Search Results (495)

Driven by stringent emission regulations, advanced combustion modes utilizing turbulent jet ignition technology are pivotal for enhancing the performance of marine low-speed natural gas dual-fuel engines. This review focuses on three novel combustion modes, yielding key conclusions: (1) Compared to the conventional DJCDC mode, the TJCDC mode exhibits a significantly higher swirl ratio and turbulence kinetic energy in the main chamber during initial combustion. This promotes natural gas jet development and combustion acceleration, leading to shorter ignition delay, reduced combustion duration, and a combustion center (CA50) positioned closer to the Top Dead Center (TDC), alongside higher peak cylinder pressure and a faster early heat release rate. Energetically, while TJCDC incurs higher heat transfer losses, it benefits from lower exhaust energy and irreversible exergy loss, indicating greater potential for useful work extraction, albeit with slightly higher indicated specific NOx emissions. (2) In the high-compression ratio TJCPC mode, the Liquid Pressurized Natural Gas (LPNG) injection parameters critically impact performance. Delaying the start of injection (SOI) or extending the injection duration degrades premixing uniformity and increases unburned methane (CH₄) slip, with the duration effects showing a load dependency. Optimizing both the injection timing and duration is, therefore, essential for emission control. (3) Increasing the excess air ratio delays the combustion phasing in TJCPC (longer ignition delay, extended combustion duration, and retarded CA50). However, this shift positions the heat release more optimally relative to the TDC, resulting in significantly improved indicated thermal efficiency. This work provides a theoretical foundation for optimizing high-efficiency, low-emission combustion strategies in marine dual-fuel engines. Full article

With the rapid advancement of urban underground space development, shield tunnel construction has seen a significant increase. However, at the initial launching stage of shield tunnels in shallow-buried weak strata, engineering risks such as face instability and sudden surface settlement frequently occur. At present, there are relatively few studies on the reinforcement technology of the initial section of shield tunnel in shallow soft ground and the evolution law of ground disturbance. This study takes the launching section of the Guanggang New City depot access tunnel on Guangzhou Metro Line 10 as the engineering background. By applying MIDAS/GTS numerical simulation, settlement monitoring, and theoretical analysis, the reinforcement technology at the tunnel face, the spatiotemporal evolution of ground settlement, and the mechanism of soil disturbance transmission during the launching process in muddy soil layer are revealed. The results show that: (1) the reinforcement scheme combining replacement filling, high-pressure jet grouting piles, and soil overburden counterpressure significantly improves surface settlement control. The primary influence zone is concentrated directly above the shield machine and in the forward excavation area. (2) When the shield machine reaches the junction between the reinforced and unreinforced zones, a large settlement area forms, with the maximum ground settlement reaching −26.94 mm. During excavation in the unreinforced zone, ground deformation mainly occurs beneath the rear reinforced section, with subsidence at the crown and uplift at the invert. (3) The transverse settlement trough exhibits a typical Gaussian distribution and the discrepancy between the measured maximum settlement and the numerical and theoretical values is only 3.33% and 1.76%, respectively. (4) The longitudinal settlement follows a trend of initial increase, subsequent decrease, and gradual stabilization, reaching a maximum when the excavation passes directly beneath the monitoring point. The findings can provide theoretical reference and engineering guidance for similar projects. Full article

The elliptic pipe jet screech is explored at a pressure ratio from 2 to 6. The pipe length to diameter ratio is 5. The fundamental screech frequency and magnitude are obtained from the sound pressure level spectrum. The screech frequency decreases as the pressure ratio increases. The minor plane has more tones than the major plane at an emission angle of 75 degrees from the jet axis. The amplitude of the screech differs among the planes. The amplitude is higher at lower emission angles from 45 to 75 degrees and lower at a sideline angle of 90 degrees. Full article

