## Abstract

Global quenching of premixed CH4/air flames with turbulent straining, equivalence ratio, and radiative heat loss effects is explored in a cruciform burner. The burner equipped with a pair of counter-rotating high-speed fans and perforated plates provides downward propagating flames through near-isotropic intense turbulence, where flame-turbulence interactions are not influenced by ignition. Several CH_{4}/air flames with different degrees of radiative heat loss, from small (N_{2}-diluted) to large (CO_{2}-diluted), are investigated. Each case covers a range of the equivalence ratio (φ) with turbulent intensities (u'/S_{L}) as much as 100, where S_{L} is the laminar burning velocity, in which high rates of strain are achieved until, ultimately, global quenching of flames occurs. A Bradley's Karlovitz number, defined as K = 0.157(u'/S_{L})^{2} = 0.157Ka, is used to quantify global quenching boundaries of these turbulent flames, where Re_{T}Re_{T}^{-0.5} and Ka are the turbulent Reynolds and Karlovitz numbers, respectively. For pure CH_{4}/air flames, the critical value of K for global quenching of rich/lean CH_{4} flames must be greater than 1.0/6.2. Values of Kc are very sensitive to φ, because Kc increases significantly as φ gradually approaches 1 from either lean or rich sides, with the maximum Kc occurring possibly near φ = 1. By comparing N_{2}- and CO_{2}-diluted flames of the same S_{L}, it is found that global quenching of lean/rich CH_{4} flames is/is not influenced by the radiatvie heat loss, respectively. The larger the radiative heat loss, the smaller the value of K_{c} for lean CH_{4} flames, in which values of K_{c} decrease from 4 (N_{2}-diluted) to 3 (CO_{2}-diluted) where S_{L} ≈ 10 cm/s and φ = 0.62. On the other hand, K_{c} ≈ 1.3 for both N_{2}- and CO_{2}-diluted rich CH_{4} flames where S_{L} ≈ 10 cm/s and φ = 1.20-1.45. These experimental results are important to the understanding of global quenching processes for turbulent premixed combustion.

Original language | English |
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Pages (from-to) | 1841-1847 |

Number of pages | 7 |

Journal | Proceedings of the Combustion Institute |

Volume | 29 |

Issue number | 2 |

DOIs | |

State | Published - 2002 |

Event | 30th International Symposium on Combustion - Chicago, IL, United States Duration: 25 Jul 2004 → 30 Jul 2004 |

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