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

Abstract

International audienceA laser-induced fluorescence (LIF) technique capable of assessing 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. Preferential evaporation is determined from the LIF-signal intensity ratio measured within two distinct spectral bands. A scheme to determine the measurement accuracy and precision was established by characterizing the collection setup through determining the ratio of LIF intensities collected within two identical spectral bands. Measurements were performed in a high-pressure, high-temperature vessel equipped with a hollow-cone injector. Experimental conditions were chosen that are representative for engine environments and favor preferential evaporation. The analysis of the preferential evaporation was based on the comparison of instantaneous and mean images of LIF ratios obtained at various temperatures. Inhomogeneous distributions of the fuel volatility classes as a consequence of preferential evaporation were observed and two-dimensionally imaged at ambient temperatures up to 550 K

Quantitative measurements of preferential evaporation effects of multicomponent gasoline fuel sprays at ECN Spray G conditions

“…High quantum yields tracers with minimum cross-talk were chosen. P-difluorobenzene and 1-methylnaphtalene were therefore selected to respectively trace high volatility components (isooctane and pentane) and low volatility component (undecane) 20,12,17 . These tracers feature well separated fluorescent spectra which enable simultaneous accurate measurements with minimum cross-talk pollution 12,24 .…”

“…This configuration requires the exact superposition (mapping) of both images to generate a meaningful image of the intensity ratio (S 292 /S 340 ). Configuration B was used for optimizing the image mapping, assessing the accuracy and precision, and calibrating relative sensitivities 12,17 . Two identical filters (292±14 nm) were placed on both sides of the image stereoscope and the ratio of the nominally identical images (S 292 /S 292 ) allows to assess experimental limitations.…”

“…Since atomization, evaporation and mixing determine the efficiency of combustion, it is of first interest to deeply understand how direct injection 1 and biofuel will influence these physical phenomena 6 . One of the processes of interest is the preferential evaporation of multicomponent fuel 11,12 . The latter happen when low and high volatility fuel components evaporate at different rates in the combustion chamber.…”

“…LIF is a two dimensional technique based on the excitation of a fluorescent molecule (the tracer) with a laser followed by light emission at specific wavelength, depending on the tracer. Recently, this technique has been adapted to the quantification of preferential evaporation of a multicomponent fuel by determining the ratio of low/high volatility components of the fuel with the imaging of two tracer 17,12,11 . Only few references are available in the literature concerning the application of this technique 18,19,15,20 .…”

Experimental assessment of the sources of regulated and unregulated nanoparticles in gasoline direct-injection engines

“…The camera lens was set to obtain a wide depth of focus reducing the diaphragm aperture: acceptable image sharpness was obtained on a wide range of distances including the cylinder head and the piston surface at BDC. TMPD boiling temperature is 260 °C: Considering the distillation curve of a commercial gasoline and the strong co-evaporation effects linked to the small tracer percentage used (0.1 %), the tracer is considered to evaporate together with the heaviest fractions of the fuel 20,20,21 .…”