ABSTRACT

The paper discusses the results of an experimental study on combustion development in a large volume filled with ultra-lean hydrogen-air mixture under terrestrial gravity conditions. For the first time, characteristicflame ball evolutionIn particular, ittheBesides, the lateral expansion of the flame ball plays an important role, defining the changes in curvature radius and stretching of the flame. Due to this, flame breaks up and secondary flame kernels arise. So, the developed structure of the ultra-lean flame occurs to be much more complex than earlier registered cap-shaped flames. Large-scale dynamics of the flame ball is of paramount interest for understanding the stability of near-limit flames and for estimation of hazards related to the development of flame balls under real conditions. Studied processes represent a possible way of energy transfer from the spatial areas filled with less reactive mixtures toward areas with high mixture reactivity. Such a phenomenon stages of the during its convective upward motion on large spatial scales are described. The physical mechanisms defining the particularities of ultra-lean flame evolution subjected to the natural convection are proposed. is shown that the key role in the process of flame propagation in the ultra-lean mixture belongs to the convective rise of the hot combustion products in the gravity field. Herewith, velocity of the flame upward motion occurs to be much higher than the laminar burning velocity in the considered ultra-lean hydrogen-air mixture. may become a reason for the development of emergencies and should be thoroughly investigated and taken into account while designing reliable fire and explosion safety systems. Experimental results are compared with previously obtained numerical data that allowed to demonstrate the correctness of the mathematical modeling and physical mechanisms identified on its basis.

摘要

本文讨论了在地面重力条件下大体积充满超稀薄氢-空气混合物的燃烧发展的实验研究结果。首次，特征性的火焰球演变尤其是火焰球的侧向膨胀起着重要作用，它定义了曲率半径和火焰伸展的变化。因此，火焰破裂并产生二次火焰核。因此，超稀薄火焰的发达结构要比早先注册的帽形火焰复杂得多。火焰球的大规模动力学对于理解近极限火焰的稳定性以及估计与真实条件下火焰球发展有关的危险至关重要。研究过程代表了从充满较少反应性混合物的空间区域向具有高混合物反应性的区域转移能量的可能方式。描述了在大空间尺度上对流向上运动的这种现象阶段。提出了定义自然对流条件下超稀薄火焰演化的特殊性的物理机制。结果表明，超稀薄混合物在火焰传播过程中的关键作用是重力场中热燃烧产物的对流上升。因此，在所考虑的超稀氢-空气混合物中，火焰向上运动的速度发生得比层流燃烧速度高得多。可能会成为紧急情况发展的原因，在设计可靠的火灾和爆炸安全系统时应进行彻底调查和考虑。将实验结果与先前获得的数值数据进行比较，从而可以证明数学模型和基于其确定的物理机制的正确性。