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

Experimental results of Nz-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.