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The changes in the flow field and combustion characteristics induced by the mode transition process of a turbine-based combined cycle (TBCC) engine may lead to failure of the mode transition. In this paper, the cold mixing characteristics, combustion efficiency, and cold and thermal flow losses of a TBCC multibypass combustor with a double-mixer configuration are investigated through numerical simulations, and the correlations between the thermal mixing efficiency and combustion efficiency is established. The results show that the thermal mixing efficiency of double-lobed mixer combustors is better at low ram inlet Mach numbers, but the ring-plus-lobed mixer combustor has better mixing and combustor characteristics at relatively high Mach numbers. However, the effect of the turbo core inlet Mach number on the combustion efficiency is not regular. The spacing between the double mixers that maximizes the mixing and combustion characteristics of the combustor is 75 mm. With increasing of expansion angle of the lobed mixer, the thermal mixing efficiency and combustion efficiency increase by 31.9 % and 23.3 %, respectively. In addition, the positive correlation coefficient between combustion efficiency and thermal mixing efficiency caused by changes in the inlet Mach number is greater than that caused by changes in structural parameters. • In-phase and antiphase double-lobed mixers are adapted to various combustor lengths. • Double-lobed mixer has better mixing efficiency at low ram inlet Mach numbers. • The spacing between double mixers that maximizes combustor characteristics is 75 mm. • Correlations between cold mixing and combustion characteristics is established. [ABSTRACT FROM AUTHOR]

Interstage combustion is known for its small axial distance, high combustion efficiency and low lean blowout boundary. However, in a compact space, the distance between the fuel injection location and the wall is confined, and the high-temperature wall may affect the fuel distribution and in turn affect the combustion efficiency. In this study, an experiment of kerosene single-droplet evaporation was conducted, and the fuel distribution in an interstage combustor was numerically simulated. The experimental results showed that the evaporation rate of fuel droplets decreased with increasing distance from the high-temperature wall, and the influence of the lower wall on fuel evaporation was greater than that of the sidewall. The fuel evaporation rate at the high-temperature position within the nonuniform wall temperature field was relatively high. The numerical simulation results indicated that with increasing temperature, the effect of the wall on fuel evaporation increased, as did the uniformity of the fuel distribution. The direction of the temperature gradient imposed the greatest effect on the fuel distribution under nonuniform temperature conditions. This will facilitate the selection of the optimal ignition location within the cavity to achieve efficient combustion. Moreover, it's possible to control the fuel distribution by adjusting the wall temperature. • The kerosene droplet evaporation experiment was conducted in the near-wall area. • The lower wall has a stronger influence on fuel evaporation than the side wall. • Increasing the temperature can improve the uniformity of fuel distribution. • The direction of the temperature gradient has an impact on the fuel distribution. [ABSTRACT FROM AUTHOR]

[Display omitted] • A single industrial camera was used to obtain the morphologies of aggregate particles in multiple views. • A general regression neural network was adopted for classification of aggregate particles. • Different equivalent geometric models for aggregate result in different multi-view shape features. • The accuracy of aggregate particle classification can be improved by increasing the frame rate. Aggregate is an important component of asphalt mixtures, and its shape has a significant influence on the road quality. In this study, a single industrial camera was used to collect images of aggregate particles during falling; then, their morphologies obtained in multiple views were analyzed. Using the equivalent geometric model, four shape characterization parameters—area variety factor, minor diameter variety factor, maximum elongation factor, and Strip-Block area variety factor—were proposed to compose the multi-view shape feature. On this basis, a general regression neural network was adopted to realize the classification of aggregate particles. The results show that the aggregate classification is slightly different when using different equivalent geometric models, while the aggregate shape can be effectively classified. The accuracy of aggregate classification can be improved by fusing parameters from different equivalent models using principal component analysis; another way is through increasing the frame rate of image collection that may increase the number of views. In general, the findings indicate that the proposed detection method can be applied to actual road engineering, which is of great significance to guarantee pavement quality. [ABSTRACT FROM AUTHOR]

Turbine-based combined cycle (TBCC) engines are characterized by strong nonuniformity flow in the turbine outlet and mode transition involving multiple bypasses, which may lead to failure of mode transition. In this paper, the mixing characteristics and flow losses of a TBCC multibypass combustor with a double-mixer configuration under nonuniform velocity and temperature inlet conditions are investigated through numerical simulation. The results show that the antiphase double-lobed mixer has a higher mixing efficiency than the in-phase double-lobed mixer at x/h < 0.8 (x/h are dimensionless axial coordinates), and the total pressure loss is greater; moreover, the mixing efficiency is reversed, and the total pressure loss is basically the same at x/h > 0.8. For both nonuniform velocity and temperature conditions, the mixing efficiency at peak profiles less than 50% is lower than that at the uniform inlet. With increasing velocity nonuniformity, the total pressure loss cost of increased mixing characteristics increases. The effect of the variation in the airflow velocity in the combustor on the total pressure loss is greater than that of the variation in airflow mixing characteristics when the mass flow rate in the combustor is changed. The change in mixing characteristics caused by the nonuniform temperature inlet profile is due to the temperature distribution and is independent of the type and performance of the mixer. [ABSTRACT FROM AUTHOR]

