Study on Flame Acceleration Phenomena at Gas Explosions

本文研究了远离固体壁面的火焰前缘处的湍流增长，得到了以下结果.设计了两种火焰传播试验装置，在传播的火焰前缘附近产生剪切流，并在垂直于火焰前缘的方向上产生速度变化。利用这些装置，在传播的火焰前缘处引起湍流，并通过高速纹影照相术记录和检查其变化。同时记录了燃烧室内的压力波动.利用胶片分析仪和计算机对所获得的高速纹影照片进行分析，并将分析结果与压力记录进行对比，发现火焰的加速或减速与压力波动有着密切的关系.通过对不同条件下湍流预混火焰运动的研究，揭示了火焰前缘的湍流度在很大程度上取决于邻近流场。在火焰加速流场中，观察到火焰前缘湍流的非常快速的发展，而在火焰延迟流场中，观察到火焰前缘湍流被抑制并且其规模变小。这些结果与计算机模拟结果吻合较好.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，压力-时间曲线更接近于实际气体爆炸时的压力-时间曲线，湍流增长使最大压力增大，达到最大压力所需的时间缩短。

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.