Addressing the urgent need to decarbonise aviation and valorise agricultural waste, this paper investigates the production of Sustainable Aviation Fuel (SAF) from corn stover. A preliminary evaluation based on a literature review indicates that among various conversion technologies, fast pyrolysis (FP) emerged as the most promising option, offering the highest fuel yield (22.5%) among various pathways, a competitive potential minimum fuel selling price (MFSP) of 1.78 USD/L, and significant greenhouse gas savings of up to 76%. Leveraging Aspen Plus simulation, SAF production via FP was rigorously designed and optimised, focusing on the heat integration strategy within the process to minimise utility consumption and ultimately the total cost. Consequently, the produced fuel exceeded the American Society for Testing and Materials (ASTM) limit for the final boiling point, rendering it unsuitable as a standalone jet fuel. Nevertheless, it achieves regulatory compliance when blended at a rate of up to 10% with conventional jet fuel, marking a practical route for early adoption. Energy optimisation through pinch analysis integrated four hot–cold stream pairs, eliminating external heating, reducing cooling needs by 55%, and improving sustainability and efficiency. Economic analysis revealed that while heat integration slashed utility costs by 84%, the MFSP only decreased slightly from 2.35 USD/L to 2.29 USD/L due to unchanging material costs. Sensitivity analysis confirmed that hydrogen, catalyst, and feedstock pricing are the most influential variables, suggesting targeted reductions could push the MFSP below 2 USD/L. In summary, this work underscores the technical and economic viability of corn stover-derived SAF, providing a promising pathway for sustainable aviation and waste valorisation. While current limitations restrict fuel quality during full substitution, the results affirm the feasibility of SAF blending and present a scalable, low-carbon pathway for future development. Full article

This study aims to establish a methodology that integrates experimental measurements with finite element analysis (FEA) to investigate the mechanical behavior and dynamic characteristics of soft–hard laminated composites fabricated via additive manufacturing (AM) under dynamic excitation. A hybrid AM technique was employed, using the PolyJet process based on stereolithography (SLA) to fabricate composite beam structures composed of alternating soft and hard materials. Initially, impact tests using a steel ball on cantilever beams made of hard material were conducted to inversely calculate the first natural frequency via time–frequency analysis, thereby identifying Young’s modulus and Poisson’s ratio. For the viscoelastic soft material, tensile and stress relaxation tests were performed to construct a Generalized Maxwell Model, from which the Prony series parameters were derived. Subsequently, symmetric and asymmetric multilayer composite beams were fabricated and subjected to impact testing. The experimental results were compared with FEA simulations to evaluate the accuracy and validity of the identified material parameters of different structural configurations under vibration modes. The research focuses on the time- and frequency-dependent stiffness response of the composite by hard and soft materials and integrating this behavior into structural dynamic simulations. The specific objectives of the study include (1) establishing the Prony series parameters for the soft material integrated with hard material and implementing them in the FE model, (2) validating the accuracy of resonant frequencies and dynamic responses through combined experimental and simulation, (3) analyzing the influence of composite material symmetry and thickness ratio on dynamic modals, and (4) comparing simulation results with experimental measurements to assess the reliability and accuracy of the proposed modeling framework. Full article

(1) While three-dimensional (3D) printing technology is increasingly being used for the fabrication of high-fidelity, patient-specific aortic models, data on the mechanical properties of polymers are sparse. Therefore, the aim of this study was to identify suitable polymers for this purpose. (2) Methods: Eight flexible polymers, with Shore A hardnesses (ShA) of 27–85, were tested to determine their suitability for PolyJet printing technology. They were tested against porcine aortic and bovine pericardial tissue for suture retention strength, uniaxial stress testing according to ISO 37, and burst pressure in a standardized test setting. (3) Results: The polymers with a ShA of 30–50 showed statistically non-inferior suture retention strength, tensile strength, and burst pressure resistance when compared to pericardial and aortic tissue, respectively. (4) Conclusions: This was the first report to analyze the mechanical properties of eight different flexible PolyJet polymers. We found that the polymers with a Shore A hardness of 30–50 most closely mimicked the mechanical properties of aortic tissue. Therefore, they can be recommended for the additive manufacturing (3D printing) of aortic phantoms for simulation and training purposes. Full article

