Search Results (868)

The blast furnace–basic oxygen furnace long process is the dominant steel production route in China. Increasing the scrap ratio is an effective way to reduce cost and carbon emissions, and scrap preheating is a key technology to achieve a high scrap ratio. To improve the low thermal efficiency and poor deep-bed melting performance of converter gas-based scrap preheating, an innovative process using oxygen-enriched combustion in a hot metal ladle is proposed. Numerical simulation is essential for capturing the complex multiphysics phenomena, as real-time monitoring of melting inside the packed scrap bed is extremely difficult. In this study, a novel multiphysics approach based on a User-Defined Function (UDF) is developed to dynamically track the progressive melting of the scrap skeleton, overcoming the key limitation of conventional enthalpy–porosity models that cannot capture the feedback between phase change and porous medium property evolution. A three-dimensional transient model was established, integrating turbulent combustion, gas–solid convective heat transfer in porous media, and solid–liquid phase change. The effects of impact pit depth, scrap porosity, and converter gas flow rate on temperature distribution, melting behavior, and thermal efficiency were systematically investigated. Results showed that porosity had the strongest influence; thermal efficiency increased from 33.92% to 65.59% as porosity rose from 0.6 to 0.8, due to a transition from conduction-dominated to coupled convection–conduction heat transfer. Converter gas flow rate exhibited a non-monotonic effect, peaking at 3688.14 m³·h⁻¹, highlighting a trade-off between energy input and gas residence time, while impact pit depth showed a limited effect with diminishing returns. A 600 s full-process simulation revealed stage-dependent melting, and the initial phase was crucial for process optimization. The optimal condition, with a pit depth of 64 cm, porosity of 0.8, and converter gas flow rate of 3688.14 m³·h⁻¹, achieved a 1.23% melting fraction and 65.59% thermal efficiency within 120 s. These findings clarify the combined roles of geometric confinement, permeability, and energy-residence time interactions, providing guidance for industrial scrap preheating design. Full article

To investigate the early-stage flame propagation and pressure response of premixed H₂-O₂ combustion under ultra-high-pressure constant-volume conditions, a transient CFD model was developed for a large-volume confined chamber. The numerical framework combines a density-based solver, the Peng–Robinson real equation of state, large eddy simulation, and a reduced H₂-O₂ chemical kinetic mechanism. Simulations were conducted at initial pressures of 30 and 40 MPa, H₂/O₂ molar ratios of 8:1 and 12:1, and three-, four-, and five-point ignition configurations. The results show that increasing the initial pressure from 30 MPa to 40 MPa advances the pressure rise onset from approximately 1.65 ms to 1.28 ms and increases the maximum pressure rise rate from 18.6 MPa·ms⁻¹ to 27.4 MPa·ms⁻¹ under the H₂/O₂ = 8:1 and three-point ignition condition. Under the investigated fuel-rich conditions, increasing the H₂/O₂ molar ratio from 8:1 to 12:1 delays the pressure rise onset from approximately 1.28 ms to 1.46 ms and reduces the maximum pressure rise rate from 27.4 MPa·ms⁻¹ to 21.1 MPa·ms⁻¹. For the 30 MPa and H₂/O₂ = 8:1 cases, the four-point ignition case produces the largest pressure rise rate of approximately 23.5 MPa·ms⁻¹, whereas the five-point ignition case shows a lower pressure fluctuation amplitude of approximately 3.6 MPa. The present conclusions are based on CFD quantitative engineering predictions and should be further validated using quantitative experimental measurements. Full article

