Two-tracer LIF imaging of preferential evaporation of multi-component gasoline fuel sprays under engine conditions

A laser-induced fluorescence (LIF) technique capable of imaging the effects of preferential evaporation of multi-component fuels was developed based on the simultaneous detection of two aromatic fluorescence tracers with complementary evaporation characteristics matched to different components of a multi-component fuel. Relative variations in the spatial distribution of fuel components as a consequence of preferential evaporation were determined from the ratio of LIF-signals measured within two distinct spectral bands. The accuracy and precision of the method was characterized from determining the LIF-signal ratio within two identical spectral bands. Measurements were performed in a high-pressure high-temperature vessel equipped with a hollow-cone injector. Experimental conditions with temperatures up to 700 K were chosen that are representative for engine environments and favor preferential evaporation. The effects of preferential evaporation were analyzed based on the comparison of instantaneous and mean images of LIF ratios obtained at various temperatures. Variations in the spatial distribution of the fuel volatility classes were observed up to 550 K.