The graph above shows the temperature -
time profile for the successful experiment. It
took about 3 1/2 hours for the whole mass to start
to heat significantly. Once it got going, the
temperature rise was pretty dramatic. I don't
know where the cotton actually started to burn.
I was guessing that it would be clear from the graph
- but it doesn't appear to be. Maybe this was
due to the temperature probe being buried in layers
of cloth that were not burning - and hence they
acted as an insulator.
Some data points:
Boils at 343 C
Flash Point 222C
Ignition Temperature 343 C
Autoignition Temp (Oily) 120 C
Glow Temperature 205 C
Flash Ignition 210 C
Self Ignition 407 C
It is interesting to compare the above numbers to
the graph above. The only real conclusion from
my experiment was that the cotton did ignite at some
temperature below 431 C. From experiment #1,
178 C is not enough.
Yes, spontaneous combustion is real!
I now have a lot more respect for proper disposal
of oily rags. (Soak them in water, and/or
store them in an air-tight container.)
Yes, spontaneous combustion can be used to start
a fire - but it does take time!
When did the cotton actually start to glow?
What other types of oils can be used?
My gut feel tells me that even more air was needed.
A can is not a good insulator. Something like
cardboard would be better for heat retention.
How much cotton is needed for "critical mass?"
How big a role does the outside air temperature