Combustion of gasolines in premixed laminar flames European certified and California phase 2 reformulated gasoline

Ultraviolet Photodissociation Dynamics of the Cyclohexyl Radical: The H-Atom Product Channel

The ultraviolet (UV) photodissociation dynamics of the jet-cooled cyclohexyl (c-C6H11) radical is studied using the high-n Rydberg atom time-of-flight (HRTOF) technique. The cyclohexyl radical is produced by the 193 nm photodissociation of chlorocyclohexane and bromocyclohexane and is examined in the photolysis wavelength region of 232-262 nm. The H-atom photofragment yield (PFY) spectrum contains a broad peak centered at 250 nm, which is in good agreement with the UV absorption spectrum of the cyclohexyl radical and assigned to the 3p Rydberg states. The translational energy distributions of the H-atom loss product channel, P(ET)'s, are bimodal, with a slow (low ET) component peaking at ∼6 to 7 kcal/mol and a fast (high ET) component peaking at ∼44-48 kcal/mol. The fraction of the average translational energy in the total excess energy, ⟨fT⟩, is in the range of 0.16-0.25 in the photolysis wavelength region of 232-262 nm. The H-atom product angular distribution of the slow component is isotropic, while that of the fast component is anisotropic with an anisotropy parameter of β ≈ 0.5-0.7. The bimodal product translational energy and angular distributions indicate two dissociation pathways to the H + C6H10 products in cyclohexyl. The high-ET anisotropic component is from a repulsive, prompt dissociation on a repulsive potential energy surface coupling with the Rydberg excited states to produce H + cyclohexene. The low-ET isotropic component is consistent with the unimolecular dissociation of hot radical on the ground electronic state after internal conversion from the Rydberg states. The similarity of the photodissociation dynamics of the cyclohexyl radical to the previously studied small linear and branched alkyls expands on the understanding of the dissociation dynamics of alkyl radicals to include larger cyclic alkyl radicals.

Differential toxic effects of methyl tertiary butyl ether and tert-butanol on rat fibroblasts in vitro

Methyl tertiary butyl ether (MTBE) is the most widely used motor vehicle fuel oxygenate since it reduces harmful emissions due to gasoline combustion. However, the significant increase in its use in recent years has raised new questions related to its potential toxicity. In fact, although available data are somehow conflicting, there is evidence that MTBE is a toxic substance that may have harmful effects on both animals and humans and an unresolved problem is the role played by MTBE metabolites, especially tertiary butyl alcohol (TBA), in determining toxic effects due to MTBE exposure. In this study, the toxic effects of MTBE have been analyzed on a normal diploid rat fibroblast cell line (Rat-1) and compared to the effects of TBA. The results obtained suggest that both MTBE and TBA inhibit cell growth in vitro but with different mechanisms in terms of effects on the cell cycle progression and on the modulation of cell cycle regulatory proteins. In fact, MTBE caused an accumulation of cells in the S-phase of the cell cycle, whereas TBA caused an accumulation in the G0/G1-phase with different effects on the expression of cyclin D1, p27Kip1, and p53. Moreover, both MTBE and TBA were also shown to induce DNA damage, as assessed in terms of oxidative DNA damage and nuclear DNA fragmentation, that appeared to be susceptible of repair by the cell DNA-repair machinery. In conclusion, these findings suggest that both MTBE and TBA can exert, by acting through different molecular mechanisms, important biological effects on fibroblasts in vitro. Further studies are warranted to shed light on the mechanisms responsible for the observed effects and on their potential significance for the in-vivo exposure.

Pollutant emissions from gasoline combustion. 1. Dependence on fuel structural functionalities

To study the formation of air pollutants and soot precursors (e.g., acetylene, 1,3-butadiene, benzene, and higher aromatics) from aliphatic and aromatic fractions of gasoline fuels, the Utah Surrogate Mechanisms is extended to include submechanisms of gasoline surrogate compounds using a set of mechanism generation techniques. The mechanism yields very good predictions of species concentrations in premixed flames of n-heptane, isooctane, benzene, cyclohexane, olefins, oxygenates, and gasoline using a 23-component surrogate formulation. The 1,3-butadiene emission comes mainly from minor fuel fractions of olefins and cyclohexane. The benzene formation potential of gasoline components shows the following trends as functions of (i) chemical class: n-paraffins < isoparaffins < olefins < naphthalenes < alkylbenzenes < cycloparaffins < toluene; (ii) carbon number: n-butane < n-pentane < n-hexane; and (iii) branching: n-hexane < isohexane < 2,2,4-trimethylpentane < 2,2,3,3-tetramethylbutane. In contrast, fuel structure is not the main factor in determining acetylene formation. Therefore, matching the benzene formation potential of the surrogate fuel to that produced by the real fuel should have priority when selecting candidate surrogate components for combustion simulations.

