Elevated Temperatures Research Articles

Numerical Investigation of In-Cylinder Combustion Behaviors in a Medium-Speed Diesel Engine

Abstract This study aims to advance understanding of in-cylinder combustion processes in medium-speed diesel engines, which are extensively employed in heavy-duty applications where electrification proves inefficient yet remains insufficiently examined in the literature. By modeling a four-stroke engine with dimensions of 210 mm bore and 310 mm stroke, operating at 900 rpm under full load, this research identifies distinct combustion characteristics that differentiate medium-speed engines from their high-speed counterparts. Key findings illustrate that super turbocharging in medium-speed engines enhances the combustion of the fuel–air mixture under elevated temperatures and pressures. Moreover, an increased stroke length promotes gas velocity and turbulence, facilitating fuel atomization and mixing. Notably, rapid fuel ignition occurs near the nozzle due to the high temperature of compressed air, reducing the ignition delay. As a result, the premixed combustion stage nearly disappears, with diffusion combustion dominating, especially pronounced with long-duration injection, a characteristic of medium-speed engines. The study also reveals a more uniform but elevated distribution of nitrogen oxide emissions in medium-speed engines, attributed to prolonged high-temperature conditions that both facilitate their formation. Early stages of diffusion combustion show high concentrations of incomplete combustion products. However, as the combustion process progresses, the conditions favor the complete oxidation of these products at high temperatures, resulting in decreased carbon-based pollutions. In addition, the larger combustion chamber and enhanced turbulence characteristic of medium-speed engines support efficient fuel and air mixing without necessitating the swirl effect required by high-speed engines, diminishing the dependence on wall impingement dynamics for air utilization. Consequently, efficiency optimization strategies for medium-speed engines, emphasizing adjustable injection parameters, encounter fewer constraints than those inherent to the spatial limitations of high-speed engines.

Community dynamics and metagenomic analyses reveal Bacteroidota's role in widespread enzymatic Fucus vesiculosus cell wall degradation

Enzymatic degradation of algae cell wall carbohydrates by microorganisms is under increasing investigation as marine organic matter gains more value as a sustainable resource. The fate of carbon in the marine ecosystem is in part driven by these degradation processes. In this study, we observe the microbiome dynamics of the macroalga Fucus vesiculosus in 25-day-enrichment cultures resulting in partial degradation of the brown algae. Microbial community analyses revealed the phylum Pseudomonadota as the main bacterial fraction dominated by the genera Marinomonas and Vibrio. More importantly, a metagenome-based Hidden Markov model for specific glycosyl hydrolyses and sulphatases identified Bacteroidota as the phylum with the highest potential for cell wall degradation, contrary to their low abundance. For experimental verification, we cloned, expressed, and biochemically characterised two α-L-fucosidases, FUJM18 and FUJM20. While protein structure predictions suggest the highest similarity to a Bacillota origin, protein–protein blasts solely showed weak similarities to defined Bacteroidota proteins. Both enzymes were remarkably active at elevated temperatures and are the basis for a potential synthetic enzyme cocktail for large-scale algal destruction.

Assessment of the hypothetical protein BB0616 in the murine infection of Borrelia burgdorferi.

bb0616 of Borrelia burgdorferi, the Lyme disease pathogen, encodes a hypothetical protein of unknown function. In this study, we showed that BB0616 was not surface-exposed or associated with the membrane through localization analyses using proteinase K digestion and cell partitioning assays. The expression of bb0616 was influenced by a reduced pH but not by growth phases, elevated temperatures, or carbon sources during in vitro cultivation. A transcriptional start site for bb0616 was identified by using 5' rapid amplification of cDNA ends, which led to the identification of a functional promoter in the 5' regulatory region upstream of bb0616. By analyzing a bb0616-deficient mutant and its isogenic complemented counterparts, we found that the infectivity potential of the mutant was significantly attenuated. The inactivation of bb0616 displayed no effect on borrelial growth in the medium or resistance to oxidative stress, but the mutant was significantly more susceptible to osmotic stress. In addition, the production of global virulence regulators such as BosR and RpoS as well as virulence-associated outer surface lipoproteins OspC and DbpA was reduced in the mutant. These phenotypes were fully restored when gene mutation was complemented with a wild-type copy of bb0616. Based on these findings, we concluded that the hypothetical protein BB0616 is required for the optimal infectivity of B. burgdorferi, potentially by impacting B. burgdorferi virulence gene expression as well as survival of the spirochete under stressful conditions.

