Search Results (177)

This study presents a detailed numerical analysis of impinging propane flames within confined enclosures using the Fire Dynamics Simulator (FDS, v6.5.3). Two archetypal configurations were examined: (i) free buoyant plumes in unconfined environments, and (ii) ceiling-impinging flames under both open and confined conditions. The investigation encompassed a range of heat release rates (0.5–18.6 kW) and five degrees of ventilation confinement. The simulation results confirm that FDS reliably reproduces flame height evolution under free plume conditions, exhibiting strong consistency with Heskestad’s empirical correlation and available experimental benchmarks. Under ceiling impingement, confinement markedly influences the thermal field, the distribution of major gas species (O₂, CO₂, C₃H₈), and the accumulation of unburnt gas. Distinct from previous works primarily centered on unconfined plume dynamics, the present study systematically characterizes the onset of auto-ignition through combined lower flammability limit (LFL) and auto-ignition temperature (AIT) criteria for confined propane combustion. The highest auto-ignition risk was identified in partially confined configurations (Conf. 2 and Conf. 3) at an HRR of 18.6 kW, where unburnt propane concentrations locally exceeded the LFL (≈0.2%) and ceiling temperatures surpassed the AIT of propane (455 °C). The findings elucidate critical trade-offs between ventilation and safety. They also contribute to a validated FDS-based methodology for evaluating fire-induced flow structures, combustion behavior, and ignition hazards in confined spaces. Full article

Decarbonization of compression-ignition engines requires evaluation of carbon-free and low-carbon fuel alternatives. Ammonia (${NH}_3$) offers zero direct carbon emissions but faces combustion challenges including low flame speed (7 $\mathrm{c}\mathrm{m}/\mathrm{s}$) and high auto-ignition temperature (657 °$\mathrm{C}$). Methanol provides improved reactivity and bound oxygen content that can enhance ignition characteristics. This computational study investigates diesel–ammonia–methanol ternary fuel blends using validated three-dimensional CFD simulations (ANSYS Forte 2023 R2; ANSYS, Inc., Canonsburg, PA, USA) with merged chemical kinetic mechanisms (247 species, 2431 reactions). The model was validated against experimental in-cylinder pressure data with deviations below 5% on a single-cylinder diesel engine (510 cm³, 17.5:1 compression ratio, 1500 rpm). Ammonia energy ratios were systematically varied (10–50%) with methanol substitution levels (0–90%). Fuel preheating at 530 K was employed for high-alcohol compositions exhibiting ignition failure at standard temperature. Results demonstrate that peak cylinder pressures of 130–145 bar are achievable at 10–30% ammonia with M30K–M60K configurations, comparable to baseline diesel (140 bar). Indicated thermal efficiency reaches 38–42% at 30% ammonia-representing 5–8 percentage point improvements over diesel baseline (31%)-but declines to 30–32% at 50% ammonia due to fundamental combustion limitations. ${CO}_2$ reductions scale approximately linearly with ammonia content: 35–55% at 30% ammonia and 75–78% at 50% ammonia. ${NO}_X$ emissions demonstrate 30–60% reductions at efficiency-optimal configurations. Multi-objective optimization analysis identifies the A30M60K configuration (30% ammonia, 60% methanol, 530 K preheating) as optimal, achieving 42% thermal efficiency, 58% ${CO}_2$ reduction, 51% ${NO}_X$ reduction, and 11% power enhancement versus diesel. This configuration occupies the Pareto frontier “knee point” with cross-scenario robustness. Full article

