Pure Hydrocarbon Liquids Research Articles

Leidenfrost behavior in drop-wall impacts at combustor-relevant ambient pressures

Liquid-fueled combustion systems demand optimal performance over a range of operating conditions—requiring predictable fuel injection events, spray breakup, and vaporization across a range of temperatures and pressures. In direct injection combustors, these sprays impinge directly on combustion chamber surfaces. Although the outcome of fuel droplets impacting a wall is primarily driven by the wall temperature and the Leidenfrost effect, the shifting liquid-vapor saturation point with pressure may influence the droplet-wall heat transfer rate and transition from nucleate to film boiling. In this paper, the role of ambient pressure on the droplet impact regimes, spreading rate, and droplet rebound velocity during impact are explored for representative low boiling point and high boiling point pure hydrocarbon liquids (n-heptane and n-decane). High-speed image sequences of the drop-wall impact were acquired for ambient pressures of 1–20 bar and wall temperatures ranging from 35–300 ∘C with a drop Weber number of ~ 50. Droplet impact sequences were recorded using a high-speed CMOS camera and were processed to measure the droplet spread, droplet rebound velocity and track the droplet centroid motion. The dynamics of the drop spreading and rebound show similar behavior across a range of ambient pressures with the largest differences observed for wetted versus non-wetted cases (above the Leidenfrost temperature). For both fluids, the onset of drop rebound remains bounded by the saturation temperature (shifting with ambient pressure) and the thermodynamic limit of liquid superheat. This leads to a decrease in the superheat temperature above the saturation point as the critical pressure is approached.

Inverse Opal Photonic Crystals as an Optofluidic Platform for Fast Analysis of Hydrocarbon Mixtures.

Most of the reported optofluidic devices analyze liquid by measuring its refractive index. Recently, the wettability of liquid on various substrates has also been used as a key sensing parameter in optofluidic sensors. However, the above-mentioned techniques face challenges in the analysis of the relative concentration of components in an alkane hydrocarbon mixture, as both refractive indices and wettabilities of alkane hydrocarbons are very close. Here, we propose to apply volatility of liquid as the key sensing parameter, correlate it to the optical property of liquid inside inverse opal photonic crystals, and construct powerful optofluidic sensors for alkane hydrocarbon identification and analysis. We have demonstrated that via evaporation of hydrocarbons inside the periodic structure of inverse opal photonic crystals and observation of their reflection spectra, an inverse opal film could be used as a fast-response optofluidic sensor to accurately differentiate pure hydrocarbon liquids and relative concentrations of their binary and ternary mixtures in tens of seconds. In these 3D photonic crystals, pure chemicals with different volatilities would have different evaporation rates and can be easily identified via the total drying time. For multicomponent mixtures, the same strategy is applied to determine the relative concentration of each component simply by measuring drying time under different temperatures. Using this optofluidic sensing platform, we have determined the relative concentrations of ternary hydrocarbon mixtures with the difference of only one carbon between alkane hydrocarbons, which is a big step toward detailed hydrocarbon analysis for practical use.

Effect of monovalent and divalent salts on the interfacial tension of pure hydrocarbon-brine systems relevant for low salinity water flooding

Interfacial tension between hydrocarbon liquids and salt water is a very important property for many industrial applications, especially in petroleum industry. Interfacial tension, in addition to other factors, has direct impact on displacement process in porous media so thus on oil recovery. Very recently, the salinity of injection brine has been regarded as a key factor in oil recovery using low salinity water flooding process. Decrease in the interfacial tension between crude oil and injection brine at low salinity condition might be a reason behind recovery improvement as suspected by some researchers; but there are also other effects associated with low salinity water flooding like wettability alteration, fine migration, mineral dissolution etc. It is suspected that the interaction of polar components at oil-water interface lead to the reduction of interfacial tension. However, the actual mechanism is not known and still under research. The main objective of this work is to determine the effect of salt concentration and type of ions present in an aqueous phase on the interfacial tension between pure hydrocarbon liquids and water. Different hydrocarbon liquids, such as aliphatic and aromatics, have been tested to understand the interaction of monovalent and divalent salts on the interfacial tension. The study reports the interfacial tension of five pure hydrocarbon liquids against solutions of three different salts (NaCl, MgCl2 and CaCl2) over a wide range of salinities. The interfacial tension measurements were done using Wilhelmy plate method by a dynamic contact angle tensiometer. All the experiments were conducted at room temperature and atmospheric pressure. The results lead us to the view that there is low a salinity concentration where the hydrocarbon/brine interfacial tension shows a minimum value. The type of salt also has a significant effect on interfacial tension of aliphatic and aromatic hydrocarbons. Monovalent salt found to be effective in reducing interfacial tension of aliphatic hydrocarbons while divalent salts were found to be effective for aromatic hydrocarbons. The possible mechanism for the reduction in IFT at low salt concentration has also been explained using Gibb's adsorption isotherm. In addition, the trend in IFT has been explained in the light of well-known Jones-Ray effect.

