Effect of ethanol addition in gasoline and gasoline–surrogate on soot formation in turbulent spray flames

The effect of ethanol on soot formation has been studied in turbulent spray flames of gasoline/ethanol and gasoline–surrogate/ethanol mixtures containing 10%, 20% and 30% of alcohol in volume. A hybrid burner specially designed to stabilize different liquid fuels flames with identical hydrodynamic conditions has been used. Spatially resolved measurements of soot volume fraction and of soot precursors concentration have been carried out by coupling Laser-Induced Incandescence (LII) at 1064 nm and Laser-Induced Fluorescence (LIF) at 532 nm. Significant reductions of the concentrations of soot and soot precursors have been observed when adding ethanol to gasoline. A similar behaviour has been obtained with a gasoline–surrogate which has been found to reproduce well the sooting propensity of the unleaded gasoline used in this work. The analysis of the correlation existing between the peak soot volume fraction measured in flames and the Threshold Soot Index (TSI) of the different mixtures tested in this work revealed that the effect of ethanol was not only a dilution one but that the oxygen contained in the alcohol also influence the soot formation. Finally, the comparison of the LII fluence curves and time decays obtained in gasoline/ethanol mixtures showed that soot particles oxidized faster when ethanol is added to the base fuel.