Thermal overload in internal combustion engines may progressively destabilize lubricant-film integrity and promote severe tribological deterioration within highly stressed contact interfaces. This study investigates the thermo-tribological degradation sequence of a high-mileage gasoline engine subjected to prolonged idle operation under impaired cooling conditions, ultimately resulting in engine seizure. The investigated engine had accumulated 356,724 km, while the lubricant had remained in service for approximately 26,724 km prior to the experiment. The post-failure investigation combined teardown inspection, geometrical camshaft assessment, reverse gravimetric reconstruction, hydraulic tappet surface profiling, XRF surface characterization, laboratory oil analysis, and SEM/EDS evaluation of wear debris. The results demonstrated strongly localized degradation concentrated primarily within the cam–tappet interfaces. Severe non-uniform camshaft wear was accompanied by pronounced hydraulic tappet surface damage and evidence of unstable boundary-lubrication conditions. Laboratory oil analysis revealed elevated wear-metal concentrations, depletion of the alkaline reserve, increased oxidation indicators, and a final Class D oil condition assessment. SEM/EDS characterization identified Fe-bearing wear debris associated with sustained material removal and debris recirculation during the final degradation stage. The combined evidence supports a coupled thermo-tribological degradation mechanism involving lubricant deterioration, boundary-lubrication instability, adhesive wear acceleration, oxidative surface degradation, and debris-assisted surface damage preceding final engine seizure. The present case study provides experimentally documented evidence of lubrication collapse under real-engine thermal runaway conditions and highlights the critical role of lubricant condition in maintaining tribological stability under severe thermal loading. Full article

This paper presents the results of an experimental investigation of woody biomass combustion under real operating conditions of a heating boiler equipped with an integrated platinum-promoted oxidation catalyst (Pt-OX) and vanadium-based catalytic reactor (V-CAT) system for pollutant emission reduction, particularly nitrogen oxides (NO_x). Various configurations of the catalytic flue gas treatment system were investigated, including single-stage, dual-stage, and multi-stage vanadium- and platinum-based catalytic reactor arrangements. The investigated system incorporated platinum-promoted oxidation catalysts and a vanadium-based monolithic catalytic reactor. No external ammonia or urea injection was applied during the experimental campaign. Therefore, the catalytic system was evaluated under realistic biomass combustion conditions involving nitrogen-containing species naturally generated during fuel conversion processes. The obtained thermal and emission parameters were compared with those recorded during boiler operation without catalytic treatment. The investigated catalytic configurations significantly reduced pollutant emissions, with the highest-performing arrangement decreasing NO emissions from 112 ppm to 11 ppm, corresponding to a reduction efficiency exceeding 90%. The results demonstrate the potential of integrated catalytic reactor systems for improving the environmental performance of small-scale biomass-fired heating units operating under real conditions. Full article

To address the high experimental costs and data scarcity inherent in Directed Energy Deposition (DED), this study proposes a data-efficient hybrid optimization framework for the precision manufacturing of Inconel 718 aerospace components. The framework leverages a two-stage strategy to bridge traditional experimental design with advanced machine learning, ensuring robust process optimization even with limited datasets. In the first stage, the Taguchi method (L16 orthogonal array) was employed for coarse-grained screening to identify influential control factors. In the second stage, a Fully Connected Neural Network (FNN) coupled with Bayesian Optimization (BO) was deployed. Crucially, this machine learning component functions as an optimization-oriented trend surrogate rather than a global regressor, successfully guiding the optimization under extreme data scarcity. The optimized process window yielded exceptional structural integrity, achieving a porosity as low as 0.03%. To thoroughly validate its practical efficacy, tensile testing (ASTM E8/E8M) and Rockwell hardness measurements (ASTM E18) were systematically conducted on the optimized specimens. The mechanical characterization demonstrated an average tensile strength of approximately 1358 MPa and a hardness of ~40 HRC. Finally, the framework was successfully validated through the robotic DED fabrication of a complex-geometry aerospace engine combustion chamber casing, bridging laboratory-scale optimization with authentic industrial applications. Full article

