Predicting Ignition Time Under Transient Heat Flux Using Results from Constant Flux Experiments

Abstract

This project investigated if ignition could be mathematically predicted when a material is subjected to a transient heat flux. Six timbers commonly used in New Zealand for construction and indoor furnishing timbers were tested in a cone calorimeter at the University of Canterbury. The experiments were run at 50, 35, 20 and 15 kW/m2 incident heat flux. The sample surface temperature and heat release data was collected for each test. From the ignition time data a value for thermal inertia was calculated and using specific heat data from the literature the thermal properties of each material was inserted into a One Dimensional Heat Transfer Model. A second series of tests were conducted on each of the materials tested at constant flux. These new tests involved subjecting the sample to a transient heat flux based on t² fire growth curves. Again surface temperature and heat release data was obtained from the tests. The one dimensional heat transfer model was used to attempt to predict the surface temperature profile and the ignition time when the test conditions were entered into it. It was found that the predicted surface temperature profile generally matched the shape of the measured temperature profile. However the model was unsuccessful in accurately predicting the ignition time in either the constant or transient flux conditions. It is considered that accurate values for the thermal conductivity and the specific heat would be required before the ignition time and temperature profile could be accurately modelled.