Auto-ignition is not spontaneous! https://youtu.be/M8thlLjEjhc?t=1225
More rigorous test of oily rags catching on fire:
-Toxic amounts of phenol at low temperature 230F – 110C
-Can take a long time, depends on ambient temp. 24-36 hrs at 60F – 15C.
-Carbon Monoxide may aid ignition
-Cotton faster than paper.
-Prodigious amounts of smoke prior to ignition
@DDSpeedShop