Diffusion In Mixtures Research Articles

Computer modeling of a diffusion in a mixture of ideal gases given the dependence of the diffusion coefficient on the entropy of mixing in Wolfram Mathematica

Objectives. The objective of the work is computer modeling of diffusion in ideal gas mixtures taking into account the dependence of the diffusion coefficient on the entropy of mixing according to the model proposed by one of the authors of the article, in Wolfram Mathematica.Methods. Built-in function NDSolveValue in Wolfram Mathematica and the default solver were used for the numerical solution of the one-dimensional task; for the numerical solution of the two-dimensional task the same function was used, for which the Numerical Method of Lines was specified as the solver.Results. The results of computer modeling of diffusion in a mixture of ideal gases are obtained taking into account the dependence of the diffusion coefficient on the entropy of mixing for two tasks in a one-dimensional formulation and one task in a two-dimensional formulation.Conclusion. The conducted research and the obtained solutions in computer modeling of diffusion in a mixture of ideal gases taking into account the dependence of the diffusion coefficient on the entropy of mixing indicate that for solving tasks in the field of computer modeling of gas mixing in modern software tools could be used a mathematical model that is an alternative to popular modern models based on the description of the hydrodynamic properties of gases and the enthalpy of mixing, as well as other entropy models.

Adsorption and Diffusion of CH4, N2, and Their Mixture in MIL-101(Cr): A Molecular Simulation Study.

A comprehensive quantitative grasp of methane (CH4), nitrogen (N2), and their mixture's adsorption and diffusion in MIL-101(Cr) is crucial for wide and important applications, e.g., natural gas upgrading and coal-mine methane capturing. Previous studies often overlook the impact of gas molecular configuration and MIL-101 topology structure on adsorption, lacking quantitative assessment of primary and secondary adsorption sites. Additionally, understanding gas mixture adsorption mechanisms remains a research gap. To bridge this gap and to provide new knowledge, we utilized Monte Carlo and molecular dynamics simulations for computing essential MIL-101 properties, encompassing adsorption isotherms, density profiles, self-diffusion coefficients, radial distribution function (RDF), and CH4/N2 selectivity. Several novel and distinctive findings are revealed by the atomic-level analysis, including (1) the significance of C=C double bond of the benzene ring within MIL-101 for CH4 and N2 adsorption, with Cr and O atoms also exerting notable effects. (2) Density distribution analysis reveals CH4's preference for large and medium cages, while N2 is evenly distributed along pentagonal and triangular window edges and small tetrahedral cages. (3) Calculations of self-diffusion and diffusion activation energies suggest N2's higher mobility within MIL-101 compared to CH4. (4) In the binary mixture, the existence of CH4 can decrease the diffusion coefficient of N2. In summary, this investigation provides valuable microscopic insights into the adsorption and diffusion phenomena occurring in MIL-101, thereby contributing to a comprehensive understanding of its potential for applications, e.g., natural gas upgrading and selective capture of coal-mine methane.

Diode Laser Absorption Spectroscopy and DSMC Calculations for the Determination of Species-Specific Diffusion Coefficients of a CO2-N2O Gas Mixture in the Transition Gas Regime

Multicomponent gas mixture diffusion in a microscale confined flow in the transition gas regime at Knudsen numbers (Kn) above 0.1 has potential engineering applications in gas-phase microfluidics. Although the calculation of the diffusion coefficient accounts for the influence of the concentration of other species in a multicomponent gas mixture, the higher rate of gas-wall collision at 0.1 < Kn ≤ 10 introduces additional complications not predicted by conventional calculation methods. Thus, simultaneous measurement of diffusion coefficients for multiple gas species ensures accurate estimation of the diffusion coefficient of a particular species that includes the effect of interactions with other species and wall surface conditions in a multicomponent gas mixture at Kn > 0.1. However, most experimental methods for measuring the diffusion coefficient are not species-specific and therefore cannot directly differentiate between the species diffusing in a gas mixture. Thus, this paper demonstrates a new experiment methodology consisting of a two-bulb diffusion configuration accompanied by a tunable diode laser absorption spectroscopy detection technique for species-specific, in-situ, simultaneous measurement of the effective diffusion coefficient for a CO2-N2O gas mixture in the transition gas regime. The experimental results are compared against direct simulation Monte Carlo calculations and the Bosanquet approximation showing a deviation that has not been reported in the literature before.

