We investigate the passage of a deflagration wave down a porous delay element in a detonator where a small part of the pyrotechnic mixture is converted to gas A one dimensional model is formulated with the wave propagated by thermal conduction and with the reaction rate described by a single step kinetic equation. Numerical solutions are obtained and compared with an asymptotic solution valid for large activation energy. It is shown that, when the gas moves ahead of, rather than through, the flame, the reduction in the amount of mass heated leads to a relative increase in the flame temperature. Although this change is small, the burning rate is very sensitive to the flame temperature and the mixture burns noticeably faster in this situation. The delay time of the detonator is thus, amongst other things, a function of the gas confinement conditions of the element.
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