Modeling flame extinction and reignition in large eddy simulations with fast chemistry

Abstract

This work seeks to support the validation of large eddy simulation models used to simulate fire suppression. The emphasis in the present study is on the prediction of flame extinction and the prevention of spurious reignition using a fast chemistry, mixing-controlled combustion model applicable to realistic fire scenarios of engineering interest. The configuration provides a buoyant, turbulent methane diffusion flame within a controlled co-flowing oxidizer. The oxidizer allows for the supply of a mixture of air and nitrogen, including conditions for which oxygen-dilution in the oxidizer leads to flame extinction. Measurements to support model validation include local profiles of thermocouple temperature and oxygen mole fraction, global combustion efficiency, and the limiting oxygen index. The present study evaluates the performance of critical-flame-temperature-based extinction and reignition models using the Fire Dynamics Simulator, an open-source fire dynamics solver. Alternate model cases are explored, each offering a unique treatment of extinction and reignition. Comparisons between simulated results and experimental measurements are used to evaluate the capability of these models to accurately describe flame extinction. Of the considered cases, those that include provisions to prevent spurious reignition show excellent agreement with measured data, whereas a baseline case lacking explicit reignition treatment fails to predict extinction.

A Study on turbulence-combustion interaction and Sub-grid Scale model in the simulation of Methane pool fire using LES

“…To calculate the sub-grid velocity fluctuations in equation ( 15), the isotropic sub-grid velocity fluctuations is assumed. An estimated value of sub-grid velocity fluctuations is obtained according to equation (16).…”

Comparison of combustion models based on fast chemistry assumption in large eddy simulation of pool fire

“…Furthermore, the SLFM model was developed under the geometrical analysis approach [20]. Equation 1is used [21] to calculate the mean reaction rate in the first three models. In Table 1, different values of constants and coefficients are given for each model.…”

Proceedings of the first workshop organized by the IAFSS Working Group on Measurement and Computation of Fire Phenomena (MaCFP)

“…FM Global and UMD used the baseline configuration of FireFOAM except for the addition of a flame extinction model based on the concept of a critical Damkohler number for premixed eddies [65] (FM Global) or the concept of a critical Damköhler number for diffusion flames [66] (UMD); the values of the global radiative loss fraction were prescribed using the measured values [16]; in the solution of the RTE, the discretization of angular space used 16 angles. NIST used the baseline configuration of FDS except for the addition of a flame extinction model based on the concept of a critical flame temperature [67, 68]; in the solution of the RTE, the discretization of angular space used 700 angles (the large number of angles is due to the fact that the NIST simulation included the heat flux gauge located at 1-m distance from the flame and was motivated by the desire to avoid any potential ray effect).…”

“…The exact value of the oxygen extinction limit is predicted within ± 10–20%. While these results are encouraging, it is worth emphasizing that the flame extinction models are complex (they in fact rely on a description of both extinction and re-ignition phenomena [65, 66, 68]) and that the models used in the FM Global, NIST and UMD simulations are based on different representations of the physics. Thus, the UMD turbulent line flame database is not capable of differentiating between the three flame extinction models and therefore does not provide sufficient insight into the underlying physics of flame suppression.…”