Autoignition temperature


Autoignition temperature

The autoignition temperature or kindling point of a substance is the lowest temperature at which it will spontaneously ignite in a normal atmosphere without an external source of ignition, such as a flame or spark. This temperature is required to supply the activation energy needed for combustion. The temperature at which a chemical will ignite decreases as the pressure increases or oxygen concentration increases. It is usually applied to a combustible fuel mixture.

Autoignition temperatures of liquid chemicals are typically measured using a 500 mL flask placed in a temperature controlled oven in accordance with the procedure described in ASTM E659 [E659 – 78 (Reapproved 2000), "Standard Test Method for Autoignition Temperature of Liquid Chemicals", ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959] .

Autoignition equation

The time t_{ig}, it takes for a material to reach its autoignition temperature T_{ig}, when exposed to a heat flux q", is given by the following equation

t_{ig} = left ( frac{pi}{4} ight ) left (k ho c ight )left [ frac{T_{ig}-T_infty}{q"} ight] [Principles of Fire Behavior. ISBN 0-8273-7732-0. 1998. ]

where "k" = thermal conductivity (W/(m·K)), "ρ" = density (kg/m³), and "c" = specific heat capacity (J/(kg·K)) of the material of interest. T_infty is the temperature, in kelvins, the material starts at (or the temperature of the bulk material), and "q"″ is the heat flux (W/m²) incident to the material.

Autoignition point of selected substances

*Triethylborane: -20°C (-4°F)
*Silane: <21°C (70°F)
*White phosphorus: 34°C (93°F)
*Carbon disulfide: 100°C (212°F)
*Diethyl ether: 170°C (338°F)
*Diesel: 210°C (410°F)
*Jet A-1: 210°C (410°F)
*Paper: 450°C (842°F) [cite web |url=http://books.google.com/books?id=qa-I8QAOUL8C&pg=PA406&lpg=PA406&dq=flash+point+of+paper&source=web&ots=FjB5FslcKK&sig=Vlr2cc8M2-TWy3qkdwzGUeK-vnM&hl=en&sa=X&oi=book_result&resnum=10&ct=result#PPA406,M1 |title=Handbook of Physical Testing of Paper, By Jens Borch, Richard E. Mark, M. Bruce Lyne |accessdate=2008-09-08]
*Gasoline (Petrol): 246°C (475°F)
*Magnesium: 473°C (883°F)
*Butane: 500°C (900°F)
*Hydrogen: 571°C (1060°F)

References

* cite web |url=http://books.google.com/books?id=qa-I8QAOUL8C&pg=PA406&lpg=PA406&dq=flash+point+of+paper&source=web&ots=FjB5FslcKK&sig=Vlr2cc8M2-TWy3qkdwzGUeK-vnM&hl=en&sa=X&oi=book_result&resnum=10&ct=result#PPA406,M1 |title=Handbook of Physical Testing of Paper, By Jens Borch, Richard E. Mark, M. Bruce Lyne |accessdate=2008-09-08

ee also

* Pyrolysis
* Flash Point
* Gas burner (For flame temperatures, combustion heat energy values and ignition temperatures)

External links

* [http://www.fire.nist.gov/bfrlpubs/fire03/art015.html Analysis of Effective Thermal Properties of Thermally Thick Materials] .


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