Characterization of the impact of ethanol on the formation of soot particles in gasoline turbulent diffusion flames
Abstract
The objective of this study was to characterize the impact of ethanol as a fuel additive on soot formation in turbulent diffusion flames of different gasoline mixtures with varying alcohol concentrations. A TRF mixture (Toluene Reference Fuel), defined as a surrogate representative of standard gasolines of type SP95, was used as the reference fuel. The experimental results obtained in this study offer important observations regarding the impact of ethanol on soot formation and provide useful data for accurate CFD prediction. 11 flames of TRF mixed with various ethanol mole fractions from 0 to 100% were studied by using two complementary approaches, keeping either the flame power (FPW) or the mass flow rate (MFR) constant. The soot volume fraction (fv) was measured by laser induced incandescence (LII). Absolute fv values were obtained by an auto-calibrated method requiring a radiation source of known luminescence to calibrate the detection system. Laser induced fluorescence (LIF) was also used to measure important soot precursors, i.e. polycyclic aromatic hydrocarbons (PAHs). The experimental results highlighted a quasi-linear reduction in soot formation with increasing substituted volume fraction of ethanol until 40%, above which the linear relation was not followed. The soot particles completely disappeared in the pure ethanol and TRF-E85* flame in the case of constant FPW and constant MFR respectively. These results also highlighted a stronger inhibiting effect of ethanol on soot formation with respect to subsequent ethanol substitution at constant MFR, characterized by a gradual decrease in the flame height. Experiments with commercial gasoline SP95-E10 and E85 were also carried out for the first time for soot formation under turbulent conditions. The measured fv and PAHs profiles illustrated that the used TRF is indeed an appropriate gasoline surrogate for studies aiming at characterizing soot formation.