Pulsation of Burner-Stabilized CH4-O2 Flames Moderated by CO2 Addition

TL;DR

This paper explores how CO2 addition influences the pulsation behavior of burner-stabilized CH4-O2 flames, revealing mode transitions, stability boundaries, and the effects of flow rate and heat release on flame oscillations.

Contribution

It provides new insights into flame oscillation modes and stability boundaries in CO2-diluted methane flames, using detailed experimental analysis.

Findings

Mode transition phenomena in flame oscillations

Identification of stability boundaries under various conditions

Influence of CO2 dilution on flame pulsation behavior

Abstract

This study investigated the pulsating instability of burner-stabilized premixed CH4-O2 flames at various levels of CO2 dilution. Experiments were conducted using a water-cooled porous-plug burner of 18 mm diameter over a wide range of mixture compositions and flow rates, during which time-resolved measurements of flame chemiluminescence and gas temperature were obtained. The primary oscillation frequencies of the pulsating flames were determined using fast Fourier transform and harmonic power analysis. Phase-locked analysis of the chemiluminescence images revealed an interesting mode-transition phenomenon of the flame oscillations. Under fuel-rich conditions with relatively low heat release rates and low flow rates, the flames exhibited quasi-periodic single-mode oscillations. At elevated flow rates, these oscillations were modulated by low-frequency flame flickering instabilities, which created sidebands around the primary oscillation frequency. At higher heat release rates, the flickering instability further triggered mode splitting, eventually leading to multi-mode oscillations. Regime diagrams of the flame oscillation modes, as well as the stability boundaries, were obtained under various fuel flow rates. These findings can be useful for both fundamental research on flame dynamics and practical applications of CO2-moderated oxy-combustion.