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 c aused 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 h ow 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 l ower strain rate when the inert jet impingement originates from the airside . (2) The global extinction strain rate for CH4 flames is insensitive to th e location and number (one vs. three) of local extinction sites. (3) For C3 H8 flames, One single inert jet impinging from the airside along the center line is more effective in causing global extinction than three inert jets i mpinging at regions away from the centerline. This suggests that flame exti nction over a larger area may depend on strategically selected smaller loca l extinction sites. Furthermore, since similar results of (3) are not obser ved in this study for CH4 flames, fuel chemistry may also play a role in th e effectiveness of local extinction transitioning to global extinction. Dif ferences between flame stabilization mechanisms with and without local exti nction are discussed and the implications for turbulent diffusion flames ar e outlined.