Showing papers on "Mole fraction published in 2017"

Measuring hydroperoxide chain-branching agents during n-pentane low-temperature oxidation

Abstract: The reactions of chain-branching agents, such as H2O2 and hydroperoxides, have a decisive role in the occurrence of autoignition. The formation of these agents has been investigated in an atmospheric-pressure jet-stirred reactor during the low-temperature oxidation of n-pentane (initial fuel mole fraction of 0.01, residence time of 2 s) using three different diagnostics: time-of-flight mass spectrometry combined with tunable synchrotron photoionization, time-of-flight mass spectrometry combined with laser photoionization, and cw-cavity ring-down spectroscopy. These three diagnostics enable a combined analysis of H2O2, C1–C2, and C5 alkylhydroperoxides, C3–C5 alkenylhydroperoxides, and C5 alkylhydroperoxides including a carbonyl function (ketohydroperoxides). Results using both types of mass spectrometry are compared for the stoichiometric mixture. Formation data are presented at equivalence ratios from 0.5 to 2 for these peroxides and of two oxygenated products, ketene and pentanediones, which are not usually analyzed during jet-stirred reactor oxidation. The formation of alkenylhydroperoxides during alkane oxidation is followed for the first time. A recently developed model of n-pentane oxidation aids discussion of the kinetics of these products and of proposed pathways for C3–C5 alkenylhydroperoxides and the pentanediones.

Liquid Viscosity and Surface Tension of n-Dodecane, n-Octacosane, Their Mixtures, and a Wax between 323 and 573 K by Surface Light Scattering

Abstract: The present contribution provides experimental data for the liquid viscosity and surface tension of n-alkane based model systems at temperatures up to 573 K. The fundamental advantage of the used surface light scattering (SLS) method lies in its application in thermodynamic equilibrium without calibration in a contactless way. The investigated systems comprise the pure fluids n-dodecane (n-C12H26) and n-octacosane (n-C28H58), their binary mixture at a n-C12H26 mole fraction of about 0.3, and the commercially available hydrocarbon wax SX-70 representing a multicomponent mixture of n-alkanes with a broad chain length distribution. For the first time, it could be demonstrated that the SLS method can simultaneously access the liquid viscosity and surface tension of such medium- to long-chained n-alkane systems close to saturation conditions over a broad temperature range from 323 to 573 K. Typical measurement uncertainties of 2% based on a coverage factor k = 2, i.e., a level of confidence of more than 95%, w...

Viscosity of Ionic Liquid–Ionic Liquid Mixtures

Abstract: The viscosities of 23 ionic liquid (IL)–IL mixtures were measured at multiple temperatures and mole fractions. Many of the mixtures involved a dialkylimidazolium bis(trifluoromethylsulfonyl)imide ([Tf2N]) IL paired with a tetra-alkylphosphonium IL containing an aprotic heterocyclic anion (AHA). As a result, most of the mixtures contained both unlike anions and cations. The mixtures ranged from strongly positive deviations from the Arrhenius model (the mole fraction weighted logarithm of the viscosity), even having mixture viscosities greater than the viscosity of either pure IL, to negative deviations. Studies of complementary pairs ([C1][A1] + [C2][A2] and [C2][A1] + [C1][A2] mixtures) have identical viscosities at overall mole fractions of 0.50, clearly indicating that the anions and cations of the mixtures exchange freely. These mixtures cannot be well-represented by the Arrhenius model assuming a random distribution of the four possible cation/anion combinations (e.g., 0.25 mole fraction of each possi...

Density, Viscosity, Speed of Sound, Bulk Modulus, Surface Tension, and Flash Point of Binary Mixtures of Butylbenzene + Linear Alkanes (n-Decane, n-Dodecane, n-Tetradecane, n-Hexadecane, or n-Heptadecane) at 0.1 MPa

Abstract: This work reports physical property measurements of binary mixtures of butylbenzene with n-decane, n-dodecane, n-tetradecane, n-hexadecane, or n-heptadecane. Densities and viscosities were measured at temperatures from (293.15 to 373.15) K, and speeds of sound were measured at temperatures from (293.15 to 333.15) K, except for those of n-heptadecane, which were measured starting at 303.15 K. Densities increased with increasing mole fraction of butylbenzene. Excess molar volumes were positive and increased with increasing alkane chain length, except for those of heptadecane which were similar to those of n-hexadecane. Analysis of excess molar volumes using the Prigogine–Flory–Patterson model showed that the interaction term contributed more to excess molar volume than the free volume or P* term. As the mole fraction of butylbenzene increased, speeds of sound increased for n-decane and n-dodecane mixtures but decreased for other alkane mixtures to values below those of both pure components before increasing...