Cross-laminated timber (CLT) is increasingly used in multi-story timber construction, but its combustible nature requires reliable fire protection, particularly in layered wall assemblies with concealed cavities. This study compares two medium-scale cross-laminated timber (CLT) sandwich wall assemblies exposed to radiant heat flux of 20 kW/m² for 90 min: an uncoated reference assembly and an assembly with PROMADUR^® intumescent coating applied to the CLT surfaces. Both specimens consisted of a 90 mm three-ply CLT panel encapsulated with 12.5 mm gypsum-fiber boards fixed to a wooden stud frame forming a 40 mm installation cavity. Fire-test observations were supplemented by simultaneous thermal analysis (STA), i.e., thermogravimetry (TG)/differential thermogravimetry (DTG)/differential scanning calorimetry (DSC), of uncoated and coated CLT specimens under oxidative conditions. During the applied medium-scale radiant exposure, the unexposed-face temperatures of both assemblies remained below the insulation temperature-rise limits defined in STN EN 1363-1; however, these limits were used only as a comparative benchmark and the test does not represent a formal fire-resistance classification. The coated assembly showed improved thermal protection during the early and intermediate stages of exposure, delaying a critical thermal event near the wooden stud by approximately 35 min. However, flaming combustion of the stud occurred at about 75 min and led to degradation of the intumescent char within the cavity. In contrast, the uncoated assembly reached higher early CLT surface temperatures but showed no flaming combustion during the test. STA results supported the fire-test interpretation: the coated specimen showed a 37% reduction in peak DTG rate, a higher residual mass at the end of the test, and substantially greater mass loss in the 150–280 °C range, consistent with intumescent activation and volatile release. The results indicate that, under the tested medium-scale exposure, the intumescent coating improved early and intermediate thermal protection of the CLT surface, but did not prevent late-stage cavity flaming involving the wooden stud. Therefore, the behavior of intumescent-coated CLT in partially enclosed cavities with combustible framing should be validated under replicated, standardized and larger-scale fire exposure. Full article

Historically, in the initial stages of solid rocket motor (SRM) development, performance parameters, such as specific impulse, total impulse, mass, and thrust, have been prioritized, with cost considerations often treated as secondary. Consequently, SRM performance optimization under cost constraints has emerged as a central objective in aerospace propulsion. To address this gap, this study establishes a cost–performance evaluation model for SRMs. A Kriging surrogate model, the Non-dominated Sorting Genetic Algorithm II (NSGA-II), and the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) are leveraged to minimize the manufacturing cost and maximize the terminal velocity of SRM engines, subject to constraints associated with the maximum operating pressure of the combustion chamber and burn time. First, a cost–performance calculation model for an SRM is developed and validated. Subsequently, Pearson correlation analysis and Sobol-based global sensitivity analysis are combined to reduce the dimensionality of the design parameters, and optimal Latin hypercube sampling is used to generate the training samples. Building on this foundation, a Kriging surrogate model is constructed. The cost–performance model of the SRM is subjected to multi-objective optimization using NSGA-II and TOPSIS to support decision-making. The results indicate that the proposed cost–performance calculation model achieves an error below 5%, demonstrating high accuracy. Among the design parameters, the combustion chamber length, nozzle outlet area, and expansion ratio significantly influence the cost and performance of SRMs. The surrogate models exhibit strong predictive accuracy, with coefficients of determination exceeding 0.9. The optimized TOPSIS scheme yields a performance improvement of 10.94% with a cost increase of 4.15% compared with the reference scheme. In summary, the cost–performance evaluation and optimization framework established in this work provides quantitative decision support for SRM design under cost constraints, and the integrated methodology can be extended to other aerospace propulsion systems or complex engineering equipment. This contributes to achieving synergistic optimization of performance and cost under resource limitations, and offers practical guidance for advancing affordability-driven design in propulsion engineering. Full article

