Investigation of the preferential evaporation of fuel mixtures in levitated single droplets

The blending of alternative fuels like ethanol with conventional fuels significantly alters their evaporation properties, which directly impacts combustion behavior. While previous studies have utilized droplet levitation to investigate evaporation dynamics and compared them to the classical D 2 -law of Langmuir, a deeper understanding of real-time concentration changes during evaporation is still needed. To address this gap, we employ a combined Raman and shadowgraphy approach to study the preferential evaporation of acoustically levitated ethanol/isooctane mixed fuel droplets. We monitor real-time concentration changes within the droplet using Raman spectroscopy, while shadowgraphy provides insights into the surface regression rate during preferential evaporation, and further, compare the results to simulated data generated by a model based on an Euler-Lagrange framework with OpenFOAM. While timescales deviated between the model and the measurement, likely due to an incomplete description of experimental boundary conditions, we found good qualitative agreement for the trends of droplet composition and surface regression rate between the measurement and the simulated data. We provide experimental data for the measured surface regression rate of ethanol/isooctane blended droplets during acoustic levitation. • Provides previously unavailable, simultaneously measured surface regression rates and time-resolved concentrations for ethanol/isooctane fuel blends. • Demonstrates the non-ideal evaporation characteristics of ethanol/isooctane blends, specifically observing the transition between isooctane and ethanol enrichment driven by azeotrope formation. • Establishes good qualitative agreement between experimental measurements and numerical data generated via an Euler-Lagrange framework in OpenFOAM.