Liquid Penetration Research Articles

GAS LIQUID FLOW IN HILLY TERRAIN PIPELINES-SINGLE AND MULTIPLE SECTIONS

A new way of calculating severe slugging behavior for hilly terrain pipe lines is presented. Analysis is based on the analytical solution of a single line/riser system and treats each section as a single system, using the results of the analytical solution. Yet interaction is needed since the "outlet pressure" in each section is calculated iteratively. The present modification leads to a more elegant and reliable solution. In addition, the modified model takes into account the inclusion of gas within the liquid in the risers. The solution presents the variation of pressure and liquid level in each inclined line with time, the maximum inlet pressure, the cycle time (frequency), the maximum penetration of liquid into the inlet section, and the pressure in each line. The solutions of multiple sections are compared to the case of a single line/riser case.

Разработка и сертификация летной годности современной ответственной детали корпуса переключателя для аэрокосмических систем, изготовленной из сплава AlSi10Mg с помощью аддитивной технологии

Aerospace applications can benefit from additive manufacturing (AM), which is highly advantageous for prototyping and rapid manufacturing. It also offers cost and weight savings, as well as integrated design capabilities. As of now, there are only a few AM standards available, many materials and equipment are involved, resulting in many variables that hinder certification and adoption. As a result, nonstandard testing is making AM in the airborne materials less appealing due to its costly and time-consuming nature. The main objective of this work is to manufacture the Selector Valve Body parts of military and civil aircraft through Laser Powder Bed Fusion (LPBF) process using AlSi10Mg powder. Further, this paper has been carried out the metallurgical properties, non-destructive and destructive testing as well as the clear explanation about the certification procedures. Moreover, this underscores the need for the developing guidelines and standards that cover all aspects of manufacturing from design to manufacturing to operation. A comprehensive analysis from liquid penetration test shows defects are within the permissible level. In addition, it exhibits higher yield strength, ultimate strength, and elongation of (259±4), (323±4) MPa, and (12.5±1.5) % respectively, along with factual evidence that the precipitation hardened AlSi10Mg indigenously developed and produced is equal in properties to the equivalent precipitation hardening aluminium alloys produced by internationally renowned manufacturers.

Influence of electro-thermal probe tip shape on thin liquid layer evolution and penetration speed in glaciers

Influence of electro-thermal probe tip shape on thin liquid layer evolution and penetration speed in glaciers

Comparative study on the spray and combustion characteristics between diesel and kerosene underlow-temperature combustion (LTC)mode conditions

Kerosene, an intermediate component of wide distillation fuel, has drawn increasing attention for low-temperature combustion mode due to its compromise of evaporation and ignition characteristics between diesel and gasoline. This study focuses on the comparison of spray and combustion characteristics between diesel and kerosene under low-temperature combustion mode conditions based on visualization tests in a constant volume chamber. Different injection pressures, ambient temperatures, and oxygen concentrations were tested at a constant ambient density of 16.67 kg/m3. The image processing results reveal that the liquid penetration distance of kerosene shows a maximum reduction of 33.5% compared to diesel with a smaller cone angle and spray area at 160 MPa and 800 K. At the same time, the ignition delay of kerosene is 0.9 ms longer than that of diesel, and the injection and combustion processes of kerosene are separated, making it much more similar to the premixed combustion. An increase in injection pressure improves the spray penetration distance but exerts little influence on the flame lift-off length and ignition delay for both fuels. Kerosene presents a lower spatially integrating natural luminosity, especially at low injection pressure. The liquid spray penetration distance and the ignition delay of kerosene are more sensitive to the increase in ambient temperature. However, the higher ambient temperature presents a greater effect on the SINL of diesel. With the decrease of ambient oxygen concentration, the ignition delay, flame lift-off length, spatially integrating natural luminosity, and soot oxidation rate of both fuels decrease obviously. Especially at 15 vol.% ambient oxygen, kerosene presents a much weaker luminosity. These results imply that kerosene exhibits a very similar trend to diesel in terms of spray and combustion characteristics. Moreover, kerosene has a stronger potential to reduce soot formation than diesel with a better fuel-air mixing process under low-temperature combustion mode conditions.