Unveiling molecular mechanisms of enhanced N2 solvation and diffusion in ionic liquid mixtures

Ammonia synthesis depends on N2 critically, a principal raw material whose solubility influences the reaction kinetics and product selectivity. Ionic liquids (ILs) possess the advantage of structure tunability to modulate N2 solubility. In practical applications, ILs are commonly mixed with other solvents to achieve a balance between reaction and transport processes. Herein, the dissolution and diffusion behaviors of N2 in mixed systems are analyzed microscopically through molecular dynamics simulations. It reveals that introducing a small quantity of trihexyl(tetradecyl)phosphonium tris(pentafluoroethyl)-trifluorophosphate into tetrahydrofuran enhances the solubility and diffusion coefficients of N2 significantly. The transition point is governed by the fraction of nanocavity, which exhibits distinct expansion, saturation, and compression zones. Furthermore, the response trend of N2 solubility in mixed systems to temperature changes varies with molar concentrations, reflecting differences in solvation enthalpy changes. These findings provide theoretical insights for the design of mixed solvents with high N2 dissolution and diffusion capabilities.

Simulation Study on Diffusion and Local Structure of CH4, CO2, SO2, and H2O Mixtures into Double-Layers Graphene.

Graphene has been widely studied as an ideal material for the adsorption and separation. In this work, we used molecular dynamics simulations to investigate the evolution of diffusion and local structure of CH4, CO2, SO2, and H2O mixtures into double-layers graphene under seven different interlayer spacings and four different CO2 concentrations. The results showed that the adsorption of CH4 and CO2 molecules on the graphene surface weakened with increased interlayer spacing. The diffusion capacities of CH4 and CO2 in the mixed system were significantly improved by increasing the interlayer spacing. In interlayer spacings ranging from 5 to 10 nm, the diffusion capacities of each component varied significantly in the order CH4 > CO2 ≫ H2O > SO2. Compared with CH4 and CO2, the local structures of SO2 and H2O were more affected by the interlayer spacing. Larger interlayer spacings or higher CO2 concentrations were advantageous for the formation of stronger hydrogen bond structures between H2O molecules. When the CO2 concentrations were between 10% and 20% and the interlayer spacing of graphene was 8 nm, the graphene structure exhibited the best adsorption and separation effects on CH4 and other components.

Experimental study of the effect of the addition of Posidonia Oceanica fiber on the thermal and acoustic insulation properties of plaster

In this work, plaster and natural Posidonia Oceanica (PO) fibers are combined to create a composite material that was recently produced. This work’s primary objective is to assess the mechanical and thermophysical performance of the composite material in order to determine whether or not it may be used as a thermal and acoustic insulation material in buildings. For this end, prismatic and parallelepipedic specimens of different dimensions were made with fiber percentages ranging from 0% to 20%. In addition, parallelepiped panels (600 mm × 600 mm × 40 mm3) were also prepared containing 10% of PO fibers. Mechanical properties (flexual strength, compressive strength), thermal properties and sound absorption coefficient were investigated. For each test specimen, the density was calculated for a proportion of fibers ranging from 0% to 20%. The results indicated a marked improvement in the compressive and flexural strength of the fiber-reinforced mixtures. This improvement is respectively 14.5% and 33.8% for mixtures containing 10% of PO fibers. Additionally, the addition of PO fibers significantly decreases density (by 40.5%), thermal conductivity (by 68.5%) and thermal diffusivity (by 36.9%) of the different mixtures. The ideal mechanical characteristics are attained when 5%–10% of the volume is made up of Posidonia Oceanica fibers. The results of the sound absorption coefficient test show that the mixture of plaster with 10% fibers has a good sound absorption coefficient of 0.78 for high frequencies between 1000 Hz and 4000 Hz. This work has shown conclusively that the incorporation of PO fibers, up to a maximum of 10% with plaster, makes it possible to obtain a lightweight composite that can potentially be used as a new insulating construction material.

