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Autoignition temperature
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The autoignition temperature or kindling point of a substance is the lowest temperature at which it spontaneously ignites in 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 ignites 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-millilitre (18 imp fl oz; 17 US fl oz) flask placed in a temperature-controlled oven in accordance with the procedure described in ASTM E659.[1]
When measured for plastics, autoignition temperature can be also 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
[hide]
1 Autoignition equation
2 Autoignition point of selected substances
3 See also
4 References
5 External links
Autoignition equation[edit]
The time t ig {\displaystyle t_{\text{ig}}} it takes for a material to reach its autoignition temperature T ig {\displaystyle T_{\text{ig}}} when exposed to a heat flux q ″ {\displaystyle q''} is given by the following equation:[3]
t ig = π 4 k ρ c [ T ig − T 0 q ″ ] 2 , {\displaystyle t_{\text{ig}}={\frac {\pi }{4}}k\rho c\left[{\frac {T_{\text{ig}}-T_{0}}{q''}}\right]^{2},}
where k = thermal conductivity, ρ = density, and c = specific heat capacity of the material of interest, T 0 {\displaystyle T_{0}} is the initial temperature of the material (or the temperature of the bulk material).
Autoignition point of selected substances[edit]
Temperatures vary widely in the literature and should only be used as estimates. Factors that may cause variation include partial pressure of oxygen, altitude, humidity, and amount of time required for ignition. Generally the autoignition temperature for hydrocarbon/air mixtures decreases with increasing molecular mass and increasing chain length. The autoignition temperature is also higher for branched-chain hydrocarbons than for straight-chain hydrocarbons.[4]
Substance
Autoignition[5]
Note
Triethylborane 7002253149999999999♠−20 °C (−4 °F) [6]
Silane 7002294150000000000♠21 °C (70 °F) [6] or below
White phosphorus 7002307150000000000♠34 °C (93 °F) [6] on contact with an organic substance, melts otherwise
Carbon disulfide 7002363150000000000♠90 °C (194 °F) [6]
Diethyl ether 7002433150000000000♠160 °C (320 °F) [7]
Gasoline (Petrol) 7002520150000000000♠247–280 °C (477–536 °F) [6]
Ethanol 7002638150000000000♠365 °C (689 °F) [6]
Diesel or Jet A-1 7002483150000000000♠210 °C (410 °F) [8] or below
Butane 7002678150000000000♠405 °C (761 °F) [9]
Paper 7002491150000000000♠218–246 °C (424–475 °F) [8][10]
Leather / parchment 7002473150000000000♠200–212 °C (392–414 °F) [8][11]
Magnesium 7002746150000000000♠473 °C (883 °F) [6]
Hydrogen 7002809150000000000♠536 °C (997 °F) [12]
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; in addition, it takes longer for the combustion of paper to start at lower temperatures.[13] Ray Bradbury named his novel Fahrenheit 451 for the autoignition temperature of paper;[14][15] this value chosen lies in the mid-range of reported values.
See also[edit]
Pyrolysis
Fire point
Flash point
Gas burner (For flame temperatures, combustion heat energy values and ignition temperatures)
References[edit]
Jump up ^ E659 – 78 (Reapproved 2000), "Standard Test Method for Autoignition Temperature of Liquid Chemicals", ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959.
Jump up ^ S. Grynko, "Material Properties Explained" (2012), ISBN 1-4700-7991-7, p. 46.
Jump up ^ Principles of Fire Behavior. ISBN 0-8273-7732-0. 1998.
Jump up ^ Zabetakis, M. G. (1965), Flammability characteristics of combustible gases and vapours, U.S. Department of Mines, Bulletin 627.
Jump up ^ Under standard conditions for pressure.
^ Jump up to: a b c d e f g Fuels and Chemicals - Autoignition Temperatures, engineeringtoolbox.com
Jump up ^ "Diethyl Ether - Safety Properties". Wolfram|Alpha.
^ Jump up to: a b c Cafe, Tony. "PHYSICAL CONSTANTS FOR INVESTIGATORS". tcforensic.com.au. TC Forensic P/L. Retrieved 11 February 2015.
Jump up ^ "Butane - Safety Properties". Wolfram|Alpha.
Jump up ^ Tony Cafe. "Physical Constants for Investigators". Journal of Australian Fire Investigators. (Reproduced from "Firepoint" magazine)
Jump up ^ "Flammability and flame retardancy of leather". leathermag.com. Leather International / Global Trade Media. Retrieved 11 February 2015.
Jump up ^ "Hydrogen - Safety Properties". Wolfram|Alpha.
Jump up ^ Forest Products Laboratory (1964). "Ignition and charring temperatures of wood" (PDF). Forest Service U. S. Department of Agriculture.
Jump up ^ Brian Palmer (June 8, 2012). "Does Paper Really Burn at 451 Degrees Fahrenheit?". Slate. Retrieved March 3, 2016.
Jump up ^ Jakub Dutka (May 19, 2014). "Book as a reflexive medium: the materiality in post-digital print". MA Media Studies, University of Amsterdam. Retrieved March 3, 2016.
External links[edit]
Analysis of Effective Thermal Properties of Thermally Thick Materials.
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