Modeling and LES of high-pressure liquid injection under evaporating and non-evaporating conditions by a real fluid model and surface density approach

Numerical modeling of high-pressure liquid fuel injection remains a challenge in various applications. Indeed, experimental observations have shown that injected liquid fuel jet undergoes a continuous change of state from classical two-phase atomization and spray droplets evaporation to a dense-fluid mixing phenomenon depending on the ambient pressure, temperature, and fuel properties. Accordingly, a predictive and efficient computational fluid dynamics (CFD) model that can represent the possible coexistence of subcritical and supercritical regimes during the fuel injection event is required. The widely used Lagrangian Discrete Droplet Method (DDM) requires parameter tuning of model constants and cannot model the dense near-nozzle region. Meanwhile, the high computational cost of Interface Capturing Methods (ICM) has prohibited their application to industrial cases. Thus, another alternative is an Eulerian Diffuse Interface Model (DIM), where the unresolved interface features are modeled instead of being tracked. Accordingly, the current work proposes a fully compressible multi-component two-phase real-fluid model (RFM) with a diffused interface and closed by a thermodynamic equilibrium tabulation method based on a real-fluid equation of state. The RFM model is complemented with a postulated surface density equation for fuel atomization modeling within the Large Eddy Simulation (LES) framework. The Engine Combustion Network (ECN) Spray A injector non-evaporating and nominal evaporating conditions are used as a reference for the proposed model validation. Simulations are performed using the proposed RFM model that has been implemented in the CONVERGE CFD solver. Under the non-evaporating condition, the RFM model can capture well the fuel mass distribution in the near-nozzle field, but also the interfacial surface area. Besides, the predicted drop size from simulations falls within the experimental data range. On the other hand, under the evaporating condition, spray liquid and vapor penetrations and fuel mixture fraction distribution are also accurately predicted. The vaporization effect on the surface area density is revealed to enhance surface generation in the dense spray region while reducing the surface density in the dilute spray region. The mean droplet size is also relatively reduced under the evaporating condition in the diluted spray region. Overall, the accuracy and computationally efficiency of the proposed RFM model coupled with the surface density equation for high-pressure fuel injection modeling are confirmed, allowing its use for high pressure industrial configurations in future studies.

Investigation on Spray Morphology, Droplet Dynamics, and Thermal Characteristics of Iso-Pentane Flashing Spray Based on OpenFOAM

Leakage of high-pressure hydrocarbon liquid from a vessel or pipe may easily result in a two-phase flashing spray due to the rapid pressure drop, which might produce catastrophic consequences. Understanding the flashing spray process is essential to prevent these consequences and minimize the impact. This paper conducted a numerical study through OpenFOAM to investigate the two-phase behavior of flashing spray using a volatile and flammable substance of iso-pentane. The evolution of spray morphology and the distributions of droplet temperature, diameter, and velocity under various initial injection pressures (Pinj) and temperatures (Tinj) were investigated. The simulation result showed good agreement with the experimental result in spray morphology under various Pinj and Tinj. The simulation results indicate that a higher Pinj causes a larger gas phase diffusion length, while Tinj contributes little to this length. However, increasing the Pinj and Tinj shortens the liquid penetration distance. Near the nozzle exit field of about 10 mm, liquid droplets experience a rapid decrease in diameter and velocity along the spray central axis. Meanwhile, spray presents an obvious expansion via the introduction of a spray angle as the input boundary condition of the simulation and droplet temperature has a large gradient toward the radial direction within this field. Droplets in the spray’s downstream region achieved a more stable state with less change in droplet diameter, velocity, and temperature.

