Background

Horizontally continuous fuel types such as pine litter can sustain flame spread along individual fuel particles, but little is known about how wind affects flame behavior at this fine scale.

Aims

We conducted experiments to examine flame spread rates along thin horizontal fuel particles (cardboard and pine needles) where wind speed and particle orientation relative to wind direction were varied.

Methods

The wind speed was controlled by mounting a fuel sample on a rotating disk turning at a specified rate.

Key results

Video measurements showed that flame spread rates on fuel samples varied with fuel orientation angle and wind speed according to the polar equation for an ellipse. The heat transfer mechanism for a wind-blown laminar flame is gas-phase conduction at millimeter scales, the same as with flame spread in opposed flow conditions on other thin cellulosic fuels.

Conclusions

Flame spread rate was directly related to the angle within the flame volume intercepted by the fuel particle.

Implications

Despite the short range of gas conduction heating, the elliptical shape implied by the data offers a small-scale physical example of the common assumption that 2D wildland fire shapes can be approximated as ellipses.