Effects of Nitrogen Dioxide on the Oxidation of Levitated -Tetrahydrodicyclopentadiene (JP-10) Droplets Doped with Aluminum Nanoparticles.

Nitrogen dioxide (NO) can significantly improve the combustion of hydrocarbon fuels, but the effect of NO on the ignition of fuels with energy densities enhanced by aluminum (Al) nanoparticles has not been studied. We therefore investigated the effects of NO on the ignition of JP-10 droplets containing Al nanoparticles initially acoustically levitated in an oxygen-argon mixture. A carbon dioxide laser ignited the droplet and the resulting combustion processes were traced in real time using Raman, ultraviolet-visible (UV-vis), and Fourier-transform infrared (FTIR) spectroscopies simultaneously with a high-speed optical or thermal imaging camera. Temperature temporal profiles of the ignition processes revealed that a 5% concentration of NO did not cause measurable differences in the ignition delay time or the initial rate of temperature rise, but the maximum flame temperature was reduced from 2930 ± 120 K to 2520 ± 160 K. The relative amplitudes of the UV-vis emission bands were used to deduce how NO affected the composition of the radical pool during the oxidation process; for example, the radicals NO, NH, and CN were detected and the OH (A Σ-X Π) band at 310 nm was less prominent with NO. Localized heating from a tightly focused infrared laser beam provided sufficient energy to activate chemical reactions between the JP-10 and NO without igniting the droplet. Raman spectra of the residue produced give information about the initial oxidation mechanisms and suggest that organic nitro compounds formed. Thus, in contrast to previous studies of hydrocarbon combustion without Al nanoparticles, NO was found not to enhance the ignition of an Al-doped JP-10 droplet ignited by a CO laser.