REVIEW: MATERIALS FOR IMPREGNATION OF POROUS METALLIZATION THERMAL SPRAYED ANTICORROSIVE COATINGS OF SUBMERSIBLEOILFIELD EQUIPMENT. Part 1

Submersible oilfield equipment undergoes aggressive corrosive effects of petroleum fluid, abrasive effects of mechanical impurities during operation, and also operates at elevated temperatures in the bottom. The most effective way to protect the outer surface of oilfield equipment is the use of metallization thermal sprayed coatings, and therefore the application of thermal spraying technology is becoming more and more in demand.However, the formation of a coating structure from many particles of molten material, due to their spraying, incomplete melting and loose packaging, leads to the formation of porosity, and porosity is one of the main disadvantages of thermal sprayed coatings. To eliminate this disadvantage, it is possible to use impregnation of porous coatings with various compositions, in which case the coating becomes composite. Depending on the operating environment, temperature conditions and operating conditions, metal, organic and inorganic impregnating compositions are used,but their use in the oil environment has been little studied, therefore the development of composite impregnated coatings is relevant for the protection of submersible oilfield equipment. The article highlights the influence of technological modes of its application on the porosity of thermal sprayed coating and the quality of substrate surface preparation. The main methods of sealing the porosity of thermal sprayed coatings by impregnation are described. The mechanism of impregnation (infiltration) of porous coatings, used methods of application and their classification are described, the determining role of wetting the coating with an impregnating material is emphasized. The effect of the rough surface of a thermal sprayed coating is shown, which consists in enhancing the wetting properties of the impregnating composition, the influence of roughness on the formation of adhesive bonds between the coating and the impregnating composition.The review presents traditional impregnating materials used in industry and their application modes.The application of metal and non-polymer inorganic impregnating compounds, represented mainly by salts of inorganic acids (nitrates, phosphates, silicates), is described. Specific test results are presented, including for the corrosion and abrasive resistance of thermal sprayed coatings after the application of impregnating compounds.

Unraveling the Effect of Elastic Stress on the Destabilization Process of Ni–Sn Eutectic Lamellae at an Elevated Temperature

Unraveling the Effect of Elastic Stress on the Destabilization Process of Ni–Sn Eutectic Lamellae at an Elevated Temperature

High performance Ce0.8Nd0.2O2-δ-carbonate hollow fiber membrane for high-temperature CO2 separation

Ceramic-carbonate dual phase (CCDP) membrane consisting of oxygen ionic conductor and molten carbonate has potential applications in clean energy delivery as it enabling the direct CO2 separation or capture at the elevated temperatures. The performance of previous CCDP membranes is not ideal either with a low CO2 flux or with a poor operational stability. In the present work, we looked at the CeO2-based oxygen ionic conductor (neodymium doped cerium (NDC)) as the porous ceramic hollow fiber support to form NDC-carbonate hollow fiber membranes. The NDC hollow fiber was fabricated by the combined phase inversion and sintering techniques and the preparation conditions were optimized to better accommodate the carbonate phase and maintain the mechanical stability. The NDC hollow fibers possessed good bending strength, reaching 91.5 MPa upon sintering at 1500 °C. The effects of feed gas composition and sweep flow rates on the CO2 separation performance were carefully investigated. The resultant dual phase hollow fiber membranes exhibited appreciably high CO2 permeation fluxes at temperatures exceeding 800 °C, which was required to activate both conductions of oxygen and carbonate ions. The achieved maximum CO2 flux of the optimized NDC-carbonate hollow fiber membranes was up to 5.08 mL min−1 cm−2 with 50%CO2–50%N2 as the feed gas at 900 °C. At 700 °C, the membrane exhibited a relatively stable CO2 permeation behavior over 120 h and the spent membrane maintained a stable structure. The high flux and good operational stability of the developed membrane make a huge step towards practical applications.