Теоретическое и экспериментальное обоснование характера взаимодействия модифицированных связующих с древесиной

There are numerous methods for analyzing surface phenomena when bonding wood materials, mutual arrangement of pores in the wood substrate, and depth of liquid adhesive penetration into wood. Electron microscopic methods such as atomic force and scanning tunneling microscopy are used along with optical methods. They allow evaluating the influence of factors describing the interaction between the liquid adhesive molecules and the porous wood surface. Phenol formaldehyde resin modified with pectol and urea formaldehyde resin modified with lignosulfonates were used for substantiation of the interaction mechanism between modified adhesives and wood. Electron microscopy was used to study the depth of adhesive penetration into veneer. The plywood was produced using modified urea and phenol formaldehyde adhesives. After conditioning, samples with a thickness of 0.025 mm were cut out and examined with a scanning electron microscope. The article shows that the interaction between liquid phenol formaldehyde adhesive modified with pectol and wood results in a sequential increase in the molecular weight of the substances and, consequently, in the penetration degree (depth). The studied wood species (birch, pine and larch) and modified thermosetting urea and phenol formaldehyde adhesives are polar materials (adhesive interacts with wood molecules with the formation of intermolecular bonds, including hydrogen bonds). The molecular weight growth and the freely joined nature of the main chain (liquid modified adhesive macromolecules), which contains a large number of polar functional groups (adhesive and wood), promote intermolecular association. The formation of an adhesive bond between urea formaldehyde adhesive modified with lignosulfonates and wood occurs due to chemical interaction between hydroxyl groups of cellulose macromolecules and methoxyl groups of urea resin with the formation of esters (hydrogen atoms of hydroxyl groups OH are substituted with hydrocarbon radicals R). The formation of a bond between the adhesive and the wood surface is the result of molecular interaction forces at the liquid adhesive – wood interface, when the distance between molecules of the same polarity (adhesive and wood) is less than 0.5 nm. Then, adsorption equilibrium sets in. For citation: Rusakov D.S., Varankina G.S., Chubinsky A.N. Theoretical and Experimental Substantiation of the Nature of Interaction between Modified Binders and Wood. Lesnoy Zhurnal = Russian Forestry Journal, 2022, no. 6, pp. 153–163. (In Russ.). https://doi.org/10.37482/0536-1036-2022-6-153-163

Tablet Disintegratability: Sensitivity of Superdisintegrants to Temperature and Compaction Pressure.

Tablet disintegration is an important pre-requisite for drug dissolution and absorption. The disintegration test is typically conducted at 37 °C, but the intragastric temperature may vary due to meals or fever. This study investigated the effects of temperature and compaction pressure on tablet disintegratability to gain deeper insights into superdisintegrant sensitivity and function. Tablets with either sodium starch glycolate or crospovidone as disintegrant were prepared at various compaction pressures and subjected to the disintegration test using different medium temperatures. Preheating of tablets was also employed to establish instant temperature equilibrium between the tablet and the disintegration medium. Liquid penetration and disintegration were faster as the medium temperature increased or compaction pressure decreased. Swelling or strain recovery disintegrants exhibited similar sensitivity to variations in the medium temperature. Preheating of the tablets resulted in slower disintegration, but this effect was reversible upon cooling, hence the slower disintegration was unlikely to be attributed to changes in the disintegrant physical state. The temperature difference between the tablet and the disintegration medium likely affected the rate of fluid flow into tablets and influenced disintegration. Understanding disintegrant temperature sensitivity would help to avoid unacceptable fluctuations in disintegration due to temperature variations. The temperature difference effect could also be harnessed to boost disintegrant performance.

Impregnation Properties of Nigerian-Grown Gmelina arborea Roxb. Wood

The success of any wood treatment process and the measure of protection conferred on treated wood are determined by the uptake and penetration of the treatment chemicals, in addition to the efficacy of the chemicals used for the treatment. Hence, the level of treatability of wood species should be pre-determined prior to the wood treatment to ensure the overall protection of the treated wood. Gmelina arborea wood, due to its low durability, requires impregnation with chemicals for preservation or chemical modification to enhance its durability. However, more details are required to establish the influence of its anatomy on impregnation to recommend appropriate treatment methods. Therefore, gmelina wood samples were treated under pressure to determine the solution uptake and penetration, while anatomical studies were carried out with light microscopy, scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX) measurements. Variations in stem heights, stem diameters, and samples from other tree stands were considered. The outcome of the study showed that the liquid uptake was generally low for gmelina wood among the selected stands (16%–23%) and there was no significant difference in stem diameters; meanwhile, penetration was less than 4 mm in the axial direction, and very low in the lateral (radial and tangential) direction. Vessels of gmelina wood have abundant tyloses, while crystalline structures with needlelike shapes are present in a large proportion of the ray parenchyma cells, and are confirmed with SEM-EDX to be made up of calcium oxalate. The low liquid uptake and penetration in gmelina wood suggest that the impregnation of chemicals into its microstructure is next to impossible. Hence, alternative treatment methods other than those involving impregnation with chemicals should be sought to enhance its durability.