Synergism between non-ionic and cationic surfactants in a concentration range of mixed monolayers at an air–water interface

Abstract: The surface properties and adsorption behavior of mixed binary surfactants containing alkylpyridinium chloride (CnPC, n = 14 and 16) and Triton X-100 (TX100) have been studied at 298.15 K. The values of the molecular interaction parameter (βs) and the mole fraction of components (Xsi) at the air–water interface in the pre-micellar region were calculated on the basis of Rosen's model. In the new approach, we proposed to estimate surface parameters (βs, Xsi, Γtot, Atot, ΓTX100 and ΓCnPC) in a pre-micellar region, using different fixed values of the surface tension instead of a single-value of surface tension. Then, the influence of surface tension on the surface properties was investigated. The interaction parameter (βs) is negative at all compositions showing a synergistic effect between the components. The βs was found to considerably decrease (less negative values) with decreasing surface tension due to more migration of TX100 to the surface layer and a reduction in electrostatic self-repulsion between head groups in the ionic surfactant. Also, the total surface area (Atot) at the air–water interface decreases with increasing Xs1 (mole fraction of TX100 in mixed monolayer) or decreasing surface tension due to the dilution effect on mixing.

Effects of n-propylbenzene addition to n-dodecane on soot formation and aggregate structure in a laminar coflow diffusion flame

Abstract: The effects of n -propylbenzene addition to n -dodecane on soot formation and aggregate structure in a laminar coflow diffusion flame is investigated. The goal is to gain insight on the influence of n -propylbenzene addition to n -dodecane on the underlying mechanisms of soot formation processes. The methane laminar coflow diffusion flame doped with pure n -dodecane establishes the base environment in this study. n -Propylbenzene is mixed into n -dodecane at three levels: 15%, 30% and 45% in mole fraction. The inlet total carbon flow rate is held constant for all of the flames. The combined laser extinction and two-angle elastic light scattering method is used to measure soot volume fraction, primary particle diameter and number density. As expected, soot volume fraction is shown to increase at all heights in the flames with increasing mole fraction of n -propylbenzene in the liquid fuel mixture. The differences in profiles of soot volume fraction suggest a non-linear relationship between the mole fraction of n -propylbenzene in the liquid fuel mixture and the increase in soot production. The relative importance of soot inception and surface growth affected by n -propylbenzene addition is shown to be different along the flame wing and centerline. Along the wing, the aromatic fuel molecular structure primarily influences the initial soot inception process at earlier times by providing a larger population of incipient soot particles for the subsequent surface growth. Along the centerline, the aromatic fuel chemistry effect is stronger, as it accelerates both the soot inception and the subsequent surface growth processes. The experimental data presented in this study is also useful for the validation of soot models of the liquid fuel surrogate components.

Aromatic ring formation in opposed-flow diffusive 1,3-butadiene flames

Abstract: This paper is concerned with the formation of one- and two-ring aromatic species in near atmospheric-pressure opposed-flow diffusion flames of 1,3-butadiene (1,3-C 4 H 6 ). The chemical structures of two different 1,3-C 4 H 6 /Ar–O 2 /Ar flames were explored using flame-sampling molecular-beam mass spectrometry with both electron and single-photon ionization. We provide mole fraction profiles of 47 components as function of distance from the fuel outlet and compare them to chemically detailed modeling results. To this end, the hierarchically developed model described by Seidel et al. [16] has been updated to accurately comprise the chemistry of 1,3-butadiene. Generally a very good agreement is observed between the experimental and modeling data, allowing for a meaningful reaction path analysis. With regard to the formation of aromatic species up to naphthalene, it was essential to improve the fulvene and the C 5 chemistry description in the mechanism. In particular, benzene is found to be formed mainly via fulvene through the reactions of the C 4 H 5 isomers with C 2 H 2 . The n- C 4 H 5 radical reacts with CH 3 forming 1,3-pentadiene (C 5 H 8 ), which is subsequently oxidized to form the naphthalene precursor cyclopentadienyl (C 5 H 5 ). Oxidation of naphthalene is predicted to be a contributor to the formation of phenylacetylene (C 8 H 6 ), indicating that consumption reactions can be of similar importance as molecular growth reactions.

Kinetic boundary conditions for vapor–gas binary mixture

Abstract: Using molecular dynamics simulations, the present study investigated the precise characteristics of the binary mixture of condensable gas (vapor) and non-condensable gas (NC gas) molecules creating kinetic boundary conditions (KBCs) at a gas–liquid interface in equilibrium. We counted the molecules utilizing the improved two-boundary method proposed in previous studies by Kobayashi et al. (Heat Mass Trans 52:1851–1859, 2016. doi: 10.1007/s00231-015-1700-6 ). In this study, we employed Ar for the vapor molecules, and Ne for the NC gas molecules. The present method allowed us to count easily the evaporating, condensing, degassing, dissolving, and reflecting molecules in order to investigate the detailed motion of the molecules, and also to evaluate the velocity distribution function of the KBCs at the interface. Our results showed that the evaporation and condensation coefficients for vapor and NC gas molecules decrease with the increase in the molar fraction of the NC gas molecules in the liquid. We also found that the KBCs can be specified as a function of the molar fraction and liquid temperature. Furthermore, we discussed the method to construct the KBCs of vapor and NC gas molecules.