumped pyrolysis Hybrid Chemistry "HyChem" method which models Jet A (dubbed A2 in this study) and alternative fuels C1 and C5, in collaboration with the National Jet Fuels Combustion Program (NJFCP). The surrogate and HyChem mechanisms for Jet A-1 and A2 in counterflow diffusion flame simulations had different productions of formaldehyde (CH2O) and benzene (C6H6), whereas light intermediates and combustion products matched well. As the 0D counterflow diffusion flames approached extinction by increase of imposed scalar dissipation rate, the fuels extinguished in the order, from lowest scalar dissipation rate to highest: C1, A2, Jet A-1, and C5. This ranking agrees with previous counterflow diffusion studies, but experiments have shown that C5 should exhibit blow-off behaviour similar to C1. LES-CMC simulations were made of a stable, low scalar dissipation rate HyChem A2 flame as well as of a stable Dagaut Jet A-1 flame with bulk velocity close to blow-off. LES-CMC was able to capture both local extinction and flame lift-off in the Dagaut flame, indicated by the presence of negligible OH regions along the stoichiometric contour of the flame and separation and withdrawal of the stoichiometric region from the bluff-body edge.