Extinction of laminar counterflow diffusion flames of CH₄ and C₃H₈ fuels with inert jet impingement

Experimental results of N₂-diluted counterflow diffusion flames of CH₄ and C₃H₈ vs. air with local extinction are reported. The local extinction was caused by inert jet impingement on flames at selected locations either from the fuel or oxidizer side of the reaction zone. This was done to simulate how local extinction affects flame extinction over a larger flame area. The results are: (1) Local extinction of both CH₄ and C₃H₈ flames occurs at a lower strain rate when the inert jet impingement originates from the airside. (2) The global extinction strain rate for CH₄ flames is insensitive to the location and number (one vs. three) of local extinction sites. (3) For C₃H₈ flames, one single inert jet impinging from the airside along the centerline is more effective in causing global extinction than three inert jets impinging at regions away from the centerline. This suggests that flame extinction over a larger area may depend on strategically selected smaller local extinction sites. Furthermore, since similar results of (3) are not observed in this study for CH₄ flames, fuel chemistry may also play a role in the effectiveness of local extinction transitioning to global extinction. Differences between flame stabilization mechanisms with and without local extinction are discussed and the implications for turbulent diffusion flames are outlined.