The region adjacent to the luminous plume generated by a plasma igniter is found to contain intense turbulence at times long after the plasma plume has cease.d to exist. The extent and growth of this sharply defined region has been recorded by photographing the induced motion of tracer columns of smoke. The photographs demonstrate that the turbulent "puff" is most effective in both propagating particles from the igniter and in eventually (30-40 mm from the igniter) inducing very fine scale mixing with the local gas.
With suitable optics it has been possible to obtain simultaneous photographs of the dispersing smoke cloud and of a schlieren image of the "puff." The schlieren image delineates the previously reported sharp temperature increase at the front of the puff and it is clear from the photographs that at least within experimental limits, the mixing process (as delineated by the smoke cloud) extends to the very front of the "puff." It is this distribution of both heat and particles which is thought to be instrumental in the known ability of the igniter to enhance the rate of combustion in its vicinity.
The speed of propagation of the "puff" in the vicinity of the igniter substantially exceeds conventional flame speeds, in consequence it is clear that current hypotheses which revoke turbulence and/or radicals as a mechanism by which igniters enhance combustion now have a mechanism by which these elements can propagate rapidly enough to interact with the flame front.
Quantitative information on the transport processes has also been obtained. The coefficient of heat conduction in the "puff" has been measured by recording the temperature gradient close to a flat surface using a schlieren deflection technique. The diffusion coefficient has been monitored by studying the dispersion of a column of smoke with a repetitive optical scanning method. Both coefficients show significant increases from their "still air" values which would be sufficient to generate substantial increases in burning velocity.