Investigation of ethanol blending on soot particle evolution in counterflow diffusion flames of a gasoline surrogate

Across all transport sectors, there is an increasing recognition of the importance of reducing not only CO 2 emissions but also other climate-impacting pollutants, such as soot particulate matter. Ethanol, a widely utilized biofuel, has the potential to significantly reduce CO 2 emissions. However, its influence on soot formation when blended with complex hydrocarbon fuels remains unclear. Previous studies showed that blending ethanol above 40 vol% reduces both the total soot volume fraction and particle diameter, while at lower blending ratios, 20 vol% ethanol or less, discrepant trends can be found in the literature. In some studies, a synergistic effect has been observed, where ethanol blending with various hydrocarbon fuels promotes soot formation. To address these uncertainties, this study investigates the effects of varying ethanol blending ratios with a gasoline surrogate (90 vol% iso-octane and 10 vol% toluene) on soot formation characteristics in a laminar counterflow diffusion flame for ethanol ratios up to 60 vol%. Experimental and numerical investigations are conducted to understand the effects of ethanol blending on gas-phase products, soot volume fraction and particle size distribution. Gas-Chromatography and two-color Time-Resolved Laser Induced Incandescence (TR-LII) were employed to measure gas species, soot volume fraction and primary particle size distribution, respectively. Numerical simulations are carried out using a detailed soot model based on the Split-based Extended Quadrature Method of Moments (S-EQMOM). Both experimental and numerical results consistently show a non-linear impact of ethanol blending on soot precursors and a non-monotonic effect on particle quantities. Small amounts of ethanol, up to 10 vol%, have little effect on soot formation. However, higher levels of ethanol significantly reduce soot formation and the diameter of large particles. Analysis of individual soot processes reveals that, when ethanol is added, PAH-related soot processes, such as inception and PAH-deposition, are the limiting steps, while the HACA and soot oxidation mechanisms are less affected. • Comprehensive counterflow gasoline flame analysis with ethanol blends up to 60 vol%. • New measurements on soot precursors, volume fraction and particle size distribution. • Numerical results support experimental trends for all ethanol blending ratios. • Non-monotonic soot yield trend observed with a decrease for ethanol blending above 20%. • Ethanol reduces PAH-related soot processes, HACA and oxidation less affected.