Comparative analysis of the structure of carbon materials relevant in combustion.

The determination of the structure of carbon materials is an analytical problem that join the research scientific communities involved in the chemical characterization of heavy fuel-derived products (heavy fuel oils, coal-derived fuels, shale oil, etc.) and of carbon materials (polycyclic aromatic compounds, tar, soot) produced in many combustion processes. The knowledge of the structure of these "difficult" fuels and of the carbon materials produced by incomplete combustion is relevant to research for the best low-environmental impact operation of combustion systems; but an array of many analytical and spectroscopic tools are necessary, and often not sufficient, to attempt the characterization of such complex products and in particular to determine the distribution of molecular masses. In this paper the size exclusion chromatography using N-methyl-pyrrolidinone as eluent has been applied for the characterization of different carbon materials starting from typical carbon species, commercially available like polyacenaphthylene, carbon black, naphthalene pitch up to combustion products like soot and soot extract collected in fuel-rich combustion systems. Two main fractions were detected, separated and molecular weights (MWs) determined by comparison with polystyrene standards: a first fraction consisted of particles with very large molecular masses (>100000 u); a second fraction consisted of species in a relatively small MW range (200-600 u). The distribution of these fractions changes in dependence on the carbon sample characteristics. Fluorescence spectroscopy applied on the fractions separated by size-exclusion chromatography has been used and comparatively interpreted giving indications on the differences and similarities in chemical structure of such different materials.

Monitoring of fuel consumption and aromatics formation in a kerosene spray flame as characterized by fluorescence spectroscopy.

The large presence of aromatic compounds in distillate fossil fuels should allow, in line of principle, to follow the fuel consumption and/or the presence of unburned fuel in a high temperature environment like a burner or the exhaust of combustion systems by exploiting the high fluorescence emission of aromatic fuel components. To this aim an UV-excited fluorescence source has to be used since the aromatic fuel components are strongly fluorescing in the UV region of the emission spectrum. In this work UV-excited laser induced fluorescence (LIF) diagnostics was applied to spray flames of kerosene in order to follow the fuel consumption and the formation of aromatic species. A strong UV signal was detected in the spray region of the flame that presented a shape similar to that found in the LIF spectra preliminary measured on the cold spray and in the room-temperature fluorescence of fuel solutions. The decrease of UV signal along the spray flame region was associated to the consumption of the fuel, but more difficult seems to be the attribution of a broad visible emission, that is present downstream of the flame. The visible emission feature could be assigned to flame-formed PAH species contained in the high molecular weight species, hypothesizing that their fluorescence spectra are shifted toward the visible for effect of the high temperature flame environment.

Fluorescence spectroscopy of aromatic species produced in rich premixed ethylene flames.

The fluorescence spectra of the condensed species (CS) collected in the soot inception region of a rich premixed laminar ethylene/oxygen flame have been measured by excitation in the UV at 266 and 355 nm excitation wavelength. The contribution of the most abundant polycyclic aromatic hydrocarbons (PAH) to the CS fluorescence has been evaluated in order to attribute the CS fluorescence at different emission wavelengths to specific aromatic structures. The fluorescence peaks detected in the UV region of the CS fluorescence spectrum was found to be mainly due to a typical PAH like fluorene, that is, the most fluorescent one among the PAH analyzed in the CS by chromatographic analysis. The CS exhibited the larger emission in the visible where the PAH contribution has been shown to be negligible and other fluorescing aromatic species, not identified by chromatographic analysis of the CS, have to be considered responsible for the visible fluorescence. Laser induced fluorescence (LIF) flame measurements excited at 266 nm and detected at two selected wavelengths (310 and 410 nm) have been performed along the flame axis and compared with the CS fluorescence intensity. The LIF and CS fluorescence signals show quite similar axial trends demonstrating that the LIF signals are related to CS fluorescence. In particular, the LIF fluorescence signals detected in the UV could be attributed to the PAH fluorescence whereas the unidentified species contained in the CS can be followed by LIF detection in the visible region.

Recurring desmoid tumor of the foot: a case study.

The desmoid tumor is benign, uncommon, and frequently recurs after excision. It can be confusing in terms of diagnosis and treatment due to its ability to achieve large size, causing functional limitation and/or pain. Its overall clinical characteristics can mimic those of its malignant counterparts. Because of its high rate of recurrence, surgical treatment should include a wide excision around the margins.