New relation between viscosity and surface tension for pure hydrocarbon liquids

ABSTRACTA new relation between viscosity and surface tension is proposed and checked for 21 pure hydrocarbon liquids, and validated with the National Institute of Science and Technology data. The performance and accuracy of the proposed relation are compared with the reported empirical correlations in the form of absolute average deviation. The proposed relation remains valid for higher hydrocarbons (up to C25H52). A total of 418 data points for 21 pure hydrocarbon liquids were taken into consideration for checking the accuracy of the proposed relation. The proposed relation gives an absolute average deviation of 5.66%, indicating high accuracy of the proposed relation.

Fast mass transport of oil and supercritical carbon dioxide through organic nanopores in shale

Hydrocarbon production from shale has grown dramatically in North America, and has the potential to do so globally. Nanoporous organic matter is probably the dominant mode of porosity occurrence in productive shale systems, but the physics of liquid transport through organic-hosted pores is still ambiguous. In the present work, molecular dynamics simulations were conducted to study the static properties and pressure-driven flow behavior of pure liquid hydrocarbons (octane) and supercritical carbon dioxide (scCO2) confined in slit-shaped organic nanopores. Carbonaceous slits having apertures ranging from 1.5 to 11.2nm were explored. A range of thermodynamic conditions, corresponding to the sedimentary reservoirs, were examined. Equilibrium molecular dynamics (EMD) enabled us to determine the density profile, from which we observed the layering structure of confined fluid and the preferential adsorption of scCO2 relative to C8H18 and CH4. As the pore size increases, the structure of the adsorbed phase transforms from a single-file chain to four and three dense monolayers for C8H18 and scCO2, respectively. Then we calculated, using nonequilibrium molecular dynamics (NEMD), their velocity profiles and studied the hydrodynamics under a pressure gradient. We found that the velocity profiles in an organic slit tend to be pluglike, which deviates significantly from the parabolic profile in inorganic nanopores, and the flow exceeds predictions of the no-slip Poiseuille equation by 1–3 orders of magnitude. We proposed two models to characterize the flow behavior, each of which can be integrated into a bottom-up framework to mimic fluid transport in shale and estimate the apparent liquid permeability. The parameters in our models, slip length and apparent viscosity, are exponentially dependent on driving force, pore size, and temperature. Our results, which highlight the need for taking into account the different nature of organic matter and inorganic minerals in flow modeling, will shed light on the development of shale resources and, more generally, mass transfer in nanoporous materials.

A Model for the Estimation of Surface Tension of Pure Hydrocarbon Liquids

Surface tension is an important property and its accurate prediction is required in most chemical engineering calculations. An equation for the surface tension of liquid hydrocarbons as a function of temperature is developed considering intermolecular attractions in liquid phase are reflected by its enthalpy. The model equation is validated with National Institute of Standards and Technology data on liquid hydrocarbon alkanes (C1 to C10 and C12) accounting for molecular shape through sphericity factor. The molecular sphericity factor correlated well with molecular weight of the hydrocarbons. The accuracy of the proposed model equation is compared with the two empirical equations, and results showed that the proposed model equation predicts the surface tension of pure hydrocarbon liquids more accurately.

Sooting tendencies of primary reference fuels in atmospheric laminar diffusion flames burning into vitiated air

In this study, the sooting tendencies of primary reference fuels (PRFs) are measured in term of yield sooting indices (YSIs) in methane diffusion flames doped with the vapors of PRFs. The present paper represents an incremental advance complementing the original methodology prescribed by McEnally and Pfefferle. The influence of both PRF formulation and CO2 dilution of the coflowing air on the YSIs is also assessed. The diffusion flames burning in a coflowing oxidizer stream are established over the Santoro’s burner and vapor of the liquid fuel to be investigated is injected into the fuel stream. Laser extinction measurements are performed to map the two-dimensional field of soot volume fraction in the flame. For the pure liquid hydrocarbons investigated, i.e., n-hexane, n-heptane, isooctane, and benzene, the YSI reported in the original paper by McEnally and Pfefferle quantitatively predict the sooting propensities, measured here at much higher dopant concentrations. The present study therefore extends the consistency of the YSI methodology on the Santoro’s burner. For blends of n-heptane and isooctane, the sooting tendency of doped flames exhibits regular and monotonic trends and decreases with increasing n-heptane mole fraction or CO2 dilution. Interestingly, the evolution of YSI with the isooctane mole fraction exhibits a strong similarity for varying CO2 mole fraction. A quadratic least-squares fit is then derived, providing a phenomenological model of YSI as a function of both isooctane mole fraction in the fuel stream and CO2 mole fraction in the oxidizer. A non-negligible cross effect of PRF formulation and CO2 dilution on YSI is revealed. The method elaborated within the framework of the present paper could be extended to surrogate fuels. This would help develop a comprehensive database and empirical correlations that could predict the sooting propensities of different surrogate fuels, therefore their potentially mitigationed soot production through control of fuel composition and/or exhaust gas recirculation. This database would also be useful for the validation of CFD simulations incorporating sophisticated model of soot production.