Compression Relaxation of Multi-Structure Polymer Composites in Penetrating Liquid Medium.

Multi-structural polymer composites are widely used in the mechanical engineering, automotive, aviation and oil refining industries, as well as in the printing industry as a shock-absorbing deckle on the offset cylinders of printing machines. During offset printing, composites come into contact with inks and washing solutions, the components of which penetrate the material and cause the polymers to swell. This process degrades the print quality, and for this reason the study of its features is relevant. The prerequisites for this work are the study of the fundamental laws of diffusion and sorption of liquids by polymers with different micro- and macro-structures in different physical states and in different forms (e.g., films, sheets, fibers and fabrics). The combination of polymer materials in the composition of multi-structural fabric blankets makes it possible to obtain materials with unique mechanical properties and high resistance to liquid penetrating media and to use them in high-tech processes of multi-color printing with high resolution and color rendering. This article reports for the first time the kinetics and thermodynamics results obtained from the swelling of multi-structural polymeric blankets in solvents used in printing, and the effect of sorption of different polar liquids on the viscoelastic strain under compression during the operation of the damping systems of printing machines. Using mathematical models of activated liquid diffusion in polymers and deformation of a viscoelastic body, the swelling rate constants, solvent diffusion coefficients (the kinetic characteristics of the swelling process) and Flory−Huggins parameters (the thermodynamic characteristics of the interaction of the solvent with the composite) for composite−solvent systems with several chemical composition variants were determined. The elastic modulus and the viscosity coefficient of the composite under liquid saturation were calculated based on the experimental cyclic compression data. The range of change in the compression and restoration times of the polymeric blankets (0.09 s ÷ 0.78 s) was determined. It was shown that the composite swelled to a limited extent in all the studied liquids. All solvents used were thermodynamically poor (χ > 0.5). It has been established that rubber−fabric blankets coated with nitrile rubber are the least resistant to the action of dichloroethane, and that blankets with layers of polyolefins are not resistant to ethyl acetate. Water significantly affects the physicochemical properties of rubber−fabric blankets with a large proportion of cotton fabric layers. The data obtained can serve as a basis for optimizing the compositions of inks and cleaning solutions, as well as a theoretical basis for the thermodynamics of composite−solvent systems.

Facile fabrication of superhydrophobic coatings with superior corrosion resistance on LA103Z alloy by one-step electrochemical synthesis

Superhydrophobic coatings are effective in avoiding corrosion of substrates due to their special wetting properties. The present work dispenses with the need for complex pre-treatments and post-modification with low surface energy substances. A facile and rapid one-step electrochemical synthesis method was used to prepare a superhydrophobic coating of [CH3(CH2)12COO]2Ca with excellent corrosion resistance on the surface of LA103Z alloy. The corrosion behavior of the coated alloy in 3.5 wt% NaCl solution was investigated using electrochemical techniques. The results show that a uniform and relatively thick surface is an effective barrier to the penetration of corrosive liquids. The best corrosion resistance of the coated samples was achieved at an electrochemical synthesis time of 30 min, with a positive shift in corrosion potential and a significant reduction in corrosion current density.

Electrospun Nanofibrous Membranes: A Versatile Medium for Waterproof and Breathable Application.

Waterproof and breathable membranes that prevent liquid water penetration, while allowing air and moisture transmission, have attracted significant attention for various applications. Electrospun nanofiber materials with adjustable pore structures, easily tunable wettability, and good pore connectivity, have shown significant potential for constructing waterproof and breathable membranes. Herein, a systematic overview of the recent progress in the design, fabrication, and application of waterproof and breathable nanofibrous membranes is provided. The various strategies for fabricating the membranes mainly including one-step electrospinning and post-treatment of nanofibers are given as a starting point for the discussion. The different design concepts and structural characteristics of each type of waterproof and breathable membrane are comprehensively analyzed. Then, some representative applications of the membranes are highlighted, involving personal protection, desalination, medical dressing, and electronics. Finally, the challenges and future perspectives associated with waterproof and breathable nanofibrous membranes are presented.

