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 .

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

$t\_\{ig\}\; =\; left\; (frac\{pi\}\{4\}\; right\; )\; left\; (k\; rho\; c\; right\; )left\; [frac\{T\_\{ig\}-T\_infty\}\{q\}\; right]$

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)
• Gasoline (Petrol): 246°C (475°F)
• Magnesium: 473°C (883°F)
• Butane: 500°C (900°F)
• Hydrogen: 571°C (1060°F)

References

• Handbook of Physical Testing of Paper, By Jens Borch, Richard E. Mark, M. Bruce Lyne. Retrieved on 2008-09-08..

See also

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

External links

• Analysis of Effective Thermal Properties of Thermally Thick Materials