Effects of thermal expansion, strain rate, and gravity force on the steady propagation of a premixed flame in semi-closed channels

Yifan Han,Luhao Liu

doi:10.1063/5.0074667

Abstract

The flame dynamics of steady propagation of a premixed flame in semi-closed channels is investigated. The hydrodynamic model takes into account impacts of channel width, thermal expansion, straining effect, and downward gravity force on the flame front. The steady flame shape and its velocity field could be determined by numerical iteration of a weakly nonlinear front equation and linearized governing equations with Fourier transform, respectively. Results reveal that the introduction of thermal expansion and gravity force enhance the flame curvature and increase the burning velocity, while the straining effect suppresses the flame bending processes. In addition, a non-monotonic dependence of the burning velocity on the Peclet number is further demonstrated. It reveals that the thermal expansion and strain effect would have impacts on the burning velocity as well.

Highlights

Premixed combustion under confinements is one of the fundamental subjects in flame studies.1 Processes of the premixed flame propagation from an open to a closed end in ducts have been investigated experimentally2–8 for decades
We analytically studied the steady propagation of a premixed flame in semi-closed planar channels with freeslip walls
The velocity components are solved by Fourier transform, and the flame shape is obtained by numerical iteration

Summary

Introduction

Premixed combustion under confinements is one of the fundamental subjects in flame studies. Processes of the premixed flame propagation from an open to a closed end in ducts have been investigated experimentally for decades. Premixed combustion under confinements is one of the fundamental subjects in flame studies.. Processes of the premixed flame propagation from an open to a closed end in ducts have been investigated experimentally for decades. Four possible stages of the downward flame propagation are observed as follows:. ● The initial flame front is ignited at the open side and forms a wrinkled surface. The curved flame front is propagating at a steady speed in the absence of the acoustic wave and propagates upstream at about twice the planar flame speed.. ● As the flame propagates downward, the flame is influenced by axial acoustic velocity fluctuations.. A large amplitude of the flame velocity is triggered via the velocity-coupling mechanism of the primary thermoacoustic instability.. The curved flame surface tends to be planar ● As the flame propagates downward, the flame is influenced by axial acoustic velocity fluctuations. A large amplitude of the flame velocity is triggered via the velocity-coupling mechanism of the primary thermoacoustic instability. The curved flame surface tends to be planar

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Results

Conclusion