In this present study, sodium- and strontium-modified bismuth titanate—Bi_0.5Na_0.5TiO₃ (BNT) and Bi_0.5Sr_0.5TiO₃ (BST)—were synthesized using the auto-combustion technique with citric acid (C₆H₈O₇) and glycine (C₂H₅NO₂) as fuels in an optimized ratio of 1.5:1. The resulting powders were characterized using X-ray diffraction (XRD), energy-dispersive X-ray (EDX) spectroscopy, UV–Visible diffuse reflectance spectroscopy (DRS), and Fourier-transform infrared (FT-IR) spectroscopy. The electrical behavior of the samples was studied using an LCR meter. XRD analysis confirmed the formation of a single-phase perovskite structure with average crystallite sizes of 18.60 nm for BNT and 22.03 nm for BST, attributed to the difference in ionic radii between Na⁺ and Sr²⁺. An increase in crystallite size was accompanied by a corresponding increase in lattice parameters and unit-cell volume. The Williamson–Hall analysis further validated the strain-size contributions. EDX (Energy-Dispersive X-ray analysis) results confirmed successful incorporation of Na⁺ and Sr²⁺ without detectable impurity phases. Optical studies revealed distinct absorption peaks at 341 nm for BNT and 374 nm for BST, and the optical bandgap (E_g), calculated using Tauc’s relation, was found to be 2.6 eV and 2.0 eV, respectively. FT-IR spectra exhibited characteristic Ti-O vibrational bands in the range of 420–720 cm⁻¹, consistent with the perovskite structure. For electrical characterization, the powders were pelletized under 3-ton pressure and sintered at 1000 °C for 3 h. The dielectric constant (ε_r), dielectric loss (tan δ), and ac conductivity (σ) of both samples increased with frequency. The combined structural, optical, and electrical results indicate that the optimized compositions of BNT and BST possess properties suitable for use in capacitors and other energy-storage applications. Full article

Cycle-to-cycle variation (CCV) is an inherent phenomenon in internal combustion engines that poses significant limitations on thermal efficiency in energy conversion. This variation can also cause structural damage. Other negative effects include increased noise and elevated emissions. This research employs large eddy simulation (LES) coupled with the G-equation model and detailed SAGE chemistry to investigate the impact of varying engine speeds on cyclic variability and energy conversion, which focuses specifically on CCV phenomena. Unlike previous studies that focus primarily on statistical pressure variations, this work uncovers the causal link between the initial flame kernel morphology and the propensity for end-gas auto-ignition. The results demonstrate that increasing engine speed significantly enhances in-cylinder turbulence intensity. Specifically, the maximum turbulence energy at 5000 rpm is about 85% higher than that at 4000 rpm. The maximum turbulence energy at 4000 rpm is about 103% higher than that at 3000 rpm. Speed alterations also change the initial conditions of temperature and fuel distribution that have a major impact on CCV characteristics. As engine speed increases from 3000 rpm to 5000 rpm, the coefficient of variation in the maximum peak pressure decreases from 14.9% to 9.48%. The coefficient of variation follows a decreasing then increasing trend with the values ranging from 7.8% to 8.1%. While a moderate increase in engine speed can reduce peak pressure fluctuation and improve combustion stability, excessively high speeds may induce delayed flame propagation and instability in kernel development, which can exacerbate the combustion phasing variations. The propensity for exhaust gas auto-ignition near the intake valve increases to raise the risk of engine knocking. Our research findings underscore the critical balancing role of engine speed in optimizing energy conversion and provide a basis for mitigating engine knock. Full article

Lignocellulosic biomass wastes are renewable carbon resources that can be available for conversion into biofuels. There is a growing interest in utilizing a broader range of alternative biomass feedstocks such as agri-crop residues aside from the traditional forest-origin wood residues for fuel pellet production. However, crop residues typically have low and inconsistent fuel quality. This paper investigated the effectiveness of the combined steam explosion and water leaching pretreatment techniques to upgrade the fuel properties of wheat straw. The experimental treatments involved auto-catalyzed steam explosion and acid-catalyzed steam with and without subsequent water leaching. Using steam explosion catalyzed by dilute H₂SO₄ at a low concentration of 0.5 wt%, results showed the highest ash, Si, and Ca removal efficiencies of 82.2%, 91.1%, and 74.3%, respectively. Moreover, there was significant improvement in fuel quality in terms of fuel ratio (0.34) and calorific value HHV (21.9 MJ/kg), as well as a pronounced increase in the comprehensive combustibility index at the devolatization stage, indicating better combustion characteristics. Overall, the results demonstrate that with adequate pretreatment, the quality of agri-pellets derived from wheat straw could potentially be on par with wood pellets that are utilized for heat and power generation and residential heating. To mitigate the dry matter loss due to steam explosion, future studies shall consider using the process effluent to produce biofuel. Full article

