The Effect of Heat Loss on the Unstable Behavior of Cellular Premixed Flames

Abstract Because combustion is essentially an Arrhenius process, premixed flames generally can only exist within certain parameter ranges, or extinction limits, that correspond to a rate of heat production that is sufficient to sustain the reaction in a given flow geometry. Nonetheless, it is frequently desirable to extend these limits, often for the purpose of increasing fuel efficiency and/or reducing the rate of formation of pollutant species. Another emerging motivation is to allow combustion to be sustained in relatively small volumes, which are characterized by larger surface-to-volume ratios, that would otherwise lead to extinguishing levels of heat loss. Surface catalysts are widely used to achieve such enhancements with respect to efficiency and pollutant formation, and we wish to now consider the role catalysts might play with respect to nonadiabatic flames.

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An Investigation of the Heat Loss Model for Predicting NO Concentration in the Downstream Region of Laminar CH4/Air Premixed Flames

Transactions of the Korean Society of Mechanical Engineers B ◽

10.3795/ksme-b.2009.33.7.486 ◽

2009 ◽

Vol 33 (7) ◽

pp. 486-494

Author(s):

Cheol-Hong Hwang ◽

Chang-Eon Lee ◽

Sung-Min Kum ◽

Kee-Man Lee ◽

Myung-Chul Shin ◽

...

Keyword(s):

Heat Loss ◽

Premixed Flames ◽

Loss Model ◽

Downstream Region

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Numerical Simulation on the Instability of Cylindrically Expanding Premixed Flames With Radiative Heat Loss at Low Lewis Numbers

ASME/JSME 2011 8th Thermal Engineering Joint Conference ◽

10.1115/ajtec2011-44181 ◽

2011 ◽

Author(s):

Takafumi Kusakai ◽

Satoshi Kadowaki

Keyword(s):

Heat Loss ◽

Thermal Instability ◽

Radiative Heat ◽

Premixed Flames ◽

Lewis Number ◽

Radiative Heat Loss ◽

Low Gravity ◽

Gravity Condition ◽

Quenching Condition ◽

Reactive Gases

The instability of cylindrically expanding premixed flames with radiative heat loss was studied by two-dimensional unsteady calculations of reactive gases, based on the diffusive-thermal model equation. When the Lewis number was unity, instability phenomena were not observed. When the Lewis number was sufficiently low, on the other hand, cellular-shaped fronts on adiabatic and non-adiabatic cylindrical flames were observed, which was due to diffusive-thermal instability. As radiative heat loss increased, the behavior of cellular fronts became more unstable. This indicated that the radiation promoted the unstable behavior of flame fronts at low Lewis numbers. When radiative heat loss was much large compared with the quenching condition of a planar flame, cylindrical flames were broken up and several small flames appeared. This was in qualitative agreement with the experimental results on the dynamic behavior of lean hydrogen-air premixed flames with radiative heat loss under the low gravity condition. Several small flames appeared on the grounds that large curvature of flame fronts was necessary to keep high temperature against radiative heat loss.

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