Visualization Studies of Evaporation and Combustion of Alternative Liquid Fuels and Aviation Liquid Droplets in Controllable Environments
Type of DegreePhD Dissertation
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This dissertation describes visualization studies of alternative fuel and aviation liquid droplet behavior in controlled environments. Three experimental setups using free-falling and suspended droplet techniques were designed, constructed, and shown to be effective methods for studying individual droplet behavior. Systematic suspended droplet studies involving ethanol and glycerol mixtures were performed in rapid heating environments inside an infra-red (IR) heater. Aviation liquid (BP Oil) was used as a representative multicomponent liquid mixture. Quantitative data obtained from low and high magnification visualizations along with the internal droplet temperature were obtained. Experimental techniques and results from the IR heater demonstrate a novel method of studying suspended droplet behavior. This research supplements existing literature on the behavior of similar fluids in high temperature environments. Studying the behavior of alternative fuels and aviation liquids in variable temperature environments was our objective. Generally, applications involve sprays or mist of droplets. A simple approach to understand the spray or mist behavior of a liquid is to consider them as a conglomeration of individual droplet behaviors. We have employed two widely used techniques, namely, the free-falling droplet technique (moving droplet) and suspended droplet technique (stationary droplet) to study individual droplet behavior. Experimental setups using a laboratory scale drop tube furnace and an infra-red heater system with visualization capabilities were constructed for this purpose. A piezoelectric droplet generator was built to perform moving droplet studies in the drop tube furnace. Stationary droplet studies were performed by either generating the droplet at the tip of a graphite fiber (drop tube furnace) or by suspending a droplet on a fine gauge thermocouple wire (IR heater). Proof of method experiments with visualization images were presented for aqueous glycerol solution, hexadecane, and BP Oil to demonstrate the feasibility of the setup to study individual droplet behavior. Systematic studies were performed in the IR heater for ethanol – glycerol (E-G) blends. Two blends, namely E30G70 and E70G30 were prepared and studied alongside pure ethanol (E100) and pure glycerol (G100), together the four liquids represent the E-G system. The E-G system was studied at different gas flowrate conditions (5-25 SCFM), different gas environment types (air and nitrogen), and alongside other liquid types such as pure methanol (M100), pure butanol (B100), standard fuel (hexadecane) and multicomponent aviation liquid (BP Oil). Low magnification visualizations were used to obtain quantitative data (quiescent, behavior, and residence times) and to exhibit various droplet behavior phenomenon such as microexplosion, microdroplet escape behavior, puffing, etc. High magnification visualizations of the E-G system suspended droplet behavior were shown; and the quantitative data obtained was used to determine the d2-law parameter and calculate the evaporation rate constant (k). Characteristic evaporation phases (transient heating phase, fluctuation evaporation phase, and equilibrium evaporation phase) were shown using temporal droplet diameter data plots (d2 vs t) for the four E-G system liquid types. Internal droplet temperature (T) and temperature period classifications (period-1, -2, and -3) that include heating rate (°C/s), time duration (Δt) and temperature change (ΔT) were presented for suspended droplet experiments in the IR heater. Proof of method experiments demonstrate the ability of our experimental setup to visualize and study the behavior of moving or stationary droplet behavior undergoing vaporization and combustion. Low and high magnification visualizations from the IR heater allowed observation of significant behavior events for droplets in different heating environments. The capability to determine droplet temperature, temporal droplet diameter change, and evaporation rate constant for a rapid radiant-heating environment such as the IR heater is a unique contribution to study suspended droplet behavior. The results demonstrate successful methods for further experimental studies with liquid types such as crude glycerol, waste oil, bio oils, and other commercially available engine oils that have real world applications.