Autoignition temperature

The time t_\text{ig} it takes for a material to reach its autoignition temperature T_\text{ig} when exposed to a heat flux q'' is given by the following equation: :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 is the initial temperature of the material (or the temperature of the bulk material). ==Autoignition temperature of selected substances==

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. ==See also==