The fuel atomization and ignition characteristics of an afterburner under subatmospheric pressure are important foundations for expanding the operating range of the afterburner at high flight altitudes. In this work, the lean ignition limits of the afterburner at subatmospheric pressure were obtained through experiments, and the fuel droplet size distribution and ignition process in the afterburner were acquired using a laser particle sizer and a high-speed camera. The results showed that the ignition equivalence ratio increased as the inlet pressure decreased and was lowest when the flame stabilizer blockage ratio was 0.3. When the inlet pressure of the combustor decreased from high pressure to subatmospheric pressure, the Sauter mean diameter (SMD) range of the fuel droplets increased from 60∼110 μm to 100∼190 μm due to the increase in the ignition equivalence ratio and the deterioration of the fuel atomization characteristics. Under subatmospheric pressure, the flame residence phase time in the ignition process decreases significantly, while the flame intensity fluctuates more dramatically during the flame growth phase due to the decrease in the equivalence ratio of the gaseous phase, the larger fuel droplet size, and the uneven fuel distribution. When the inlet pressure is high pressure, the flame propagates from the ignition position to the trailing edge of the flame stabilizer first and anchors within the shear layer behind the flame stabilizer, whereas under subatmospheric pressure, the flame does not propagate to the anchoring point in the first place, which is one reason for the difficulty of ignition of combustors under high-altitude conditions. [ABSTRACT FROM AUTHOR]

• New configuration designs of hydrogen combustion chamber based on micro-mix combustion are proposed and studied. • New configurations increase the normalized energy density without an obvious increase in NO x emissions. • Flow field physics parameters in different configurations were discussed. • The follow-up research questions are summarized. In this study, the configurational characteristics of a new type of hydrogen staged combustion chamber based on the principle of a micromix combustor were numerically studied. Thus, providing a reference for the staged configuration design of hydrogen combustors. The effects of the staged configuration, the connection modes between the middle panel and the front and rear stages of combustors with the staged configuration, the power distribution of the front and rear stage combustors, and the symmetry of the staged configuration on the flow performance and combustion performance in the combustion chamber were studied from various aspects. The research results show that compared with the conventional configuration of a micromix combustion chamber, the new staged hydrogen combustor designed with the application of protective panels and a suitable flow path structure can influence an increase in the normalized energy density at a small cost of NO x emissions, which has wide application prospects and value for further research. [ABSTRACT FROM AUTHOR]

Fuel injection schemes based on close-coupled injection are usually used in compact combustor design. In this paper, an experimental method is adopted to study the fuel spray Sauter mean diameter (SMD) and combustion characteristics when different fuel injection schemes, strut cavity structures, and fuel/air jet momentum flux ratios are applied. Four fuel injection schemes based on close-coupled injection schemes and premixed injection schemes are proposed for use in a compact integrated combustor to compare the effects of the fuel injection schemes. Three struts are designed to study the influence of the cavity on the close-coupled fuel injection scheme. The results show that the spray and combustion characteristics of the close-coupled injection scheme differ from those of premixed injection schemes. Specifically, the SMD in the close-coupled scheme is in the range of 70-150 μm, which is larger and more uneven than that of the premixed scheme (15-40 μm), and the close-coupled scheme has better ignition performance at a temperature of 450 K. The flame structure of the close-coupled injection schemes with reverse mainstream inside the cavity has better radial uniformity, but more fuel is attached to the strut surface, resulting in a lower flame intensity and increased diffusion flame. The cavity on the strut sidewall can effectively promote fuel atomization by approximately 25% when the jet momentum flux ratio is low, make the fuel more uniform in the strut radial direction, increase the flame intensity, and reduce diffusion flame zone. In the close-coupled injection scheme, the large jet momentum ratio will lead to the collision and fusion of multiple fuel streams downstream of the struts, thus increasing the fuel droplet size and limiting the promoting effect of the strut wall structure. In summary, this paper provides further understanding of the combustor spray and combustion characteristics of different fuel injection schemes. [ABSTRACT FROM AUTHOR]

• Integration of solar energy and energy storage for heating and cooling systems. • Phase change materials as energy storage unit for the sustainable built environment. • Leaf vein bionic fins to enhance phase change material charging performance. • Efficient melting performance is achieved in thermal energy storage systems. • Non-dimensional quantities analysis for melting enhancement evaluation. In the present study, we investigated the effect of different structures of a novel leaf vein bionic fin and various arrangements in the tube on the complete melting time of phase change materials (PCM) in a triplex-tube thermal energy storage (TES) system. RT82 was adopted as the phase change material. The enthalpy-porosity method was employed for this numerical study. The numerical model was validated against experimental data from a previous reference. The simulation results demonstrate that the novel fins deliver significant reductions in the duration of complete melting. Based on fin-branched vein numbers of 1, 2 and 3, increasing the fin angle from 30° to 60° can reduce the complete melting time by up to 14.3%. Additionally, adjusting the fin arrangement can save up to 6.35% of the complete melting time. The proper arrangement of the fins can improve the heat transfer performance of the PCM. The non-dimensional quantities analysis of the calculated results shows that the melting time is negatively correlated with the non-dimensional angle. As the non-dimensional parameter, fin arrangement number decreases from 1, the complete melting time corresponding to the fins of different structures first decreases and then increases for the phase change material. [ABSTRACT FROM AUTHOR]

