The autoignition temperature or self-ignition temperature, often called spontaneous ignition temperature or minimum ignition temperature (or shortly ignition temperature) and formerly also known as kindling point, of a substance is the lowest temperature in which it spontaneously ignites in a normal atmosphere without an external source of ignition, such as a flame or spark.[1] This temperature is required to supply the activation energy needed for combustion. The temperature at which a chemical ignites decreases as the pressure is increased.
Substances which spontaneously ignite in a normal atmosphere at naturally ambient temperatures are termed pyrophoric.
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.[2]
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.[3]
The time it takes for a material to reach its autoignition temperature when exposed to a heat flux is given by the following equation:[4]
where k = thermal conductivity, ρ = density, and c = specific heat capacity of the material of interest, is the initial temperature of the material (or the temperature of the bulk material).
Autoignition temperature of selected substancesedit
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.[5]
^ abcdefghijLaurendeau, N. M.; Glassman, I. (1971-04-01). "Ignition Temperatures of Metals in Oxygen Atmospheres". Combustion Science and Technology. 3 (2): 77–82. doi:10.1080/00102207108952274.
^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), ISBN1-4700-7991-7, p. 46.
^"Flammability and flame retardancy of leather". leathermag.com. Leather International / Global Trade Media. Retrieved 11 February 2015.
^Tony Cafe. "Physical Constants for Investigators". Journal of Australian Fire Investigators. (Reproduced from "Firepoint" magazine)
External linksedit
Analysis of Effective Thermal Properties of Thermally Thick Materials.
February 20, 2024
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The autoignition temperature or self ignition temperature often called spontaneous ignition temperature or minimum ignition temperature or shortly ignition temperature and formerly also known as kindling point of a substance is the lowest temperature in which it spontaneously ignites in a normal atmosphere without an external source of ignition such as a flame or spark 1 This temperature is required to supply the activation energy needed for combustion The temperature at which a chemical ignites decreases as the pressure is increased Substances which spontaneously ignite in a normal atmosphere at naturally ambient temperatures are termed pyrophoric 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 2 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 3 Contents 1 Autoignition time equation 2 Autoignition temperature of selected substances 3 See also 4 References 5 External linksAutoignition time equation editThe time t ig displaystyle t text ig nbsp it takes for a material to reach its autoignition temperature T ig displaystyle T text ig nbsp when exposed to a heat flux q displaystyle q nbsp is given by the following equation 4 t ig p 4 k r 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 nbsp where k thermal conductivity r density and c specific heat capacity of the material of interest T 0 displaystyle T 0 nbsp is the initial temperature of the material or the temperature of the bulk material Autoignition temperature of selected substances editTemperatures 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 5 Substance Autoignition D NoteBarium 550 C 1 022 F 550 90 1 C Bismuth 735 C 1 355 F 735 20 1 C Butane 405 C 761 F 6 Calcium 790 C 1 450 F 790 10 1 C Carbon disulfide 90 C 194 F 7 Diesel or Jet A 1 210 C 410 F 8 Diethyl ether 160 C 320 F 9 Ethanol 365 C 689 F 7 Gasoline Petrol 247 280 C 477 536 F 7 Hydrogen 535 C 995 F 10 Iron 1 315 C 2 399 F 1315 20 1 C Lead 850 C 1 560 F 850 5 1 C Leather parchment 200 212 C 392 414 F 8 11 Magnesium 635 C 1 175 F 635 5 1 B C Magnesium 473 C 883 F 7 B Molybdenum 780 C 1 440 F 780 5 1 C Paper 218 246 C 424 475 F 8 12 Phosphorus white 34 C 93 F 7 A B Silane 21 C 70 F 7 or belowStrontium 1 075 C 1 967 F 1075 120 1 C Tin 940 C 1 720 F 940 25 1 C Triethylborane 20 C 4 F 7 A On contact with an organic substance melts otherwise B There are two distinct results in the published literature Both are separately listed in this table C At 1 atm The ignition temperature depends on the air pressure D Under standard conditions for pressure See also editFire point Flash point Gas burner for flame temperatures combustion heat energy values and ignition temperatures Spontaneous combustionReferences edit a b c d e f g h i j Laurendeau N M Glassman I 1971 04 01 Ignition Temperatures of Metals in Oxygen Atmospheres Combustion Science and Technology 3 2 77 82 doi 10 1080 00102207108952274 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 Zabetakis M G 1965 Flammability characteristics of combustible gases and vapours U S Department of Mines Bulletin 627 Butane Safety Properties Wolfram Alpha a b c d e f g Fuels and Chemicals Autoignition Temperatures engineeringtoolbox com a b c Cafe Tony PHYSICAL CONSTANTS FOR INVESTIGATORS tcforensic com au TC Forensic P L Retrieved 11 February 2015 Diethyl Ether Safety Properties Wolfram Alpha Hydrogen Autoignition Point Wolfram Alpha Flammability and flame retardancy of leather leathermag com Leather International Global Trade Media Retrieved 11 February 2015 Tony Cafe Physical Constants for Investigators Journal of Australian Fire Investigators Reproduced from Firepoint magazine External links editAnalysis of Effective Thermal Properties of Thermally Thick Materials Retrieved from https en wikipedia org w index php title Autoignition temperature amp oldid 1145358702, wikipedia, wiki, book, books, library,
