Experimental investigation of processes of typical forest fuel ignition by a high-temperature steel particle

In spite of the fact that the processes of forest fuel ignition is a determinative stage of a fire, there are just a few published works representing experimental data that describe the laws of ignition of various forest fuels influenced by high-temperature small-size sources. Experiments were performed according to the classical plan with randomization because the mathematical model describing the dependence of the delay time of forest fuel ignition on the initial temperature of a local heating source has not been defined till now. Experiments were carried out with a group of graphite particles identical in size, as well as with birch leafs gathered in 2012, dried up, and cleared of foreign impurities. Experiments were carried out with forest fuel samples represented by 5-6 leaves joined together or a group of several tens of needles. The packaging of the forest fuel was equable. Visual observation of forest fuel ignition processes and video images allowed us to formulate a physical model of forest fuel ignition with heating by a small-size particle. The flame torch was formed around the entire perimeter of the particle in the majority of observations. Sometimes the volumetric flame torch over the entire surface of the particle arose in a split second. The approximation dependence of the ignition delay time on the initial temperature of the particle is a linear function and differs substantially from typical curves for solid fuels. This difference is connected with the significant structural heterogeneity of a forest fuel element heated up by a local source and conditions of heat sink in the heating zone.