An experimental study of isolated turbulent flame puffs with a co-flow

Abstract

Pulsed, turbulent jet diffusion flames in the presence of co-flowing air of variable strength were examined experimentally. An injection system employing an electronically-controlled solenoid valve was used to inject isolated puffs of unheated ethylene fuel into a combustor with an air co-flow at one atmosphere pressure. In all cases the flames were fully-modulated, that is, the fuel flow was completely shut off between pulses. For small injection volumes and short injection times; compact, puff-like structures were generated. The flame length of these puffs was as much as 79% less than that of a steady-state flame for the same injection Reynolds number. More elongated flame structures, with a flame length closer to that of steady-state flames, resulted from longer injection times and larger injection volumes. For short injection times, the addition of an air co-flow, with a strength of up to Ucsf/~~ = 0.02, resulted in an increase in flame length of up to 46%. The fractional increase in the flame length due to co-flow of pulsed flames with longer injection times, as well as steady flames, was correspondingly less. The observed effects of co-flow on flame length are in good agreement with a scaling argument developed as part of this investigation.