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Energies 2014, 7(8), 4938-4956; doi:10.3390/en7084938

Buoyant Unstable Behavior of Initially Spherical Lean Hydrogen-Air Premixed Flames

School of Mechanical, Electronic and Control Engineering, Beijing Jiaotong University, Beijing 100044, China
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Received: 31 March 2014 / Revised: 16 July 2014 / Accepted: 23 July 2014 / Published: 31 July 2014
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Abstract

Buoyant unstable behavior in initially spherical lean hydrogen-air premixed flames within a center-ignited combustion vessel have been studied experimentally under a wide range of pressures (including reduced, normal, and elevated pressures). The experimental observations show that the flame front of lean hydrogen-air premixed flames will not give rise to the phenomenon of cellular instability when the equivalence ratio has been reduced to a certain value, which is totally different from the traditional understanding of the instability characteristics of lean hydrogen premixed flames. Accompanied by the smoothened flame front, the propagation mode of lean hydrogen premixed flames transitions from initially spherical outwardly towards upwardly when the flames expand to certain sizes. To quantitatively investigate such buoyant instability behaviors, two parameters, “float rate (ψ)” and “critical flame radius (Rcr)”, have been proposed in the present article. The quantitative results demonstrate that the influences of initial pressure (Pint) on buoyant unstable behaviors are different. Based on the effects of variation of density difference and stretch rate on the flame front, the mechanism of such buoyant unstable behaviors has been explained by the competition between the stretch force and the results of gravity and buoyancy, and lean hydrogen premixed flames will display buoyant unstable behavior when the stretch effects on the flame front are weaker than the effects of gravity and buoyancy. View Full-Text
Keywords: lean hydrogen flame; initial spherical flame; buoyant behaviors; experimental observation lean hydrogen flame; initial spherical flame; buoyant behaviors; experimental observation
This is an open access article distributed under the Creative Commons Attribution License (CC BY 3.0).

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MDPI and ACS Style

Sun, Z.-Y.; Li, G.-X.; Li, H.-M.; Zhai, Y.; Zhou, Z.-H. Buoyant Unstable Behavior of Initially Spherical Lean Hydrogen-Air Premixed Flames. Energies 2014, 7, 4938-4956.

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