| Abstrakt: |
In previous work, the authors designed and built a laboratory apparatus that subjects a confined bed of granular propellant to essentially a planar hot-gas ignition wave. Diagnostics include wall-mounted pressure transducers to monitor the time history of the pressure field, and fast-response thermocouples protected within custom sting-mounted steel holders which protrude into the propellant bed to measure gas temperature. The present investigation examines convective ignition behavior of five different granular solid propellants under nearly identical flow conditions. This was made possible by employing special lots of M 10 (single-base) JA2 (double-base), M30 (triple-base), M43 and XM39 (nitramine composites), each as identical-sized 7-perf grains. Since the initial flow characteristics of these propellant beds are the same, differences in chamber ignition response are the direct result of propellant composition. Ignition delays for M10, JA2, and M30 are essentially within the range of 2.3–6 ms: the response is independent of composition. However, the nitramine composite M43 (energetic binder) exhibits delays of 220–300 ms, during which the gas-phase temperatures within the bed drop from 1100 K to below 400 K before a runaway reaction finally ruptures the shear disc in the chamber. It is more difficult to ignite the nitramine composite XM39 (inert binder): time delays can exceed 600 ms. The data also suggest an inverse dependence on pressure, which is consistent with the hypothesis that gas-phase chemical reactions are controlling chamber response. When the chamber configuration is altered to promote a rapidly rising pressure field, ignition delays for both nitramine propellants are reduced to less than 1 ms. |
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