More on Global Quenching of Premixed CH₄/Diluent/Air Flames by Intense Near-Isotropic Turbulence

Abstract

In 2002, Yang and Shy reported a global quenching (GQ) criterion of premixed CH₄ flames by turbulence characterized by a Karlovitz number (Ka) estimated at reactant temperature and an equivalence ratio (φ).This article re-analyzes such criteria based on a modified Ka estimated at mean temperature of reactants and products together with newly obtained GQ data at even higher Ka. This modified criterion is compared with a recently found ignition transition, which are then used to evaluate the boundary of thin and broken RZ regimes (Ka = 100) proposed by Peters (2000). It is found that flame GQ occurs beyond the broken RZ regime, where critical Ka ≥ 100 at 0.6 ≤φ < 1.3 forms a parabolic curve with the maximum Ka _c ≈ 365 occurring possibly near φ = 1, except for very rich flames where Ka _c = 28 at φ = 1.45. A simple model is proposed to explain these results.

Keywords:

• Equivalence ratio
• Flame global quench
• Ignition transition
• Reaction zone Péclet number
• Turbulent Karlovitz number
• Turbulent premixed combustion

ACKNOWLEDGMENTS

The continuous support by the National Science Council, Taiwan (under the grants NSC 97-2221-E-008-085-MY3; 98-2221-E-008-058-MY3; 100-3113-E-008-004; 100-ET-E-008-001-ET; 101-ET-E-008-002-ET; and 101-3113-E-008-004) is gratefully acknowledged. The authors would like to thank three reviewers for their valuable comments.

Notes

¹Values of S _L are extracted from the work of Mauss and Peters (1993). ²Values of T _ad are obtained from computer codes in the text book of Turns (2000). ³ T _m = (T _ad + T _R)/2, where T _R = 300 K. ⁴Thermal diffusivity (α≡α_Tm ≡α_RZ) estimated at T _m between reactants and products. ⁵δ_L = α/S _L. ⁶ u′ = 0.0462 f, where f is the fan frequency having a maximum value of 182 Hz. ⁷ L _I = 0.0107 f ^0.34, but levels off at 0.045 m when f > 100 Hz. ⁸Kinematic viscosity of the air at T _R (ν = ν_air). ⁹ Re _T = u′L _I/ν_air. ¹⁰η_K = L _I(u′L _I/ν_Tm)^−0.75, where ν_Tm≈α_Tm≡α≡α _RZ for gases. ¹¹ Ka = (u′/S _L)^1.5(L _I/δ_L)^−0.5. ¹² Pe = u′η_K/α_RZ. ¹³Quench or nonquench status at the maximum value of Ka (or Pe) for the actual experiments. ^14,15Critical values for flame GQ, where the superscript. *Indicates the predicted values and the maximum Ka _c2 ≈ 365 occurs at φ = 0.95.

Published as part of the 23rd International Colloquium on the Dynamics of Explosions and Reactive Systems (ICDERS) Special Issue with Guest Editor Derek Dunn-Rankin.