A Study on Flame Extinction Characteristics along a C-Curve

A study has been conducted both experimentally and numerically to clarify impacts of curtain flow and velocity ratio on low strain rate flame extinction and to further display transition of shrinking flame disk to flame-hole. Critical mole fractions at flame extinction are provided in terms of velocity ratio, nitrogen curtain flow rate, and global strain rate. Flame extinction modes are grouped into four on a C-curve, which is characterized by a flame-hole, the shrinking of edge flame, and edge flame oscillation. It is seen that varying curtain flow rate does not impact on edge flame oscillation, flame extinction, and even flame extinction modes. Variation of velocity ratio extends to the low strain rate flame extinction modes beyond the turning point. It is found that the expanding and shrinking flames always have negative flame propagation speed; it is also recognized that the decrease of flame radius is prone to extinguish due to the dominant role of radial conduction heat loss. The examination of energy fraction is also presented to stress the role of radial conduction heat loss, particularly at the outer flame edge part.