A Reverse Nonequilibrium Molecular Dynamics Algorithm for Coupled Mass and Heat Transport in Mixtures.

We present a new method for introducing stable nonequilibrium concentration gradients in molecular dynamics simulations of mixtures. This method extends earlier reverse nonequilibrium molecular dynamics (RNEMD) methods, which use kinetic energy scaling moves to create temperature or velocity gradients. In the new scaled particle flux (SPF-RNEMD) algorithm, energies and forces are computed simultaneously for a molecule existing in two nonadjacent regions of a simulation box, and the system evolves under a linear combination of these interactions. A continuously increasing particle scaling variable is responsible for the migration of the molecule between the regions as the simulation progresses, allowing for simulations under an applied particle flux. To test the method, we investigate diffusivity in mixtures of identical but distinguishable particles and in a simple mixture of multiple Lennard-Jones particles. The resulting concentration gradients provide Fick diffusion constants for mixtures. We also discuss using the new method to obtain coupled transport properties using simultaneous particle and thermal fluxes to compute the temperature dependence of the diffusion coefficient and activation energies for diffusion from a single simulation. Lastly, we demonstrate the use of this new method in interfacial systems by computing the diffusive permeability of a molecular fluid moving through a nanoporous graphene membrane.

Mutual Diffusivities of Mixtures of Carbon Dioxide and Hydrogen and Their Solubilities in Brine: Insight from Molecular Simulations.

H2-CO2 mixtures find wide-ranging applications, including their growing significance as synthetic fuels in the transportation industry, relevance in capture technologies for carbon capture and storage, occurrence in subsurface storage of hydrogen, and hydrogenation of carbon dioxide to form hydrocarbons and alcohols. Here, we focus on the thermodynamic properties of H2-CO2 mixtures pertinent to underground hydrogen storage in depleted gas reservoirs. Molecular dynamics simulations are used to compute mutual (Fick) diffusivities for a wide range of pressures (5 to 50 MPa), temperatures (323.15 to 423.15 K), and mixture compositions (hydrogen mole fraction from 0 to 1). At 5 MPa, the computed mutual diffusivities agree within 5% with the kinetic theory of Chapman and Enskog at 423.15 K, albeit exhibiting deviations of up to 25% between 323.15 and 373.15 K. Even at 50 MPa, kinetic theory predictions match computed diffusivities within 15% for mixtures comprising over 80% H2 due to the ideal-gas-like behavior. In mixtures with higher concentrations of CO2, the Moggridge correlation emerges as a dependable substitute for the kinetic theory. Specifically, when the CO2 content reaches 50%, the Moggridge correlation achieves predictions within 10% of the computed Fick diffusivities. Phase equilibria of ternary mixtures involving CO2-H2-NaCl were explored using Gibbs Ensemble (GE) simulations with the Continuous Fractional Component Monte Carlo (CFCMC) technique. The computed solubilities of CO2 and H2 in NaCl brine increased with the fugacity of the respective component but decreased with NaCl concentration (salting out effect). While the solubility of CO2 in NaCl brine decreased in the ternary system compared to the binary CO2-NaCl brine system, the solubility of H2 in NaCl brine increased less in the ternary system compared to the binary H2-NaCl brine system. The cooperative effect of H2-CO2 enhances the H2 solubility while suppressing the CO2 solubility. The water content in the gas phase was found to be intermediate between H2-NaCl brine and CO2-NaCl brine systems. Our findings have implications for hydrogen storage and chemical technologies dealing with CO2-H2 mixtures, particularly where experimental data are lacking, emphasizing the need for reliable thermodynamic data on H2-CO2 mixtures.

Deeper Insights into Mixed Crowding through Enzyme Activity, Dynamics, and Crowder Diffusion.

