Radiative Cooling of a Turbulent Flame Front

Temperature profiles arising from simultaneous radiation and turbulent diffusion in combustion gas products in the vicinity of a turbulent flame front are obtained analytically. Account is taken of the highly nongray nature of the gas absorption and emission by use of band absorption properties and slab band absorptance functions. Radiative cooling is shown to be quite effective, not by acting directly upon the eddies themselves at the flame front, but by acting indirectly to cool greatly the gases in the vicinity of the flame front, which in turn cool the eddies through turbulent mixing. Generalized dimensionless results, as well as particularized examples, are presented. It was found that CO₂, being an intense emitter, reduces flame front temperature to a greater degree than H₂O, a less intense emitter, even though the total emissivity of H₂O exceeds that of CO₂. For this reason flue gas recirculation appears more advantageous than water or steam injection in achieving radiative cooling.