Structure and Flame Length of Fully-Modulated, Turbulent Diffusion Flames

• Published in: Combustion science and technology 2000-06, Vol.155 (1), p.203-225
• Main Authors: HERMANSON, J.C., DUGNANI, R., JOHARI, H.
• Format: Article
• Language: English
• Subjects: Applied sciences; Combustion of gaseous fuels; Combustion. Flame; Energy; Energy. Thermal use of fuels; Exact sciences and technology; Theoretical studies. Data and constants. Metering
• ISSN: 0010-2202; 1563-521X
• DOI: 10.1080/00102200008947290

The turbulent flame structure and flame length of fully-modulated diffusion flames was examined over a range of pulsing frequencies, injection flow rates, and duty-cycles. An injection system employing an electronically-controlled solenoid value was used to discharge puffs of unhealed natural gas and ethylene fuel into still air at one atmosphere pressure. Video imaging of the luminosity from the sooting regions of the flame revealed two distinct types of flame structure. For small injected volumes and short injection times, compact, puff-like structures with a short flame length were generated. More elongated "cigar-shaped" structures, with a longer flame length closer to that of steady-state flames, resulted from longer injection times and larger injected volumes. An injection parameter which characterizes the transition from puff-like to cigar-shaped flame behavior is presented. For puffs, an increase in duty-cycle generally led to an increase in flame length. This increase was less for cigar-shaped flames. The downstream location of the puff-like flame structures increased roughly with time to the 1/2 power, in agreement with buoyant thermals and starting jets.