The influence of M site substitution in MCr₂O₄ nanoceramics on their properties is examined in this research. This study is an attempt to correlate the structural, morphological, and optical properties of M-site-modified chromites. The MCr₂O₄ nanoceramics-CuCr₂O₄, CoCr₂O₄, and NiCr₂O₄ were synthesized using a wet chemical sol–gel auto-combustion method, and all three samples were annealed for 4 h at 900 °C. X-ray diffraction analysis showed that the XRD patterns of CuCr₂O₄, CoCr₂O₄, and NiCr₂O₄ correspond to single-phase cubic crystal structures with the space group Fd-3m. Using the Scherrer equation, the crystallite sizes were found to be 9.86 nm, 6.73 nm, and 10.73 nm for CuCr₂O₄, CoCr₂O₄, and NiCr₂O₄, respectively. Other parameters, including crystal structure, micro-strain, lattice constant, unit cell volume, X-ray density, packing factor, and the stacking fault of the calcined powder samples, were determined from data acquired from the X-ray diffractometer. Energy dispersive X-ray spectroscopy (EDX) was employed to confirm the appropriate chromite elements in their expected stoichiometric proportions, removed from other impurities. The identification of the functional groups of the samples was performed using Fourier Transform Infrared Spectroscopy (FTIR). The absorption bands characteristic of tetrahedral and octahedral coordination compounds of the spinel structure are found between 450 and 750 cm⁻¹ for all three samples in the spectrum. From the UV-absorption spectra, and using Tauc’s plot, the energy bandgap values for CuCr₂O₄, CoCr₂O₄, and NiCr₂O₄ were measured to be 1.66 eV, 1.82 eV, and 2.01 eV, respectively. The dielectric properties of the chromites were studied using an LCR meter. Frequency-dependent dielectric properties, including Dielectric constant and Tangent loss, were calculated. These findings suggest the feasibility of the use of these synthesized chromites for optical devices and other optoelectronic applications. Full article

Textile production contributes significantly to water pollution, making dye removal crucial for protecting water resources from toxic textile waste. The use of nano-adsorbents for water purification has emerged as a promising approach to removing pollutants from wastewater. Nickel Ferrite (NiFe₂O₄), Iron Oxide (Fe₂O₃), and Nickel Oxide (NiO) nanoparticles (NPs) were prepared via an auto-combustion sol–gel technique using chitosan as a capping and stabilizing agent. The prepared nanomaterials were characterized using various techniques such as XRD, UV-Vis DRS, FT-IR, Raman, EDX, SEM, and TEM to confirm their structure, particle size, morphology, functional groups on the surface, and optical properties. Subsequently, the adsorption of the methylene blue (MB) dye using the prepared nanomaterials was studied. NiFe₂O₄ NPs exhibited the best adsorption behavior compared to the mono-metal oxides. Moreover, all prepared nanomaterials were compatible with the pseudo-second-order model. Further investigations were conducted for NiFe₂O₄ NPs, showing that both the Freundlich and Langmuir isotherm models can explain the adsorption of the MB dye on the surface of NiFe₂O₄ NPs. Factors affecting MB dye adsorption were discussed, such as adsorbent dose, concentration of the MB dye, contact time, pH, and temperature. NiFe₂O₄ NPs exhibited a maximum removal efficiency of the MB dye, reaching 96.8% at pH 8. Different water sources were used to evaluate the ability of NiFe₂O₄ NPs to purify a wide range of water types. Full article

