Flame describing function of conical laminar premixed flames subjected to parasite-velocity decoupled equivalence ratio oscillation

IF 5.8 2区工程技术 Q2 ENERGY & FUELS Combustion and Flame Pub Date : 2025-02-26 DOI:10.1016/j.combustflame.2025.114078

Zhixin Zhao, Ze Wang, Mingchen Sun, Hongwei Chen, Dong Yang, Bo Zhou

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引用次数: 0

Abstract

Thermoacoustic instability presents a prominent challenge widely occurring in combustion systems, with equivalence ratio (ϕ) oscillation plays a vital role. The present work demonstrated a ϕ-modulation system from which the parasite velocity oscillation introduced from the mechanical motion ϕ-modulation is eliminated, and the influence of ϕ-modulation on a Bunsen-type premixed CH₄/air laminar flame was systematically investigated for various modulation amplitudes (ɛ), modulation frequencies (f, from 2 Hz to 40 Hz or Strouhal number, St, from 0 to 4) and mean equivalence ratios (ϕ₀=1.2 and ϕ₀=1.0). Synchronized measurements of ϕ, CH* emission, pressure and velocity perturbations were performed. The flame describing functions (FDF) of flame surface area (F_A), surface-integrated burning velocity (

F_{s_{L}}

) as well as the heat release rate (F_Q) with respect to ϕ-modulation were constructed and compared with analytical small-perturbation (SP) solutions for the first time. It is found that the FDFs (both gain and phase) including F_A,

F_{s_{L}}

and F_Q show generally a good agreement with the SP solution at a small perturbation amplitude of ɛ=0.05. However, as ɛ increased, the FDFs deviated from the SP solution to varying extents, which is in line with the quasi-steady-state analysis (QSSA) through a necessary fourth-order Taylor expansion of S_L(ϕ), showing a strong nonlinear effect for ϕ-modulation. The QSSA also highlights the FDFs can be highly dependent on ϕ₀. Ultimately, flame-generated acoustic oscillations were detected from the flames subjected to the ϕ-modulation, introducing an additional mechanism that further contributes to the deviation from the SP solution. An improved agreement of the measured FDFs with the SP solution was observed for the introduction of Helmholtz resonators in the burner system.

In summary, the present experimental platform can be easily applied to turbulent flames, and will allows for future studies on the coupling between equivalence ratio fluctuation with velocity fluctuation as well as the response of entropy waves to equivalence ratio fluctuations, which are important aspects when the flame response goes beyond the linear regime.

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来源期刊

Combustion and Flame 工程技术-工程：化工

CiteScore

9.50

自引率

20.50%

发文量

631

审稿时长

3.8 months

期刊介绍： The mission of the journal is to publish high quality work from experimental, theoretical, and computational investigations on the fundamentals of combustion phenomena and closely allied matters. While submissions in all pertinent areas are welcomed, past and recent focus of the journal has been on: Development and validation of reaction kinetics, reduction of reaction mechanisms and modeling of combustion systems, including: Conventional, alternative and surrogate fuels; Pollutants; Particulate and aerosol formation and abatement; Heterogeneous processes. Experimental, theoretical, and computational studies of laminar and turbulent combustion phenomena, including: Premixed and non-premixed flames; Ignition and extinction phenomena; Flame propagation; Flame structure; Instabilities and swirl; Flame spread; Multi-phase reactants. Advances in diagnostic and computational methods in combustion, including: Measurement and simulation of scalar and vector properties; Novel techniques; State-of-the art applications. Fundamental investigations of combustion technologies and systems, including: Internal combustion engines; Gas turbines; Small- and large-scale stationary combustion and power generation; Catalytic combustion; Combustion synthesis; Combustion under extreme conditions; New concepts.