• Complete rectangular test section of afterburner with all typical components. • Fuel distribution and flow field in the whole space of afterburner test section. • The experimental system that can realize the wide working range of the afterburner. • The fuel spatial distribution is not sensitive to the change of pressure. • The fuel particle size at the vortex core section is the smallest. The fuel space distribution is a key factor in the combustion performance of afterburner. We have investigated the fuel space distribution and flow field in afterburner with all typical components. In this study, the complete afterburner test section of the afterburner is composed of a typical mixing diffuser, fuel supply system, flame stabilizer and heat shield. At the same time, we built an experimental system that enables a wide operating range of the afterburner. A temperature measuring rake, a pressure measuring rake, a Particle Image Velocimetry (PIV) system and a laser particle sizer were used to measure the flow field and fuel distribution in the combustor. It was found that the fuel particle size in the combustor space along the flow direction decreases, then increases and then gradually decreases. This is because the fuel particle size is smallest at the vortex nucleus in the recirculation zone after the stabilizer. The increase of the incoming Mach number will lead to an increase in the range of the recirculation zone behind the stabilizer, thus making the fuel distribution in the entire combustor more uniform. When the diffusion ratio is increased from 1.0 to 1.4, a significant asymmetric counter-rotating vortex pair can be formed after the stabilizer. Compared with the blockage ratio of 0.2 and 0.4, when the blockage ratio is 0.3, the fuel particle size will be reduced by 24%–32%. The spatial distribution of the fuel is not sensitive to pressure changes, and under the experimental conditions, the fuel particle size will increase by 9–25 µm with the decrease of pressure. In summary, when the diffusion ratio is 1.4 and the blockage ratio is 0.3, the afterburner has the most reasonable fuel distribution and flow field, which is conducive to the stable and efficient operation of the afterburner.. [ABSTRACT FROM AUTHOR]

We developed a theoretical model based on 8-band k.p method to calculate the temperature-dependent band structure of Ge x Sn 1-x /Ge quantum well. The E-k dispersion relation is calculated using two different sets of Luttinger-Kohn’s Hamiltonian effective mass parameters. The spontaneous emission rate spectra including and excluding the contribution of indirect L subbands are compared. Instead of the expected direct band-gap energy transition, we observe indirect band-gap energy transitions which are verified by having abnormal temperature-dependent spontaneous emission rate even for large Sn fraction up to 24%. This phenomenon can be explained by the effect of quantum restriction and build-in compressive strain through our model which are the main obstacles for realizing direct band-gap GeSn/Ge quantum well. [ABSTRACT FROM AUTHOR]

Ge x Sn 1-x is one of the most promising materials in optoelectronics for its direct band-gap nature. In this paper, we report high-quality Ge and Sn thin films deposited on Si (001) substrates by magnetron sputtering. We found that the growth power and chamber pressure affect the quality of the Ge and Sn thin films significantly but in different ways. By optimizing the deposition conditions, high quality Ge and Sn films are achieved. A clear peak of Ge (004) phase in the x-ray diffraction (XRD) pattern which indicates a high-quality Ge lattice formed is observed, and post-treatment like rapid thermal annealing does not significantly affect the quality of the thin films. [ABSTRACT FROM AUTHOR]

With the increased attention to low heat value gas fuels in recent years, research on NOx emissions from the combustors of low heat value gas fuels is necessary. This study introduces integrated learning algorithms to the NOx pollution emission prediction from gas turbine combustors. The combustor is a self-designed low heat value gas rich-quench-lean combustor and 92 sets of emission data have been obtained using simulation methods. The simulation data has been experimentally verified. The effect of four control parameters on NOx emissions has been investigated: inlet air temperature, inlet air mass flow rate, swirler installation angle, and combustor lean burn zone length. Pearson correlation coefficients show that four control parameters have very low correlations. The three integrated learning algorithms used in this study are the random forest regression algorithm, the extreme gradient boosting algorithm, and the natural gradient boosting algorithm. The hyperparameters of the three integrated learning algorithms are optimised using the Bayesian optimization algorithm. Three integrated learning algorithms are utilized to predict pollutant emission characteristics and the results show that NGboost provides the best predictions and Random Forest the worst, with NGboost suffering from overfitting problems. The results of the algorithm predictions were analyzed to understand the impact of different control parameters on the NOx emissions. A feature importance evaluation shows that the influence of inlet air temperature on NOx emissions far outweighs the other three parameters. • Random forest, XGboost, and NGboost for estimating NOx emissions of low heat value gas RQL combustor. • Accuracy Analysis of the developed models using statistical evaluation. • Analysis of the effect of different control parameters on NOx emissions. • NGboost surpasses in accuracy compared to the other algorithms. [ABSTRACT FROM AUTHOR]