Nanosecond repetitively pulsed plasmas with MHz bursts for CO2 dissociation

A novel pulsed power source capable of nanosecond pulses with burst frequencies up to 1 MHz is employed to create atmospheric pressure pulsed plasma in pure CO2 gas. The short bursts contain up to four nanosecond pulses. The CO2 conversion and corresponding energy efficiency are measured ex-situ with Fourier-transform infrared absorption spectroscopy. Trends in the absorption line profile of in-situ quantum cascade laser infrared absorption spectroscopy indicate an elevated vibrational temperature of CO2 with an increasing number of pulses per burst. The key result of this paper is that the dissociation energy efficiency is higher when operating the plasma in burst mode. Furthermore, a larger number of pulses in a burst is associated with a further increase of the dissociation efficiency. The highest efficiency measured is (17.7±0.3) % for single pulses spaced 2 ms apart, and (20.0±0.3) % for bursts of three pulses, with an in-burst frequency of 1 MHz and bursts spaced 4 ms apart.

A simple model for predicting oxygen depletion in lakes under climate change

ABSTRACT The advent of climate change has placed aquatic ecosystems at risk for potential declines in water quality, including an increase in the number of lakes experiencing substantial dissolved oxygen (O2) depletion. Through its influence on the thermal structure of lakes via elevated water temperatures and alterations in stratification phenology, climate change intensifies biogeochemical and ecological processes involved in O2 consumption, giving rise to conditions like hypoxia/anoxia. However, predicting O2 dynamics is difficult, with in situ O2 depletion rates showing considerable lake-dependent variability, underpinned by distinct underlying mechanisms. Our study attempts to overcome these lake-specific features and targets distilling key components of O2 depletion into a simple and transferable conceptual model applicable across a diverse array of lakes and at large scales. Using O2 depletion rates from literature reflecting variability in trophic state, we quantified the typical O2 depletion rate ranges for oligotrophic, mesotrophic, and eutrophic lakes and assessed their temperature sensitivity for a broader climate impact assessment. Our model gave reasonable estimates for O2 depletion and risks of anoxia through 3 explanatory variables: trophic state, stratification duration, and hypolimnion temperature. We validated our model predictions using data from 5 German lakes and assessed the relative importance of the 3 influencing factors. This easy-to-use approach has potential for lake management to attain rapid assessments of possible future problems with O2 dynamics in a given lake, even in the absence of in situ data. Moreover, it allows scaling of O2 dynamics continentally/globally without lake-specific hydrological or morphological details.

Enhancing strength-ductility properties of immiscible W–Cu composite by creating low-energy phase interfaces

The immiscible bimetallic composites play an important role in civilian industries and aerospace fields owing to their integrated mechanical and physical properties. However, metallic composites of immiscible constituents suffer from one critical drawback of weak interface bonding, which makes the composites particularly vulnerable at elevated service temperatures. Here we proposed a novel strategy to resolve the challenge by creating low-energy phase interfaces in a typical immiscible bimetallic W–Cu composite. This was achieved by in-situ reactions of WO3 and CuO with WC, which acts in a dual function as the reducing agent for the reactions and an interface forming agent. The sintered W-WC-Cu composite possessed a significant number of low-energy WC/W and WC/Cu interfaces and exhibited a compressive strength of 609 MPa and a compressive ductility of 22.6 % at 600 °C, which ranks among the highest in similar composites. The characteristics of WC/W and WC/Cu interfaces and their effects on the mechanical behavior of the composite were demonstrated by the timely and atomic-resolved high-temperature mechanical investigations. The introduced stable interfaces were also found to induce [1‾ 11]BCC→ [011]FCC phase transformation of W as another mechanism of plastic deformation in addition to dislocation activities in W and Cu. This study provides a new approach to greatly enhance the mechanical properties of the immiscible metallic composites.