Capillary penetration for the development of a method for the assessment of shelf-life of foods

Temperature sensitive foods require monitoring of their time–temperature history in order to assure their safety and high quality. The same holds for other perishable products such as medical and pharmaceutical. The best means to have information on the time–temperature history of a product is by having measurement of these variables along the whole product shelf-life. As an answer to this need several time–temperature indicators have been developed and commercialized for monitoring the quality of food products. In this work a full history time–temperature indicator (TTI) has been designed and developed based on capillary penetration of safe and low surface tension liquids in micro porous polyethylene porous media. For the development of the indicator the appropriate porous media and penetration liquids were selected and capillary penetration of the selected liquids took place at two different temperatures. Based on the results of the capillary penetration experiments the TTI was developed and a prototype was evaluated in a food product in order to assess its capability to be used in food packaging. The results showed that the TTI is simple in use and could provide a quantitative and easy-to-read response. Moreover, the response of the TTI could be calibrated by changing several design parameters, in order to match the quality deterioration kinetics of the specific food product to be monitored.

Modeling Spray C and Spray D with FGM within the framework of RANS and LES

In this study, two different diesel-like igniting sprays are investigated: Engine Combustion Network (ECN) Spray C and D. In particular, this study focuses on the respective performances of the RANS and LES models to predict a turbulent, igniting spray using the OpenFOAM platform. The breakup model, discretization schemes, and case setups, including the combustion model, are kept constant in order to mitigate any potential effect on the simulation apart from intrinsic differences due to turbulence modeling. A classic κ-ε model is applied for the RANS approach, while a dynamic structure model is used to solve the momentum equation in the LES approach. The κ-ε model constants are tuned to obtain a suitable prediction of inert experiments. Both approaches exhibit a reasonable agreement with the inert experiments regarding the global spray characteristics, the liquid length, and the vapor penetration. However, the transient local properties, including the spatial distribution of mixture fraction variance and the species distributions, are not identical. For reacting conditions, the Flamelet Generate Manifold (FGM) model is adopted in both the LES and RANS simulations, using several enthalpy levels as the fourth dimension in the tabulation to account for local heat loss. The results show good agreement between the two turbulence models, in terms of liquid length, vapor penetration, and lift-off length, while a short ignition delay is registered for both sprays and turbulence frameworks. Turbulence–chemistry interaction (TCI) is considered by applying a presumed probability density function (β-PDF) to the mixture fraction, and is found to play a key role in the reproduction of species distribution in the domain.

An experimental study on penetration and mixing characteristics of liquid fuel in preheated supersonic airflows

The effect of air temperature on the penetration and mixing of a liquid hydrocarbon fuel injected into supersonic airflows was investigated. The supersonic air of Mach 1.8 with a total temperature in the range of 373–673 K was supplied to the test section. The liquid fuel was injected into the supersonic airflow by means of an alternating-wedge pylon with a fuel-to-air momentum flux ratio of 15. A laser sheet imaging system using Mie scattering has been used to investigate the instantaneous and ensemble-averaged characteristics of the fuel plume, the fuel/air mixing process, and fuel evaporation. As the air temperature increased, the Mie scattering signal gradually weakened due to fuel-air mixing enhancement and fuel evaporation downstream of the pylon. At an air temperature of 673 K, most of the fuel evaporated before reaching the outlet of the test section (X/d = 703). As the air temperature increased from 373 to 673 K, the total pressure loss without fuel injection decreased from 20.6 to 15.4%. In addition, the total pressure losses due to fuel injection was about 3.5% greater than that without fuel injection. As the air temperature increased, the fuel penetration height decreased. However, at the air temperatures higher than the fuel boiling temperature, the fuel jet/spray penetration heights were almost similar, showing little effect of temperature any further.

