破膜压力对氢-空气预混气体燃爆特性的影响

Effects of vent burst pressure on explosion characteristics of premixed hydrogen-air gases

利用自主设计的5.00 m长矩形管道,对氢气体积分数为30%的氢气-空气预混气体进行了不同破膜压力(p_(v))下的系列燃爆实验,重点研究了p_(v)对管道内外火焰传播行为及爆炸超压的影响。实验结果表明:管道内的火焰传播行为受pv影响显著。在靠近泄爆口的压力传感器所监测的压力-时间曲线上,可以观察到3个压力峰值(p_(b)、p_(out)、p_(ext)),分别对应于铝膜破裂、燃烧混合物泄放以及外部爆炸,大多数情况下,p_(b)为最大压力峰值。管道内部最大超压随着pv升高而增大,但最大内部超压出现的位置受p_(v)的影响。管道外部火焰传播行为与pv有关,但不同p_(v)下外部火焰的最大长度无明显差异。最大外部超压与p_(v)之间呈现非单调变化规律。

By using a self-designed 5.00-m-long duct with a cross-section of 0.30 m × 0.30 m, a seris of experiments were performed on premixed hydrogen-air gases in which volume fraction of hydrogen was 30%. And the effects of vent burst pressure(pv) on the flame propagation and pressure-time histories in the duct were experimentally iveatigated. The explosion flames were recorded by a high-speed camera at a frequency of 2.5 kHz. Five piezoelectric pressure transducers were employed to record the internal and external overpressure. The duct had been evacuated using a vacuum pump before the experiment, and the premixed hydrogen-air gases with volume fraction of 30% was prepared according to Dalton’s law of partial pressure. The variation of the vent burst pressure was achieved by changing the thickness of the aluminum foil which was used as vent cover.The results show that the first three stages of the flame structure in the duct are hemispherical, finger-shaped and tulip flame,respectively. pvhas a significant effect on the structure of tulip flame and its subsequent development. Three pressure peaks(p_(b),p_(out), p_(ext)) can be distinguished from the pressure-time histories monitored by the pressure transducer near the vent,corresponding to three different generation mechanisms: burst of the aluminum film, venting of burned mixtures, and the external explosion, respectively. The three pressure peaks increase with an increase in p_(v). p_(b) is the dominant pressure peak in most cases. The maximum internal overpressure increases as pvincreases, and the position where the maximum internal overpressure was measured depended on pv. The maximum internal overpressure was obtained at the center of the duct(PT2)when pv≤42 kPa, but near the open end of the duct(PT3) if pv>42 kPa. When the flame reached the vent, it ejected from the vent and then ignited the external combustible cloud. Therefore, the external explosion is triggered. pvsignificantly affects the flame evolution outside the duct, but there is no significant difference in the maximum length of the external flame at various pv. A non-monotonic trend between the maximum external overpressure and pvwas observed.