Design of Reversible Adhesives by Using a Triple Function of Ionic Liquids

AbstractReversible adhesives are crucial for a circular economy of composites as they play a key role for rework, repair, and recycling of adhesively bonded components. Herein, electrically debondable adhesives are prepared by introducing ionic liquids in dynamic thiol–epoxy networks. The function of the ionic liquid in the networks is threefold as it accelerates the curing reaction between thiol and epoxy monomers, facilitates electrical debonding, and catalyzes thermoactivated transesterification reactions, required for rebonding at elevated temperature. A library of 1,3‐dibutylimidazolium‐based ionic liquids with varying anions is synthetized and it is found that 1,3‐dibutyl‐1H‐imidazol‐3‐ium dicyanamide (DiButIm─N(CN)2) is superior in accelerating bond‐exchange reactions between hydroxy and ester moieties at elevated temperature. Thus, a thiol–epoxy resin containing 20 wt% of DiButIm─N(CN)2 is used to impregnate glass fiber mats yielding adhesive connections for aluminum substrates with 10.2 MPa pull‐off strength. The adhesive connections are successfully debonded at the metal–adhesive interface by applying 120 V. The samples are then rebonded via the thermoactivated change in the networks’ viscoelastic properties and ≈80% (8.1 MPa) of their original bond strength can be regained. By providing a simple strategy to synthetize reversible adhesives, this approach paves a way toward improved recyclability and repairability of adhesively bonded structures.

Stability of Immobilized Chemosensor‐Filled Vesicles on Anti‐Fouling Polymer Brush Surfaces

AbstractThe characterization of phospholipid membrane permeability for small molecules is crucial for many applications in drug discovery and biomedical research in general. Here, chemosensor‐laden vesicles offer an attractive platform for permeability assays. In this work, the stability of immobilized chemosensor‐filled vesicles is explored on anti‐fouling polymer brush surfaces for potential use in monitoring small molecule membrane permeability. The study focuses on the development of a method for immobilizing sensor‐loaded vesicles into arbitrary patterns on surfaces and characterizing their stability under changing temperatures and compositions. As substrate to enable intact, long‐term stable vesicle immobilization reactive polymer brushes with anti‐fouling properties are used. Utilizing microchannel cantilever spotting, biotin moieties are introduced on the polymer brush surface, enabling stable tethering of vesicles through streptavidin‐biotin interactions. The immobilized vesicles are monitored through fluorescence microscopy for their response to analytes under changing environmental parameters and vesicle composition. A higher stability of immobilized vesicles compared to free‐floating ones is observed, with permeability only at elevated temperatures. By tuning vesicle compositions, permeability at lower temperatures can be raised again. Overall, the study provides insights into a novel approach for vesicle immobilization, showcasing the potential of surface‐bound vesicles for applications in microfluidic systems and as biosensors in various assays.

Status of h-BN quasi-bulk crystals and high efficiency neutron detectors

III-nitrides have fomented a revolution in the lighting industry and are poised to make a huge impact in the field of power electronics. In the III-nitride family, the crystal growth and use of hexagonal BN (h-BN) as an ultrawide bandgap (UWBG) semiconductor are much less developed. Bulk crystals of h-BN produced by the high-temperature/high-pressure and the metal flux solution methods possess very high crystalline and optical qualities but are impractical to serve as substrates or for device implementation as their sizes are typically in millimeters. The development of crystal growth technologies for producing thick epitaxial films (or quasi-bulk or semi-bulk crystals) in large wafer sizes with high crystalline quality is a prerequisite for utilizing h-BN as an UWBG electronic material. Compared to traditional III-nitrides, BN has another unique application as solid-state neutron detectors, which however, also require the development of quasi-bulk crystals to provide high detection efficiencies because the theoretical efficiency (ηi) relates to the detector thickness (d) by ηi=1−e−dλ, where λ denotes the thermal neutron absorption length which is 47 μm (237 μm) for 10B-enriched (natural) h-BN. We provide an overview and recent progress toward the development of h-BN quasi-bulk crystals via hydride vapor phase epitaxy (HVPE) growth and the attainment of thermal neutron detectors based on 100 μm thick 10B-enriched h-BN with a record efficiency of 60%. The thermal neutron detection efficiency was shown to enhance at elevated temperatures. Benchmarking the crystalline and optical qualities of h-BN quasi-bulk crystals with the state-of-the-art mm-sized bulk crystal flakes and 0.5 μm thick epitaxial films identified that reducing the density of native defects such as vacancies remains the most critical task for h-BN quasi-bulk crystal growth by HVPE.

