Plasmonics Resonance Enhanced Active Photothermal Effects in Aluminum Nanoenergetics for Propulsion Applications

In this dissertation, aluminum nanoparticles (Al NPs) are shown capable to on-demand enhance and control the local photothermal energy deposition, both spatially and temporally, via active photothermal effects initiated by the localized surface plasmon resonance (LSPR) phenomenon, and amplified by the Al exothermal oxidation reactions. Experiments in dry and wet environments along with computational modeling of the photothermal process are very desirable for gaining fundamental understanding, ignition optimization and parameter exploration.

Combined phenomena of motion and ignition of Al NPs are explored first in this study. Both resulting from exposing a pile of the nanoenergetics in hand to a single Xenon-tube flash in air, the movement extent is five orders of magnitude higher than that from femtosecond/nanosecond laser-induced photothermal ejection of gold nanodroplets and the ignition delay is two orders of magnitude faster compared to that from conductive heating.

Then experiments in wet conditions are conducted, mainly in propane-air flames, where flash-activated photothermal effect of the Al NPs is proved to ignite flows of those mixtures. In comparison with regular spark ignition, the ordeal of quenching distance is no more present and the opto-thermal minimum ignition energy (MIE) is at least 67 times less than that from conventional ignition tools.

In the last part of this thesis, organically coating the Al NPs in addition to modulating their geometry and configurations are shown to have significant effects on the absorption cross section of Al. Shift of the plasmon resonance affecting thermal ohmic losses, local electric field enhancements leading to heat generation, and match of the spectra of the activation source and nanoenergetics can all be used to enhance the energy density of fuels in propulsion systems via active photothermal effects of Al NPs.