Given the fact that the cellular interior is crowded by many different kinds of macromolecules, it is important that in vitro studies be carried out in the presence of mixed crowder systems. In this regard, we have used binary crowders formed by the combination of some of the commonly used crowding agents, namely, Ficoll 70, Dextran 70, Dextran 40, and PEG 8000 (PEG 8), to study how these affect enzyme activity, dynamics, and crowder diffusion. The enzyme chosen is AK3L1, an isoform of adenylate kinase. To investigate its dynamics, we have carried out three single point mutations (A74C, A132C, and A209C) with the cysteine residues being labeled with a coumarin-based solvatochromic probe [CPM: (7-diethylamino-3-(4-maleimido-phenyl)-4-methylcoumarin)]. Both enzyme activity and dynamics decreased in the binary mixtures as compared with the sum of the individual crowders, suggesting a reduction in excluded volume (in the mixture). To gain deeper insights into the binary mixtures, fluorescence correlation spectroscopy studies were carried out using fluorescein isothiocyanate-labeled Dextran 70 and tetramethylrhodamine-labeled AK3L1 as the diffusion probes. Diffusion in binary mixtures was observed to be much more constrained (relative to the sum of the individual crowders) for the labeled enzyme as compared to the labeled crowder showing different environments being faced by the two species. This was further confirmed during imaging of the phase-separated droplets formed in the binary mixtures having PEG as one of the crowding agents. The interior of these droplets was found to be rich in crowders and densely packed, as shown by confocal and digital holographic microscopy images, with the enzymes predominantly residing outside these droplets, that is, in the relatively less crowded regions. Taken together, our data provide important insights into various aspects of the simplest form of mixed crowding, that is, composed of just two components, and also hint at the enhanced complexity that the cellular interior presents toward having a detailed and comprehensive understanding of the same.

Thermodiffusion, diffusion and Soret coefficients of binary polymeric mixtures in toluene and cyclohexane

Abstract We present the results of experimental study on measuring the thermodiffusion, molecular diffusion and Soret coefficients of polystyrene (4,880 g/mol) in the pure solvents toluene and cyclohexane at 298 K and atmospheric pressure. The experiments have been carried out for a wide range of concentrations, starting from the diluted state with 2 % polystyrene mass fraction (proposed in the DCMIX4 project) up to the semidilute regime of 20 % polystyrene mass fraction. In addition, we present a complete characterisation of the thermophysical properties of the analysed mixtures. Thermodiffusion, molecular diffusion and Soret coefficients of binary polymeric samples have been measured by combining the traditional thermogravitational column technique, the thermogravitational microcolumn and the optical beam deflection method. In toluene, the obtained experimental results are consistent with literature, showing that the magnitude of the mass transport thermoproperties decrease significantly with increasing polystyrene concentration, which is a first indication of an approaching glass transition in the concentrated regime. The results for thermodiffusion and molecular diffusion coefficients in cyclohexane as a function of concentration exhibit a similar trend. Nevertheless, the Soret coefficient seems to show an opposite tendency for the two solvents, increasing in magnitude for cyclohexane, at least up to the analysed polystyrene concentration.

SIMMER code two-fluid model well-posedness and stability for simulating liquid metal (lead–lithium eutectic), water vapor, and non-condensable gases multi-component multi-phase flows

Liquid metals are employed as a coolant in liquid metal fast reactors (LMFR) and are considered breeders and coolants for future power-producing fusion reactors. The interaction of liquid metals with other coolants, such as air and water, is one of the possible occurrences in liquid metal-cooled reactors. Although the SIMMER-III computer code is currently in the validation and verification phase, it is a prospective candidate code for correctly investigating possible accidents. This study aims to determine the stability and well-posedness of the SIMMER-III code Eulerian-Eulerian two-fluid model (TFM) under any such accident scenario. This work also considers the influence of the virtual mass force and diffusion forces in momentum on TFM stability in accelerated liquid metal, steam, and non-condensable gaseous flows throughout all flow regimes. The characteristics method is used to assess the ill-posed nature of TFM for all types of accidents and accident scenarios in a hypothetical simplified system model with several components (Lead–Lithium, non-condensable gases, and water vapor). It has been discovered that the analysis findings vary from the air and water two-component two-phase flows (characteristics roots spectrum and error growth rate patterns) and are particularly sensitive to the diffusion and virtual mass coefficients. This is because liquid metals have a higher density than liquid water and steam, resulting in strong virtual mass forces and weak diffusion forces in liquid-metal and gas two-phase flows. Because of the extensive range of possible interactions between fluxes of different components, producing an accurate representation of diffusion in multi-component mixtures is difficult. Because of this, it is strongly suggested that the virtual mass coefficient and diffusion coefficients be handled more accurately for these kinds of flows. The values of these coefficients significantly affect how accurate proposed TFM predictions are, but there hasn't been much research on how to estimate them. The study also sheds light on the model's accuracy and highlights the areas where the model's predictions will be mathematically trustworthy.