Optimizing Red Soil-Based Geopolymer Bricks: A Sustainable Approach towards Environmentally Friendly Construction Materials

In the whole world, construction activities are happening rapidly as a result of the population increase and also due to the lifestyle of people in the 20th century, intensifying the pressure on resources needed for construction. It also causes bad effects on the environment, such as the carbon footprint associated with cement production and the waste management of emission waste like fly ash in thermal power plants. Counteracting and stabilizing the adverse environmental consequences, this study adopts an experimental approach to utilize thermal power plant waste Class C Fly ash (pozzolanic), locally available red soil, and stone dust, along with geopolymer precursors, to manufacture bricks, which are the most demanding material for infill masonry work. The mechanical, durability, and microstructural characterization of the bricks were studied for various mix proportions, along with various concentrations of geopolymer precursors, cured at elevated temperatures and ambient curing. An optimum methodology was obtained to develop a red soil-based geopolymer brick.

Isobaric Heat Capacity Measurements of Methanol by Flow Calorimeter at Elevated Temperatures and Pressures

Isobaric Heat Capacity Measurements of Methanol by Flow Calorimeter at Elevated Temperatures and Pressures

Experimental Evaluation of Mechanical Properties, Micro Structure and Post-Fire Strength of Fiber Reinforced Geopolymer Concrete

Geopolymer mixtures offer an enhanced alternative to implement an eco-friendly solution in construction industry. These mixtures exhibit similar or better mechanical and structural properties in comprising of cement and can use recycling and by-product materials. Against this background, an eco-friendly advantageous were achieved from the engineers and researchers by using waste materials to replace cement and attention to reduce CO2 emission during its procedure. This study attempted to evaluate compressive and tensile strength, micro structure and post-fire characteristic of the geopolymer mixtures. For this aim, the geopolymer mixtures were exposed to elevated temperature between 200, 500 and 800 0C. Then, the post-fire and mechanical behaviour were investigated. The proposed research supported the slight decrease in the GPC's compressive stress by fibres, and the 1.25% PP fibres displayed the least performance, indicating nearly 13% decrease than the unreinforced mixtures. As exhibited by the post-fire behaviour of mixtures, the GPC's compressive strength increased first for all mixes but in the range of 400 - 800°C it decreased at a higher rate because of the geopolymer matrix-related dehydration. Besides, fiber melting under high temperatures and the thermal reaction procedure related to free water evaporation reduce the mechanical properties under temperatures ranging from 400°C to 800°C. DOI: https://doi.org/10.52783/pst.349

Fracture behaviour of thin-walled cold-formed steel at elevated temperatures

Cold-formed steel (CFS) is being increasingly used in structural applications due to its high strength-to-weight ratio, ease of construction and versatility. The performance of CFS structures in fire has received signification recent attention, but the fracture behaviour of thin-walled CFS at elevated temperatures, which is fundamental to the fire response of the key components, like connections has yet to be extensively studied; this is therefore the subject of the present paper. First, using experimental data on cold-formed grade S280GD+Z275 steel at elevated temperatures from the literature, damaged true stress-strain curves considering the post-necking behaviour are determined. Then, a fracture prediction approach, implemented in the finite element analysis software Abaqus and considering ductile damage and a damage evolution law is calibrated and validated against the experimental data. Finally, the applicability of the proposed approach to different types of CFS material, including high-strength CFS, is assessed. The results show that the proposed model can accurately predict the fracture behaviour of CFS at elevated temperatures.

Influence of Few-Layer Graphene on Frictional Properties of Lithium Compound Grease

The frictional properties of lithium compound grease (LCG) with different percentage compositions of few-layer graphene (FLG) were investigated, and the mechanisms of temperature and loading effects on LCG containing FLG are also considered. The concluding effect shows that 1 wt% FLG is more appropriate for friction and wear modifiers for lithium compound grease at elevated temperatures and less suitable at ordinary temperatures. Thickener chemisorption film, FLG layering film, and tribo-reaction film consisting of FeO(OH), Fe2O3, Fe3O4, Li2O, and other oxides assist in the establishment of a lubricating boundary film on the friction interfaces lubricated with LCG containing FLG. The poor fluidity of lithium compound grease at low temperatures leads to poor dispersion of FLG, decreasing friction reduction capability. Under elevated temperature and low load condition, adding 1wt% FLG to LCG can only improve its wear-resistant property, the abrasion volume of steel plate reduced by 24.49%. Under elevated temperature and high load condition, adding 1wt% FLG to LCG can only enhance its anti-friction characteristics.. Conversely, FLG is unsuitable as an anti-friction and wear-resistant additive for LCG at low-temperature conditions.

