Investigation on the highly negative curved syngas Bunsen flame and the critical local Karlovitz number when tip opening

The characteristics of local extinction on the tip of syngas premixed Bunsen flames with different hydrogen fractions have been investigated experimentally with OH-PLIF technique and numerical simulation. Coupled effects of stretch and diffusion on the syngas Bunsen flame with highly negative curvature were studied. Local Karlovitz number was introduced to indicate the onset of local extinction at the Bunsen flame tip. Results showed that the onset equivelance ratio of local extinction at the syngas Bunsen flame tip does not change with the outlet velocity. The coupled effects of stretch and diffusion result in the decrease of flame reaction rate along the syngas Bunsen flame at fuel-lean condition. When the flame reaction rate decrease to a critical extent, local extinction of Bunsen flame tip occures. The local Karlovitz number can be considered as a parameter of the critical condition. The syngas Bunsen flame tip will extinguish when the local Karlovitz number reaches around 4, irrespective of hydrogen fractions and outlet velocity. This means that Bunsen flame tip starts to appear local extinction when the tangential flow time is comparable to normal chemical reaction time, which is the same as counterflow flames with positive stretch. Furthermore, results also showed that there is no H2 leakage even the syngas Bunsen flame tip extinguishes at the numerical study conditions.