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 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.[1]
When measured for plastics, autoignition temperature can also be measured under elevated pressure and at 100% oxygen concentration. The resulting value is used as a predictor of viability for high-oxygen service. The main testing standard for this is ASTM G72.[2]
Contents |
Autoignition equation [edit]
The time 
it takes for a material to reach its autoignition temperature 
when exposed to a heat flux 
is given by the following equation
![t_{ig} = \left ( \frac{\pi}{4} \right ) \left (k \rho c \right )\left [ \frac{T_{ig}-T_{o}}{q''} \right]^2](http://upload.wikimedia.org/math/1/9/6/1968b7d5a90781ae54f8f0566d0af074.png)
where k = thermal conductivity (W/(m·K)), ρ = density (kg/m³), and c = specific heat capacity (J/(kg·K)) of the material of interest. 
is the temperature, in Kelvin, the material starts at (or the temperature of the bulk material), and is the heat flux (W/m²) incident to the material.
Autoignition point of selected substances [edit]
Temperatures vary widely in the literature and should only be used as estimates. Factors which may cause variation include partial pressure of oxygen, altitude, humidity, and amount of time required for ignition.
| Substance | Autoignition point °C | Autoignition point °F |
|---|---|---|
| Triethylborane | -20 °C | −4 °F |
| Silane | <21 °C | <70 °F |
| White phosphorus | 34 °C | 93 °F (ignites on contact with an organic substance, melts otherwise) |
| Carbon disulfide | 90 °C | 194 °F |
| Diethyl ether | 160 °C | 320 °F[4] |
| Diesel or Jet A-1 | 210 °C | 410 °F |
| Gasoline (Petrol) | 246-280 °C | 475–536 °F[5] |
| Ethanol | 363 °C | 685 °F[5] |
| Butane | 405 °C | 761 °F[6] |
| Paper | 450 °C or 218-246 °C |
842 °F[7] or 424–475 °F[8] |
| Magnesium | 473 °C | 883 °F |
| Hydrogen | 536 °C | 997 °F[9] |
For paper, there is considerable variation between sources, mainly because there are many physical variables over different kinds of paper, like thickness, density and composition, partially because it takes longer for the combustion of paper to start at lower temperatures.[10]
See also [edit]
- Pyrolysis
- Fahrenheit 451
- Flash point
- Gas burner (For flame temperatures, combustion heat energy values and ignition temperatures)
References [edit]
- ^ E659 – 78 (Reapproved 2000), "Standard Test Method for Autoignition Temperature of Liquid Chemicals", ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959
- ^ S. Grynko, "Material Properties Explained" (2012), ISBN 1-4700-7991-7, p. 46.
- ^ Principles of Fire Behavior. ISBN 0-8273-7732-0. 1998.
- ^ "Diethyl Ether - Safety Properties". Wolfram|Alpha.
- ^ a b Fuels and Chemicals - Autoignition Temperatures, engineeringtoolbox.com
- ^ "Butane - Safety Properties". Wolfram|Alpha.
- ^ Jens Borch, Richard E. Mark (2001). Handbook of Physical Testing of Paper 2. CRC Press. p. 406. ISBN 0-8247-0499-1. "The ignition temperature of paper is about 450°C, but is somewhat dependent upon the paper quality."
- ^ Tony Cafe. "Physical Constants for Investigators". Journal of Australian Fire Investigators. Unknown parameter
|note=ignored (help) - ^ "Hydrogen - Safety Properties". Wolfram|Alpha.
- ^ Forest Products Laboratory (1964). "Ignition and charring temperatures of wood". Forest Service U. S. Department of Agriculture.
External links [edit]
- Analysis of Effective Thermal Properties of Thermally Thick Materials.
- Autoignition Temperature of 100 Common Organic Chemical Compounds.
|
|||||||||||||||||||||||
