Study of the behaviour of a flame resulting from the combustion of pine needles in a cylindrical basket

This experimental and numerical study examines the behaviour of a flame resulting from the combustion of pine needles. The objective of this work is to evaluate the performances of two models of combustion, the validity of these being discussed by comparing the results with experimental measurements. An apparatus was designed to simulate and study in laboratory conditions the flame and the near-field plume stemming from the combustion of an isolated shrub. The burner was made of a cylindrical wire mesh basket filled with pine needles ignited at the lower circumference of the basket. Particle Image Velocimetry (PIV) and Laser Doppler Anemometry (LDA) were used to characterize the velocity field in the proximity of the fuel and to identify the propagation of the flame. A set of time-dependent equations is obtained for each phase and the coupling between the gas phases is rendered through exchange terms of mass, momentum and energy. Turbulence is approached by using a k – ε statistical model constructed from the Favre averaging method. The chemical kinetics is assumed as infinitely fast compared with other characteristics of the flow. Two models of turbulent combustion are tested. The first is the EDC model, which considers an immediate reaction and the direct transformation of fuel into water and carbon dioxide. The second is the β-PDF model, which is based on an instantaneous thermodynamic equilibrium at any point. The solution is performed numerically by a finite-volume method. The numerical results obtained are presented and compared to experimental measurements.