Purpose: To retrospectively evaluate risk factors related to incomplete computed tomography (CT)-guided radiofrequency (RF) ablation of metastatic and primary lung tumors.Materials and Methods: This study included 93 patients with 147 tumors: 70 men, 23 women; median age 54 y (range, 19-81 y); 24 cases of primary lung tumors, 69 cases of metastases; average largest diameter of tumors, 1.8 cm ± 1.2 (range, 0.3-6.0 cm). Local efficacy was evaluated based on CT follow-up scans. Complete ablation rates (CARs) for tumors were calculated according to several variables; independent risk factors for local tumor progression (LTP) were examined by binary logistic regression analysis.Results: CAR of tumors was 60.54% within first 6 months after lung RF ablation; median interval of LTP was 1.5 months (mean, 1.3 months ± 1.0; range, 0 days to 3 months). Compared with tumors > 3 cm, CAR of tumors ≤ 3 cm was significantly higher (68.55% vs 17.39%, P < .001). CAR of tumors with complete ablation margin (AM) was dramatically higher compared with tumors with incomplete AM (74.77% vs 16.67%, P < .001). Among tumors with complete AM, CAR of tumors with shortest distance between outer edge of tumor and AM (ablative margin D) ≥ 5 mm was compared with tumors with ablative margin D 1-4 mm (85.96% vs 62.96%, P = .005). Multivariate regression analysis showed that lobulation and/or spicules, contact with blood vessels, and ablative margin D < 5 mm were independent risk factors for incomplete lung RF ablation. LTP was likely to develop at the edge of ablated lesions and especially the site of incomplete AM or shortest AM.Conclusions: RF ablation for lung cancers should be individualized based on tumor size, morphology, and tumor type to obtain an adequate AM. [ABSTRACT FROM AUTHOR]

• The interaction between the strut recirculation zone and cavity recirculation zone is the reason for the generation of the streamwise vortices. • Reasonable distribution of streamwise vortices is beneficial to the mass exchange between the cavity and mainstream and the uniformity of the combustor temperature. • An ultra-compact integrated combustor based on reasonable streamwise vortices distribution is designed, which has good flow and combustion characteristics. The combination of the strut and cavity is a common structural configuration for ultra-compact combustor in the gas turbine. The streamwise vortices inside the cavity play the role of stabilizing the flame and mass exchange in the spanwise direction, which is very important for the compactness and ignition performance. In this paper, the numerical simulations and the experiments were performed to study the influence of the combustor strut blocking ratio, cavity length-to-depth ratio, and strut inclination angle on the flow, the streamwise vortices distribution, as well as the combustion characteristics. We also discussed the generation of streamwise vortices and the effects of streamwise vortices on the flow and combustion performance. The results showed that the strut blocking ratio and cavity length-to-depth ratio mainly affect the strut recirculation zone and the cavity recirculation zone, the interaction of which is the key to the generation of the streamwise vortices. The reasonable distribution of the streamwise vortices promotes the mass exchange and the uniformity of the temperature distribution. In addition, the strut inclination angle has a great influence on the flow characteristics, and the forward-inclined strut is more conducive to combustion. Based on the obtained conclusions, a new design of ultra-compact integrated combustor is proposed, and it has improved flow and combustion performance. [ABSTRACT FROM AUTHOR]

The turbine-based combined cycle (TBCC) engine, as a hypersonic air-breathing propulsion system, involves the transition between multiple bypasses during flight. During the transition process, the flow field of the combustor is affected. In this paper, the flow field of a TBCC multibypass combustor with typical structures is investigated experimentally. The effect of the combined structure on the mixing performance, total pressure loss and flow field distribution downstream of the TBCC multibypass combustor is investigated by changing the inlet aerodynamic parameters and structural parameters of the combustor. The results show that the diffusion ratio increased from 1.0 to 1.4, the thermal mixing efficiency decreased by 24.7%, and the total pressure recovery coefficient increased by 1.86%. Meanwhile, the recirculation zone is wider, and the velocity distribution behind the stabilizer is more uniform. The thermal mixing efficiency increases by 55.8% with the increase in the down inclination (35°∼45°) of the lobe mixer. The mixing characteristic of the triple-bypass combustor is greater than that of the double-bypass combustor. There is an obvious "phase difference" of the vortex shedding in the double-bypass combustor at different spanwise sections, while it does not exist in the triple-bypass combustor. The turbulence disturbance degree in the recirculation zone behind the stabilizer in the triple-bypass combustor is slightly higher than that in the double-bypass combustor, but the velocity distribution is more uniform. The increase in inlet Mach number increases the flow losses and decreases the mixing performance. However, the thermal mixing efficiency is positively impacted with respect to the inlet temperature. In addition, the turbulent kinetic energy of the shear layer behind the stabilizer is large, while it is relatively small in the recirculation zone. There is not only spanwise vortices but also radial vortices behind the stabilizer. [ABSTRACT FROM AUTHOR]

