Dynamics of Premixed Flames Near Lean and Rich Blowout

ABSTRACT

Practical combustors in furnaces, industrial heaters, and gas turbine engines face a sudden loss of flame due to rich blowout (RBO) at an extremely rich fuel-air mixture or lean blowout (LBO) at an extremely lean fuel-air mixture. Thus, the stability limits of the combustion regime are governed by RBO and LBO. In the present study, we focus on the dynamics of swirl-stabilized premixed combustion near lower and higher flammability limits, where the possibilities of LBO and RBO, respectively, are observed. Near RBO and LBO, we employ metrics from statistics and dynamical systems theory to characterize the transition in flame dynamics. We observe that the range of frequencies obtained using Fourier Transform near RBO and LBO is alike. The emergence of dominantly low-frequency oscillation near those blowout limits is investigated using Hilbert Transform. The mean frequency of the combustion system gradually reduces near both blowout limits due to behavioral oscillations prominently observed. The scaling property of flame oscillation is examined using the Hurst exponent, and we observe a decreasing trend of the parameter as combustion approaches both LBO and RBO. Therefore, for the gradual reduction of the Hurst exponent near both flammability limits, we can use the parameter as a precursor for both RBO and LBO.

KEYWORDS:

• Rich blowout
• lean blowout
• premixed flame
• Hilbert transform
• hurst exponent

Acknowledgement

Sabyasachi Mondal acknowledges the financial support from National Doctoral Fellowship scheme of AICTE (Application Number: 63572). Further, Somnath De, Achintya Mukhopadhyay, and Swarnendu Sen would like to acknowledge the funding obtained from RUSA 2.0, Jadavpur University (Reference no. R-11/274/19).

Disclosure statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.