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Atomization and Sprays, Vol.7, No.3, 317-337, 1997
Experimental study of pure and multicomponent fuel droplet evaporation in a heated air flow
The dynamics and vaporization of both pure and multicomponent fuel droplets in a laminar-flow field are investigated Extensive data are obtained on the velocity and size history of a fuel droplet injected into a well-characterized hot laminar flow. Fuels considered are n-hexane, n-decane, and a bicomponent mixture of equal amounts of hexane and decane. The droplet velocity and size histories are measured by phase Doppler particle analyzer, and compared with the predictions from three different liquid-phase models, the infinite-diffusion, diffusion-limit, and thin-skin models. Predicted results generally show good agreement with measured data. For the conditions of this study, it is shown that the use of a solid-sphere, steady-state drag late adequately reproduces the measured velocity history for small to moderate droplet accelerations, provided the variable-property effects are included in the model. However, the quasi-steady drag equation is not able to capture either the large deceleration experienced by the droplet near the injection location, nor the measured inflection point, where the droplet acceleration changes sign, underscoring the importance of unsteady effects oil droplet motion. The comparison of vaporization history indicates that, under relatively low-temperature conditions, the predictions of both the infinite-diffusion and the diffusion-limit models are in close agreement with experiments. However, the thin-skin model overpredicts the vaporization rate, and shows significant differences with experiments, especially for less volatile (n-decane) and multicomponent fuel droplets. The comparison also indicates that the thermophysical properties of the gas film surrounding the droplet should be calculated accurately; in particular, the effect of fuel vapor should be considered.