ABSOLUTE FLAMMABILITY LIMITS AND FLAME-BALLS

We examine flame balls that are not optically thin so that radiation f rom the hot burned gas is not lost but is reabsorbed by the surroundin g cool gas. The steady solution is shown to be multivalued in general and defines an intrinsic (apparatus independent) flammability limit fo r a sufficiently small ignition source. Beyond the flammability limit a steady solution exists for arbitrarily weak mixtures, but is unreali zable since it is unstable to one-dimensional perturbations. An unstea dy propagating flame solution is also possible for arbitrarily weak mi xtures, but can only be generated by a large ignition source. Observat ions of flame-strings in SF6-diluted mixtures are reported and suggest that the peculiar nature of the radiative properties of SF6 is respon sible for peculiar dynamics.