Cooling technologies are playing critical roles in the development of advanced gas turbine combustors. The present experimental investigation has studied the effects of geometric factors such as gap distance, impingement hole diameter, and effusion hole arrangement on the wall temperature of a novel impingement-effusion cooling system. The wall temperature of the effusion plate was directly measured by high-precision thermocouples. The wall temperature distribution of the cooling unit was obtained by biharmonic spline interpolation based on the measured temperature data. The cooling performance of cooling systems with different structures under different working conditions was compared. The experimental results indicate that the increase of gap distance weakens the strength of impinging jet, and the overall cooling performance decreases, accordingly. The smaller the diameter of the impingement hole is, the weaker the cooling film is, leading to a poor overall cooling performance at the same cooling airflow. However, better overall cooling performance can be obtained at the same blowing ratio at the cost of much more cooling airflow. Dense and uniform effusion hole arrangement has a very favorable impact on improving the cooling film quality and cooling performance. [ABSTRACT FROM AUTHOR]

• Novel fin configurations to enhance phase change material charging performance. • Efficient melting performance is achieved in thermal energy storage systems. • Effect of fin structures on PCM melting performance was analysed. • PCM melting performance is improved by 66% with the novel fin configurations. Phase change material (PCM) has promising applications as an energy storage material in thermal energy storage (TES) systems. However, the low thermal conductivity of PCM limits its applications. To reduce the response time of TES systems, various configurations of fins are used to improve the heat transfer performance of PCM. The Y-structured fins utilize the Y-structure, a common structure in nature, and this study investigates the different structures of Y-shaped fins and the effect of HTF on melting time. A numerical research method based on the enthalpy-porosity method is adopted used for the study. The numerical model of the study is validated using previous experimental data. The simulation results have been obtained, including solid–liquid interface contours, isotherm contours, and evolution of the PCM liquid fraction. The results show that the melting process of the PCM is divided into three main stages and integrated solid fins within the PCM effectively reduce the melting time. Under certain operating conditions, reducing the fin thickness, increasing the fin angle, and increasing the HTF temperature can effectively reduce the PCM melting time. Transient heat transfer rates and dimensionless quantities are analyzed based on numerical results. This study provides potential applications of novel fin structures for new industrial products related to thermal energy storage and management. [ABSTRACT FROM AUTHOR]

We use eight-band k·p energy band structure model to help design novel GaInSb/AlGaInSb mid-infrared multiple quantum well (MQW) structures with an emitting mid-infrared waveband of 4-5 μm. Simulation results suggest that the number of quantum wells has little influence on the spontaneous emission rate and gain because of no strong coupling between quantum wells and they just simply follow scaling laws. The SiLENSe software module from STR-soft is used to investigate injection efficiency of the designed MQW structures. Simulation results indicate that the MQW structures offer better carrier confinement i.e. higher carrier injection efficiency compared with traditional bulk active regions which are currently used for mid-infrared LEDs and sensors. Experimental investigations show that the MQW LEDs with a seven wells structure show an increase of a factor 2 in wall plug efficiency and output power compared with conventional bulk LEDs at the same wavelength. [ABSTRACT FROM AUTHOR]

[Display omitted] • High temperature and low pressure air crossflow is one of inlet conditions of TBCC (Turbine Based Combined Cycle Engine) ramjet combustor when working at high altitude, but it is difficult to achieve because of the high requirements for the experimental system. • The dimensionless formula of jet trajectory of aviation kerosene injected into high temperature and low pressure air crossflow under single injection point and multi-injection point is fitted, and the SMD distribution of aviation kerosene along the flow direction is measured. • The effects of liquid/air momentum flux ratio, the number of radial and axial injection points on jet trajectory, penetration depth and Sauter mean diameter (SMD) distribution of aviation kerosene injected into high temperature and low pressure air crossflow were studied. There are the key factors affecting the combustion performance of the burner, including the jet trajectory, fragmentation and evaporation process of fuel jet in air crossflow and the uniform characteristics of fuel-gas mixing. In our experimental investigation, we studied the effects of liquid/air momentum flux ratio, the number of radial and axial injection points on jet trajectory, penetration depth and Sauter mean diameter (SMD) distribution of aviation kerosene injected into high temperature and low pressure air crossflow. Specifically, the pressure of air crossflow was set to 0.06–0.09Mpa, the speed 0.1 Ma, and the temperature 500 K. The jet trajectories of aviation kerosene were captured using a triggered image sensor (CCD) camera; the SMD of the aviation kerosene along the flow direction was measured using a Malvern laser particle sizer. The main observation results are: (1) The liquid/air momentum flux ratio is still the main factor affecting the penetration depth of liquid jet, fitting the dimensionless formula of jet trajectories of aviation kerosene injected into high temperature and low pressure lateral airflow. The fitting formula of single injection point and multiple injection points is y / d =0.4357 q 0.8384 x / d 0.4797 and y / d =0.513 q 0.8869 x / d 0.3661 respectively. (2) When the air crossflow pressure goes down, it will reduce the aerodynamic Weber number and increase the penetration depth, while it will reduce the Reynolds number of jet liquid and increase the average droplet size. For every 0.01Mpa decrease in air crossflow pressure, the aviation kerosene particle size SMD increases by 5–20 µm. (3) When the number of radial jet points goes up, it will enhance the interaction between CVP (Counter Rotating Vortex Pairs) and complex vortex system between multiple jets, which leads to rising growth rate of jet liquid column surface wave and the premature break-up, reducing the penetration depth by 15–25 mm; Compared with the single injection point, the influence of liquid/air momentum flux ratio on the jet trajectory and penetration depth of the multi-injection point becomes smaller, and the difference is more obvious under the condition of high liquid/air momentum flux ratio. [ABSTRACT FROM AUTHOR]

