Unsteady flow effects in pyrotechnic actuators are examined quantitatively and are shown to significantly affect the performance of a pyrotechnic device when the function time or the stroke time of the device is in the order of a characteristic gasdynamics timescale of the product gases in the device. A one-dimensional "purely" gasdynamics model is developed to simulate the unsteady effects in a closed-bomb firing and in a normally open pyrotechnic valve. The model results are compared to test data and are found to agree well with the data. The results of the gasdynamics model are also compared with those of a quasi-equilibrium model, and the limitations of both models are investigated. Consequently, a nondimensional time parameter τ c is established, which can be used to approximate the level of unsteady effect on the total energy output of a given pyrotechnic device. It is concluded that the unsteady effects can be neglected with a reasonable degree of accuracy when τ c > 1.
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