Study of evaporation, micro-explosion, and combustion of nanofluid fuel droplets

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Many industrial applications involve evaporating liquid containing small-size particles. One example is to manufacture pharmaceutical powder aggregates in a way that they would be easily inhaled or ingested. In this application, the shape and density of aggregates determine the easiness with which the patient take the medication. Burning fuels containing particles, such as heavy fuel oils or rocket propellants, also involves similar evaporation process. In the case of burning fuels, the shape and density of the particle aggregates also affect the means and effectiveness with which particles are captured to minimize pollutant emissions. In this project, effects of particle size and concentration on liquid evaporation and burning will be characterized. The effort will be mainly experimental, aided by theoretical analysis for a full understanding of the evaporation, burning, and aggregate formation mechanisms. Both undergraduate and graduate students with diverse backgrounds will be recruited and involved in this project.The proposed study uses the combination of the electrospray technique to generate fuel droplets containing nano-size energetic particles, which are freely suspended in space by the electro-dynamic balance. The droplet will then be ignited for combustion study, and the results will be compared with those without adding nano particles. The proposed study will answer the following specific questions: (1) Does the droplet burning follow the conventional d-square law due to the presence of particles and why? (2) Can the existing theory explain the non-d-square behavior? (3) How does the droplet burn when the droplet is electrically charged? (4) Is there secondary atomization during the single-droplet evaporation due to the Rayleigh charge limit (the critical charge density of a droplet)? (5) How does the aluminum particle affect the secondary atomization, Rayleigh limit, ignition, and burning? The proposed study is of great significance in advancing the power density of energy systems. This work has the main application in propulsion as adding metal energetic particles to liquid propellants can increase both the gravimetric and volumetric energy density of the propellant, thus increasing the range of the atmospheric flights and space vehicles. In addition to combustion, this work is also relevant to the dynamics of functional droplets, sprays, and heat/mass transfer. The results also have implications for other applications, such as food, pharmaceutical, ceramic, chemical, and nanotechnology.