Soot emission, thermal radiation, and laminar instability of acetylene diffusion flames

Abstract

Soot emission and radiant heat loss from turbulent or largely turbulent vertical free diffusion flames of acetylene in still air have been studied over a broad range of the buoyancy Richardson ratio Ri L . Soot emission reaches a peak equal in mass to 12% of the fuel carbon around Ri L = 600. The radiant heat loss there reaches 75% of the theoretical combustion heat release. The flames at large Ri L were initially laminar, and a predominantly sinuous instability was observed in the transition to turbulent flow. The instability was studied stroboscopically, utilizing soot-scattered light. The Strouhal ratio based on burner exit conditions is independent of the exit Reynolds ratio but proportional to the cube of the diameter.