The adoption of vortex combustion technology is a relatively recent phenomenon. Among such technology is the trapped vortex combustor, which demonstrates a wide range of stable combustion and low pollutant emissions and accordingly has good application prospects in the field of aeroengines. A new type of single-cavity vortex combustor with air blast atomisers is introduced in this paper. This study conducted a combustion experiment that detailed the influence of the mainstream parameters, fuel parameters and combustion organisation on the combustion characteristics of the liquid-fuelled combustor. The results of this experiment suggest that this new type of vortex combustor has a reasonably designed structure and demonstrates good combustion performance. In addition, pollutant emissions under a low power state are predicted using a semi-empirical formula in which the effects of flow parameters, fuel parameters and atomisation characteristics of the fuel supply equipment are considered. Furthermore, the predicted value obtained is consistent with the experimental value. The results of this study provide a reference for the structural design and engineering application of the vortex combustor. [ABSTRACT FROM AUTHOR]

High-g combustion technology belongs to ultra-compact combustion technology. g-load is an important dimensionless parameter that affects the combustion performance of high-g ultra-compact combustors. In this paper, the numerical simulation method is used to indirectly and qualitatively analyze the relationships between the g-load and combustion results by studying characteristics including flow field, temperature field structure, combustion efficiency, and outlet temperature distribution. Research shows that reducing the radial incidence angle or increasing the primary and secondary flow ratios can increase g-load. The overall flow rate, temperature and the combustion efficiency in the combustion chamber will increase with the primary and secondary flow ratios because the combustion reaction will be promoted. There is an optimal radial incidence angle to make the combustion reach the optimal state. Increasing or decreasing the angle can affect the combustion negatively. The research results are beneficial to further study of the compact interstage combustor. [ABSTRACT FROM AUTHOR]

As a crucial component of aircraft engine combustors, the external-mixing prefilming atomizer exhibits significant advantages in enhancing combustion efficiency and reducing pollutant emissions. However, the intricate relationship between spray characteristics, droplet breakup mechanisms, flow fields, and geometric parameters of the external-mixing prefilming atomizer remains poorly understood. This paper presents a novel external-mixing prefilming atomizer, aiming to address this knowledge gap. Additionally, particle image velocimetry (PIV), high-speed Schlieren photography, and particle image analysis (PIA) measuring systems were employed to gain insights into the spray characteristics and droplet breakup mechanism of the external-mixing prefilming atomizer under various swirl flow fields. The obtained results reveal the formation of two distinct regions, namely a low-density area and a high-density area. Notably, the number of droplets in the low-density area, located within 0–2 cm from the central axis, is significantly lower compared to the high-density area situated further away from the central axis. The breakup of droplets in the low-density region is primarily attributed to the inner swirl airflow, while the outer swirl airflow induces droplet breakup in the high-density region. As the Reynolds number of the incoming flow increases, the air-liquid ratio (ALR) and Weber number also increase, thereby enhancing the fuel breakup effect. The Schlieren results reveal a two-stage spray development process. The initial stage is characterized by the dominant momentum of the dense spray, with the spray tip penetration (STP) exhibiting a relatively slow increase. The aerodynamic force of airflow plays a crucial role in governing the breakup and transport of droplets, leading to a linear variation of STP over time. As the swirl number increases, there is an enhanced momentum exchange between droplets and airflow, resulting in accelerated spray penetration and droplet breakup. [ABSTRACT FROM AUTHOR]

Abstract The development of modern energy technology made more demands for the performance of the gas turbine, and more attention was paid to the engine's stability, efficiency and cleanliness. The technical level of combustor played an important role in the engine's efficiency and emissions issues. In order to broaden the stable working range and reduce emissions of the combustor, the fuel concentration distribution and combustion characteristics of trapped vortex combustor was numerically and experimentally analyzed in this study. The influences of swirl field and fuel injection mode were studied, and the research was conducted under the non-reaction condition and the reaction condition, respectively. Based on the numerical simulation results of fuel concentration distribution, a new type of trapped vortex combustor with centrifugal nozzles was designed, and the combustion characteristics of the combustor were experimentally evaluated. The results showed that a vertical double vortex structure could be formed in the cavity under various conditions. The air velocity of cavity inlet, the spray cone angle, and Sauter mean diameter of kerosene droplets had different effects on the liquid and gaseous fuel concentrations. High efficiency and low emissions combustion could be achieved, which was beneficial to improve gas turbine efficiency and reduce pollution emissions. Graphical abstract Image 1 Highlights • Gaseous and liquid fuel distribution is influenced by velocity and droplet diameter. • Fuel distribution is obviously different for non-reaction flow and reaction flow. • New combustor using liquid fuel for gas turbine is designed. • High efficiency and low emissions combustion is achieved. [ABSTRACT FROM AUTHOR]

