High Velocity Research Articles

Probing trade-off between critical size and velocity in cold-pray: An atomistic simulation

The detailed mechanism of bonding in the cold spray process has remained elusive for both experimental and theoretical parties. Adiabatic shear instability and hydrodynamic plasticity models have been so far the most popular explanations. Here, using molecular dynamics simulation, we investigate their validity at the nanoscale. The present study has potential applications in the fabrication of ultrathin layers in the electronics industry. For this aim, we considered Ti nanoparticles of different diameters and Si substrates of different orientations. It is shown that very high spray velocities are required for a jet to be observed at the nanoscale. We propose a method for thermostating the substrate that enables utilizing high spray velocities. For the first time, we demonstrate an oscillatory behavior in both the normal and radial stress components within the substrate that can propagate into the particle. We have shown that neither the adiabatic shear instability model nor the hydrodynamic plasticity model can be ignored at the nanoscale. In addition, the formation of a low-resistance titanium silicide proper for electronic application is illustrated.

Sliding-Induced Rehydration in Hydrogels for Restoring Lubrication and Anticreeping Capability.

Fluid exudation in cartilage under normal loading can be counteracted by a sliding-induced rehydration phenomenon, which has a hydrodynamic origin related to a wedge effect at the contact inlet. Similar to cartilage, hydrogels also exhibit tribological rehydration properties, and we mimic this phenomenon to restore hydration lubrication and overcome creeping. It occurs within a specific velocity range and is mainly dependent on the applied load and hydrogel network structures. Crucially, a certain velocity in the mixed lubrication regime can produce a hydrodynamic pressure peak at the wedge and drive the rehydration inflow to overcome the extrusion. At lower sliding velocities in the boundary lubrication regime, inflows are insufficient to counteract fluid exudation, whereas at higher velocities in the hydrodynamic lubrication regime, the inlet wedge effect would diminish. These results suggest that tribological rehydration offers a novel approach to enhancing load-bearing capacity and maintaining lubrication in the hydrogels.

Influence of Dopants on Pt/Al2O3-Based Monolithic Catalysts for Autothermal Oxidative Coupling of Methane

Autothermal oxidative coupling of methane (OCM) is a highly attractive approach for methane utilization. If platinum-based catalysts are operated in short-contact-time reactors with high space velocities, high methane conversion can be achieved. Using a 1 wt.% Pt/Al2O3 catalyst as a benchmark, the present study elucidates how different dopants, namely Ni, Sn, and V2O5, affect the OCM reaction. Kinetic catalyst tests reveal that acetylene (C2H2) is the predominant C2 product, irrespective of the catalyst formulation or operation conditions. Furthermore, the use of bimetallic catalysts allows either for the maintenance or even the improvement of the C2 selectivity during OCM, which is attributed to synergistic effects that occur when expensive Pt is partially replaced by cheaper dopants. In particular, the 1 wt.% Pt/Al2O3 reference catalyst yielded a maximum C2 selectivity of 8.2%, whereas the best-performing doped sample 0.25 wt.% Pt 0.75 wt.% V2O5/Al2O3 yielded a total C2 selectivity of 11.3%.

Gradient-Wettable Multiwedge Patterned Surface for Effective Transport of Droplets against the Temperature Gradient.

With the rapid advancement of electronic integration technology, the requirements for the working environment and stability of the heat dissipation equipment have become increasingly stringent. Consequently, studying a high-efficiency gas-liquid two-phase heat transfer surface holds significant importance. Aiming at the limited liquid transport performance caused by the temperature gradient in the heat transfer process, this paper combines the wetting gradient with the shape gradient and proposes a gradient-wettable multiwedge patterned surface, where droplets can be transported over long distances and at high velocities. In this paper, the effect of the average wetting gradient on droplet transport performance is investigated by designing a multiwedge hydrophilic pattern and adjusting the wetting properties of the hydrophobic region. The study focuses on the temperature gradient resistance of gradient-wettable, multiwedge patterned surfaces, providing a mechanistic explanation of the surface's ability to resist temperature gradients through theoretical analysis. It is shown that the gradient wettability multiwedge patterned surface has better resistance to the temperature gradient that hinders the droplet movement, and the droplets can still achieve transport of ∼38 mm at an average speed of ∼158 mm/s under the temperature gradient of 0.59 °C/mm. The research in this paper provides some insights into the application of temperature gradient resistance on heat transfer surfaces and contributes to heat dissipation methods for electronic integrated environments.

