On the flame structure and stabilization characteristics of autoignited laminar lifted n-heptane jet flames in heated coflow air
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- On the flame structure and stabilization characteristics of autoignited laminar lifted n-heptane jet flames in heated coflow air
- Jung, Ki Sung; Kim, Seung Ook; Chung, Suk Ho; Yoo, Chun Sang
- Issue Date
- Elsevier BV
- COMBUSTION AND FLAME, v.223, pp.307 - 3019
- 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 liftoffheight with the fuel jet velocity, U 0 . It is found that a lifted flame with the MILD combustion mode can exist further downstream of the stoichiometric mixture fraction isoline due to au- toignition 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 au- toignited laminar lifted n -heptane jet flames can be stabilized as one of the following forms depending on the inlet temperature, T 0 , and U 0 : 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 U 0 and Damköhler number space.
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