153 research outputs found
Controlling steps in the low-temperature oxidation of n-heptane and iso-octane
No full textThe low-temperature oxidation of n-heptane and iso-octane in mixtures with air in a jet-stirred-how reactor have been compared under suitable high-pressure conditions, such that the two mixtures of hydrocarbon and air showed comparable fuel conversions and phenomenologies. The large presence of aldehydes in the products of the low-temperature oxidation of n-heptane was attributed to a degenerate chain-branching path involving the addition of molecular oxygen to heptylhydroperoxy radicals and isomerization by internal H-atom abstraction. The latter step is particularly favored in linear alkanes where easy-to-abstract H-atoms are available. On the other hand, cyclic ethers and fuel-conjugate olefins were the dominant products of the low-temperature oxidation of iso-octane. This is due to a lack of H-atoms for internal abstraction; this limits the degenerate chain-branching route and favors the propagation path toward species having the same skeleton of the fuel, such as cyclic ethers and fuel-conjugate olefins. The prevalence of a degenerate chain-branching path for n-heptane compared with the propagation reactions in iso-octane oxidation is responsible for the different autoignition tendencies of n-heptane and iso-octane. (C) 1998 by The Combustion Institute
Caratterizzazione Chimico-Fisica del Particolato Nanometrico (Ultrafine) Emesso da Sistemi di Combustione
No full textA comparative study of mesogenic structures. The crystal structures of bis[(4-butoxycarbonyl)phenyl] terephthalate and bis[(4-valeroyloxy)phenyl] terephthalate.
No full textSmectogenic bis[(4-butoxycarbonyI)-phenyl]terephthalate (B-A) and nemato-
genic bis[(4-~aleroyloxy)-phenyl]terephthalate (V-A) have been synthesized and their crystal and molecular structure have been determined, at room temperature, by direct methods
Crystal Structure of a mesogenic compound: bis-n-butanoyloxy(-1,4-phenylene, methylvinylene-1,4-phenylene)
No full text
Blue, green and yellow carbon dots derived from pyrogenic carbon: Structure and fluorescence behaviour
No full textFluorescence lifetimes and quantum yields featuring polycyclic aromatic hydrocarbons (PAHs) and other organics constituting pyrogenic carbon particulate matter (PM) are seldom measured. In this work, PM sampled in a fuel-rich ethylene flame was firstly separated in organic carbon (OC), soluble in dichloromethane, and refractory organic carbon (ROC), soluble in N-methyl pyrrolidinone, and then analyzed by size exclusion chromatography (SEC) coupled with online UV and fluorescence detection, and by offline fluorescence spectroscopy and mass spectrometry. It was found that three classes of differently light emitting carbon dots (CDs) could be bottom-up synthesized in the same flame system by selecting appropriately the residence time. Actually, OC presented blue fluorescence regardless the residence time, whereas ROC sampled at low and high residence time emitted fluorescence in the green (green CDs) and in the yellow (yellow CDs) region, respectively. The SEC molecular weight of all CDs presented similar trimodal distributions, centered around 300, 1000 and 10,000 u. For the first time fluorescence lifetimes and quantum yields of pyrogenic CD fractions were measured as additional parameters useful for discriminating the fluorescent components and inferring their structural properties, with the support of mass spectrometry. The different spectroscopic features of CDs could be associated to different compositional characteristics as the polydispersity of molecular components featuring blue CDs, opposed to the oligomer-like nature of green and yellow CDs. Pyrogenic CDs showed different fluorescence emission ranges, quantum yield and lifetimes, appealing for their possible applications in the fields of imaging, electronics and sensors
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