After the heater was turned off (t = 44 min), the reaction
was self-sustaining as evidenced by the succession of nearly
constant peak temperatures. The figure illustrates that the smoldering
front required 20 min to propagate the length of the column
and, following the reaction’s natural extinction when all the fuel
was consumed, 50 min for the column to cool down. The average
peak temperature (ignoring the first thermocouple to remove the
boundary effect) was 543.0 ± 0.2 ◦C and the average velocity of the
smoldering front was 0.56 ± 0.08 cm/min. These values fall within
the range of those reported for 15%–50% saturation crude oil in
medium sand