Effect Of Ceria Nanoparticles On Soot Inception And Growth In Toluene-Oxygen-Argon Mixtures

Soot formation from the combustion of toluene (C6H 5CH3) and of two concentrations of nano-sizedceria-laden toluene was monitored using a shock tube to observe the effect of the organometallic additive on the formation of soot from its point of inception. Two concentrations of ceria, of chemical composition CeO1.63, were employed to examine the effect on soot production of toluene over the range of temperature 1588-2370 K using two levels of inert gas dilution in which reflected-shock pressure was maintained near 1.5 atm. The ceria nanoparticles were synthesized using a microemulsion technique which employs sodium dioctyl sulfosuccmate (AOT), a surfactant, to retard agglomeration. Introduction of the nanoparticles into the shock tube is achieved using a novel, two-stage injection procedure. Soot yield measurements reveal that the presence of ceria has no direct implications on peak soot concentration near 1950 K. A shift in the parabolic soot profile of toluene in the direction of increased temperature was observed for each concentration of ceria with a larger shift occurring for increased concentration of ceria, although the same effect was exhibited for the toluene-AOT mixtures in absence of ceria, supporting an inefficaciousness of ceria on soot suppression on kinetic timescales. It is evidenced in measured soot delay times that the presence of the surfactant in absence of ceria significantly slows the rate of soot growth for T \u3c 2000 K, while the presence of ceria has a relatively negligible impact. Under conditions of higher fuel concentration, a remarkable decrease in soot accumulation on the shock tube walls was observed in experiments using the ceria-toluene mixtures over that yielded by pure toluene combustion. In the present paper, the authors report the first measurements of nanoparticle-influenced combustion of a hydrocarbon as performed in a shock tube. © 2009 The Combustion Institute. Published by Elsevier Inc. All rights reserved

Oxidation kinetics of n-nonane: Measurements and modeling of ignition delay times and product concentrations

International audienceOxidation of n-nonane (n-C9H20) under conditions of high dilution (>97% inert) has been studied over a broad range of temperature (530 < T (K) < 1591) and equivalence ratio (0.5, 1.0, 2.0) at pressures near 1 and 10 atm using shock-tube and jet-stirred reactor facilities. Excited-state hydroxyl radical (OH*) time histories were measured using emission spectroscopy of OH behind reflected shock waves from which ignition delay and peak formation times were extracted. Temperature-dependent species concentrations were measured using gas chromatography, FTIR, TCD, and FID of jet-stirred reactor combustion products. Ignition delay times show a strong dependence on equivalence ratio, increasing by a factor of nearly 5 at both 1 and 10.4 atm. An overall ignition delay time correlation was constructed, revealing a pressure dependence of P^^0.48. Experimental data from both facilities were utilized to develop and validate a chemical kinetics mechanism for n-nonane oxidation. Kinetic model predictions of ignitiondelay time compare well, particularly for the lean and stoichiometric mixtures. Jet-stirred reactor data show excellent overall agreement with major species, as well as alkanes and alkenes present in the combustion products. Alkenes up to C9 were produced from n-nonane oxidation and ethylene, a dominant product of n-nonane thermal decomposition, is identified as the most abundant among them. The present studyprovides an extensive series of fundamental measurements on n-nonane oxidation, resulting in the formulation of a mechanism used to describe and predict associated reaction kinetics

Direct measurements of conformer-dependent reactivity of the criegee intermediate CH3CHOO

Although carbonyl oxides, "Criegee intermediates," have long been implicated in tropospheric oxidation, there have been few direct measurements of their kinetics, and only for the simplest compound in the class, CH2OO. Here, we report production and reaction kinetics of the next larger Criegee intermediate, CH3CHOO. Moreover, we independently probed the two distinct CH3CHOO conformers, syn- and anti-, both of which react readily with SO2 and with NO2. We demonstrate that anti-CH3CHOO is substantially more reactive toward water and SO2 than is syn-CH3CHOO. Reaction with water may dominate tropospheric removal of Criegee intermediates and determine their atmospheric concentration. An upper limit is obtained for the reaction of syn-CH3CHOO with water, and the rate constant for reaction of anti-CH3CHOO with water is measured as 1.0 × 10(-14) ± 0.4 × 10(-14) centimeter(3) second(-1)