Abstract
In this work, the possibility of using planar droplet sizing (PDS) based on laser-induced fluorescence (LIF) and Mie scattering was investigated within the framework of measuring the droplet Sauter mean diameter (SMD) of direct-injection spark-ignition (DISI) spray systems. For this purpose, LIF and Mie signals of monodisperse fuel droplets produced by a droplet generator were studied at engine relevant diameters (20–50 µm). The surrogate gasoline fuel Toliso (consisting of 65 vol. % isooctane, 35 vol. % toluene) and the biofuel blend E20 (consisting of 80 vol. % Toliso, 20 vol. % ethanol) were used and which were doped with the fluorescence dye “nile red”. The effects of ethanol admixture, dye concentration, laser power, and temperature variation on the LIF/Mie ratio were studied simultaneously at both macroscopic and microscopic scale. The deduced calibration curves of the LIF and Mie signals of both fuels showed volumetric and surface dependent behaviors, respectively, in accordance with the assumptions in the literature. The existence of glare points and morphology-dependent resonances (MDRs) lead to slightly higher LIF and Mie exponents of E20 in comparison to Toliso. In principle, these calibration curves enable the determination of the SMD from LIF/Mie ratio images of transient fuel sprays.
Highlights
The addition of renewable biofuels, such as ethanol in fossil gasoline fuels, can contribute to the reduction of CO2 emissions
Nile red (C20 H18 N2 O2 ) is another laser-induced fluorescence (LIF)-tracer which has already been employed in a previous study in commercial gasoline and diesel fuels [24] for the investigation of the primary breakup of sprays in the near-nozzle region
The microscopic and macroscopic LIF and Mie signals of micrometric monodisperse fuel droplets doped with nile red were investigated and the suitability of this tracer for planar droplet sizing was discussed
Summary
The addition of renewable biofuels, such as ethanol in fossil gasoline fuels, can contribute to the reduction of CO2 emissions. Nile red (C20 H18 N2 O2 ) is another LIF-tracer which has already been employed in a previous study in commercial gasoline and diesel fuels [24] for the investigation of the primary breakup of sprays in the near-nozzle region. To ensure that aromatic fuel components of a realistic gasoline fuel do not become excited by the laser, a visible wavelength is preferred This criterion is fulfilled by the dye nile red, as it can be excited to fluoresce using a 532 nm Nd:YAG-laser. For application of the LIF/Mie ratio technique in DISI engine sprays, a temperature insensitive signal ratio is advantageous in order to achieve accurate and reliable measurements. The microscopic and macroscopic LIF and Mie signals of micrometric monodisperse fuel droplets are investigated using nile red, and the suitability of this technique for planar droplet sizing is discussed.
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