Identifier

etd-07132012-105303

Degree

Doctor of Philosophy (PhD)

Department

Mechanical Engineering

Document Type

Dissertation

Abstract

Biofuels are currently being explored as a carbon-neutral fuel alternative to petroleum-based fuels. However, biofuels such as ethanol has lower energy density (~27MJ/kg) relative to petroleum fuels (~ 45 MJ/kg). Adding high-energy density particles (such as boron with heating value of ~ 58.5 MJ/kg) to biofuels can generate fuel slurry with higher energy density than the base fuel, and represents a potential strategy toward making biofuels more viable. However, the combustion of boron is inhibited (specifically, the ignition is delayed) by the initial presence of an oxide layer, and its high evaporation and boiling temperatures. The present study investigates the combustion behavior of commercially available boron nanoparticles and explores the underlying effects of the particle morphology and size on the combustion characteristics. Detailed characterizations of these particles (using XRD, SEM, TGA, BET surface area and porosimetry) have been carried out before (and after) injecting them into a controlled biofuel (ethanol) combustion environment. Measurements were made in the flame and of the particles captured post-flame. Chemiluminescence and spectroscopic measurements clearly showed evidence of intermediate species of boron combustion and these measurements were used to monitor the ignition and combustion characteristics of the boron particles. The results show that particle size plays a major role on the burning behavior of the particles – larger particles have slower burning rate compared to the smaller counter parts. The combustor’s exit temperature data suggest a positive thermal contribution and increased temperatures due to boron combustion and heat release. A near-linear trend in increasing temperature and energy release is observed with increasing particle loading. Efforts at catalytically coating the boron particle with cerium oxide have shown improvement in the boron ignition (reduction in ignition delay). The XRD and TG analysis of the post-combustion particles reveal that product particles contain boric acid or hydrated B2O3 and no un-burnt boron. The droplet combustion experiments conducted on the burning behavior of single ethanol droplet containing energetic nanoparticles of boron or boron-metal (iron, aluminum and titanium) nanocomposites suggest that improved ignition characteristics of boron can be achieved in presence of metal additives.

Date

2012

Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Acharya, Sumanta

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