Appearance of flamelets spreading over thermally thick fuel

作者：Matsuoka Tsuneyoshi; Nakashima Kentaro; Nakamura Yuji; Noda Susumu

来源：Proceedings of the Combustion Institute, 2017, 36(2): 3019-3026.

DOI：10.1016/j.proci.2016.07.112

• Fingering
• Flamelet
• Flame separation
• Diffusive-thermal instability
• Thermally thick

Flame spreading behavior in narrow gap constituted by parallel combustible thermally thick solid plates was experimentally investigated. Ten millimeter thick PMMA was used as fuel and the gap height was varied from 1 to 4 mm. Pure oxygen was flowing into the channel and the opposed flame spread was attained. It was found that the transition from a uniform flame to the flamelets spreading to form a fingering pattern occurred as the flow velocity was close to the limiting condition. Although fingering pattern burning has been well known for smoldering or flame spread on thin solid, e.g., paper, this is the first observation with a thick solid. The number of flamelets altered strongly depending on the gap height, while there was a slight increasing tendency on the flow velocity. A flammability map, including flamelet regime, was presented as a function of the oxidizer flow velocity and the gap height. Observation from the side view revealed that a one-sided flame established in between parallel PMMA plates in flamelet regime, while a symmetric flame having two leading edges occurred for the uniform flame regime. Experiments with inert plates showed that heat loss toward the opposite side has no significant effect on the flammability limit. The spread rate was found to be well-summarized by the effective Lewis number for the gap heights of 1 and 2 mm, suggesting that flame separation is likely caused by the diffusive-thermal instability of thin solid.

• 出版日期2017