Subsurface combustion in coal mines poses a significant threat to ecosystem integrity, geological stability, and public safety. Effective risk mitigation requires continuous monitoring and accurate detection of combustion dynamics. In this study, an improved subsurface combustion index (SCI) was developed based on multisource remote sensing indicators, and long-term time series observations (2010–2025) were used to characterize its spatiotemporal evolution. Results show that dREGI achieved the highest anomaly discrimination among all evaluated vegetation indices, with an M-statistic of 1.4186, outperforming NDVI (1.1073) and EVI (0.8226). Adaptive principal component analysis identified dREGI and H as the dominant contributors to SCI construction. Separability analysis further demonstrated that integrating dREGI with LST and H improved the performance of the composite SCI by 16.3%, increasing its M-statistic from 0.959 to 1.115 relative to the dREGI-only baseline. Temporally, subsurface combustion exhibits a multi-stage evolution, with initial anomalies emerging around 2013, followed by a transitional phase during 2014–2018. Activity intensifies during 2019–2023, peaks in 2023, and declines in 2024, indicating residual combustion. Spatially, high-risk areas are concentrated in the eastern region, while moderate and low-risk zones occur in the central and western regions, respectively. These results demonstrate that the proposed indices provide a more robust and sensitive framework for early warning and spatial delineation of subsurface combustion zones. Full article

Traditional coal mining methods have led to prominent issues of coal resource waste and large-scale solid waste emissions. The integrated “excavation–backfilling–retention” mining technology for inter-section coal pillars and gate roads is one of the key technologies to solve these problems. However, the excavation and mining process associated with this technology imposes higher requirements on the ventilation system. Aiming at addressing the ventilation challenges existing during the implementation of the “excavation–backfilling–retention” method, research on ventilation safety assurance technology for inter-section coal pillars was carried out. Using COMSOL5.5 software, a full-stage ventilation system design model was constructed, adopting a ventilation mode that combines full-air-pressure ventilation with auxiliary local ventilation. The dynamic variation characteristics of the ventilation system under the “excavation–backfilling–retention” method and its capability to prevent and control the risks of O₂ and CO gas accumulation and coal spontaneous combustion were studied. The results show that during the bypass excavation period, the air supply from the auxiliary fan is sufficient, and during the excavation period for the two gate roads, due to the increased ventilation distance, insufficient airflow occurs near the heading face, accompanied by temperature rise, O₂ concentration decrease, and local CO accumulation, posing risks of coal spontaneous combustion and toxic gas accumulation. During the inter-section coal pillar excavation period and the cyclic operation period, after the full-air-pressure ventilation system is established, the airflow becomes stable, ventilation resistance decreases, and both temperature and gas concentrations are controlled within safe limits. However, in the corner areas, auxiliary local ventilation measures are still required due to insufficient O₂ and CO accumulation. The study verifies the feasibility and safety of the integrated “excavation–backfilling–retention” ventilation system, providing a safe ventilation approach for the integrated mining method and supporting the green mining of coal mines and the synergistic development of coal-based solid waste resource utilization. Full article

To elucidate the combustion behavior and molecular-scale reaction mechanisms of Fushun oil shale kerogen under oxy-fuel atmospheres, ReaxFF molecular dynamics simulations were performed based on a previously constructed kerogen model. Five reaction systems were established: 21% O₂/79% N₂, 21% O₂/79% CO₂, 35% O₂/65% CO₂, 55% O₂/45% CO₂, and 75% O₂/25% CO₂. Under programmed heating, the evolution of chemical bonds, gaseous products, char, tar and gas transformation, and system potential energy was systematically analyzed. The results show that, at the same O₂ concentration, CO₂ delays low-temperature oxidation, shifting C–C and C–H bond cleavage and O₂ consumption to higher temperatures. At elevated temperatures, however, CO₂-related pathways promote carbon skeleton fragmentation and CO formation. Increasing O₂ concentration from 21% to 75% advances O₂ participation and H₂O formation, suppresses low-temperature CO accumulation, accelerates char consumption, and drives the system toward complete oxidation dominated by small-molecule gases. Potential energy analysis further indicates that higher O₂ concentrations advance the intense exothermic oxidation stage. A four-stage oxy-fuel combustion mechanism is proposed, providing molecular-level insight into the coupled effects of CO₂ and O₂ concentration. Full article