Influence of Detonation Spraying Parameters on the Microstructure and Mechanical Properties of Hydroxyapatite Coatings.

The process of osteointegration depends significantly on the surface roughness, structure, chemical composition, and mechanical characteristics of the coating. In this regard, an important direction in the development of medical materials is the development of new techniques of surface modification and the creation of bioactive ceramic coatings. Calcium-phosphate materials based on hydroxyapatite have been proposed as bioactive ceramic coatings on titanium implants for the effective acceleration of bone tissue healing. To obtain bioactive ceramic coatings, pulse power sources are best suited, namely detonation spraying, in which the energy of the explosion of gas mixtures is used as a source of pulse action. The pulse mode of operation in the detonation spraying method is preferable for the formation of bioactive ceramic coatings. It provides a high velocity of hydroxyapatite particles, which promotes their effective fixation on the titanium substrate, while minimizing the heating of the material. This approach preserves the substrate structure and improves the coating adhesion. Four different types of coatings with varying O2/C2H2 molar ratios, ranging from 2.6 to 3.7, were obtained using detonation spraying. Powders and obtained coatings of hydroxyapatite were studied by Raman spectroscopy and XRD structural analysis. The results of XRD phase analysis showed the partial conversion of the hydroxyapatite phase to the α-tricalcium phosphate (α-TCP) phase during the detonation spraying process. The results obtained by Raman spectroscopy indicate that hydroxyapatite is the main phase in coatings. All hydroxyapatite-based coatings exhibited hydrophobic properties, which was confirmed by contact-angle values above 90° in wettability tests, characteristic of hydrophobic surfaces. The adhesive strength of the coatings was measured by the scratch test method. Tribological tests were conducted using the ball-on-disk method under both dry conditions and in Ringer's solution. This approach enabled the evaluation of wear resistance and friction coefficient of the coatings in different environments, simulating both lubrication-free conditions and those resembling physiological environments.

High-performance near-substrate heat sink with Tesla-like rotor-wing microchannel for chiplet cooling application

Microchannel heat sink provides a viable solution for enhancing thermal management in high-power chiplets. However, in consideration of cooling efficiency, low pressure drop, cost-effectiveness and reliability, it’s challenging to create an effective heat sink for a million-watt chip. Inspired by Tesla structure, this study introduces a Tesla-like rotor-wing microchannel (TRWM) to boost cooling performance. Due to the features of main channels, branch channels, and micro-islands in TRWM design, fluid in microchannel is effectively mixed and stirred with varied flow patterns, high temperature gradients and significant velocity gradients, which enhances the cooling capacity through precise fluid dynamics adjustment. Three different TRWMs are designed and compared by simulations. And the simulated results show that TRWM of 135° model achieves a maximum heat flux of 1514 W cm−2 @0.1 cm2 under a 60 K temperature rise, improving cooling efficiency by 19.4 % over the traditional channel design with 1221 W cm−2 @0.1 cm2. And then, the TRWM is fabricated using Ultraviolet Lithgraphie Galvanoformung Abformung (UV-LIGA) and bonding processes. Ultimately, the fabricated 135° TRWM sample demonstrated a heat dissipation capacity of up to 1446 W cm-2 @0.1 cm2 with a temperature increase of 60 K, which corresponds well with the simulated results. Moreover, the discrepancy between the actual and simulated values is less than 6.3 % under the same conditions. This performance provides a practical design solution for chiplet cooling and highlights the potential of bioinspired microfluidics.