The electronic structure and optical property of GeTe/SnSe van der Waals heterojunction are investigated by first-principles method. We find GeTe/SnSe van der Waals heterojunction is a type-II heterojunction with an indirect band gap of 0.71 eV. The band gap can be tuned and semiconductor-semimetal phase transition is observed under both positive and negative electric field. The band offset of GeTe/SnSe van der Waals heterojunction can be controlled, and thus the potential barrier can be controlled by applying a gate voltage. Combined with the calculation of effective mass and absorption spectrum we predict that GeTe/SnSe van der Waals heterojunction has important applications in the fields of solar cell and photodetector devices. • The band gap can be tuned by both positive and negative electric field. • The semiconductor-semimetal phase transition is observed. • The band offset, and thus the potential barrier can be controlled by applying a gate voltage. [ABSTRACT FROM AUTHOR]

In this paper, we used the 8-band k · p model with valence force field considerations to investigate the effect of size and shape on electronic and optical properties of cadmium selenide quantum dots. Major factors related to their properties including band mixing probabilities, spatial charge distributions, transition matrix elements and Fermi factors were studied. Volumetrically larger CdSe dots were found to have smaller band-gaps but higher transition matrix elements and Fermi factors. The maximum optical gain for dots was observed to have an initially positive and then negative correlation with their real-space size as a result of combined effects of various factors. For the shape effects, cubic dots were found to have smaller band-gaps, Fermi factors and transition matrix elements than spherical dots due to higher level of asymmetry and different surface effects. Consequently, cubic dots have lower emission energy, smaller amplification. The occurrence of near E1–H1 transition broadens the gain spectrum of cubic dots. Cubic and spherical dots are both proven to be promising candidates for optical devices under visible range. We have demonstrated that size and shape change could both effectively alter the properties of quantum dots and therefore recommend consideration of both when optimizing the performance for any desired application. [ABSTRACT FROM AUTHOR]

Abstract: The unstrained “natural” valence band offsets of dilute GaAs1− x N x and GaAs are calculated using the first-principles method. For calculated the band offset, we fit the lattice constants and the elastic stiffness constants, C 11, C 12, and C 44 of GaAs and GaAs1− x N x . The calculated results show that the natural valence band offset is weak type-I when x is less than 5.56%, and the natural is almost the same as the nature . However, the natural valence band offset is weak type-II. [Copyright &y& Elsevier]

Increasing the utilization of copper tailing and flue gas desulfurization is significant for copper smelters. Copper tailing, derived from the copper production, was applied to flue gas desulfurization and increasing utilization of copper tailing and smelting gas with low concentrations of SO 2 by preparing slurries composed of copper tailing and water. The effects of different factors, including the inlet SO 2 concentration, the ratio of solid to liquid, the absorption temperature, the O 2 concentration, the gas flow rate, the initial copper tailing slurry pH, and the presence of a coexisting gas were investigated systematically. The resulting products and the mechanism driving the flue gas desulfurization were also studied. The results indicated that desulfurization efficiency was primarily influenced by the inlet SO 2 concentration, the ratio of solid to liquid, the absorption temperature, and the gas flow rate. An appropriate amount of NO facilitated the desulfurization. The desulfurization efficiency was maintained at or above 80% for 60 h under optimal conditions. The total weight of the copper tailing was reduced by approximately 8%. Ferric sulfate and magnetite could be recycled through evaporation and magnetic separation. Liquid phase catalytic oxidation by metal ions, including ferric and manganese, played a vital role in the flue gas desulfurization. Copper tailing is the solid waste produced by pyrometallurgical process for copper production. Approximately 2 tons of copper tailings are produced in the process of 1 ton of copper. Traditional approaches of reuse have significant disadvantages, including high capital costs for installation and complicated construction and operating costs, including massive acid consumption. We firstly use the copper tailing and water as desulfurization agents to removal SO 2 -containing gas, which provides a practical reference to flue gas desulfurization from the copper industry, thus promoting the flue gas desulfurization at a lower cost and meanwhile realizing the goal of effective copper tailing recycling. Unlabelled Image • A novel, inexpensive wet desulfurization method with copper tailing is proposed. • Formed metal ions, including Fe2+ and Mn2+, play a vital role in removing SO 2. • Up to 75% copper is leached with high efficient desulfurization simultaneously. • Copper tailing was reduced 8% when solid waste is used to remove SO 2. [ABSTRACT FROM AUTHOR]

