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CB Radios, Cellphones and Gasoline Vapor Ignition
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March 21st 04, 11:13 PM
Bill Sloman
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(John Michael Williams) wrote in message om...
(Bill Sloman) wrote in message . com...
...
The controlling relationship is between the volume of the sphere in
which the reaction is first initiated, and the surface area of that
sphere - if the intial volume is too small, not enough energy is
released to heat the surrounding shell of gas to the ignition
temperature.
...
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Bill Sloman, Nijmegen
This makes sense. I think I can see a spark 0.1 mm in
radius, at say 4000 K. That's about 4 cubic picometers
in volume and about 0.1 square micron in surface area (assuming
sparks have smooth surfaces). But, I'm not sure how to relate
that to the threshold of flame propagation.
If energy is a factor, rather than power, the duration of
the spark would seem to be relevant, too.
Sparks are much faster than flame fronts - when I was involved in
instrinsic safety nobody paid any attention to spark duration, and for
all practical purposes the energy stored in the capacitance of a spark
gap is dumped into the gas much faster than it can be dissipated.
------
Bill Sloman, Nijmegen
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