Droplet vaporization for conventional and alternative jet fuels at realistic temperature conditions: Systematic measurements and numerical modeling

Abstract

The desired reduction of fossil fuel consumption of the aviation sector requires the introduction of alternative jet fuels from renewable sources. A major hurdle for their introduction is the cost-intensive assessment of fuel effects on combustion performance, which relies on fuel-dependent processes such as atomization, vaporization and chemical reaction. The present work describes results from a newly designed experiment that provides accurate measurements of vaporization of free-falling droplets of realistic size (D≈80 µm) in a vertical laminar flow with temperatures typical of technical combustors. Measurements are performed for a set of systematically chosen conventional and alternative multi-component jet fuels for which detailed compositions are available, and for three single species. The results show that the differences of their vaporization can be accurately resolved and related to physical properties. In particular, it is found that the effect of fuel boiling point on vaporization is largest for ambient gas temperatures T ∞ below ≈1000 K, whereas for higher T ∞ the influence of heat of vaporization is dominant. The well-defined boundary conditions of the experiment further enable a numerical simulation of the ambient flow and the droplet vaporization, where the latter uses a multi-component vaporization model based on a continuous thermodynamic representation of chemical species. Comparisons to measurements show that the present model accurately predicts the temporal evolution of droplet diameters and fuel-dependent effects on vaporization.

Numerical Simulation and Uncertainty Quantification of a Generic Droplet Evaporation Validation Test Case

“…This is explained by the higher heat of vaporization of 1-hexanol (H v = 603 J/g) in comparison to the one of n-dodecane (H v = 361 J/g) (Kim et al, 2019). A more detailed discussion of the (temperature-dependent) influence of latent heat on evaporation rate is provided in our recent study (Stöhr et al, 2020). Second, Fig.…”

“…It is noteworthy that the experiment can also be operated with a matrix burner instead of the electrical heater, which enables investigation of droplet evaporation at temperatures up to 1200 K, as demonstrated in a recent study (Stöhr et al, 2020).…”

The Addition of Particles to an Alternative Jet Fuel

“…It is essential to mention that the auto-ignition of Jet A-1 occurs at a smaller distance from the tip of DTF injector related to the HVO. This fact can be attributed to compounds with lower boiling points (lighter compounds) present in Jet A-1 composition [50]. As displayed in Figure 7, at T = 800 • C the droplet ignites in the region between x = 3 and x = 4 cm.…”

Adaptation of a PTV method for droplets evaporating in vicinity of a flame

“…Direct measurement by filming the evaporation of the droplets provides excellent results [1][2][3][4][5]. Even when the droplet evolves in an environment with an inhomogeneous temperature, it is still possible to obtain results with a high degree of accuracy [6]. However, this diagnosis quickly reaches its limits when the trajectory of the droplets is not known in advance or when the droplets become very small.…”