Predictive correlations for liquid heat capacity – including the critical region

A predictive correlation relating isobaric liquid specific heat capacity to absolute temperature and elemental composition was recently reported. The Dadgostar–Shaw correlation, valid where CV≫T(∂V/∂T)P(∂P/∂T)V, is modified in the present work to accommodate the critical region and the consequent variation of liquid phase isobaric heat capacity among isomers at the same absolute temperature. The results obtained for a training data set and a test data set are presented and compared with results obtained with the Dadgostar–Shaw correlation, and two variants of the Rowlinson–Bondi correlation. The CP° contribution is calculated using either compound specific correlations or the predictive universal Laštovka–Shaw equation for ideal gases. For pure hydrocarbon liquids where compound specific CP° correlations, Tc and ω are available, the Rowlinson–Bondi based approach should be used to compute saturated liquid heat capacities. If only Tc and ω are available, the Rowlinson–Bondi based approach+the predictive Laštovka–Shaw equation for CP° values is preferred. If the liquid is a multicomponent or ill-defined hydrocarbon liquid, the modified Dadgostar–Shaw correlation is preferred over the Dadgostar correlation as long as Tc is available or can be estimated. The accuracy penalty for use of the modified Dadgostar–Shaw correlation appears small relative to either Rowlinson–Bondi based calculation approaches.

Prediction of the aniline point temperature of pure hydrocarbon liquids and their mixtures from molecular structure

A quantitative structure property relation method for predicting the aniline point temperature of pure hydrocarbon liquids is presented. The method was used to probe the structural groups that have significant contribution to the overall aniline point property and arrive at the set of groups and their contribution values that can best represent the aniline point temperature of about 133 different substances. The 23 structural groups listed were derived from the Joback definition of group contributions and modified to account for the location of the structural groups in the molecule. The proposed method is very simple yet far superior to other methods and was able to predict the aniline point temperature of a testing set of pure hydrocarbons and of multicomponent mixtures from the knowledge of only the molecular structure with an average percentage error of 0.6% and 1.43%, respectively.

Scattering Dynamics of Hyperthermal Oxygen Atoms on Ionic Liquid Surfaces: [emim][NTf2] and [C12mim][NTf2

Collisions of hyperthermal oxygen atoms, with an average laboratory-frame translational energy of 520 kJ mol−1, on continuously refreshed ionic liquids, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide ([emim][NTf2]) and 1-dodecyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide ([C12mim][NTf2]), were studied with the use of a beam-surface scattering technique. Time-of-flight and angular distributions of inelastically scattered O and reactively scattered OH and H2O were collected for various angles of incidence with the use of a rotatable mass spectrometer detector. For both O and OH, two distinct scattering processes were identified, which can be empirically categorized as thermal and nonthermal. Nonthermal scattering is more probable for both O and OH products. The observation of OH confirms that at least some reactive sites, presumably alkyl groups, must be exposed at the surface. The ionic liquid with the longer alkyl chain, [C12mim][NTf2], is substantially more reactive than the liquid with the shorter alkyl chain, [emim][NTf2], and proportionately much more so than would be predicted simply from stoichiometry based on the number of abstractable hydrogen atoms. Molecular dynamics models of these surfaces shed light on this change in reactivity. The scattering behavior of O is distinctly different from that of OH. However, no such differences between inelastic and reactive scattering dynamics have been seen in previous work on pure hydrocarbon liquids, in particular, the benchmark, partially branched hydrocarbon, squalane (C30H62). The comparison between inelastic and reactive scattering dynamics indicates that inelastic scattering from the ionic liquid surfaces takes place predominantly at nonreactive sites that are effectively stiffer than the reactive alkyl chains, with a higher proportion of collisions sampling such sites for [emim][NTf2] than for [C12mim][NTf2].

