Application of Planar Time-Resolved 2C-LII for Soot Emission Measurements in Diffusion Flames of DME Blends and in Swirl Spray Flames

This paper investigated soot emission measurements from self-calibrated planar time-resolved two-colour laser-induced incandescence (2C-LII) in a range of co-flow laminar diffusion flames of methane and ethylene blended with di-methyl ether (DME), and in turbulent swirl spray flames of n-heptane and iso-pentanol. It discusses the dependence of measurement parameters such as laser fluence levels, acquisition delay times, and acquisition durations (TTL) on the quantification of soot volume fractions (SVFs) and effective primary particle diameter (ePPDs). In laminar flames, it showed a slight inverse correlation in between the incident laser energy to the quantification of the soot concentrations with a discrepancy less than 1% in SVF. The effect on the acquisition delay time showed a variation in soot particle temperatures (around 10 K) and in SVF measurements (less than 1%). The ePPDs obtained from the measured temperature decay from the 2C-LII measurements were calculated. A variation in the derived ePPDs was found with different acquisition durations (10, 20 and 40 ns TTL). The addition of DME to the methane or ethylene flames showed a decrease in the overall soot concentration, and an increase in the ePPDs by about 70% compared to the ethylene flame. A feasibility study of applying the planar 2C-LII method in turbulent swirl flames of heptane/iso-pentanol to measure soot emission distributions was also conducted. The spatial-averaged SVF in turbulent heptane flames reduces with larger acquisition duration. The addition of iso-pentanol to n-heptane fuel was found to decrease the overall SVF. However, opposite trends were found for the ePPDs with addition of iso-pentanol at low (20 ns and 40 ns) and high (100 ns) TTLs. This work highlights the effect of acquisition parameters in quantitative soot emissions measurements via the 2C-LII technique. It contributes to the application of 2C-LII to help understanding soot formations in model gas turbine combustors and from alternative fuels in the next step.