Opposed-flow flame spread over carbon fiber reinforced plastic with different carbon fiber orientations

Abstract

Herein, carbon fiber reinforced plastic (CFRP) sheets with different carbon fiber (CF) orientations were combusted in an environment of variable opposed-flow velocity (Vg) and oxygen concentration, and the effects of the CF orientation angle (θ) on the flame spread characteristics were studied. The limiting oxygen concentration increased with θ and linearly decreased with increasing Vg. The flame spread rate (Vf) was the highest when the CF orientation corresponded to the flame spread direction (i.e., θ = 0 deg.) and increased with Vg. Conductive heat transfer sideways became more significant as θ increased, which signifies increased heat loss. Thus, the net heat transfer rates that directly contributed to the flame spread decreased, leading to low flammability and weak flame spread. Vf was calculated using our previous CFRP flame spread model. The calculated Vf was higher than the measured Vf, and the difference between them increased as Vg increased. This is because the flame height (Hf) decreased considerably with increasing Vg, resulting in high heat transfer rate from the flame and high Vf. The Hf model was thus revised based on the dataset of the opposed-flow flame spread tests; then, the calculated Vf agreed well with the measured Vf. The Vf for the buoyant-flow flame spread assuming Vg = 35 cm/s was also calculated using the flame spread model with the original and revised Hf models, and no significant difference was noted between the calculated and measured Vf. Thus, this study succeeded in improving the CFRP flame spread model to deal with both the opposed-flow flame spread and the buoyant-flow flame spread. This revised model will help understand the physics of the flame spread over CFRP sheets and assess the fire risk of CFRP products for fire safety.