Experimental and Numerical Investigations of Soot Suppression in Diffusion Flames of Oscillating Acetylene

Combustion-generated soot remains a significant environmental and health concern, necessitating effective mitigation strategies. This study investigates the suppression of soot in acetylene diffusion flames through fuel flow oscillation, employing both experimental and numerical approaches. The effects of relative amplitude (<i>A</i> _out) on soot production rates (<i>R</i> _soot) and sound pressure level (SPL) were examined across a range of excitation frequencies (<i>f</i> from 25 to 1200 Hz), acetylene flow rates <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mo>(</mml:mo> <mml:msub><mml:mi>Q</mml:mi> <mml:mrow> <mml:msub><mml:mrow><mml:mi>C</mml:mi></mml:mrow> <mml:mrow><mml:mn>2</mml:mn></mml:mrow> </mml:msub> <mml:msub><mml:mrow><mml:mi>H</mml:mi></mml:mrow> <mml:mrow><mml:mn>2</mml:mn></mml:mrow> </mml:msub> </mml:mrow> </mml:msub> <mml:mo>)</mml:mo></mml:math> , and nozzle inner diameters (<i>D</i> _in from 1.05 to 6 mm). Additionally, the formation of standing acoustic waves was analyzed to reduce energy consumption. Results indicate that <i>R</i> _soot is minimally influenced by <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>Q</mml:mi> <mml:mrow> <mml:msub><mml:mrow><mml:mi>C</mml:mi></mml:mrow> <mml:mrow><mml:mn>2</mml:mn></mml:mrow> </mml:msub> <mml:msub><mml:mrow><mml:mi>H</mml:mi></mml:mrow> <mml:mrow><mml:mn>2</mml:mn></mml:mrow> </mml:msub> </mml:mrow> </mml:msub> </mml:math> but is predominantly controlled by the ratio <i>A</i> _out/<i>D</i> _in. There exists an optimal <i>f</i> at which both <i>R</i> _soot and SPL reach their minima when <i>A</i> _out/<i>D</i> _in ≤ 2 mm^-1, highlighting the role of combustion-acoustic coupling. Notably, the SPL increases sharply with ignition intensification. When standing waves are established within the fuel delivery tube, <i>R</i> _soot can be reduced by 96.7% with a remarkably low speaker power of only 1.4 mW. These findings demonstrate a promising, energy-efficient method for soot mitigation in combustion systems through controlled acoustic oscillations.