Comments on unmixedness

Unmixedness in flames refers to the condition in which eddies of fuel and oxidant have engulfed each other but where the molecular mixing necessary for complete reaction has not taken place. This phenomenon is studied experimentally using a flow geometry consisting of a coaxial Mach 2 hydrogen jet surrounded by a parallel cold Mach 2 air stream. Gas sample measurements taken downstream in the region near the flame revealed the presence of unreacted hydrogen and oxygen in the same sample. The data were analyzed by means of the CHARNAL program which uses a step function variation with time for instantaneous concentration.