Hydrogen is a promising alternative fuel for internal combustion engines due to its high specific energy, fast flame speed, and carbon-free combustion. In dual-fuel operation, it offers a practical route to reducing greenhouse gas emissions while remaining compatible with existing engine hardware. This work evaluates how the hydrogen energy substitution ratio (HSR = 50, 70, and 90%) influences spray dynamics, combustion characteristics, and emissions in a heavy-duty compression ignition engine. Simulations are validated against experiments and use a URANS RNG k–ε framework with a hybrid combustion model: the Eddy Dissipation Concept (EDC) coupled with detailed kinetics (111 species, 768 reactions) for auto-ignition and diffusion burning of diesel, and a G-equation for propagation of a hydrogen-rich premixed flame. The results reveal clear spray–combustion linkages. At HSR 50, the higher Weber number induces stronger breakup, yielding a smaller Sauter mean diameter and higher number-averaged droplet velocity; at HSR 90, the spray is more stable and less atomized, with larger droplets and a shorter vapor penetration length. Increasing the HSR reduces unburned hydrocarbons (UHCs) by more than 50% from HSR 50 to HSR 90 while modestly altering combustion phasing (a later CA50 and a shorter burn duration due to faster hydrogen flame propagation). The validated model provides a practical tool for optimizing dual-fuel settings and HSR–EGR–SOI trade-offs to balance efficiency and emissions. Full article

Supercapacitors are required to store energy from renewable resources to ensure a pollutant-free environment. To further encourage its study, researchers are interested in introducing green methods to produce electrode materials. Green synthesis is an innovative and emerging field because plant extracts are the best substitute for toxic chemicals. They are considered eco-friendly and cost-effective. In this work, two plant extracts, orange juice (ORJ) and lemon juice (LMJ), are used to synthesize the Sr_0.8Ce_0.2Fe_0.8Co_0.2O₃ perovskite using the auto-combustion method. The electrochemical performance of Sr_0.8Ce_0.2Fe_0.8Co_0.2O₃ made from LMJ and ORJ is compared to check their effectiveness. LMJ proved to be a better reducing agent than ORJ with a higher specific capacity of 300 C/g (544 F/g) at 1 A/g current density due to increased oxygen vacancies and surface area. These findings show that green-synthesized perovskites can be utilized in high-performance hybrid supercapacitor devices. Full article

Combustion of aviation jet fuel emits a complex mixture of pollutants linked to adverse health outcomes among airport personnel and nearby communities. While epidemiological studies showed the detrimental effects of aviation-derived air pollutants on human health, the molecular mechanisms of the interactions of these pollutants with cellular biomolecules like proteins that drive the adverse health effects remain poorly understood. In this study, we performed molecular docking simulations of 272 pollutant–protein complexes using AutoDock Vina 1.2.7 to characterize the binding strength of the pollutants with the selected proteins. We selected 34 aviation-derived pollutants that constitute three chemical categories of pollutants: volatile organic compounds (VOCs), polyaromatic hydrocarbons (PAHs), and organophosphate esters (OPEs). Each pollutant was docked to eight proteins that play critical roles in endocrine, metabolic, transport, and neurophysiological functions, where functional disruption is implicated in disease. The effect of binding of multiple pollutants was analyzed. Our results indicate that aliphatic and monoaromatic VOCs display low (<6 kcal/mol) binding affinities while PAHs and organophosphate esters exhibit strong (>7 kcal/mol) binding affinities. Furthermore, the binding strength of PAHs exhibits a positive correlation with the increasing number of aromatic rings in the pollutants, ranging from nearly 7 kcal/mol for two aromatic rings to more than 15 kcal/mol for five aromatic rings. Analysis of intermolecular interactions showed that these interactions are predominantly stabilized by hydrophobic, pi-stacking, and hydrogen bonding interactions. Simultaneous docking of multiple pollutants revealed the increased binding strength of the resulting complexes, highlighting the detrimental effect of exposure to pollutant mixtures found in ambient air near airports. We provide a priority list of pollutants that regulatory authorities can use to further develop targeted mitigation strategies to protect the vulnerable personnel and communities near airports. Full article

This study presents the first successful integration of Fe₃O₄ and Li_0.5Cr_0.5Fe₂O₄ into a well-defined core/shell nanostructure through a two-step synthesis that combines co-precipitation and sol–gel auto-combustion methods. Unlike conventional composites, the core/shell design effectively suppresses the magnetic dead layer and promotes exchange coupling at the interface, leading to enhanced saturation magnetization, superior magnetic heating (specific absorption rate; SAR), and improved dielectric properties. Our research introduces a novel interfacial engineering strategy that simultaneously optimizes both magnetic and dielectric performance, offering a multifunctional platform for applications in magnetic hyperthermia, electromagnetic interference (EMI) shielding, and microwave devices. Full article