Thermochemical heat storage and material behavior of calcium hydroxide fine powder in a fluidized bed reactor

The Ca(OH)2/CaO reaction has attracted much attention in thermochemical heat storage. However, commercial Ca(OH)2 is usually offered as a fine powder that tends to agglomerate in the fluidized bed and affects heat storage performance. The experimental study on these issues is incomplete. In this paper, a fluidized bed thermochemical heat storage test system is built to study the heat storage and release process of Ca(OH)2 fine powder. The experimental results indicate that the water vapor is the primary factor in agglomeration. The increase in heat storage temperature, fluidization velocity, and inlet water flow rate can all reduce reaction time. However, the effect of heat storage temperature on agglomeration is negligible. While a high fluidization velocity can alleviate the agglomeration, a high inlet water flow rate intensifies the agglomeration. The heat storage density decreases by about 12 % after 5 cycles owing to the material loss, while the agglomeration is trending upward. The specific surface area and specific pore volume decrease by 46.59 %, and 13.89 % respectively, which slows down the heat storage process. This work can serve as a reference for alleviating the agglomeration, as well as the operation and adjustment of the fluidized bed.

Bubble boundary R-CNN: A multitask model for segmenting and reconstructing overlapping bubbles

When measuring the dynamic characteristics of bubbles using image-based methods, the images including complex overlapping of bubbles with irregular shape pose a huge challenge to current bubble reconstruction algorithms. Based on the Mask R-CNN architecture, a multitask model “Bubble Boundary R-CNN” is proposed for detection, segmentation and shape reconstruction of overlapping bubbles with high deformation at high gas velocities. By leveraging shared deep features from detection and segmentation, model achieves flexible bubble reconstruction and accurate size distribution extraction from high gas velocity bubble flows. To overcome the limitations of Mask R-CNN and address the challenges posed by high-deformation and overlapping bubbles, a semantic segmentation auxiliary head and the Boundary-preserving Mask Head (BMask Head) are introduced to enhance edge information and extract bubble boundary features. Additionally, an Overlapping Boundary Prediction Network (OBPN) is proposed to reconstruct boundary features that are lost due to bubble occlusion and predict the complete bubble shapes. The optimized model shows its ability to flexibly and accurately reconstruct overlapped and deformed bubbles by varying occlusion rates and circularity. The new model has also proven its reliability when applied to bubble images from a bubble column at gas velocities of up to 0.067 m3/s. In future work, more efforts are needed to further enhance the detection capability of the model and reduce missed and multiple detections at high gas velocity.

Optimal design and experimental testing of EMPI system for plasma disruption mitigation on J-TEXT

Plasma disruptions can cause significant damage to tokamak. Currently, the primary method for mitigating disruptions is the injection of a substantial amount of impurities. The electromagnetic injection method offers a high injection speed and rapid response time, making it a promising technique for impurity injection. The first Electromagnetic Pellet Injection System (EMPI), developed by the J-TEXT team, is capable of launching pellets at high velocities and features a specialized deceleration rail that ensures safe separation of the armature and pellet. However, this system lacks an armature recovery device and a vacuum system. In this work, a second generation EMPI has been developed, which has a vacuum system and a curved recovery rail. The curved recovery rail facilitates the smooth retrieval of the armature, enhancing the safety of the recycling process. Additionally, this new system employs an augmented rail design that improves launch performance. Test results indicate that the maximum current of the new EMPI has been reduced by approximately 60%, while the maximum launch speed has increased by around 20%.

