Effect of thermal properties on self-propagating fronts in reactive nanolaminates

The effects of thermal diffusion on flame front dynamics in a (1:1) Ni/Al multilayered system are computationally investigated. A systematic refinement of the thermal conductivity model is performed, namely by incorporating the effects of concentration, direction, and temperature dependence. The resulting thermal conductivity models are incoporated into the reduced reaction formalism developed by Salloum and Knio [Combust. Flame 157(6),1154 (2010]). Computations using constant and variable conductivity models are contrasted with each other, for axial and normal front propagation. Notable differences between the predictions of the various conductivity models are observed, particularly concerning the thermal and reaction widths. Differences in the average front propagation velocity are, unexpectedly, less pronounced. Brief computational experiments are finally conducted for 3D front propagation using constant and variable thermal conductivity models. The 3D variable-conductivity computations reveal the occurrence of transient, spinlike reactions that appear to be consistent with recent experimental observations, whereas stable front behavior is observed when a constant-conductivity model is used. Thus, the present experiences suggest that thermo-diffusive instabilities are likely to play a role in the onset and manifestation of some of the experimentally-observed transient front propagation regimes.