Evaporation rates of pure hydrocarbon liquids under the influences of natural convection and diffusion

Evaporation of liquid hydrocarbons was studied in order to better understand the relative influences of diffusion and buoyancy-induced convection of the vapors on the evaporation rate. Evaporation rates were measured using a simple gravimetric technique and the behavior of the vapor layer that quickly forms above the film was observed using schlieren imaging. Even for conditions for which the influence of buoyancy is strong, the evaporation rates are well correlated by a one-dimensional diffusion model if an effective vapor layer thickness is used.

Viscosity and Density of Five Hydrocarbon Liquids at Pressures up to 200 MPa and Temperatures up to 473 K

We report the results of simultaneous measurements of the viscosity and density of five pure hydrocarbon liquids (octane, decane, 1,3-dimethylbenzene, 1,2,3,4-tetrahydronaphthalene, and 1-methylnaphthalene) at temperatures between (298.15 and 473.15) K and at pressures ranging from 0.1 MPa to approximately 200 MPa. The measurements were made with a vibrating-wire instrument, and the estimated expanded relative uncertainties are ± 2 % for viscosity and ± 0.2 % for density with a coverage factor of 2. The densities were correlated by means of a modified Tait equation, while the viscosities were correlated both with the theory of Dymond and Assael and in terms of an empirical function of temperature and pressure. We also present correlations of the viscosity of dodecane and octadecane based on results that we published previously [Caudwell et al. Int. J. Thermophys. 2004, 25, 1340−1352]. Extensive comparisons with literature data are presented.

Prediction of Sooting Tendency for Hydrocarbon Liquids in Diffusion Flames

A theoretical method for predicting the smoke point of pure hydrocarbon liquids is presented. The method is based on a structural group contributions approach and does not require any experimental procedures or information of fuel properties, other than the molecular structure of the fuel molecules. The proposed correlation is presented in the form of a multivariable regression. The average deviation is only 1.3 TSI (threshold soot index) units for ∼70 compounds from low-sooting paraffins to highly sooting aromatics, and the average relative error is 9.08%. The results of three different sets of structural groups derived from the Quann and Joback group contribution methods are tested and compared. For a mixture with a defined composition, the estimation of smoke point is also discussed. The method is of potential value for the formulation of surrogate fuels of hydrocarbon mixtures, where matching the fuel's sooting tendency is important.

Structural Group Contribution Method for Predicting the Octane Number of Pure Hydrocarbon Liquids.

Structural Group Contribution Method for Predicting the Octane Number of Pure Hydrocarbon Liquids.

Charging Ability of Pure Hydrocarbons and Lubricating Oils

An experiment using a purpose-built test rig to examine the effect of oil chemistry on the charging ability of various oils revealed that the charge produced depends on two extrinsic properties; the electric field (used to charge the droplet) and the droplet radius. A normalization parameter was developed from these dependencies and used to compare the results from the tests described herein. Four classes of liquids were tested. These were pure hydrocarbon liquids (hexadecane, decane, and squalane), base oils (both mineral and synthetic stocks), formulated oils (mineral base oil with additives), and commercial oils (fully formulated mineral and synthetic oils, available over-the-counter). The charging for both pure hydrocarbons and base oils indicates that the charged species have a low mobility and thus are likely to be large, bulky molecules. For this reason, the charging of the base oils is noticeably time dependent and the charge imparted on the oil did not always reach saturation. The charging (rate) of base oils appears to follow the level of impurities (particularly sulfur). Generally, both pure hydrocarbons and base oils tend to charge more when a positive field is applied. Conductivity values help to explain the measured charge levels. This would be expected as conductivity is related to the ionic species (charge carriers) present. The majority of the formulated and commercial oils tested reached charge saturation for all conditions tested, resulting in a normalized value of around 0.1 pC mm− 1 V− 1 , comparable with a theoretical calculated value. The formulated and commercial oils that did not reach saturation have conductivities comparable with base oils and therefore behave in a fashion similar to the base oils.

OTDR fiber-optical chemical sensor system for detection and location of hydrocarbon leakage

A distributed sensing system for apolar hydrocarbons is presented which is built from a polymer-clad silica fiber adapted to an optical time domain reflectometer (OTDR) set-up. OTDR measurements allow locating and detecting chemicals by measuring the time delay between short light pulses entering the fiber and discrete changes in the backscatter signals that are caused by local extraction of hydrocarbons into the fiber cladding. The light guiding properties of the fiber are affected by interaction of the extracted chemicals with the evanescent wave light field extending into the fiber cladding. Distributed sensing of pure liquid hydrocarbons (HC) and aqueous HC solutions with a commercially available mini-OTDR adapted to sensing fibers of up to 1 km length could be demonstrated. A pulsed laser diode emitting at the 850 nm telecommunication wavelength was applied in the mini-OTDR to locate the HCs by analyzing the step drop (light loss) in the backscatter signal, which is induced by local refractive index (RI) increase in the silicone cladding due to the extracted HC. The prototype instrument can be applied for monitoring hydrocarbon leakage in large technical installations, such as tanks, chemical pipelines or chemical waste disposal containments.

