S. P. M. Bane
R. Mével
J. E. Shepherd
California Institute of Technology

Cellular structure of an unstable flame ignited
in a mixture of hydrogen and nitrous oxide.

An explosion is ignited in a gaseous mixture of hydrogen (H₂) and nitrous oxide (N₂O) at 40 kPa by an electric spark between two electrodes.  The flame front propagates outwards and initially maintains an approximately spherical shape.  The flame front is perturbed as it passes over the electrodes, resulting in “cracks” that grow across the flame surface as the perturbation is amplified by the thermo-diffusive instability. 

As the flame continues to grow it becomes subject to hydrodynamic instability as well.  By approximately 24 ms after the flame was initiated, the flame surface is completely covered by a cellular structure of instabilities. 

Thermo-diffusive and hydrodynamic instabilities and the effects of flame stretch all contribute to the unstable nature of the flame.  The development and appearance of the unstable flame front is affected by the mixture composition and initial conditions.  Flame instabilities cause a flame to accelerate, which can lead to larger peak pressures or possible transition to a detonation.  This H₂-N₂O flame is an example of an extremely unstable explosion. 

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Reporters may freely use this image. Credit: S. P. M. Bane, R. Mével, and J. E. Shepherd, California Institute of Technology (2010).