Spontaneous ignition delays of propane injected into a hot air stream.

The process of combustion may be regarded as an exothermic chemical reaction which tends to accelerate and is accompanied by flame. The rate at which it proceeds depends on several factors, the most significant probably being the temperature, for a combustible mixture will not usually burn unless the temperature is raised to a critical value (other factors constant). Closely associated with “spontaneous ignition temperature”, as it is called, is the phenomenon of ignition delay, which represents the time interval between the attainment of conditions suitable for combustion and the onset of ignition