Abstract
A novel planar droplet sizing (PDS) technique based on laser-induced fluorescence (LIF) and Mie-scattering is utilized for the characterization of the spray structure under gasoline direct-injection spark-ignition (DISI) conditions. Fuel effects on the spray structure and cyclic variations are studied for a gasoline surrogate fuel (Toliso, consisting of 65 vol.% isooctane and 35 vol.% toluene) and the gasoline-ethanol blend E20 (20 vol.% ethanol admixture). Sauter mean diameter (SMD) results are compared with those from phase-Doppler anemometry (PDA) measurements showing good agreement especially at early points in time (up to 1.2 ms after start of injection). The liquid spray propagation and SMD are very similar for both fuels indicating similar atomization behavior. Both investigated fuels show comparable cyclic variations of the spray shape. A larger width and slightly larger droplet sizes are observed for the E20 spray when stronger evaporation occurs (at 2 ms). At these later points in time, the PDS-measured droplet sizes differ from the PDA-results. Here the limitation of the PDS-technique becomes obvious as a partial evaporation of the droplets may lead to large systematic errors. A numerical simulation of single droplets is provided for clarification of issues of droplet evaporation in PDS.Graphic abstract
Highlights
The spray formation controls the combustion process of IC engines in terms of pollutant emissions, efficiency and CO2-emissions
The quantified laser-induced fluorescence (LIF)/Mie ratios of the Toliso and E20 in terms of the Sauter mean diameter (SMD) are shown in Fig. 5 and the corresponding average images and coefficient of variation (COV) images are exhibited in Figs. 6 and 7
The SMDs derived from the structured laser illumination planar imaging (SLIPI) LIF/Miemeasurements are compared to point-wise phase-Doppler anemometry (PDA) measurements
Summary
The spray formation controls the combustion process of IC engines in terms of pollutant emissions, efficiency and CO2-emissions. The spray formation of gasolineethanol fuel blends is studied in a constant volume chamber with the LIF/Mie ratio technique For this purpose, the PDS-technique is combined with 2-phase structured laser illumination planar imaging (SLIPI) to reduce effects of multiply scattered light in denser spray regions [for details see (Koegl et al 2019a; Mishra et al 2017; Storch et al 2016b)]. The limitations of the presented LIF/Mie-technique under conditions with low evaporation rate (gas and fuel temperature 293 K, injection pressure 16 MPa, chamber pressure 0.2 MPa) are presented For this purpose, a numerical simulation of the single droplet evaporation process is provided as well, which describes different sources of error (such as temperature and dye concentration effects) on the accuracy of the PDS technique. The effect of the evaporation rate on the accuracy is determined for various base fuels, which show different boiling points and evaporation enthalpies
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