Ignition and Combustion of Boron Nanoparticles in Ethanol Spray Flame

Biofuels such as ethanol have lower energy density than conventional petroleum-based fuels; therefore, enhancing their energy density by addition of higher-energy-density components is an attractive option. Boron is considered to be a good choice as a fuel additive because it has almost the highest volumetric heating value among potentially suitable additives. The present study deals with an experimental investigation of boron combustion in an ethanol spray flame. Measurements have been made of the emission of the intermediate suboxide BO2 using spectroscopy and chemiluminescence imaging with interference filters. The size, surface structure, and chemical composition of the injected boron nanopowders were characterized by x-ray diffraction, porosimetry, thermogravimetric analysis, and scanning electron microscopy. The postburn particles were also characterized by x-ray diffraction and thermogravimetric analysis. The effects of boron nanoparticles on the hydrocarbon combustion in terms of heat releasewere determined usingCHchemiluminescence and temperaturemeasurements. The chemiluminescence and spectroscopic signatures indicate that boron underwent combustion and simultaneously increased the CH-radical emission and flame temperatures. The x-ray diffraction and thermogravimetric analysis measurements of the particles collected at the exhaust indicate that complete conversion of the boron was achieved. The effect of particle size on the combustion of the boron nanoparticles was examined, comparing small commercial particles to sintered particles. A demonstrable size effect was observed with the larger particles, which exhibited their initial BO2 signatures at distances further above the dump plane, indicating greater ignition delay times.