Polyethersulfone (PES) membranes are essential in separation processes; however, their inherent hydrophobicity can limit their effectiveness in water-intensive applications. This study aims to enhance PES membranes by modifying them with a NiFe₂O₄–nanoclay composite nanoparticle to improve both their hydrophilicity and photocatalytic potential as a photocatalytic membrane. The nanoparticles were synthesized using the sol–gel auto-combustion method and incorporated into PES membranes through mixed-matrix embedding (1 wt% and 3 wt%) and surface coating. X-ray diffraction confirmed the cubic spinel structure of the composite nanoparticles, which followed the second order kinetic reaction during the photodegradation–adsorption of crystal violet. The mixed-matrix membranes displayed a remarkable 170% increase in water flux and a 25% improvement in mechanical strength, accompanied by a slight decrease in contact angle at 1 wt% of nanoparticle loading. In contrast, the surface-coated membranes demonstrated a significant reduction in contact angle to 18°, indicating a highly hydrophilic surface and increased roughness. All membranes achieved high dye removal rates of 98–99%, but only the coated membrane system exhibited approximately 50% photocatalytic degradation, following mixed kinetics. These results highlight the critical importance of surface modification in advancing PES membranes, as it significantly reduces fouling and enhances water–material interaction qualities essential for future filtration and photocatalytic applications. Exploring hybrid strategies that combine both embedding and coating approaches may yield even greater synergies in membrane functionality. Full article

The measurement error of sound travel time, one of the most critical parameters in acoustic temperature measurement, is significantly affected by the type of sound source signal. In order to select more appropriate sound source signals, a sound source signal preference study of loose coal acoustic temperature measurement was performed and is described herein. The results showed that the absolute error of the swept signal and the pseudo-random signal both increased with increased acoustic wave propagation distance. The relative error of the swept signal showed a relatively stable upward trend; in comparison, the pseudo-random signal showed a general decrease with a large fluctuation in the middle section, and both the relative and absolute errors for the pseudo-random signal were larger than those of the swept signal. Therefore, the swept signal is expected to perform better than the pseudo-random signal in the loose coal medium. Based on the experimental results, the linear sweep signal was selected as the sound source signal for the loose coal temperature inversion experiments: the average error between the inverted temperature value and the actual value was 4.86%, the maximum temperature difference was 2.926 °C, and the average temperature difference was 1.5949 °C. Full article

Hydrogen–gasoline dual-fuel spark ignition (SI) engines represent a promising transitional solution toward cleaner combustion and reduced carbon emissions. In a previous study, a predictive engine model was developed to simulate the performance and combustion characteristics of such systems; however, its accuracy was constrained by the use of estimated combustion parameters. This study presents an experimental validation based on high-resolution in-cylinder pressure measurements performed on a naturally aspirated SI engine operating with a 20% hydrogen energy share. The objectives are twofold: (1) to refine the combustion model using empirically derived combustion metrics, and (2) to evaluate the feasibility of moderate hydrogen enrichment in a stock engine configuration. To facilitate a more accurate understanding of how key combustion parameters evolve under different operating conditions, Vibe function was fitted to the ensemble-averaged heat release rate curves computed from 100 consecutive engine cycles at each static full-load operating point. This approach enabled the extraction of stable and representative metrics, including the mass fraction burned at 50% (MFB50) and combustion duration, which were then used to recalibrate the predictive combustion model. In addition, cycle-to-cycle variation and combustion duration were also investigated in the dual-fuel mode. The combustion duration exhibited a consistent and substantial reduction across all of the examined operating points when compared to pure gasoline operation. Furthermore, the cycle-to-cycle variation difference remained statistically insignificant, indicating that the introduction of 20% hydrogen did not adversely affect combustion stability. In addition to improving model accuracy, this work investigates the occurrence of abnormal combustion phenomena—including backfiring, auto-ignition, and knock—under enriched conditions. The results confirm that 20% hydrogen blends can be safely utilized in standard engine architectures, yielding faster combustion and reduced burn durations. The validated model offers a reliable foundation for further dual-fuel optimization and supports the broader integration of hydrogen into conventional internal combustion platforms. Full article