Diffusivities in water or aqueous solutions of sodium chloride with dissolved hydrogen and methane by dynamic light scattering

Knowledge of diffusion in water or aqueous solutions of sodium chloride with dissolved hydrogen and methane is important for geological hydrogen storage. This study examines the accessibility of diffusivities in the corresponding mixtures through dynamic light scattering at macroscopic thermodynamic equilibrium and provides corresponding data for hydrogen-storage-relevant temperatures T up to 393 K and pressures up to 20 MPa. The thermal and mutual diffusivities are simultaneously accessible in mixtures of water and hydrogen. Moreover, for water with dissolved mixtures of hydrogen and methane, the thermal diffusivity and an apparent diffusivity related to the diffusion of the gas mixture can be accessed. In aqueous solutions of sodium chloride at T > 300 K, a strong molecular association leading to a quasi-static light-scattering pattern in the liquid sample was observed, which hindered the determination of the molecular gas diffusivities. However, the salt diffusion coefficient was accessible for all T values.

A double-pass optical beam deflection instrument for the measurement of diffusion, thermodiffusion and Soret coefficients in liquid mixtures and its application to polymer analysis

Abstract We have developed a new double-pass optical beam deflection instrument for the measurement of diffusion, thermodiffusion and Soret coefficients in liquid mixtures. The increased sensitivity of the instrument results from a second passage of the readout laser beam through the Soret cell containing the sample. An elegant description of the total beam deflection is achieved by means of a transfer matrix formalism. The higher sensitivity allows for a reduction of the length of the detection arm and a compact and stiff design of the instrument. The performance of the new apparatus is demonstrated by its application to polymer analysis for the determination of the molar mass distribution of the polymer from the distribution of diffusion rates by means of the CONTIN algorithm.

Effects on the magnetic properties and microstructure of Nd-Fe-B diffusion-processed using Tb oxyfluoride

Diffusion process has been proved to be an effective way to enhance the performance of Nd-Fe-B permanent magnets. In present work, the mixture of TbF3 and Tb4O7 has been used as diffusion sources and their influences on the microstructure and magnetic properties have been investigated. The results reveal that the binary mixture diffusion system outperforms the individual diffusion using either TbF3 or Tb4O7 as diffusion source. Diffusion-processed at 900 ℃ for 7 h followed by subsequently aged at 500 ℃ for 1 h, the coercivity of the magnet is increased substantially from 0.95 T to 2.33 T. The (Nd, Tb)2Fe14B/Nd2Fe14B core–shell-type structure has been formed with continuous Tb-rich grain shell.

Emission and Heat Release Characterization of Propane/Syngas Mixture Diffusion Flame Under Oxygen-Enhanced Combustion and Preheated-Air Combustion Conditions

