Large Eddy Simulations of forced ignition of a non-premixed bluff-body methane flame with Conditional Moment Closure

• Published in: Combustion and flame Vol. 156; no. 12; pp. 2328 - 2345
• Main Authors: Triantafyllidis, A., Mastorakos, E., Eggels, R.L.G.M.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Inc 01.12.2009; Elsevier
• Subjects: ACCURACY; Applied sciences; BURNERS; COMBUSTION; COMBUSTION KINETICS; COMBUSTION PRODUCTS; Combustion. Flame; Conditional Moment Closure; CONVECTION; DIFFUSION; DISTRIBUTION; ELECTRIC SPARKS; Energy; Energy. Thermal use of fuels; EQUATIONS; Exact sciences and technology; EXPANSION; EXPERIMENTAL DATA; FEASIBILITY STUDIES; FLAME PROPAGATION; FLAMES; Forced ignition; GASES; IGNITION; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; Large Eddy Simulations; Large-Eddy Simulation; MATHEMATICAL MODELS; METHANE; Non-premixed combustion; SIMULATION; SIZE; STABILIZATION; TEMPERATURE RANGE 1000-4000 K; Theoretical studies; Theoretical studies. Data and constants. Metering; THREE-DIMENSIONAL CALCULATIONS; TRANSIENTS; TURBULENCE; ZONES; Forced ignition; Non-premixed combustion; Conditional Moment Closure; Large Eddy Simulations; Methane; Bluff body; Ignition; Turbulent combustion; Flame propagation; Convection; Accuracy; Large eddy simulation; Diffusion flame; Flame structure
• ISSN: 0010-2180; 1556-2921
• DOI: 10.1016/j.combustflame.2009.05.005

Large Eddy Simulations (LES) of forced ignition of a bluff-body stabilised non-premixed methane flame using the Conditional Moment Closure (CMC) turbulent combustion model have been performed. The aim is to investigate the feasibility of the use of CMC/LES for ignition problems and to examine which, if any, of the characteristics already observed in related experiments could be predicted. A three-dimensional formulation of the CMC equation was used with simple and detailed chemical mechanisms and sparks with different parameters (location, size) were used. It was found that the correct pattern of flame expansion and overall flame appearance were predicted with reasonable accuracy with both mechanisms, but the detailed mechanism resulted in expansion rates closer to the experiment. Moreover, the distribution of OH was predicted qualitatively accurately, with patches of high and low concentration in the recirculation zone during the ignition transient, consistent with experimental data. The location of the spark relative to the recirculation zone was found to determine the pattern of the flame propagation and the total time for the flame stabilisation. The size was also an important parameter, since it was found that the flame extinguishes when the spark is very small, in agreement with expectations from experiment. The stabilisation mechanism of the flame was dominated by the convection and sub-grid scale diffusion of hot combustion products from the recirculation zone to the cold gases that enter the burner, as revealed by analysis of the CMC equation.