TY - JOUR
T1 - On the flame structure and stabilization characteristics of autoignited laminar lifted n-heptane jet flames in heated coflow air
AU - Jung, Ki Sung
AU - Kim, Seung Ook
AU - Chung, Suk Ho
AU - Yoo, Chun Sang
N1 - KAUST Repository Item: Exported on 2020-10-29
Acknowledgements: This work was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT (NRF-2018R1A2A2A05018901). SHC was supported by KAUST. This research used the resources of the KAUST Supercomputing Laboratory and UNIST Supercomputing Center.
PY - 2020/10/19
Y1 - 2020/10/19
N2 - The characteristics of the flame structure and stabilization of autoignited laminar lifted n-heptane jet flames in heated coflow air are investigated by performing 2-D numerical simulations with a 68-species skeletal chemical mechanism of n-heptane oxidation. The present simulations can reproduce a distinct transition of a lifted jet flame from a tribrachial edge flame mode to a moderate or intense low-oxygen dilution (MILD) combustion mode observed from a previous experimental study, featuring a significant variation in the liftoff height with the fuel jet velocity, U0. It is found that a lifted flame with the MILD combustion mode can exist further downstream of the stoichiometric mixture fraction isoline due to autoignition occurring upstream of the flamebase. The displacement speed and chemical explosive mode analyses reveal that the autoignition of lean mixtures plays a critical role in stabilizing lifted flames with the MILD combustion mode. It is further elucidated from additional numerical simulations that an autoignited laminar lifted n-heptane jet flames can be stabilized as one of the following forms depending on the inlet temperature, T0, and U0: a MILD combustion, a partially-premixed edge flame, a tribrachial edge flame, and a tetrabrachial edge flame. Based on the flame structures and stabilization mechanisms of the lifted flames, a flame regime diagram is constructed in the normalized U0 and Damköhler number space.
AB - The characteristics of the flame structure and stabilization of autoignited laminar lifted n-heptane jet flames in heated coflow air are investigated by performing 2-D numerical simulations with a 68-species skeletal chemical mechanism of n-heptane oxidation. The present simulations can reproduce a distinct transition of a lifted jet flame from a tribrachial edge flame mode to a moderate or intense low-oxygen dilution (MILD) combustion mode observed from a previous experimental study, featuring a significant variation in the liftoff height with the fuel jet velocity, U0. It is found that a lifted flame with the MILD combustion mode can exist further downstream of the stoichiometric mixture fraction isoline due to autoignition occurring upstream of the flamebase. The displacement speed and chemical explosive mode analyses reveal that the autoignition of lean mixtures plays a critical role in stabilizing lifted flames with the MILD combustion mode. It is further elucidated from additional numerical simulations that an autoignited laminar lifted n-heptane jet flames can be stabilized as one of the following forms depending on the inlet temperature, T0, and U0: a MILD combustion, a partially-premixed edge flame, a tribrachial edge flame, and a tetrabrachial edge flame. Based on the flame structures and stabilization mechanisms of the lifted flames, a flame regime diagram is constructed in the normalized U0 and Damköhler number space.
UR - http://hdl.handle.net/10754/665683
UR - https://linkinghub.elsevier.com/retrieve/pii/S0010218020304284
UR - http://www.scopus.com/inward/record.url?scp=85092933593&partnerID=8YFLogxK
U2 - 10.1016/j.combustflame.2020.10.008
DO - 10.1016/j.combustflame.2020.10.008
M3 - Article
SN - 1556-2921
VL - 223
SP - 307
EP - 319
JO - Combustion and Flame
JF - Combustion and Flame
ER -