Soot microstructure in steady and flickering laminar methane/air diffusion flames

Journal Article · Sun Mar 01 04:00:00 EST 1998 · Combustion and Flame

OSTI ID:619586

Zhang, J; Megaridis, C M ^[1]

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1. Univ. of Illinois, Chicago, IL (United States). Dept. of Mechanical Engineering

An experimental investigation is presented to identify the mechanisms responsible for the enhanced sooting behavior of strongly flickering methane/air jet diffusion flames when compared to their steady counterparts. The work extends the implementation of thermophoretic sampling in flickering, co-flow, laminar, diffusion flames. Acoustic forcing of the fuel flow rate is used to phase lock the periodic flame flicker close to the natural flicker frequency ({approximately} 10 Hz for a burner diameter of {approximately} 1 cm). Soot primary sizes, determined as functions of flame coordinates, indicate that the largest soot primary units in strongly flickering methane/air flames are larger by {approximately} 60% than those measured in steady flames with the same mean reactant flow rates. The primary particle size measurements, when combined with the soot volume fractions reported by other investigators, indicate that soot surface areas in the flickering flame are three to four times larger than those under steady conditions. These results, along with the fact that residence times in the flickering flame are twice as long as those in the steady flame, suggest that specific soot surface growth rates under unsteady combustion conditions can be similar or even lower than those in the corresponding steady flames. Finally, the number of densities of soot primaries in flickering flames are found to be higher by 30--50% than those in steady flames, thus suggesting stronger and/or extended soot inception mechanisms under flickering conditions. The combination of longer flow residence times and greater population of incipient soot particles in flickering flames appears to be primarily responsible for the higher sooting propensity of methane under laminar unsteady combustion conditions.

• OSTI ID: 619586
• Journal Information: Combustion and Flame, Journal Name: Combustion and Flame Journal Issue: 4 Vol. 112; ISSN 0010-2180; ISSN CBFMAO
• Country of Publication: United States
• Language: English

Related Subjects

03 NATURAL GAS
COMBUSTION INSTABILITY
COMBUSTION KINETICS
LAMINAR FLOW
METHANE
MICROSTRUCTURE
PARTICLE SIZE
SOOT
SURFACE AREA
UNSTEADY FLOW