ABSTRACT In this study, the emission and heat release characterization of propane/syngas opposed jet diffusion flame under oxygen-enhanced and preheated-air combustion conditions was conducted. The impacts of different operating conditions were examined, namely, the fuel mixture composition, where the propane mole fraction was varied from 0.3 to 0.7, while syngas was assumed as an equimolar mixture of hydrogen and carbon monoxide. The oxidizer was assumed to be an enriched air where the oxygen mole fraction was varied from 0.21 to 0.3. The oxidizer injection temperature was varied from 300 K to 500 K; in contrast, the fuel injection temperature was kept constant and equal to 300 K. The injection velocity of both fuel and the oxidizer is equal and varied from ignition to extinction in terms of strain rate. Finally, the pressure is constant and equal to 1 atm. The combustion chemical kinetics mechanism USC II for H2/CO/C1-C4 coupled with the Gri 2.11 N-sub mechanism was adopted. It is found that increasing syngas mole fraction in the fuel mixture enhances flame temperature, extends the flammability limits, promotes heat release rate, reduces CO/CO2 emission, and increases NO emissions through the thermal route nevertheless, the prompt route remained the dominant NO production route. Moreover, it was noted that under the oxygen-enhanced combustion condition, CO/CO2 emission increases, the heat release rate experiences an increase, and the flame temperature is significantly enhanced hence a considerable increase in NO emission through the thermal route, which evolves to be the dominant NO production route. Furthermore, it was remarked that under the preheated-air combustion condition, the flame temperature experiences a considerable increase; consequently, the CO emission increases due to CO2 disposition thus, its reduction, and the NO emission slightly increases through the thermal route, which becomes the dominant NO production route in the syngas-rich mixture, in contrast, the heat release rate decreases.

Unveiling the competitive diffusion of binary gas mixtures in polymers: The case of carbon dioxide and alkanes in nanoporous-crystalline polyphenylene oxide

The competitive diffusion of multicomponent gases in polymeric materials has been long debated and rarely observed experimentally. In this contribution, we explore the diffusion of binary gas mixtures of CO2 and either CH4, C2H6 or C3H8 in semicrystalline Poly(2,6-dimethyl-1,4-phenylene)oxide (PPO) films at sub atmospheric pressure. FTIR Spectroscopy in the transmission mode was exploited to investigate both the gas and the polymer phases coupling this technique with Barometry. The IR signals of methane, ethane and propane were isolated for the first time in a polymer phase and their molar absorptivity calibrated from pure gas sorption experiments. Then, during sorption tests involving binary gas mixtures, the same IR signals were used to quantify the simultaneous diffusion of the two gases in the polymer phase and their solubility at thermodynamic equilibrium. The experimental conditions were carefully chosen to prevent any sorption induced modification of the polymer structure. For the first time, in addition to the analysis of sorption equilibrium, a complete picture of the sorption process of a binary gas mixture in polymer films is given and the mutual effects of the diffusing species during the sorption process is unveiled.

Oxygen diffusion in biochar-based mixtures as plant growth media: Experimental and modelling.

A large amount of agricultural waste is produced annually. Producing biochar is an excellent solution for waste management, resource recovery, emission reduction, energy production, reduction in transportation and enhancing carbon sequestration. This study was done to investigate the aeration status of biochar-based growth media as compared with the commercial soilless medium of cocopeat-perlite. Biochars from oven-dried residues were produced by slow pyrolysis at 300 (B300) and 500°C (B500) with a rate of 2°C min-1 and using a continuous inflow of nitrogen. Sawdust (Sd), wheat straw (WS), rice hull (Rh), palm bunches (Plm) and sugarcane bagasse (SC), their biochars, vermiculite (V) and zeolite (Z) were used to prepare 13 mixed growth media. Oxygen diffusion coefficient (Dp) of media was measured at six matric potentials (h) of -5, -10, -15, -20, -40 and -60 hPa. Troeh et al. (1982) model was fitted to Dp/D0 versus air-filled porosity (AFP) data. Although AFP was more than 0.1 m3 m-3 for some media, the Dp/D0 was very low. Considering optimum Dp/D0 (i.e. 0.010-0.015) for growth substrates at h = -8 hPa, aeration status of four media (cocopeat-perlite, Rh-SCB300-Z, Sd-SCB300-Z and WSB500-Rh-V) was optimum. Highest Dp/D0 at h = -8 hPa was observed for Rh-SCB300-Z. The AFP at h = -10 hPa was highest for Rh-SCB300-Z, cocopeat-perlite and WSB500-Rh-V. Biochar-based media with good aeration status and water retention can be a suitable substitute for commercial soilless culture in greenhouse production. Overall, WSB500-Rh-V is a suitable substitute for cocopeat-perlite.

