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地面常重力(1g)条件下,丙烷/空气预混火焰向上传播的富燃极限为9.2%C_3H_8,而向下传播时的富燃极限仅为6.3%C_3H_8,二者之间存在明显差距。利用微重力条件下的实验,对燃料浓度从6.5%到8.6%(微重力实验中测定的可燃极限)范围内的丙烷/空气预混火焰特性进行了研究。实验发现,重力对近极限丙烷/空气火焰的传播有显著影响,影响程度随着当量比的增加而增大。微重力下丙烷/空气的富燃极限为8.6%C_3H_8(φ=2.24),明显高于1g条件下向下传播火焰的可燃极限,略低于向上传播火焰的可燃极限。随着当量比的增大,根据压力变化曲线计算的火焰层流燃烧速度从8.5cm/s逐渐减小到2.7 cm/s,可燃极限处的层流燃烧速度与前人实验数据一致。
Under constant gravity (1 g), the enrichment limit of propane / air premixed flames propagating upwards was 9.2% C_3H_8, while that of downward propagation was only 6.3% C_3H_8. There was a clear gap between them. The propane / air premixed flame characteristics over the concentration range of 6.5% to 8.6% (combustibility limit determined in microgravity experiments) were studied using microgravity experiments. The experiment found that gravity has a significant impact on the propagation of near-limit propane / air flame, and the degree of influence increases with the equivalence ratio. The enrichment limit of propane / air under microgravity is 8.6% C_3H_8 (φ = 2.24), which is obviously lower than the flammability limit of flame propagating downward under 1g, slightly lower than the flammability limit of upward propagation flame. With the increase of equivalence ratio, the combustion rate of flame laminar flow reduced from 8.5cm / s to 2.7cm / s according to the pressure curve. The laminar flow velocity at the combustible limit is consistent with the previous experimental data.