Space Weather Forecasts of Ground Level Space Weather in the UK: Evaluating Performance and Limitations

AbstractGeomagnetically Induced Currents (GICs) are a severe space weather hazard, driven through coupling between the solar wind and magnetosphere. GICs are rarely measured directly, instead the ground magnetic field variability is often used as a proxy. Recently space weather models have been developed to forecast whether the magnetic field variability (R) will exceed specific, extreme thresholds. We test an example machine learning‐based model developed for the northern United Kingdom. We evaluate its performance (discriminative skill and calibration) as a function of magnetospheric state, solar wind input and magnetic local time. We find that the model's performance is highest during active conditions, for example, geomagnetic storms, and lowest during isolated substorms and “quiet” intervals, despite these conditions dominating the training data set. Correspondingly, the performance is high when the solar wind conditions are elevated (i.e., high velocity, large total magnetic field strength, and the interplanetary magnetic field oriented southward), and at a minimum when the north‐south component of the magnetic field is highly variable or around zero. Regarding magnetic local time, performance is highest within the dusk and night sectors, and lowest during the day. The model appears to capture multiple modes of magnetospheric activity, including substorms and viscous interactions, but poorly predicts impulsive phenomena (i.e., storm sudden commencements) and longer timescale coupling processes. Future models of mid‐latitude magnetic field variability will need to effectively use longer time intervals of unpropagated (i.e., observations from L1) solar wind to more completely describe the magnetospheric conditions and response.

Molecular dynamics simulation of friction in DLC films with different Cr doping levels

This study systematically investigates the impact of varying Cr doping levels on the friction properties of DLC films using molecular dynamics simulations. The results demonstrate that under identical friction velocities and load conditions, the friction force of DLC films significantly decreases when the Cr doping content reaches 16.5 %. High Cr doping levels lead to the formation of Cr atomic clusters at the interface, hindering contact and reducing the number of interface bonds. These clusters act as lubricants, filling the interface gaps and thereby reducing the friction force. Internal stress calculations indicate that Cr doping effectively reduces the average internal stress of DLC films. For DLC films with lower Cr doping levels, the friction force exhibits similar trends under different friction velocities, while films with higher Cr doping levels show a more pronounced response, with friction force increasing at higher velocities. Increasing the load significantly raises the friction force, especially for DLC films with higher Cr doping levels. Furthermore, high Cr doping levels under high loads lead to significant structural damage and adhesive wear. This study provides theoretical and technical references for optimizing the friction performance of DLC films.

Enhancing Thermal–Hydraulic Performance in Nuclear Reactor Subchannels with Al2O3 Nanofluids: A CFD Analysis

In this paper, the performance of aluminum-based nanofluids with a possible application in pressurized water reactors is numerically investigated. A 605 mm long 4-rod array square (2 × 2) subchannel geometry with a uniform heat flux of 50 kW/m2 has been used in CFD simulation. This analysis has been carried out using the RNG k-epsilon turbulence model with standard wall function in ANSYS FLUENT 2022R1. The impact of various flow conditions and nanofluid concentrations has been examined. The effects of variable velocities on nanofluid performance have been studied using different Reynolds numbers of 20,000, 40,000, 60,000, and 80,000. The analysis was conducted with Al2O3/water nanofluid concentrations of 1%, 2%, 3%, and 4%. A comparison of the Nusselt number based on five different correlations was conducted, and deviations from each correlation were then presented. The homogeneous single-phase mixer approach has been adopted to model nanofluid characteristics. The result shows a gradual enhancement in the heat transfer coefficient with increasing volume concentrations and Reynolds numbers. A maximum heat transfer coefficient has been calculated for nanofluid at maximum volume concentrations (ϕ = 4%) and highest velocities (Re = 80,000). Compared to the base fluid, heat transfer was enhanced by a factor of 1.09 using 4% Al2O3. The Nusselt number was calculated with a minimal error of 3.62% when compared to the Presser correlation and the maximum deviation has been found from the Dittus–Boelter correlation (13.77%). Overall, the findings suggest that aluminum-based nanofluids could offer enhanced heat transfer capabilities in pressurized water reactors.

