Pressure effects on soot formation in turbulent CH4 flames in an O2/CO2 atmosphere

• Soot volume fraction increased by up to 14× as pressure rose from 1 to 5 bar in turbulent oxy-methane flames. • Higher pressure led to earlier soot inception, denser soot fields, and reduced intermittency in the flame. • Normalizing soot by fuel flow revealed near-linear scaling with pressure. This study investigates the effect of pressure on soot formation in turbulent oxy-fuel methane jet flames using Planar Laser-Induced Incandescence (PLII) calibrated using Light Extinction Measurements (LEM). The bulk jet velocity was held constant while the pressure was increased from 1 bar (Re = 3500) to 3 bar (Re = 10,600) and 5 bar (Re = 17,700) inside our new high-pressure vessel. DSLR imaging revealed increased flame luminosity and reduced flame length with rising pressure, consistent with previous literature. Planar soot volume fraction (SVF) measurements showed a significant increase in soot levels with pressure, with the maximum mean SVF increasing by factors of 7 and 14 at 3 bar and 5 bar, respectively. The intermittency analysis indicated a more continuous soot field at elevated pressures, while the Probability Density Function (PDF) analysis demonstrated a shift toward higher soot concentrations with reduced variability. Radially and volumetrically integrated SVF further confirmed a pressure dependence, with total soot loading (volume-integrated SVF) showing a P 2.1 pressure dependence. However, when normalized by the fuel mass flow rate, this dependence weakens to show almost linear behavior, suggesting that both pressure and additional carbon input contribute to the observed trends. These findings provide new insights into the pressure-driven mechanisms governing soot formation in high-pressure turbulent oxy-fuel flames and provide dataset for validating numerical models.