This study investigates the deformation characteristics and base stability of a circular diaphragm wall support system (external diameter: 90 m, wall thickness: 1.5 m) with pit bottom reinforcement for the South Anchorage deep foundation pit of the Zhangjinggao Yangtze River Bridge, which uses layered and partitioned top-down excavation combined with lining construction. Through field monitoring (deep horizontal displacement of the diaphragm wall, vertical displacement at the wall top, and earth pressure) and numerical simulations (PLAXIS Strength Reduction Method), we systematically analyzed the deformation evolution and failure mechanisms during construction. The results indicate the following: (1) Under the synergistic effect of the circular diaphragm wall, lining, and pit bottom reinforcement, the maximum horizontal displacement at the wall top was less than 30 mm and the vertical displacement was 0.04%H, both significantly below code-specified thresholds, verifying the effectiveness of the support system and pit bottom reinforcement. (2) Earth pressure exhibited a “decrease-then-increase” trend during the excavation proceeds. High-pressure jet grouting pile reinforcement at the pit base significantly enhanced basal constraints, leading to earth pressure below the Rankine active limit during intermediate stages and converging toward theoretical values as deformation progressed. (3) Without reinforcement, hydraulic uplift failure manifested as sand layer suspension and soil shear. After reinforcement, failure modes shifted to basal uplift and wall-external soil sliding, demonstrating that high-pressure jet grouting pile reinforcement had positive contribution basal heave stability by improving soil shear strength. (4) Improved stability verification methods for anti-heave and anti-hydraulic-uplift were proposed, incorporating soil shear strength contributions to overcome the underestimation of reinforcement effects in traditional pressure equilibrium and Terzaghi bearing capacity models. This study provides theoretical and practical references for similar deep foundation pit projects and offers systematic solutions for the safety design and deformation characteristics of circular diaphragm walls with pit bottom reinforcement. Full article

Channel fire poses a great threat to personnel safety and structural strength, in which the temperature profile is worthy of attention. In this paper, the longitudinal temperature profile of a ceiling jet induced by a wall-attached fire with different channel slopes was experimentally investigated using a 1:8 reduced-scale channel. The results show the following: (1) For channel fire with a horizontal ceiling, the influence of the burner aspect ratio and source-ceiling height on the temperature profile is monotonous in the cases considered in this work. With a larger burner aspect ratio and larger source-ceiling distance, more ambient air could be entrained; hence, the longitudinal temperature under the ceiling decays faster. (2) For channel fire with an inclined ceiling, when the burner aspect ratio and source-ceiling distance remain constant, the asymmetric entrainment induced by the flame under larger channel slope leads to more hot smoke being transported upstream. Consequently, the temperature profile is not symmetric, with higher temperatures upstream and lower temperatures downstream. (3) Combining the influence of the burner aspect ratios, source-ceiling distance, and burner aspect ratio, the characteristic length scale was modified. Based on this, a model describing the ceiling temperature profile was proposed and then verified with previous data. Full article

The present article offers a detailed analysis of helium jet velocity and vorticity intensity distribution using the particle image velocimetry (PIV) technique. A gaseous fuel injector featuring an interchangeable tip was implemented. The test campaign involved the use of three nozzle patterns characterized by different orifices shape and orientations. The helium was injected into a constant volume chamber (CVC) and the delivery pressure varied, as well as that inside the chamber, in order to obtain pressure ratios (PRs) ranging from 2 to 20. The synchronization system was set to record two consecutive frames at different time-instants after the start of energizing (aSOE). Green light from a dual cavity Nd:YAG laser was used for illumination and a 4-megapixel PIV-camera for image capture. Vegetable oil particles were seeded into the chamber to trace the helium jet structure and cross-correlation methodology employed to measure their instantaneous displacements. The role of orifices size and orientations has been deeply scrutinized and related to the morphological outcomes. The least-oriented nozzle (first) exhibited the highest values of jet penetration and well-defined vortex structures. In contrast, the more the orifices are oriented, the wider the regions interacting with surrounding environment. Specifically, geometry with smaller orifice sizes (third) returned an overall absence of localized significant vortex structures. This deficiency is counterbalanced by a large distribution of small vortices that were observed to replace the main rings for each condition examined. Full article