Bond behaviour at high temperatures between concrete and CFRP or steel strengthening bars applied according to the Embedded Through-Section (ETS) technique

The embedded through-section (ETS) technique is an efficient shear-strengthening method for reinforced concrete (RC) structures, in which fibre reinforced polymer (FRP) or steel bars are bonded in holes predrilled in RC members. Compared to conventional FRP strengthening methods, ETS systems are expected to present better performance when exposed to high temperatures/fire, due to the insulation provided by concrete to both adhesive and FRP/steel components. Yet, the mechanical/bond properties of the strengthening materials are highly affected when the glass transition temperatures (Tg) of their components is attained/exceeded; however, there are no studies available about the influence of elevated temperatures on the performance of ETS systems. This paper presents an experimental study that addresses the effects of elevated temperatures on the bond behaviour of ETS systems – pull-out tests were conducted on steel rebars or sand-coated carbon-FRP (CFRP) rods bonded with epoxy adhesive on concrete cylinders at temperatures up to 90 °C. The results obtained confirm that the strength and stiffness of the bonded interfaces decrease when the temperature in the adhesive approaches/exceeds its Tg; moreover, with sand-coated CFRP rods, failure was also influenced by the bond between the sand coating and the CFRP rods core, and thus the average bond capacity was significantly reduced for temperatures below the Tg of the epoxy adhesive. Bond-slip relations were calibrated for different elevated temperatures for the steel/CFRP-concrete interfaces using data obtained from the pull-out tests; these bond laws can be used to simulate the mechanical behaviour of ETS-strengthened-RC members subjected to elevated temperatures.

Study the correlation between microstructural features and geotechnical properties of collapsing soil at elevated temperatures

This study explores the consequences of elevated temperatures on the geotechnical and microstructural properties of collapsible soil. Through a lab-scale setup, geotechnical characteristics were accurately investigated within a temperature range spanning from 50°C to 200°C. The focus was on understanding how temperature fluctuations, in conjunction with varying water contents, influence layer spacing, macropores, mesopores, and surface tension – all of which are integral in forming collapsible soil structures. The assessment involved an evaluation of microstructural properties for natural soil and soil subjected to temperatures, with specific attention to a 10% water content condition. The microstructure, identified as a critical determinant in soil collapse, was the primary focus of this study. The impact of high temperatures was probed, reaching up to 200 °C, on soil X-ray diffraction (XRD) responses and permeability efficiency. Higher temperatures were observed to produce smaller particles, leading to reduced pore sizes and a denser soil structure, a phenomenon validated through spectroscopic research. These findings were congruent with the geotechnical data, which indicated an enhancement in soil collapse resistance, maximum dry density, and overall geotechnical properties. Our study stresses elevated temperatures' significant effect on the microstructural and geotechnical facets of collapsible soil. These findings provide valuable insights into the behavior of collapsing soil under varying temperature conditions, contributing to a deeper understanding of this complex phenomenon.

Flammability limits of methanol/methacrolein mixed vapor under elevated temperatures and pressures

The one-step oxidative esterification of methanol and methacrolein to yield methyl methacrylate (MMA) at elevated temperatures and pressures is a crucial chemical procedure for producing MMA. However, the conditions under which fire and explosions may occur during this procedure must be determined. This study models gas mixing to predict concentration distribution. Simulation results indicate stability with increasing pressure but wider gradients with higher temperature. Experimental studies on the flammable limits of methanol and methanol/methacrolein vapor mixtures under high temperatures and pressures show that the initial pressure has a significant impact on expanding the explosive limit of flammable vapor, whereas temperature has a relatively minor effect. The combustible limit of the mixed vapor is predicted using the heat balance approach, and a comparison with experimental data shows that the anticipated and real values coincide well.