Dependence of flame propagation on pressure andpressurizing gas for an Al/CuO nanoscale thermite

摘要

The pressure dependence of flame propagation in an Al/CuO nanoscale thermite was studied. Experimentswere performed by loosely packing the Al/CuO mixture in an instrumented burn tube, which wasplaced in a large volume, constant pressure chamber with optical windows. A high-speed camera was usedto take photographic data, and six pressure transducers equally spaced along the length of the burn tubewere used to measure the local transient pressure. Ambient pressures were varied between 0 and 15 Mpa,and three different pressurizing gases were used: argon, helium, and nitrogen. Three modes of propagationwere observed. The pressure at which the mode of propagation changed was similar for argon and nitrogen,however, when pressurized with helium, transition occurred at lower pressures. In the low-pressureregime (on0–2 Mpa) a constant velocity mode with speeds on the order of 1000 m/s was observed. In thisregion, a convective mode of propagation was dominant. An accelerating regime was observed for a pressurerange of approximately 2–5 Mpa in argon and nitrogen, with speeds ranging from 100 to 800 m/s. Inhelium, however, if an accelerating region existed it occurred over a narrow pressure range which was notobserved in the present experiments. An oscillating regime was observed in all three gases, in a pressurerange of on5–9 Mpa for argon and nitrogen, and a range of on2–4 Mpa for helium. Velocities in this regionare bimodal, and differ by orders of magnitude, suggesting that the propagation mechanism was oscillatingbetween convective and conductive. At relatively high ambient pressures, a constant velocity mode withspeeds on the order of 1 m/s was observed for all three gases. The conductive mode of propagation waslikely dominant in this region.