Measurement of acrolein and 1,3-butadiene in a single puff of cigarette smoke using lead-salt tunable diode laser infrared spectroscopy

Acrolein and 1,3-butadiene in cigarette smoke generally are measured using two separate analytical methods, a carbonyl derivative HPLC method for acrolein and a volatile organic compound (VOC) GC/MS method for 1,3-butadiene. However, a single analytical method having improved sensitivity and real-time per puff measurement will offer more specific information for evaluating experimental carbon filtered cigarettes designed to reduce the smoke deliveries of these constituents. This paper describes an infrared technique using two lead-salt tunable diode lasers (TDLs) operating with liquid nitrogen cooling with emissions at 958.8 cm(-1) and 891.0 cm(-1) respectively for the simultaneous measurement of acrolein and 1,3-butadiene, respectively, in each puff of mainstream cigarette smoke in real time. The dual TDL system uses a 3.1l volume, 100 m astigmatic multiple pass absorption gas cell. Quantitation is based on a spectral fit that uses previously determined infrared molecular line parameters generated in our laboratory, including line positions, line strengths and nitrogen-broadened half-widths for these species. Since acrolein and ethylene absorption lines overlap and 1,3-butadiene, ethylene and propylene absorption lines overlap, the per puff deliveries of ethylene and propylene were determined since their overlapping absorption lines must be taken into account by the spectral fit. The acrolein and 1,3-butadiene total cigarette deliveries for the 1R5F Kentucky Reference cigarette were in agreement with the HPLC and GC/MS methods, respectively. The limit of detection (LOD) for 1,3-butadiene and acrolein was 4 ng/puff and 24 ng/puff, respectively, which is more than adequate to determine at which puff they break through the carbon filter. The retention and breakthrough behavior for the two primary smoke constituents depend on the cigarette design and characteristics of the carbon filter being evaluated.

Study on combustion of gasoline/MTBE in laminar flame with synchrotron radiation

Synchrotron radiation offers important advantages with the use of tunable vacuum ultraviolet (VUV) lasers for molecular beam sampling mass spectrometry (MBMS). These advantages include superior signal-to-noise, soft ionization, and access to photon energies outside the limited tuning ranges of current VUV laser sources. Combining MBMS with tunable synchrotron radiation photoionization, two similar types of fuels, gasoline/oxygen and gasoline/MTBE/oxygen in low-pressure premixed laminar flame were investigated. Photoionization efficiency (PIE) measurements were used to identify the intermediates isomers within flame. The two combustion processes are discussed by comparing the intermediates and their spatial profiles within the two kinds of flame mentioned above.

Combustion Modeling and Kinetic Rate Calculations for a Stoichiometric Cyclohexane Flame. 1. Major Reaction Pathways

The Utah Surrogate Mechanism was extended in order to model a stoichiometric premixed cyclohexane flame (P = 30 Torr). Generic rates were assigned to reaction classes of hydrogen abstraction, beta scission, and isomerization, and the resulting mechanism was found to be adequate in describing the combustion chemistry of cyclohexane. Satisfactory results were obtained in comparison with the experimental data of oxygen, major products and important intermediates, which include major soot precursors of C2-C5 unsaturated species. Measured concentrations of immediate products of fuel decomposition were also successfully reproduced. For example, the maximum concentrations of benzene and 1,3-butadiene, two major fuel decomposition products via competing pathways, were predicted within 10% of the measured values. Ring-opening reactions compete with those of cascading dehydrogenation for the decomposition of the conjugate cyclohexyl radical. The major ring-opening pathways produce 1-buten-4-yl radical, molecular ethylene, and 1,3-butadiene. The butadiene species is formed via beta scission after a 1-4 internal hydrogen migration of 1-hexen-6-yl radical. Cascading dehydrogenation also makes an important contribution to the fuel decomposition and provides the exclusive formation pathway of benzene. Benzene formation routes via combination of C2-C4 hydrocarbon fragments were found to be insignificant under current flame conditions, inferred by the later concentration peak of fulvene, in comparison with benzene, because the analogous species series for benzene formation via dehydrogenation was found to be precursors with regard to parent species of fulvene.

The mutagenicity testing of tertiary-butyl alcohol, tertiary-butyl acetate™ and methyl tertiary-butyl ether in Salmonella typhimurium

Tertiary-Butyl alcohol (TBA), tertiary-butyl acetate (TBAc) and methyl tertiary-butyl ether (MTBE) are chemicals to which the general public may be exposed either directly or as a result of their metabolism. There is little evidence that they are genotoxic; however, an earlier publication reported that significant results were obtained in Salmonella typhimurium TA102 mutagenicity tests with both TBA and MTBE. We now present results of testing these chemicals and TBAc against S. typhimurium strains in two laboratories. The emphasis was placed on testing with S. typhimurium TA102 and the use of both dimethyl sulphoxide and water as vehicles. Dose levels up to 5000 microg/plate were used and incubations were conducted in both the presence and absence of liver S9 prepared from male rats treated with either Arochlor 1254 or phenobarbital-beta-naphthoflavone. The experiments were replicated, but in none of them was a significant mutagenic response observed, thus the current evidence indicates the TBA, TBAc and MTBE are not mutagenic in bacteria.

Determination of molecular parameters for 1,3-butadiene and propylene using infrared tunable diode laser absorption spectroscopy

A technique has been developed for the determination of molecular parameters, including infrared absorption line positions, strengths, and nitrogen-broadened half-widths for 1,3-butadiene (C(4)H(6)) and propylene (C(3)H(6)). The parameters for these two molecules are required for quantitation using Tunable Diode Laser Absorption Spectroscopy (TDLAS). These molecules have populations of highly overlapping infrared absorption lines in their room temperature spectra. The technique reported here provides a procedure for estimating the molecular parameters for these overlapping absorption lines from quantitative reference spectra taken with the TDLAS instrument at different pressures and concentrations. The system was developed for the quantitation of gaseous constituents in a single puff of cigarette smoke and this paper will describe the procedure and some of the factors that influence the accuracy of quantitation for 1,3-butadiene, including the approach taken to minimize the adverse effects of the absorption due to propylene in the same spectral region.