Oxy-Coal Combustion Flamelet Dynamics From High-Speed Video Analysis

At 3,000 frames per second and shutter speeds of 1/250,000 of a second, the action in a turbulent flame in an oxy-coal combustion system is stopped.  Analysis of these images shows the instantaneous temperature field and how it changes due to the mixing and reaction of eddies that contain volatiles that have evolved from coal in the radiation field of the furnace and oxygen.  The soot generated by this reaction is observed with the video camera.  Using image analysis, the macroscopic velocity field and the local flamelet velocity, flamelet heating and flamelet cooling rates are measured.  The results show that flamelet temperatures have a probability density distribution that depends on the local composition.  Maximum flamelet temperatures approach the adiabatic flame temperature for the coal.  The flamelet velocity ranges from 1 to 10 m/s corresponding to sub sonic combustion or micro deflagrations.  An analysis of the flamelet heating and cooling allows the size of the soot particles generated in the flamelet to be determined.