Recent research conducted at the Missoula Fire Lab has found that the amount of radiant heat in wildland fires is not sufficient to ignite fine fuel particles such as needles and grasses. These fine fuels are highly efficient at convective heat transfer, so any amount of airflow can easily offset the radiant heat generated by the fire. As a consequence, fine wildland fuels do not ignite until bathed by the flame. As radiant heating has been assumed to drive ignition in wildland fires as it does in structural fires, ignition by convective heating is not well understood.
Experiments are underway to determine if and how ignition due to convective heating is different than that from radiative heating. We built an apparatus using two electrical heaters to heat air up to 1200°C (2200°F).
For more information, please visit the complete project page at https://www.firelab.org/project/convective-ignition