Simulations and experiments on the ignition probability in turbulent premixed bluff-body flames
Combustion Theory and Modelling
Taylor & Francis
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Sitte, M., Bach, E., Kariuki, J., Bauer, H. o., & Mastorakos, E. (2016). Simulations and experiments on the ignition probability in turbulent premixed bluff-body flames. Combustion Theory and Modelling, 20 548-565. https://doi.org/10.1080/13647830.2016.1155756
The ignition characteristics of a premixed bluff-body burner under lean conditions were investigated experimentally and numerically with a physical model focusing on ignition probability. Visualisation of the flame with a 5 kHz OH* chemiluminescence camera confirmed that successful ignitions were those associated with the movement of the kernel upstream, consistent with previous work in non-premixed systems. Performing many separate ignition trials at the same spark position and flow conditions resulted in a quantification of the ignition probability P_ign, which was found to decrease with increasing distance downstream of the bluff body and a decrease in equivalence ratio. Flows corresponding to flames close to the blow-off limit could not be ignited, although such flames were stable if reached from a richer already ignited condition. A detailed comparison with the local Karlovitz number and the mean velocity showed that regions of high P_ign are associated with low Ka and negative bulk velocity (i.e. towards the bluff body), although a direct correlation was not possible. A modelling effort that takes convection and localised flame quenching into account by tracking stochastic virtual flame particles, previously validated for non-premixed and spray ignition, was used to estimate the ignition probability. The applicability of this approach to premixed flows was first evaluated by investigating the model’s flame propagation mechanism in a uniform turbulence field, which showed that the model reproduces the bending behaviour of the S_T -versus-u' curve. Then ignition simulations of the bluff-body burner were carried out. The ignition probability map was computed and it was found that the model reproduces all main trends found in the experimental study.
spark ignition, ignition probability, turbulent premixed flames, ignition modelling, bluff-body stabilised flames
M.P. Sitte gratefully acknowledges financial support from the Gates Cambridge Trust. The experiments were carried out by E. Bach who was a Masters student from Karlsruhe Institute of Technology visiting the University of Cambridge in 2011.
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External DOI: https://doi.org/10.1080/13647830.2016.1155756
This record's URL: https://www.repository.cam.ac.uk/handle/1810/254000