Characterization of ammonia spray combustion and mixture formation under high-pressure, direct injection conditions

Ammonia has the potential to replace fossil fuels in internal combustion engines (ICEs). However, ammonia is characterized by unfavorable combustion characteristics and a propensity to form pollutants during combustion. The pilot-ignited high pressure, direct-injection of ammonia is promising regarding its prospective performance with ammonia as fuel. In this work, optical investigations (Mie-scattering (MS), shadowgraphy (SG), OH* chemiluminescence (CL)) and heat release rate (HRR) analysis are complemented by 1-D spray modeling to provide fundamental insight into distinctive features of ammonia spray combustion and mixture formation under engine-relevant conditions in a rapid-compression-expansion-machine (RCEM). CL measurements reveal that ammonia spray flames do not stabilize after ignition by a diesel pilot injection. Instead, the lift-off length gradually increases until the end of injection and beyond. To aid in the interpretation of the lift-off behavior, a 1-D, mixing-limited spray model is validated by experimental results for ammonia spray penetration and stationary liquid length (LL) under non-reactive conditions. Modeling results reveal that ammonia sprays are marked by low temperatures close to the nozzle exit, followed by a rapid decrease in mean equivalence ratios well below 1. Based on a mechanism that suggests flame stabilization by product re-entrainment and subsequent auto-ignition, the inhibition of flame stabilization in ammonia sprays is explained by high mixing requirements with combustion products to undergo auto-ignition. Implications of the lack of a self-stabilized flame on combustion characteristics are discussed and diesel post-injections, fuel pre-heating and reduction of the natural lift-off length are suggested as measures to avoid extensive pollutant formation in regions upstream of the lift-off length after the end of ammonia injection.

3D-Powder-Bed-Printed Pharmaceutical Drug Product Tablets for Use in Clinical Studies.

Printing of phase 1 and 2a clinical trial formulations represents an interesting industrial application of powder bed printing. Formulations for clinical trials are challenging because they should enable flexible changes in the strength of the dosage form by varying the active pharmaceutical ingredient (API) percentage and tablet mass. The aim of this study was to investigate how powder bed 3D printing can be used for development of flexible platforms for clinical trials, suitable for both hydrophilic and hydrophobic APIs, using only conventional tableting excipients. A series of pre-formulation and formulation studies were performed to develop two platform formulations for clinical trials using acetaminophen and diclofenac sodium as model compounds and lactose and starch as excipients. The results showed that the type of starch used as the formulation binder must be optimized based on the type of API. Moreover, powder blend flow and liquid penetration ability proved to be critical material attributes (CMAs) that need to be controlled, particularly at high drug loading. Optimization of these CMAs was performed by selecting the appropriate particle size of the API or by addition of silica. A critical process parameter that had to be controlled for production of tablets of good quality was the quantity of the printing ink. After optimization of both the formulation and process parameters, two platform formulations, that is, one for each API, were successfully developed. Within each platform, drug loading from 5 up to 50% w/w and tablet mass from 50 to 500 mg were achieved. All 3D-printed tablets could be produced at tensile strength above 0.2 MPa, and most tablets could enable immediate release (i.e., >80% w/w within 30 min).

Effects of full transient Injection Rate and Initial Spray Trajectory Angle profiles on the CFD simulation of evaporating diesel sprays- comparison between singlehole and multi hole injectors

This paper investigates experimental and computational diesel sprays of single hole and multi hole injectors under vaporizing conditions. Two single hole and two ten-hole injectors with the same nozzle hole size are tested with the 120 MPa injection pressure. Experiments implement Laser Absorption Scattering technique. This method utilizes two wavelengths (Visible and Ultraviolet) of light and fuel's mixture concentrations are measured by attenuations of these lights. On the other hand, sprays are simulated in the Eulerian Langrangian two-phase fluid framework where KHRT and Multicomponent models are used as droplet breakup and evaporation models respectively. Full transient profiles of Injection Rate and Initial Spray Trajectory Angle are used as input boundary conditions for the spray simulation and effects on the spray characteristics are observed. Injection rates are measured with Bosch Long Tube and Initial Spray Trajectory Angles are extracted from the near nozzle field spray images. Experiments reveal that multi-hole injectors (0.101 mm and 0.133 mm) injectors depict longer liquid and shorter vapor penetrations. However, longer simulation liquid and vapor penetrations are seen for single hole injectors due to increased initial ramp-up phase. Sprays of Multi-hole injectors are diffused radially which promote air entrainment, better mixture formation, improved combustion, and lower exhaust emissions. Overall, simulated sprays using unfiltered injection rate profile as an input parameter showed an excellent agreement with experiments. While sprays using low-pass filtered injection rates showed a clear disagreement. Parameters including Liquid Length, Vapor Penetration and Evaporation ratios were found to be influenced by the IR profile rather than ISTA. Whereas vapor equivalence ratios depend on both input parameters plus breakup model constants.

