On Determining Spontaneous Ignition in Porous Materials

A guide is developed that lays out the process of analyzing spontaneous ignition likelihood. The Frank-Kamenetskii (F-K) theory forms the basis of the approach. The Damkohler number, defined as the dimensionless heat generation parameter for a self-heating body, is described in terms of two key material constants and these materials are related to real incident spontaneous ignition scenarios. The Damkohler number is compared to the critical Damkohler number, value of heat generation at the onset of runaway condition, to determine if spontaneous ignition is likely. Corrections to the critical Damkohler number are described for cases of finite Biot number, low activation energy, and reactant consumption. Heat transfer analysis is needed in terms of a Biot number, and its calculation is described. A specific measurement of the heat transfer in an oven is described. Application of the spontaneous ignition hazard analysis for a real case is presented.