Particle impact in high-pressure homogenizer valves – a step towards understanding wear and cell breakup in food and beverage processing

In many liquid food processing applications using high-pressure homogenizers (HPHs), particles impact with the solid surfaces of the homogenization device. This may lead to costly wear. For some applications, impact is also postulated to control the desired cell disruption. This contribution uses computational fluid dynamics to study impact of particles on solid surfaces in HPHs, as a step towards design optimization. Effects of particle diameter, density, homogenizing pressure, and impact distance are studied. Results show impacts both on the forcer and on the impingement ring. Few particles hit the forcer, at low velocities and with low angles (‘bracing impacts’). More particles hit the impact ring. These impacts are with higher velocities and typically occur head-on. The effect of both homogenizing pressure and impact ring distance scales according to a previously suggested stagnation pressure model. Results are discussed in the light of wear and cell disruption observations.

Self-reported physical activity and gait in older adults without dementia: A longitudinal study.

Physical activity (PA) is associated with higher gait speed. We aimed to examine the associations between PA and change in spatial and temporal gait measures as well as fall risk in community-dwelling individuals free of dementia. Longitudinal study among 4173 individuals aged ≥50 years (mean age 71 years; 2078 males; median follow-up 4 years) enrolled in the Mayo Clinic Study of Aging. Self-reported late-life PA was used to calculate overall PA and moderate-vigorous PA (MVPA) scores. Gait was assessed using GAITRite® and Zeno™ systems. Incident falls information was based on diagnostic codes retrieved from medical records. We ran linear mixed effects models to examine associations between z-scored PA variables and longitudinal gait parameters, adjusted for age, sex, education, body mass index (BMI), medical comorbidities, and including interactions between PA and time since baseline. In secondary analyses, we calculated Cox Proportional hazard models with age as time scale predicting incident falls by PA, adjusting for sex, education, BMI, medical comorbidities, and falls history. At baseline, higher PA was associated with higher velocity (overall PA: estimate 2.9935; MVPA: 2.2961; p < 0.001), higher cadence (overall PA: 1.0665; MVPA: 0.9073; p < 0.001), greater stride length (overall PA: 2.0805; MVPA: 1.4726; p < 0.001), shorter double support time (overall PA: -0.0257; MVPA: -0.0205; p < 0.001), and lower stance time variability (overall PA: -0.0204, p < 0.001; MVPA: -0.0152; p = 0.006). Overall PA was longitudinally associated with less decline in cadence, and MVPA with less increase in intraindividual stance time variability. Overall PA (Hazard ratio 0.892, 95% confidence interval 0.828-0.961, p = 0.003) and MVPA (HR 0.901; 95% CI 0.835-0.973, p = 0.008) were associated with a decreased risk of incident falls. Late-life PA was associated with favorable gait outcomes and decreased risk of incident falls. Thus, late-life PA may help to maintain gait performance and decrease fall risk in old age.

In Vitro Vascularization Improves In Vivo Functionality of Human Engineered Cardiac Tissues

Engineered human cardiac tissues hold great promise for disease modeling, drug development, and regenerative therapy. For regenerative applications, successful engineered tissue engraftment in vivo requires rapid vascularization and blood perfusion post-implantation. In the present study, we engineered highly functional, vascularized cardiac tissues (“cardiopatches”) by co-culturing human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) and endothelial cells (hiPSC-ECs) in optimized serum-free media. The vascularized cardiopatches displayed stable capillary networks over 4 weeks of culture, the longest reported in the field, while maintaining high contractile stress (>15 mN/mm2) and fast conduction velocity (>20 cm/s). Robustness of the method was confirmed using two distinct hiPSC-EC sources. Upon implantation into dorsal-skinfold chambers in immunocompromised mice, in vitro vascularized cardiopatches exhibited improved angiogenesis compared to avascular implants. Significant lumenization of the engineered human vasculature and anastomosis with host mouse vessels yielded the formation of hybrid human-mouse capillaries and robust cardiopatch perfusion by blood. Moreover, compared to avascular tissues, the implanted vascularized cardiopatches exhibited significantly higher conduction velocity and Ca2+ transient amplitude, longitudinally monitored in live mice for the first time. Overall, we demonstrate successful 4-week vascularization of engineered human cardiac tissues without loss of function in vitro, which promotes tissue functionality upon implantation in vivo. Statement of SignificanceComplex interactions between cardiac muscle fibers and surrounding capillaries are critical for everyday function of the heart. Tissue engineering is a powerful method to recreate functional cardiac muscle and its vascular network, which are both lost during a heart attack. Our study demonstrates in vitro engineering of dense capillary networks within highly functional engineered heart tissues that successfully maintain the structure, electrical, and mechanical function long-term. In mice, human capillaries from these engineered tissues integrate with host mouse capillaries to allow blood perfusion and support improved implant function. In the future, the developed vascularized engineered heart tissues will be used for in vitro studies of cardiac development and disease and as a potential regenerative therapy for heart attack.