The global push for low-carbon electricity generation has made hydrogen-enriched natural gas an attractive near-term decarbonization option. This paper combines experimental and thermodynamic analyses of H₂–CH₄ combustion in gas turbine combustion chambers. Experiments were conducted on a patented two-stage swirl burner across 240 operating conditions. The effects of hydrogen fraction (γ = 0–40%), swirler vane angle (30°, 45°, 60°), equivalence ratio (φ = 0.17–1.00), and fuel injection strategy were measured against NOx and CO emissions and lean blowout stability. Each 10% increase in hydrogen content raised NOx by 23–24% via the Zel’dovich thermal mechanism, while CO fell by up to 28.5% at φ = 0.3 and 60° due to enhanced OH-radical activity. The minimum recorded NOx was 12.08 ppm (Type 2 injection, 30°, γ = 0%, φ = 0.3). Hydrogen addition improved lean blowout stability by 32–46% per 10% H₂. A parallel thermodynamic analysis showed that integrating an organic Rankine cycle (ORC) and supplementary H₂–CH₄ firing in the heat recovery steam generator cuts specific CO₂ emissions by 7.5–10% and raises net efficiency by 0.79–4.0 percentage points. Critical comparison with 28 published studies identified an optimal operating window: γ = 20–30%, φ = 0.5–0.7, 45° vane angle (SW = 0.8). Full article

This study investigated the co-combustion behavior of loblolly pine (LP100), kaolin clay (KC100), and LP-KC blends (LP75KC25, LP50KC50, and LP25KC75) using thermogravimetric analysis under air gas flow at heating rates of 5, 10, and 20 °C min⁻¹. The objective was to evaluate how biomass–mineral blending affects thermal degradation, reaction-stage development, kinetic behavior, and thermodynamic properties. The TGA-DTG results were interpreted using Coats–Redfern model-fitting kinetics, Flynn–Wall–Ozawa (FWO) model-free kinetics, and thermodynamic analysis. LP100 and LP-KC blends exhibited two main stages: Phase II oxidative devolatilization and Phase III char oxidation with overlapping kaolinite dehydroxylation, while KC100 showed one dominant high-temperature mineral transformation. In Phase III, the blends’ DTG peak temperatures ranged from 401.7 to 474.3 °C at 5 °C min⁻¹, 427.0 to 500.3 °C at 10 °C min⁻¹, and 478.3 to 509.0 °C at 20 °C min⁻¹. Coats–Redfern Ea values were 58.16–70.50 kJ mol⁻¹ for LP100 in Phase III, and 178.85–181.59 kJ mol⁻¹ for KC100 in Phase III, while the blends’ Ea values ranged from 24.07 to 81.31 kJ mol⁻¹ in Phase II and 30.00 to 59.59 kJ mol⁻¹ in Phase III. FWO analysis confirmed conversion-dependent Ea behavior, with KC100 showing the highest energy barrier. Thermodynamic analysis showed positive ∆G values of 170.59–188.34 kJ mol⁻¹ in Phase II and 197.38–240.84 kJ mol⁻¹ in Phase III. ∆H ranged from 19.67 to 76.55 kJ mol⁻¹ in Phase II and reached 172.53–175.43 kJ mol⁻¹ for KC100 in Phase III, while negative ∆S values of −0.07 to −0.28 kJ mol⁻¹ K⁻¹ indicated ordered activated complexes. In conclusion, LP lowered the apparent kinetic and thermodynamic barriers of KC transformation during co-combustion. Full article