Structural Group Contribution Method for Predicting the Octane Number of Pure Hydrocarbon Liquids

A theoretical method for predicting the octane number of pure hydrocarbon liquids is presented. The method is based on a structural group contribution approach and requires no experimental procedure or knowledge of the physical or chemical properties only the chemical structure of the molecule. The proposed model is simple and can predict the research and motor octane numbers of more than 200 pure hydrocarbon liquids with an average deviation of 4 and 5.7, respectively. The results of two different sets of structural groups derived from the Joback group contribution approach are tested and compared. The method is notable for the absence of any theoretical procedure which has previously been used to estimate the pure-component octane number. In addition, the method has the potential advantage of synthesis of additional hydrocarbons with knock measurements as a major objective.

Surface Tension of Pure Hydrocarbons

A new correlation scheme for the surface tension of a homologous series of pure liquid hydrocarbons, as a function of molecular weight and temperature, is presented. Using orthobaric surface tension data from literature for four homologous series of hydrocarbons, i.e., n-alkanes, 1-alkenes, cycloalkanes, and aromatics, the adjustable parameters for two new surface tension equations are obtained individually for each series. The agreement between experimental values and those calculated with the two new generalized surface tension equations is very good, i.e., the temperature and molecular weight dependences of surface tension are well reproduced.

The Compressibility of Alkyltrimethylammonium Bromide Micelles

Ultrasonic measurements have been carried out for solutions of octyl-, decyl-, dodecyl-, tetradecyl-, and hexadecyltrimethylammonium bromides (CnTAB) over a wide range of concentrations above and below their critical micelle concentrations (CMC) at 25°C. The apparent molar adiabatic compressibilities of the surfactants in monomer, (Φks)f, and in micellar forms, (Φks)mic, have been determined. The values for (Φks)fdecrease with increasing chain length of the surfactant by an increment of −0.87 × 10−4cm3mol−1bar−1per –CH2– group. The opposite trend has been found for the value of (Φks)mic, the compressibility of surfactants in the micelle, which is positive, and increases with increasing chain length of the surfactant by 9.5 × 10−4cm3mol−1bar−1per –CH2– group. The coefficient of adiabatic compressibility of the internal cores of micelles is estimated to be 59.5 × 10−6bar−1, which is close to, but slightly lower than the coefficient of adiabatic compressibility of pure hydrocarbon liquids having the same number of –CH2– groups.

Organic inclusions as an indicator of oil/gas potential assessment of carbonate reservoir beds

Organic inclusions could be formed at the stages of either primary or secondary migration of hydrocarbons so long as mineral crystallization or recrystallization takes place in the sediments, presenting a direct indicator of oil/gas evolution, migration and abundance. Based on the study of organic inclusions in carbonate-type reservoir beds of commercial importance from North China, Xingjing, North Jiangsu, Jianghan, Sichuan and Guizhou in China, many inclusion parameters for oil/gas potential assessment of carbonate reservoir beds are summarized in this paper, including: 1) Types of organic inclusion: Commercially important oil beds are characterized by inclusions consisting of either pure liquid hydrocarbons or liquid plus minor gaseous hydrocarbons, while commercially important gas reservoirs are characterized by inclusions consisting of either pure gaseous hydrocarbons or gas plus minor liquid hydrocarbons. 2) Quantity of organic inclusions: The number of organic inclusions in commercially important oil/gas reservoirs is over 60% of the total inclusion percentage. 3) Temperature of saline inclusions: The homogenization temperatures of contemporaneous saline inclusions in oil reservoirs range from 91–161 °C, while in gas reservoirs from 150–250 °C). 4) Inclusion composition: In commercially important oil reservoirs, C1/C2=2−10, C1/C3=2−4, C1/C4=2−21, (C2−C4)/(C1−C4)(%)>20, (CH4+CO+H2)/CO2 (molecules/g)=0.5−1.0, and in C2−C3−nC4 triangle diagram there should be an upside-down triangle with the apex within the ellipse, while in commercial gas reservoirs, C1/C2=10−35, C1/C3=14−82, C1/C4=21−200, (C2−C4)/(C1−C4)(%) 1, and there would be an upright triangle with the apex within the ellipse.