Dynamic characterization of the flow field of air classifier disturbed structures and application to efficient separation of fly ash

Classification is crucial for the resource utilization of fly ash, impacting both utilization rates and product quality. This study introduces an enhanced flow field structure in a perturbed rotating centrifugal air classifier by optimizing toothed and tail blade designs for efficient fly ash classification. Using numerical simulations and experiments, we examine the flow field performance and separation efficacy at various speeds, and employ Dynamic Mode Decomposition (DMD) for modal analysis. Results show the toothed blade, angled at 35°, produces small-scale turbulence with high pressure and velocity, while the tail blade’s rightward bend induces large-scale vortices, aiding flow control. Modal analysis highlights that both Drs-types 1 and 2 predominantly exhibit weakly attenuated modes. Optimal classification occurs at Rs = 950rpm and fv = 0.3kg/s, with both Drs-types surpassing the original structure in effectiveness and pressure. These findings provide new directions for industrial applications and the design of cyclone air classifiers.

Effect of explosives charges types on the jet characteristics, penetration performance and fragmentation patterns of shaped charges

Different explosive materials have been studied numerically and experimentally to assess the efficiency of a small diameter shaped charge in terms of produced jet characteristics and penetration depth into RHA steel targets. 26 different explosives have been simulated numerically using Autodyn hydrocode, whereas recommended explosives have been loaded into small diameter shaped charges by pressing technique and tested by static firing against RHA targets in order to validate the numerical calculations. The numerical analysis has presented an intensive global view about the variation of the shaped charge jets as a potential of the loaded explosive charge efficiencies. A successful trial has been performed to measure the shaped charge jet velocity using detonation velocity VOD 812 apparatus, where its measured value was only 3.6% different from the numerical one for HMX-V5 explosive. Besides, TITAN (L3) flash X-ray radiograph has also been implemented to explore the jet profile using the same explosive type and to measure its jet tip velocity, which has only 2.1% different from that estimated numerically. Extensive fragmentation analysis has been presented, which showed increase in both the fragment number and the fragment speed when the used explosive charge is of high detonation velocity. CL-20 explosive exhibited the largest jet tip velocity and its scaled collapse velocity was found to be 140% of TNT explosive. The calculated average fragment speed has been validated and the measured fragment speed has only 2.3% difference when compared to the SPH calculations.