Cool flame wave propagation in high-pressure spray flames

Cool flame has an important impact on the performance and emission of advanced low-temperature combustion (LTC) internal combustion engines (ICEs) in which the liquid fuel is injected earlier at a lower ambient temperature (Tam) than that in the conventional diesel combustion engines. However, the cool flame characteristics of spray combustion under ICEs conditions are not fully understood, e.g., the effect of cool flame on the spray ignition and flame stabilization is not well studied. In this paper, the so-called cool flame wave propagation (CFWP) in the Engine Combustion Networks Spray A flames at three ambient temperatures Tam (800 K, 900 K and 1000 K) is analyzed using the data from large eddy simulation with an improved Eulerian based transported probability density function sub-grid combustion model. A good agreement between the LES results and experimental data is obtained for the spray liquid penetration length, vapor fuel penetration length, mean pressure rise profile, and flame liftoff length. It is shown that CFWP in the spray ignition process promotes the ignition of the fuel-rich and cold reactant mixture, leading to the most reactive mixture shifting toward fuel-richer locations due to the spatial stratification of temperature and concentration, and turbulent mixing. As a result, the high temperature ignition (HTI) can be shortened compared to the ignition in the homogeneous mixture. At Tam = 800 K, the HTI kernels are consistently formed following the CFWP propagating toward the spray head region. However, as Tam increases, the spatial correlation between HTI kernels and CFWP fronts is weakened. On the other hand, the turbulent mixing (quantified using local scalar dissipation rate) contributes more to the formation of HTI kernels at higher Tam. The present results indicate that CFWP is more profound at lower Tam in the spray ignition process. Finally, it is found that cool flame propagates mainly into pre-reacted fuel-rich mixture in an ignition wave propagation mode from the spray upstream region toward downstream region, whereas the ignition assisted flame mode is found in the spray upstream region where the combustion heat release is negligible.

Numerical and Experimental Investigations on the Ignition Behavior of OME

On the path towards climate-neutral future mobility, the usage of synthetic fuels derived from renewable power sources, so-called e-fuels, will be necessary. Oxygenated e-fuels, which contain oxygen in their chemical structure, not only have the potential to realize a climate-neutral powertrain, but also to burn more cleanly in terms of soot formation. Polyoxymethylene dimethyl ethers (PODE or OMEs) are a frequently discussed representative of such combustibles. However, to operate compression ignition engines with these fuels achieving maximum efficiency and minimum emissions, the physical-chemical behavior of OMEs needs to be understood and quantified. Especially the detailed characterization of physical and chemical properties of the spray is of utmost importance for the optimization of the injection and the mixture formation process. The presented work aimed to develop a comprehensive CFD model to specify the differences between OMEs and dodecane, which served as a reference diesel-like fuel, with regards to spray atomization, mixing and auto-ignition for single- and multi-injection patterns. The simulation results were validated against experimental data from a high-temperature and high-pressure combustion vessel. The sprays’ liquid and vapor phase penetration were measured with Mie-scattering and schlieren-imaging as well as diffuse back illumination and Rayleigh-scattering for both fuels. To characterize the ignition process and the flame propagation, measurements of the OH* chemiluminescence of the flame were carried out. Significant differences in the ignition behavior between OMEs and dodecane could be identified in both experiments and CFD simulations. Liquid penetration as well as flame lift-off length are shown to be consistently longer for OMEs. Zones of high reaction activity differ substantially for the two fuels: Along the spray center axis for OMEs and at the shear boundary layers of fuel and ambient air for dodecane. Additionally, the transient behavior of high temperature reactions for OME is predicted to be much faster.