Experimental study of droplet vaporization for conventional and renewable transportation fuels: Effects of physical properties and chemical composition

As part of the global energy transition, an increasing number of sustainable liquid fuels with a wide range of physical and chemical properties becomes available for gas turbine and IC engines. For an optimal design and operation of these engines, an improved understanding of the effects of fuel properties on atomization, vaporization and combustion kinetics is required. The present work provides a comprehensive experimental study of fuel effects on droplet vaporization for numerous conventional and alternative fuels. The study employs a recently developed flow channel, where free-falling droplets with initial diameters of D & alpha; 77 & mu;m vaporize under technically relevant gas temperatures Tg of up to 1300 K. The evolution of droplet diameters over travel distance and time is measured using microscopic shadow imaging. A total of 13 single fuel components, five bi-and tri-component mixtures, six conventional and alternative jet fuels and mixtures thereof, and three IC engine fuels and mixtures thereof have been tested under well-reproducible ambient conditions. The fuels represent a wide range of chemical classes such as n-alkanes, iso-alkanes, cycloalkanes, aromatics, alcohols and oxymethylene ethers, and most of them were measured for the first time with realistic D and Tg. The results for the single fuel components reveal in detail the temperature-dependent effects of physical properties such as boiling point Tb, liquid density l and enthalpy of vaporization Hv. In particular, it was found that for high gas temperatures of about 1250 K, the vaporization rate is almost completely determined by the product of Hv and l. By comparison with the results for single n-alkanes, the measurements for bi-and tri-component mixtures accurately characterize the preferential vaporization of individual fuel components over droplet lifetime. The results for various multi-component fuels reveal complex interplays of preferential vaporization and temperature-dependent influences of physical properties. It is shown that the vaporization for conventional and corresponding alternative fuels can differ significantly. Finally, the droplet vaporization is characterized for mixtures of PRF90+ethanol and ethanol+water, which exhibit a non-ideal vapor-liquid equilibrium.