More on Minimum Ignition Energy Transition for Lean Premixed Turbulent Methane Combustion in Flamelet and Distributed Regimes

Abstract

At the 31st Combustion Symposium, Shy et al. found a transition on minimum ignition energy (MIE) of methane-air mixtures at the equivalence ratio φ = 0.6 in intense isotropic turbulence, where ignition energies of a spark-electrode was quantitatively measured by an energy-adjustable high-power pulse ignition system. Using the same methodology, this paper presents for the first time two new MIE data sets at φ = 0.7 and 0.8 over a wide range of turbulent intensities. It is found that MIE transition due to different modes of turbulent combustion depends on a turbulent Karlovitz number (Ka) indicating the time ratio between chemical reaction and turbulence, for which MIE first increases gradually with Ka and then increases drastically when Ka > K a _c  ≈  4  ∼  9 depending also on φ. The effect of the electrode gap on ignition energies and turbulence influence to centrally-ignited, outwardly propagating flames are also discussed.

Keywords:

• Flamelet and distributed regimes
• Ignition transition
• Lean premixed turbulent combustion
• Minimum ignition energy

The authors would like to thank the National Science Council, Taiwan for her continuous financial supports (NSC 94-ET-7-008-008-ET, 94-2212-E-008-021, 95-2218-E-008-018 and 96-2218-E-008-004).