Challenges in determining critical mass flux for ignition

Traditionally in fire modelling, a solid fuel has been assumed to ignite when the solids surface reaches a specific temperature or when the heat flux upon the solid reaches a critical level. Although these approaches of determining ignition for the condensed phase are practical, ignoring the gas phase conditions may lead to incorrect assumptions regarding material safety. A more 'physical' explanation for piloted ignition cases may be that ignition occurs when the fuel-air-mixture around the location of a pilot has reached the lower flammability limit. In this study, challenges of retrieving a critical mass flux for piloted ignition is theoretically evaluated. Then a simple model is presented, by which the critical mass flux (analogous to the piloted fire point) of a solid fuel's effluents may be obtained. Finally, the model is validated against literature data. Initial results indicate that the model predicts ignition reasonably well, however further validation needs to be done, both when it comes to predicting ignition for different types of materials and for other environments