Effects of rare-earth oxide catalysts on the ignition and combustion characteristics of boron nanoparticles

Boron is a potential choice as a fuel additive, especially for biofuels, because it has a high volumetric heating value among different practical metal additives. Although theoretically it can yield a great amount of energy upon complete combustion, its combustion is retarded by the initial presence of boron oxide which coats the particle surface. The present study deals with an experimental investigation of the ignition and combustion behaviors of boron and ball-milled samples of boron and rare earth oxide catalysts in an ethanol spray flame. Commercial boron nanoparticles and both commercial and synthesized ceria-based catalysts have been used for this study. A simple ball-milling technique was employed to prepare the catalyst coated samples, and this technique can be easily adapted for production of large batches. It was observed that the addition of nano-sized catalyst particles to boron nanoparticles improved the ignition characteristics (significant reduction in ignition delay) of the boron. Three different percentages of catalyst loading were tested to determine the effects of catalyst loading on both the ignition behavior of the boron and the primary combustion reaction. Analysis of BO2∗ emissions and of the exiting particles confirmed complete boron combustion in the combustor geometry. The nanoparticles containing ceria demonstrated improvements in both boron ignition (reduced ignition delay time) and (less significantly) the ethanol combustion.