Treatment of local extinction in CFD fire modeling A.Yu. Snegirev ⇑ , A.S. Tsoy St.-Petersburg Polytechnic University, St.-Petersburg, Russia Abstract A simplified approach capturing the major flame extinction mechanisms has been formulated and calibrated against the measurement data for critical strain rates of laminar diffusion counter-flow flames with fuel and (or) oxidizer streams diluted by nitrogen. The model is based on the perfectly stirred reactor concept, thereby assuming rapid reactant mixing in the reaction zone, where reactants are delivered at stoichiometric proportions. Model simplicity is achieved by considering the single-step global reaction model. Advancing previous studies, we demonstrate that this model is able to replicate critical strain rates at extinctions of both counter- and co-flow flames in a range of experimental configurations including opposed gaseous streams and evaporating liquid pool with a normally impinging oxidizer stream, in the entire range of gaseous diluent concentration enabling flaming combustion. The model correctly predicts the minimum extinguishing concentrations of different inert diluents (argon, nitrogen, water vapor and carbon dioxide) used in practice of fire suppression. The algorithm is simple and computationally afford- able enough to be incorporated in a CFD fire model. A worked example is demonstrated in simulations of flame suppression by sprinkler sprays at different water flow rates. The proposed algorithm can be used for any practical fuel, as soon as the global kinetic model of fuel oxidation is calibrated using the procedure developed in this work. Ó 2014 The Combustion Institute. Published by Elsevier Inc. All rights reserved. Keywords: Flame extinction; Fire modeling; Perfectly stirred reactor; Global mechanism 1. Introduction Consideration of local extinction in turbulent diffusion flames is crucial for modeling of under- ventilated fires and fire suppression. Although combustion in fires is normally treated as mixing- controlled in fast chemistry limit, extinction is essentially non-equilibrium and kinetically con- trolled phenomenon. To date, several approaches are exploited to model local extinction. Most fre- quently, the critical flame temperature concept [1] is used, and the extinction criterion is formulated for the minimum temperature and oxygen concen- tration required for combustion to proceed [2]. Alternatively, critical concentration of extinguish- ing agent is applied in the extinction model used in Ref. [3], where actual fluctuating concentration is assumed to obey log-normal distribution, and the local burning rate is multiplied by the probabil- ity of exceeding the critical value. None of these approaches consider the effects of strain; the reac- tants are assumed to burn regardless of the local http://dx.doi.org/10.1016/j.proci.2014.07.051 1540-7489/Ó 2014 The Combustion Institute. Published by Elsevier Inc. All rights reserved. ⇑ Corresponding author. Address: Department of Fluid Dynamics (Thermal Physics), St.-Petersburg State Polytechnic University, Polytechnicheskaya, 29, St.-Petersburg 195251, Russia. E-mail address: a.snegirev@phmf.spbstu.ru (A.Yu. Snegirev). Available online at www.sciencedirect.com ScienceDirect Proceedings of the Combustion Institute xxx (2014) xxx–xxx www.elsevier.com/locate/proci Proceedings of the Combustion Institute Please cite this article in press as: A.Y. Snegirev, A.S. Tsoy, Proc. Combust. Inst. (2014), http:// dx.doi.org/10.1016/j.proci.2014.07.051