Date of Award

Spring 2023

Document Type

Open Access Thesis

Department

Computer Science and Engineering

First Advisor

Sang Hee Won

Abstract

Preferential vaporization of isolated single droplets was evaluated in this study. A previously verified lab-scale experiment using flow acceleration to counteract the effects of buoyancy in a converging channel with a decreasing cross section was utilized to investigate the single isolated droplet combustion. The previous experimentation revealed differences between results and values predicted by a one-dimensional numerical simulation. To investigate if the observed differences were the result of turbulent flow and the development of a boundary layer within the channel, a model was designed and analyzed in Ansys Fluent.

The developed Ansys simulation indicated that turbulent flow and growth of the boundary layer were significant enough to affect the burning behavior of the droplets. However, the intensity of these effects was not great enough to invalidate the ability of the converging channel to be used as an investigative system for single isolated droplet combustion, especially in the upper half of the channel where the measurements were taken.

A binary mixture of isocetane and n-heptane was formulated with different initial mole fractions. Isocetane is less volatile and heavier than n-heptane and was expected to remain in the liquid phase while n-heptane vaporized. The diameter of the droplets and flames were observed at various points along the converging channel to evaluate the burning behavior. The diameter of the binary fuel droplets was determined by taking images with backlight and a Photron Fastcam SA-Z high-speed camera. The flame diameter was observed with an Andor iStar intensified complementary metal oxide semiconductor (ICMOS) camera.

The extent of preferential vaporization was determined by evaluating the mole fractions of each fuel component at various locations along the channel. The collected samples were analyzed using nuclear magnetic resonance (NMR). The ignition process was found to play a significant role in the vaporization characteristics of the droplet.

From this study, the change in chemical composition over time provided evidence for preferential vaporization. While the apparatus used to conduct the experiment was validated, the effects of turbulence and the development of the boundary layer could not be discounted completely. To minimize these effects for future work, an axisymmetric channel was designed and modeled in Ansys Fluent.

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