Battery thermal runaway (TR) is usually accompanied by a large amount of heat release, as well as a jet of flame. This not only causes harm to the surrounding environment but even exacerbates thermal runaway propagation (TRP). At this stage, many types of materials are used to suppress TRP, and people tend to focus on improving one characteristic of the material while ignoring other properties of the material. This may leave potential pitfalls for TRP suppression, suggesting the need to study multiple properties of multiple materials. In order to better weigh the advantages and disadvantages of different types of materials when suppressing TRP, we compared three typical materials for suppressing TRP behavior in lithium-ion batteries (LIBs). These materials are phase change materials (PCM), ceramic fibers, and glass fibers. They are all available in two different thicknesses, 2 mm and 3 mm. The experiments started with a comparative analysis of the TR experimental phenomena in the presence of the different materials. Then, the temperature and mass loss of the battery module during TR were analyzed separately and comparatively. The 3 mm glass fiber showed the best inhibition effect, which extended the TR interval between cells 1 and 2 to 894 s and successfully inhibited the TR of cell 3. Compared with the blank group, the total mass loss decreased from 194.3 g to 182.2 g, which is a 6.2% reduction. Subsequently, we comprehensively analyzed the performance of the three materials in suppressing TRP by combining their suppressing mechanisms. The experimental results show that glass fiber has the best effect in suppressing TRP due to its excellent thermal insulation and mechanical properties. This study may provide new insights into how to trade-off material properties for TRP suppression in the future. Full article

OT 355 (4FGL J1734.3 + 3858) is a relatively rarely studied but highly variable, moderate-redshift (z = 0.975) flat-spectrum radio quasar (blazar). With this work, we aim to study its optical variability on different timescales, which can help us to better understand the physical processes in relativistic jets operating in blazar-type active galactic nuclei. OT 355 was observed in four colors (BVRI) during 41 nights between 2017 and 2023 using three 1 and 2 m class telescopes. The object was also monitored on intra-night timescales, for about 100 h in total. In addition, secondary standard stars in the field of OT 355 were calibrated in order to facilitate future photometric studies. We detected significant intra-night and night-to-night variations of up to 0.5 mag. Variability characteristics, color changes, and a possible “rms-flux” relation were studied and discussed. Using simple arguments, we show that a negative “rms-flux” relation should be expected if many independent processes/regions drive the short-term variability via Doppler factor changes, which is not observed in this and other cases. This finding raises arguments for the idea that more complex multiplicative processes are responsible for blazar variability. Studying blazar variability, especially on the shortest possible timescales, can help to estimate the strength and geometry of their magnetic fields, the linear sizes of the emitting regions, and other aspects, which may be of importance for constraining and modeling blazars’ emitting mechanisms. Full article

Fontan circulation is a fragile system in which imperfections at any of multiple levels may compromise the quality of life, produce secondary pathophysiology, and shorten life span. Increased inferior vena caval pressure itself may play a role in “Fontan failure”. This study describes a mock flow loop model (MFL) designed to quantitatively estimate pulmonary flow entrainment induced by continuous and pulsed flow injections. A patient generic 3D-printed phantom model of the total cavopulmonary connection (TCPC) with average dimensions matching those of a 2–4-year-old patient was inserted in an MFL derived from a reduced lumped parameter model (LPM) representing cardiovascular circulation. The LPM comprises four 2-element Windkessel compartments (compliance and resistance), approximating the upper and lower systemic circulations and the right and left pulmonary circulations. The prescribed cardiac output is about 2.3 L/min for a body surface area of $0.675{ \mathrm{m}}^2$. The injections originate from an external pump through a 7–9 fr catheter, following a strict protocol suggested by the clinical team, featuring a variation in injection rate (flow rate), injection volume, and injection modality (continuous or pulsed). The key measurements in this study are the flow rates sampled at the distal pulmonary arteries, as well as at the upper and lower body boundaries. These measurements were then used to calculate effective entrainment as the difference between the measured and expected flow rates, as well as jet relaxation (rise and fall time of injection). The results show that for continuous or pulsed injections, varying the total volume injected has no significant influence on the entrainment rate across all injection rates. On the other hand, for both injection modalities, increasing the injection rate results in a reduction in entrainment that is consistent across all injected volumes. This study demonstrates the effectiveness of a high-speed injection jet entraining a slow co-flow while determining the potential for fluid buildup, which could ultimately cause an increase in caval pressure. To avoid the increase in caval pressure due to mass accumulation, we added a fenestration to our proposed injection jet shunt-assisted Fontan models. It was found that for a set of well-defined parameters, the jet not only can be beneficial to the local flow, but any adverse effect can be obviated by careful tuning. These results were also cross-validated with similar in silico findings. Full article