This work presents a theoretical analysis of optical and electronic properties of uniform and random silver (Ag) and aluminum (Al) nanowire (NW) layers. At low concentrations of NWs the uniform and random layers possess similar average transmittance in the visible spectrum. However, at high concentrations of NWs the random Ag and Al layers demonstrate up to 38% and 45% average transmittance, respectively. Moreover, at high concentrations of NWs the uniform and random Ag layers outperform identical Al layers up to 15% and 5% average transmittance, respectively. Our results indicate that metallic random NW transparent conductive layers benefit in optoelectronic devices demanding lowest sheet resistance, such as solar cells and light-emitting diodes. [ABSTRACT FROM AUTHOR]

Abstract: This paper investigated the lean blow-out (LBO) performance of several combustors which utilized trapped vortex in the cavity to improve the flame stability. Experiments and simulation study had been performed for various height to length ratios of the cavity. The experiment results showed that the minimum pressure drop across the combustor occurred when the ratio was 0.8; and that very low overall LBO equivalence ratios were observed over a wide range of primary air flows at the same ratio. In the simulations, the large eddy simulation (LES) was used to predicate the transient flow field in the cavity. Simulation results showed that the core of the trapped vortex was in the middle of the cavity at , and the velocity profile of the vortex was better organized than those of other combustors with different ratios. Moreover, the simulated period of vortex swirling was the shortest at . Therefore, the experimental observations on the LBO performance of several combustors with different ratios were well explained by the present simulation results. Based on the experimental data, a preliminary study of the empirical correlation of LBO was conducted on trapped vortex combustor (TVC). Compared with Lefebvreʼs empirical correlation, the proposed new empirical correlation has better agreement with the experimental data. [Copyright &y& Elsevier]

Abstract: The performance of an annular slight temperature-raise single trapped vortex combustor was experimentally investigated in simulation conditions. The slight temperature-raise TVC, consisting of an inlet rig, an outlet rig, and a cavity, was placed coaxially outside of the combustor liner. Liquid fuel and hot air were premixed, and then injected from the inner face of an afterbody. The evaluation performed on the slight temperature-raise single trapped vortex combustor involved ignition, lean blow out, emissions, efficiency, exit temperature profile, and combustor liner temperatures. The Mach numbers of main air were between 0.3 and 0.6, the air flow rates into the cavity were 15–150 g/s, and fuel/air mixtures with a temperature of 293, 423, and 573 K, were tested. As a result, for a temperature raise of 100–200 K, stable combustion was achieved at a high Mach number of main air, as well as at low blowout limit for fuel air ratio (as low as 0.002). The combustion efficiency obtained was above 96% in most conditions, the ignition overall fuel air ratio was about 0.0054, and the NO x emission was less than 20 ppm (15% oxygen). [ABSTRACT FROM AUTHOR]

Semi-conductive MXene Sc 2 CO x is synthesized by using magnetron sputtering. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) is performed to determine the composition of sample. The bandgap of Sc 2 CO x sample is determined by ultraviolet-visible (UV–VIS) range absorption and photoluminescence (PL) spectrum. The Tauc plot indicates that Sc 2 CO x is a direct bandgap material. The high sensitivity of scandium to oxygen makes the sample contain both scandium carbide and scandium oxide. Thermal annealing introduces more oxidation into the sample. Structure of MXene will be broken when the annealing temperature is higher than 600 °C. [ABSTRACT FROM AUTHOR]

• Cyclic loading and unloading tests of sandstone with different lower limit of cyclic stress are carried out. • The effects of different lower limit of cyclic stress on the mechanical properties and AE spectrum of samples are compared. • The damage accumulation and deformation characteristics of the sample during cyclic loading and unloading are investigated. This study is aimed at exploring the effect of the lower limit of cyclic stress (LLCS) on the loading and unloading failure process of sandstone. First, cyclic loading and unloading experiments were performed on sandstone samples under different stress paths. Furthermore, the variations of mechanical properties and acoustic emission (AE) signals of samples during cyclic loading and unloading were analyzed. The results show that the equivalent residual strain produced by a single loading and unloading with a low LLCS is larger than the residual strain produced by that with a high LLCS. Under cyclic loading and unloading, the loading elastic moduli of samples grow as the number of cycles increases. In the loading failure stage, the loading elastic modulus under a high LLCS is greater than that under a low LLCS. In the 2nd and 3rd stages, the AE counts, main frequency signals and high-amplitude signals generated under loading and unloading with a high LLCS all account for smaller proportions than those generated under loading and unloading with a low LLCS. Low-frequency and high-amplitude signals appear in both the third stage and the loading failure stage under a low LLCS, while they only appear in the loading failure stage under a high LLCS. In the 2nd and 3rd stages, the b value first grows and then decreases under a low LLCS, while it keeps rising under a high LLCS. A high LLCS is conducive to suppressing the axial deformation of sandstone and reducing the amount of damage caused during a single loading and unloading. This study boasts theoretical reference value for the monitoring of coal rock stability and the prevention of dynamic disasters. [ABSTRACT FROM AUTHOR]