An Empirical Correlation for Burning of Spruce Wood in Cone Calorimeter for Different Heat Fluxes

This article proposes an empirical expression to describe the pyrolysis and charring of spruce wood in bench-scale experiments for a wide range of incident heat fluxes. Spruce wood samples were exposed to a cone radiant heater oriented vertically with varying intensities, ranging from \(\dot{q}_{\text {cone}}^{''}\) = 22 kW m\(^{-2}\) to 93.5 kW m\(^{-2}\) over 53 test samples. The mass loss rate (MLR), the position of the char front and a preliminary additional heat source from smoldering or flaming combustion were experimentally determined. The experimental data were processed to express the burning rate as a function of heat flux and char front position. A grouping of the experimental curves was obtained, allowing to predict the MLR outcome over time regardless of the incident heat flux. A linear regression at the quasi-steady state regime allowed the determination of the fitting coefficients of the correlation, which ultimately correspond to the mass of volatiles produced per unit of energy input into the material. A comparison was made with theoretical analysis of the pyrolysis of charring materials from the literature, and the discrepancies with the proposed approach and its limitations were finally discussed. The main advantage of this approach is that it provides a generalized expression, requiring minimal input of material properties, which predicts the MLR change over time for any heat flux within engineering accuracy.