Study on Flame Acceleration Phenomena at Gas Explosions

对远离固体壁面的火焰前缘湍流增长进行了研究，尽管它对理解气体爆炸时火焰的整体加速度很重要，但仍然是模糊的，得到了以下结果。设计了两种火焰传播试验装置，在火焰传播前沿附近诱导剪切流动，并在火焰前缘法向方向诱导速度变化。利用该装置，在火焰传播前产生湍流，并通过高速纹影摄影记录其变化，并对其进行检测。同时，记录燃烧室内的压力波动。利用胶片分析仪和计算机对获得的高速纹影照片进行了分析，并将结果与压力记录进行了比较，发现火焰的加速或减速与压力波动有密切的关系。通过对不同条件下湍流预混火焰运动的研究，揭示了火焰锋面湍流在很大程度上取决于周围的流场。在火焰加速流场中，火焰锋面湍流发展非常迅速，而在阻燃流场中，火焰锋面湍流受到抑制，且规模变小。这些结果与计算机模拟的结果很吻合。考虑火焰加速对瓦斯爆炸压力升高的影响，预测了压力-时间图。结果表明，考虑湍流增长后的压力-时间图与实际气体爆炸的压力-时间图较为接近，湍流增长提高了最大压力，缩短了达到最大压力的时间。

The turbulence growth at flame fronts far from solid walls, which has remained ambiguous in spite of its importance for understanding overall flame acceleration at gas explosions, has been studied and the following results have been obtained.1. Two types of flame propagation test apparatus were designed to induce a shear flow near a propagating flame front and velocity change in the direction normal to the flame front. By using these apparatus, turbulence at a propagating flame front was caused, and its variation was recorded by high speed schlieren photography and examined. At the same time, the pressure fluctuation in the combustion chamber is recorded.2. The obtained high-speed schlieren photographs were analyzed using film analyzer and computer, and comparing the result to the pressure record, a close relation was found between the flame acceleration or deceleration and pressure fluctuation.3. By examining the motions of turbulent premixed flames under various conditions, it was revealed that the flame front turbulence depends largely on the neighboring flow field. In the flow field for flame acceleration, very rapid development of flame front turbulence was observed, while in the flow field for flame retardation, flame front turbulence was observed to be suppressed and its scale became small. These results coincide well with those of a computer simulation.4. The pressure-time diagrams were predicted by considering the effects of flame acceleration on pressure increase in gas explosions. The results indicate that the pressure-time diagrams become close to those at actual gas explosions by considering the turbulence growth and that turbulence growth increases the maximum pressure and reduces the time to it.