This study experimentally investigates the breakup mechanisms and atomization characteristics of liquid jets in subsonic crossflows and develops a penetration depth model that incorporates the incidence angle. Experimental data show that the model fits well, with a minimum R² value of 0.924 and an average of 0.969. High-speed imaging techniques were used to systematically analyze the effects of liquid- and gas-phase Weber numbers and incidence angles on the penetration and atomization of liquid jets. The experimental results indicate the following: (1) As the liquid Weber number (We_l) increases, the penetration depth increases, while the gas Weber number (We_a) is inversely related to penetration depth. (2) A decrease in the incidence angle (ranging from 45° to 90°) significantly reduces penetration performance. (3) As We_a increases, the volume median diameter (VMD) of droplets decreases by 61.70% to 83.09%, while smaller incidence angles cause a 42.96% increase in the VMD. The VMD shows a non-linear trend with respect to We_l, reflecting the complex interaction between inertial forces and surface tension. These findings provide a theoretical basis for understanding the atomization behavior of transverse jets and the key parameters affecting penetration and droplet formation. The results are of practical significance for the structural optimization and performance enhancement of air-assisted atomizing nozzles used in precision agricultural spraying systems. Full article

The Tibetan Plateau (TP) serves as a vital ecological safeguard and water conservation region in China. In recent decades, substantial efforts have been made to promote vegetation greening across the TP; however, these interventions have added complexity to the local water balance and evapotranspiration (ET) processes. To investigate these dynamics, we apply the Priestley–Taylor Jet Propulsion Laboratory (PT-JPL) model to simulate ET components in the TP. Through model sensitivity experiments, we isolate the contribution of vegetation greening to ET variations. Furthermore, we analyze the role of climatic drivers on ET using a suite of statistical techniques. Based on satellite and climate data from 1982 to 2018, we found the following: (1) The PT-JPL model successfully captured ET trends over the TP, revealing increasing trends in total ET, canopy transpiration, interception loss, and soil evaporation at rates of 0.06, 0.39, 0.005, and 0.07 mm/year, respectively. The model’s performance was validated using eddy covariance observations from three flux tower sites, yielding R² values of 0.81–0.86 and RMSEs ranging from 6.31 to 13.20 mm/month. (2) Vegetation greening exerted a significant enhancement on ET, with the mean annual ET under greening scenarios (258.6 ± 120.9 mm) being 2.9% greater than under non-greening scenarios (251.2 ± 157.2 mm) during 1982–2018. (3) Temperature and vapor pressure deficit were the dominant controls on ET, influencing 53.5% and 23% of the region, respectively, as identified consistently by both multiple linear regression and dominant factor analyses. These findings highlight the net influence of vegetation greening and offer valuable guidance for water management and sustainable ecological restoration efforts in the region. Full article

This paper investigates how octanol, used as a renewable additive in Jet A fuel, influences the performance and emissions of aviation micro-turbo engines. Blends containing 10%, 20%, and 30% octanol, with an additional 5% n-heptane, were tested to closely replicate Jet A’s physical–chemical properties. Mathematical models validated using density and viscosity data achieved accurate predictions, with maximum absolute errors of 0.0018 g/cm³ for density and 0.4020 mm²/s for viscosity. Performance assessments showed that fuel consumption increased due to octanol’s lower calorific value, requiring higher fuel flow to sustain engine speed. Combustion temperature variations ranged from a decrease of 5.38% in Regime 1 (30% octanol) to increases of up to 1.47% and 1.13% in Regimes 2 and 3, respectively, without compromising engine stability. Thrust variations were minimal, with decreases up to 0.72% observed at 30% octanol concentration. Emission analysis indicated significant reductions in CO and NO_x levels with increased octanol content, attributed to enhanced combustion completeness and additional oxygen availability. SO₂ emissions also decreased slightly due to the lower sulfur content. Thermal efficiency marginally declined from 5.04% (Jet A) to approximately 4.92–4.97% for octanol blends. These findings support octanol as a viable sustainable additive, offering substantial emission benefits with only minor efficiency trade-offs. Full article