Internal flame structures of thermo-diffusive lean premixed H2/air flames with increasing turbulence

Turbulent flow fields, instantaneous flame structures, and internal thermo-chemical states of lean premixed hydrogen/air jet flames at an initial equivalence ratio of 0.4 are experimentally investigated by simultaneous laser-induced fluorescence of hydroxyl radicals (OH-LIF) and particle image velocimetry (PIV), and quasi-simultaneous 1D Raman/Rayleigh and 2D Rayleigh scattering measurements over a range of Karlovitz numbers (Ka) from 50 to 730. At low Ka, intense burning characterized by elevated local equivalence ratio, high water mole fraction (XH2O), and super-adiabatic flame temperature is mainly observed in post-flame regions surrounded by positively curved flame surfaces, where the fast diffusive hydrogen is locally focused. The flame features stronger differential diffusion and curvature effects than that in the planar laminar flame, which indicates that both molecular and turbulent mixing play significant roles, and thermo-diffusive instabilities have synergistic interactions with turbulence at low turbulence level. With increasing Ka, the burning intensity in corresponding regions is weakened, even though the flame surface is more disturbed by the turbulence. At the highest Ka, no intense burning region is observed in the jet flame as the turbulent transport dominates over the molecular diffusion. In the temperature domain, the conditional means of hydrogen mole fraction (XH2) and local equivalence ratio feature effects of diffusive instabilities with broad distributions at low-Ka conditions. Elevated XH2O and local equivalence ratios with super-adiabatic flame temperatures are observed, which is attributed to differential diffusion in hydrogen-containing mixtures and the fuel focusing effect near positively curved flame surfaces. At high Ka, the XH2 shows a more linear decreasing trend and the local equivalence ratio profile becomes flatter over temperature with a narrower distribution, indicating the dominance of turbulent mixing.

INVESTIGATION OF THE DIFFUSION OF TWO GASES EQUALLY DILUTED WITH DIFFERENT BALLAST GASES

Both liquid and gaseous mixes have significant significance in numerous natural and artificial processes. This elucidates the comprehensive examination of such systems in a diverse array of various applications. The presence of several processes of heat and mass transfer in gas mixtures without an interfacial boundary in the system causes the emergence of thermoconcentration gravitational fluxes, resulting in density inhomogeneity of the medium. Isothermal diffusion in helium and methane gas mixtures in a stationary medium of propane and nitrous oxide ballast gases at various pressures has been experimentally studied. It is shown that in systems where the two main gases helium and methane were diluted with propane, and then helium with propane, and methane with nitrous oxide, a repetitive unstable diffusion state of varying intensity occurs with increasing pressure. The effect of the diluent gas on the transfer of two main gases in three-component and four-component systems is significant, since the ballast gas can either accelerate, slow down, or leave the diffusion mixing process unchanged. The comparison between experimental and calculated data on the Stefan-Maxwell theory shows a noticeable difference between them.Key words:convection, diffusion, ballastgas, multicomponent gas mixtures.

Study on the effect of injection strategy on the combustion and emission characteristics of direct injection spark ignition bio-butanol engine

Owing to its physicochemical similarities with gasoline and renewable nature, n-butanol (bio-butanol) has garnered significant researcher interest. However, the lower atomization and volatility of n-butanol pose challenges when implemented in direct-injection spark-ignition (DISI) engines, leading to inhomogeneous air-fuel mixtures which subsequently results in a deterioration of combustion performance and an uptick in pollutant emissions. This study uses numerical simulations to examine the effects of injection pressure and timing on mixture formation, combustion, and emission characteristics in n-butanol DISI engines. The results indicate that for n-butanol, characterized by its reduced volatility and atomization capabilities, enhancing injection pressure from 10 MPa to 20 MPa effectively improves combustion and emission performance. However, the benefits taper off with subsequent increases in pressure. At injection pressure of 20 MPa, optimizing injection timing offers better combustion and emission results than merely increasing injection pressure. An early injection, represented by −300°CA start of injection, provides extended evaporation and mixture diffusion, significantly improving mixture quality and resulting in better combustion and emission outcomes. At −260°CA start of injection, while peak in-cylinder pressures can be achieved more favorably, the resultant inhomogeneous in mixture distribution results in increased emissions of CO, soot, and HC.