An experimental investigation of flame spreading from bluff body flameholders

摘要

Flame spreading from 1/16 to l inch circular cylinder flame holders in two-dimensional flow was studied experimentally. Combustion wake widths were determined by use of spark Schlieren photographs at distances up to 36 inches downstream of the flame-holder in a 3 by 6 inch duct. The effect on wake width and flow parameters of several geometric and operating variables was observed.The data show that above a critical approach gas velocity, corresponding to the transition from laminar to turbulent flow in the flame front, the wake width was independent of velocity and remained constant. Below the critical velocity the wake width was a strong function of velocity. Small but real effects were found on changing fuel-air ratios. The wake width was smallest and the wake spreading rate lowest at the stoichiometric fuel-air ratio. An eight to one variation in flameholder diameter resulted in only a 30 per cent variation in wake width at a distance of one duct height downstream. Farther downstream the variation was even less. Total and static pressure measurements showed that combustion processes fix the total pressure wake and that the losses associated with flameholder drag were not important in fixing the wake spreading rate.