Characteristics of exothermic reaction fronts in the gasless combustion system

Gasless combustion model of the self-propagating high-temperature synthesis process was numerically studied in the non-adiabatic cylindrical sample. The model equations, which are very stiff in the dimension of length as well as time, were solved using finite difference method on adaptive meshes. Travelling waves with constant pattern were observed for adiabatic systems. For higher values of heat of reaction and activation energy, combustion fronts started to oscillate for adiabatic and non-adiabatic systems. Simple and complex oscillatory fronts were observed. Multi-peak and irregular oscillations were also detected to presumably result in the gasless chaotic combustion. In oscillatory fronts the temperature can overshoot the adiabatic reaction temperature to result in the complete conversion of solid reactant. In the two dimensional non-adiabatic cylindrical sample in the domain of longitudinal and angular directions, oscillatory piston waves were observed. In addition asymmetrical fingering as well as rotating waves were detected for an asymmetrical perturbation. For the adiabatic annulus cylindrical sample, the velocity of propagating fronts increased with time and the temperature overshooted the adiabatic reaction temperature if the sample were ignited from the inside. If the sample were ignited from the outside, the velocity of propagating fronts decreased with time and the temperature again overshooted the adiabatic reaction temperature. For smaller diameter of sample, the temperature increased very slowly with time for inside ignition. The temperature after ignition increased very fast overshooting the adiabatic reaction temperature for outside ignition. After several oscillations, the reaction rate decreased and the region with very slow reaction was established.