Outcomes Of Early And Delayed Intervention Of Maxillofacial Trauma

Background: Maxillofacial trauma is routinely evaluated on the basis of high and low velocity injuries, types of fractures in the literature. On the other hand, we have evaluated them on the basis of timing of surgery after trauma and their outcomes. In India RTA (Road traffic accidents) scenario is quite different from other countries. The highway traffic consists of a variety of vehicles from a cyclist, a two-wheeler, a four-wheeler to a heavy loaded truck. Animals like cows and dogs frequent the highways. Hence, we have classified the patients based on Single jaw and Panfacial fractures with or without the presence of extensive soft tissue injuries. Materials and Methods: In this retrospective record-based descriptive study, 200 patients that were treated at Sri Aurobindo Hospital between January 2023 to July 2024 for maxillofacial trauma were reviewed. Of which 176 patients were surgically operated, averaging 30 years of age and ranging from 12-70 years. For the purpose of our study these 176 patients were categorized into two groups, first of single jaw fractures(108 patients) and second of Panfacial fractures (68 patients). Single Jaw fractures were further divided as mandibular (84 patients); maxilla &amp; zygomaticomaxillary complex fractures (24 patients). These were further evaluated and categorized as those patients who were treated within 72 hours (Early) and after 72 hours (Delayed) following injury. All patients of both the groups were treated with open reduction and internal fixation. Individual complications that of soft tissue dehiscence, plate/bone exposure, bone graft rejection, oroantral/palatal fistula, non-union of fractured segments, infections were analyzed. These complications were again assessed on the basis of their timing; those occurring within 72 hours and those after 72 hours. Results: When each type of complication was compared and evaluated, there was significantly more complication noted among delayed group than in early group. Conclusion: The restoration of the aesthetics and functionality of the face, post-trauma is a critical and an arduous task. As the anatomical complexity of the face must be addressed, timely intervention to achieve optimal functional and aesthetic outcomes is pertinent. Thus, the treatment should be done at the earliest when feasible

Effect of solid loading and particle size on bubble behavior and flow field structure in slurry bubble column

The complexity of fluid dynamics in a slurry bubble column reactor introduces significant uncertainty in reactor design and scale-up. This paper investigates the hydrodynamic performance of the gas–liquid–solid system within the reactor by employing computational fluid dynamics-population balance modeling numerical simulations alongside particle image velocimetry (PIV) experiments. The effect of superficial gas velocity and particle conditions on the overall gas holdup were analyzed, focusing on the effects of particle size and solid concentration on bubble size, bubble behavior, flow field structure, and local gas holdup distribution at high superficial gas velocities. Bubble size was evaluated using calibrated image measurements, and the impact of varying solid conditions was thoroughly explored. The results revealed that an increase in solid size correlated with higher gas holdup and smaller bubble sizes, whereas a greater solid concentration resulted in decreased gas holdup and larger bubble sizes. PIV experiments indicated that bubbles exhibited a tendency to migrate toward the central region of the reactor, leading to the formation of larger bubbles that accelerated the rise of surrounding bubbles, while smaller bubbles near the wall moved downward. As the slurry bed height increased, the range of local gas holdup distribution expanded, resulting in a symmetrical distribution of radial local gas holdup in the fully developed stage at a height of 0.16 m.

Impacts of low-temperature heat release on unstretched laminar burning velocity in advanced flex-fuel gasoline-ethanol engines

Improving brake thermal efficiency (BTE) of flex-fuel engines can contribute to decarbonizing conventional and hybridized vehicles running on spark-ignited (SI) engines. High compression ratio (CR) and burning velocity under exhaust gas recirculation (EGR) conditions can improve the engine BTE. Ethanol fuel, which has been attracting increasing attention recently, can improve brake thermal efficiency due to its high-octane number and fast laminar burning velocity (LBV). With higher CRs, low-temperature heat release (LTHR) occurs in the unburned mixture, which affects the compositions, oxidation, and in-cylinder temperature. Such thermodynamic changes on unstretched LBV have not been thoroughly investigated, especially in production-intent next-generation flex-fuel engines. This study aims to clarify the LTHR impacts on LBV under EGR conditions using ethanol-blended gasoline surrogate fuels. The testbed used a single-cylinder SI engine fueled by E0 (gasoline surrogate), E20 (20 % ethanol + 80 % E0 by volume), E40, E60, E85, and E100. Detailed chemical reaction calculations were conducted using the boundary conditions obtained from production-intent, strong-tumble flow, and flex-fuel engine experiments. This work predicted LTHR in an unburned mixture using a zero-dimensional detailed chemical reaction calculation. LBV is predicted by a 1D kinetic laminar flame code. As a result, LTHR proceeds before the main combustion. The results show that the temperature increase associated with LTHR increases the burning velocity, while the partial oxidants decrease the burning velocity. Moreover, this work examined higher CRs using detailed chemical reaction calculations, and the results show that fuels with higher ethanol blending ratios can increase LBV in the late combustion phase.