Combustion of eucalyptus bark firebrands in varying flow incidence and velocity conditions

To validate the use of the combustion laws of embers that can be potential sources of spot fires, namely mass loss prediction laws determined in fixed or pure static conditions to changing flow or particle orientation properties, a series of tests in which these parameters were changed during particle combustion were performed. Hollow cylindrical pieces of bark of eucalyptus trees (Eucalyptus globulus Labill.) burning from one extremity to the other in a vertical flow were tested. It was found that ember combustion in varying conditions of flow velocity or incident flow direction (dynamic or quasistatic conditions) was quite different from that observed in pure static tests for the same values of the reference parameters, indicating that the combustion laws for pure static conditions are not applicable in cases where an ember is immersed in a varying flow. It was found that mass loss coefficients depend not only on the flow velocity and flow particle incidence, but also on the sign and magnitude of variation of these parameters. Mass loss coefficients obtained in pure static conditions were usually a lower limit of the corresponding parameter for dynamic and quasistatic conditions. It was concluded that significant errors can be committed when using common experimental static-condition parameters to predict maximum spotting distance in real situations in which the flow conditions vary continuously.