This work presents the thermodynamic design and performance assessment of an integrated process line for the separation, liquefaction, storage, and valorization of carbon dioxide (CO₂) and nitrogen (N₂) from flue gas streams. The proposed system aims to combine carbon capture with cryogenic energy storage by exploiting the thermophysical properties of the main flue gas constituents. A representative flue gas derived from complete methane combustion (9.5% CO₂, 71.5% N₂, and 19% H₂O by volume) is considered as the feed stream. The process is developed and simulated in DWSIM v9.0.5, adopting a steady-state mass and energy balance framework coupled with rigorous thermodynamic modeling of phase equilibria and unit operations. The plant configuration is based on sequential cooling, compression, and expansion stages, enabling the selective condensation of H₂O, CO₂, and N₂ at different temperature levels. The system integrates heat exchangers, compressors, pumps, turboexpanders, phase separators, and cryogenic storage tanks, while a portion of the liquefied CO₂ is reused as an energy carrier through vaporization and expansion in a dedicated turbine. The results demonstrate that the process achieves a CO₂ capture ratio of 81.7%, with a specific electric consumption (SEC) of 10.44 kWh/kg_CO2 and 1.71 kWh/kg_N2. The overall net electric demand is 1.29 kWh/kg of treated flue gas, while the round-trip efficiency (η_RT,CO2) is 18.6%. A significant amount of energy can further be recovered from the “waste” exhaust water stream (12.94 kg_L-H2O/kg_flue-gas, at 91 °C and 1.2 bar) up to 800 Wh/kg_flue-gas, improving the performance of the entire process (SEC_CO2: 3.86 kWh/kg_CO2, η_RT,CO2: 69.8%). The study confirms the thermodynamic feasibility of the proposed configuration and identifies nitrogen liquefaction as the dominant energy-intensive step. Future optimization efforts should therefore focus on reducing exergy destruction in the deep cryogenic section through improved heat integration, enhanced cold-energy recovery, optimized compression–expansion staging, and reduced pressure losses. Full article

In spite of the intense research interest in the integration of Pressure Gain Combustion (PGC) systems with a turbomachinery module, limited studies have been conducted regarding the experimental investigation of the strong spatio-temporal perturbations of these unconventional machines’ outflow. This paper focuses on experimentally characterizing the perturbing exhaust flow of a Constant-Volume Combustor (CVC). Preceding numerical analysis offers a transition duct able to attenuate the CVC’s produced unsteadiness and connect this PGC with a turbomachinery module. In fact, the transition duct is manufactured, while a pair of windows are introduced allowing for high-frequency Particle Image Velocimetry (PIV) analysis. In addition, fast-response pressure sensors in the combustion chamber, upstream and downstream of the transition duct, are implemented. A parametric analysis of the rotational frequency of the inlet–outlet rotary valve pair is conducted. The perturbing outflow of this PGC is characterized and experimentally visualized for the first time. Moreover, the attenuation performance of the transition duct on the CVC’s produced unsteadiness is evaluated for different cycle frequencies. The transition duct is proved to be able to alleviate the spatial and time-dependent unsteadiness by CVC, offering crucial evidence and conclusions for the future industrial integration of the CVC with a High-Pressure Turbine stage. Full article

To clarify the effect of water immersion duration on the spontaneous combustion behavior of high−sulfur coal, coal samples with a sulfur content greater than 3% were immersed for 15, 30, and 45 d. Mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM), Fourier−transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA) were used to characterize the pore−fracture structure, surface micromorphology, functional−group distribution, and thermal response of the samples. The results show that, with increasing immersion duration, the pore−fracture system gradually evolved from local opening to enhanced connectivity, while the coal surface became rougher and more porous. The 45 d sample exhibited the most pronounced pore−fracture openness. FTIR analysis indicated staged changes in oxygen−containing functional groups after immersion, with the strongest hydroxyl (−OH) response occurring in the 45 d sample. TGA results showed that the main reaction stage of the immersed samples shifted toward a higher temperature region; the 30 d sample showed relatively prominent mass−loss and heat−release intensities, whereas the 45 d sample exhibited more evident pore−fracture openness, functional−group activation, and a stronger tendency for heat accumulation. Overall, prolonged water immersion strengthened coal–oxygen contact conditions and self−heating sensitivity in high−sulfur coal, and the 45 d sample showed the highest potential spontaneous combustion propensity. Full article