No abstract

The emissions characteristics of two combustion platforms, a T63 turboshaft engine and an atmospheric swirl-stabilized research combustor, fueled with conventional military jet fuel (JP-8), a natural-gas-derived Fischer−Tropsch synthetic jet fuel (also referred herein as synjet or FT), and blends of the two were investigated. Nonvolatile particulate matter (PM) and gaseous emissions were analyzed to assess the impacts of the aromatic- and sulfur-free synjet fuel on the combustion products of the two platforms. The engine was operated at two power settings, and the combustor at several equivalence ratios, to evaluate the emission production over a wide range of combustion temperatures. Conventional aerosol instrumentation was used to quantify particle number (PN), size, and PM mass emissions, while a Fourier Transform Infrared analyzer was used to quantify the gaseous species. Planar laser-induced fluorescence and laser-induced incandescence techniques were employed on the research combustor to study the effects of the FT fuel on the formation and oxidation of particles in the combustor primary zone. Test results show dramatic reductions in particle concentrations and mean size on both combustion platforms with the neat FT and synjet fuel blends relative to operation with JP-8. Reductions of over 90% in PN were observed on both platforms for several operating conditions with neat FT fuel. For the engine, over an 80% reduction in smoke number was observed with neat synjet relative to operation on JP-8. As expected, reductions in sulfur oxide emissions and slight increases in water vapor (measured only in the atmospheric combustor) resulted due to the sulfur-free nature and higher hydrogen-to-carbon ratio of the synthetic fuel. Minor impacts were observed for other gaseous emissions. American Society for Testing and Materials fuel specification tests showed that JP-8/synjet blends up to 50/50% by volume satisfied the JP-8 military fuel requirements and that only the minimum specific gravity requirement was not satisfied at higher synjet concentrations. Impacts of the synjet fuel on the emissions of the atmospheric combustor and the T63 engine, a comparison of emissions between the two platforms, and results of in situ laser-based measurements in the combustor reaction zone are discussed.

We report size-dependent photodissociation and geminate recombination dynamics of the 1 1 chromophore in mass-selected I2-(CO2)" cluster ions, 0 I n I 22, by using nanosecond and picosecond pulsed laser sources in conjunction with a tandem time-of-flight mass spectrometer. Photoexcitation of these cluster ions results in the formation of two types of photofragment ions: 12--based photofragment ions, in which the photodissociated 12-chromophore has recombined and vibrationally relaxed, and I--based photofragment ions, in which an iodine atom has escaped the cluster ion. The "caging fraction", or quantum yield for formation of photofragment ions containing recombined I, , is strongly dependent on the cluster ion size, varying from zero to unity over the size range studied. Picosecond pumpprobe studies reveal a transient bleach in the sequential two-photon absorption of these 12-(C02), cluster ions. A single laser pulse time-resolved experiment indicates that the time scale for absorption recovery is =30 ps for cluster ions with 9 I n I 13 and -15 ps for n = 15 and 16, with a dramatic decrease in absorption recovery time over the size range 13 I n I 15. These results are interpreted in terms of recent Monte Carlo simulations performed in this laboratory and molecular dynamics studies performed by Amar and Perera.