The transient ignition of nonmetallic materials in a pure oxygen environment is considered. Assuming that ignition is caused by an exothermic heterogeneous reaction occurring at the gas/solid interface, a mathematical model is developed to simulate the ignition behavior.
For a general oxygen system, the ignition temperature is a function sensitive to the external heating rate, as well as system parameters. The fundamental ignition parameters are the minimum ignition heat flux and the corresponding minimum ignition temperature. As oxygen pressure increases, the minimum ignition temperature decreases. As the oxygen pressure becomes sufficiently high, spontaneous ignition occurs. Based on an approximate solution to the governing equations, an upper limit of the maximum “safe” operating pressure (that which prevents spontaneous ignition) is established.
Numerical results generated by the model were correlated with the reported ignition data for polyethylene, Teflon, and nylon. At an external heating rate much higher than the required minimum ignition heat flux, the ignition temperature is relatively insensitive to oxygen pressure.