Sub-millimeter sized multi-component jet fuel surrogate droplet combustion: Physicochemical preferential vaporization effects

Isolated droplet burning behaviors of fuel mixtures that all share the fully pre-vaporized combustion behaviors of the same global Jet-A real fuel are investigated numerically to elucidate the effects of preferential vaporization. Predictions are generated using three such multi-component hydrocarbon mixtures (Mixture-1: n-decane/iso-octane/toluene 42.7/33.0/24.3, Mixture-2: n-dodecane/iso-octane/1,3,5 trimethyl benzene 49.0/21.0/30.0 and Mixture-3: n-hexadecane/iso-octane/1,3,5 trimethyl benzene 36.5/31.0/32.5 molar ratios), each having very different distillation properties. Simulations are performed using a transient onedimensional sphero-symmetric model, involving numerically reduced detailed chemical kinetics, and multicomponent gas-phase diffusive transport. The interactions among the different liquid-phase components are modeled using UNIFAC activity coefficient methodology. The predictions using Mixture-1 are found to be in good agreement with previously published drop-tower experiments for 550 mu m droplet combustion in air. Stagnant and internally mixed liquid-phase behaviors are both considered. Near fully mixed internal conditions and including sooting effects (observed in the experiments) result in predictions that are in good agreement with experimental drop diameter and flame-standoff ratio histories. By comparing predictions for the three mixtures, preferential vaporization effects exhibit strong non-linear dependences on initial droplet diameter and ambient pressure. At low pressures and for droplet sizes typical of those found in multi-phase gas turbine combustors, comparable diffusion and vaporization characteristic times favor frozen limit vaporization. However, at pressures typical of those found in applications, batch distillation dominates and preferential vaporization chemical property differences are found to become as significant as physical property effects in influencing combustion behaviors. (c) 2020 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Automated summary

Isolated droplet burning behaviors of fuel mixtures with fully pre-vaporized combustion behaviors were numerically studied to investigate the effects of preferential vaporization. Three multi-component hydrocarbon mixtures were used for predictions, showing strong non-linear dependences on initial droplet diameter and ambient pressure for preferential vaporization effects.