Structure of inorganic and carbonaceous particles emitted from heavy oil combustion.

The combustion of heavy fuel oil for power generation is a great source of carbonaceous and inorganic particle emissions, even though the combustion technologies and their efficiency are improving. The information about the size distribution function of the particles originated by trace metals present into the fuels is not adequate. In this paper, we focused our attention on the larger distribution mode of both the carbonaceous and metallic particles. Isokinetic sampling was performed at the exhausts of two typical heavy oil flames and the samples were size-segregated by mean of an 8-stages Andersen impactor. Further investigation performed on the samples using electronic microscopy coupled with X-ray analysis (EDX) evidenced the presence of solid spherical particles, called plerosphere(1) as analogy with cenosphere, with typical dimensions ranging between 200 nm and 2-3 microm, whose atomic composition contains a large amount of the trace metals present in the parent oils (Fe, V, Ni, etc). EDX analyses revealed that the metal concentration increases as the plerosphere dimension decreases.

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.

Analysis of exhausts emitted by i.c. engines and stationary burners, by means of u.v. extinction and fluorescence spectroscopy.

Optical investigations of the exhausts emitted by internal combustion (i.c.) engines and a stationary burner were performed, in order to assess their relative role as sources of organic matter to the atmosphere. Extinction spectra of air-diluted exhausts in the 200-400 nm u.v. band reveal the expected existence of gaseous trace-species (NO, NO2 and SO2) and carbonaceous particulate matter (soot). In addition, after subtracting the absorption contribution from known species, a strong residual absorption band remains below 250 nm, which is attributed to organic aromatic matter, involving no more than two aromatic rings. A set of ex situ extinction and laser induced fluorescence (LIF) experiments were carried out on condensed combustion-water samples. Extinction measurements from the water samples show absorption spectra similar to those observed from air-diluted samples, which are attributed to low volatility organic compounds, as they are trapped in the condensed phase. Combining the indications of extinction data for both air-diluted and condensed samples, it is suggested that the absorbing species might be molecular clusters of one/two aromatic rings. LIF spectra from condensed samples evidence two fluorescence bands, centered above 300 and 400 nm, respectively, whose intensities correlate with the combustion regimes. Analogous optical analysis on rain samples, collected in an urban area, showed that rain absorption and fluorescence spectra are similar to those found in condensed exhaust samples, which is consistent with the prevailing contribution of i.c. engines to the urban air pollution. The combined experimental data suggest that the absorbing and fluorescent species trapped in the condensed samples are organic (aromatic) compounds, involving mostly one two aromatic rings structural units, since they do not absorb above 250 nm. The overall molecular weight of the trapped material is likely heavy as they show low volatility.