Spatially and temporally resolved measurements of soot propensity, temperature, radiation, and cold flow velocity of laminar ethylene non-premixed flames under acoustic forced injection

An acoustically forced axisymmetric laminar non-premixed flame is experimentally studied to evaluate soot volume fraction, temperature and radiation throughout the phases of its periodic cycle. The configuration corresponds to the ISF-4, co-flow 6 - condition A flame of the international sooting flames (ISF) Workshop, generated with a Yale type burner. The flame is forced to 50% modulation at 20 Hz. The profile velocities and amplitude of the pulsation was calibrated with PIV measurements. Line-of-sight attenuation (LOSA) and flame emission measurements at two wavelengths were employed to obtain soot volume fraction and temperature simultaneously. These results allowed to estimate soot radiation in each phase by solving the radiative transfer equation. Results show a predictable and stable fuel forcing based on modulating the signal amplitude of the fuel forcing, producing an injection velocity variation of 25–90 cm/s for the studied flame. Phases in which the flame was detached from the burner exit exhibited the highest soot volume fraction, above the stationary case. In general, soot volume fraction and soot temperature estimations were in accordance to those reported in the literature, which were measured with different techniques, providing data with higher spatial and temporal resolution to the ISF results. In addition, the injection velocity profile near the burner exit was characterized and correlated with the speaker modulation. Finally, an estimation of local soot radiation is provided, reaching maximum values of about 5 MW/m³ for detached phases in locations where soot volume fraction was higher.