Search Results (33)

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

A highly loaded axial flow compressor often leads to significant flow separation, resulting in increased pressure loss and deterioration of the pressure increase ability. Improving flow separation within a compressor is crucial for enhancing aeroengine performance. This study proposes adding a fin structure to the jet cavity of the Coanda jet cascade to improve flow separation at the trailing edge and corner area. The fin structure is optimized using response surface technique and a multi-objective genetic algorithm based on numerical simulation, enabling more effective control of the simultaneous separation of the boundary corner and trailing edge of the layer. The response surface model developed in this study is accurately validated. The numerical results demonstrate a 2.13% reduction in the optimized blade total pressure loss coefficient and a 12.74% reduction in the endwall loss coefficient compared to those of the original unfinned construction under the same air injection conditions. The optimization procedure markedly improves flow separation in the compressor, leading to a considerable decrease in the volume of low-energy fluid on the blade’s suction surface, particularly in the corner area. The aerodynamic performance of the high-load cascade is enhanced. Full article

Reducing CO₂ emissions in general aviation is a critical challenge, where battery electric and fuel cell technologies face limitations in energy density, cost, and robustness. As a result, hydrogen (H₂) dual-fuel combustion is a promising alternative, but its practical implementation is constrained by abnormal combustion phenomena such as knocking and pre-ignition, which limit the achievable H₂ energy share. In response to these challenges, this paper focuses on strategies to mitigate these irregular combustion phenomena while effectively increasing the H₂ energy share. Experimental evaluations were conducted on an engine test bench using a one-cylinder dual-fuel H₂ kerosene (Jet A-1) engine, utilizing two strategies, including water injection (WI) and rising the air–fuel ratio (AFR) by increasing the boost pressure. Additionally, crucial combustion characteristics and emissions are examined and discussed in detail, contributing to a comprehensive understanding of the outcomes. The results indicate that these strategies notably increase the maximal possible hydrogen energy share, with potential benefits for emissions reduction and efficiency improvement. Finally, through the use of 0D/1D simulations, this paper offers critical thermodynamic and efficiency loss analyses of the strategies, enhancing the understanding of their overall impact. Full article

Amid escalating global energy demand and heightened environmental concern, this study presents an innovative photovoltaic–thermal flash-tank vapor injection heat pump (PFVHP). This system integrates a photovoltaic–thermal (PVT) module into a conventional flash-tank vapor injection heat pump (FVHP) to realize simultaneous heating and power generation. Two distinct operation modes are designed for the PFVHP: TS-mode (two-source mode) for most solar radiation conditions and AS-mode (air-source mode) for low- or no-solar-radiation conditions. The energy, exergy, economic, and operational emission performance of the PFVHP are theoretically analyzed and compared with those of the FVHP. The findings reveal that the PFVHP can achieve a maximum cycle and system coefficient of performance (COP) at the respective optimal intermediate pressures. Exergy analysis indicates that enhancing solar radiation helps the PFVHP produce more heat exergy and electricity, but reduces the system exergy efficiency. As the evaporating temperature ranges from −20 °C to 5 °C, the cycle COP and system COP of the PFVHP are, respectively, 8.5% to 6.3% and 50.0% to 35.2% higher than the COP of the FVHP. The exergy flow comparison demonstrates that the PFVHP significantly enhances the system performance by reducing the overall exergy loss in devices excluding a PVT module, benefiting from the absorption of solar exergy by the PVT module. Economic and operational emission analyses indicate that the PFVHP offers a payback period of 9.38 years and substantially reduces the air pollution emissions compared to the FVHP. Full article

Artificial upwelling (AU), a geoengineering technique aimed at transporting nutrient-enriched deep-sea water to the sunlit surface layers through artificial systems, is increasingly recognized as a promising approach to enhance oceanic fertility and stimulate primary marine productivity, thereby bolstering the ocean capacity for carbon sequestration. Several air-lifted AU systems have been implemented in countries such as Norway and China. However, research on the optimization of the air injection pipeline network (AIPN)—a critical component of the air-lifted AU system—remains limited. This paper introduces a refined minimum spanning tree algorithm to propose a novel approach for optimizing the AIPN. Furthermore, the bubble-entrained plume loss rate (N_BEP) is developed as a model to assess the efficiency of air-lifted AU systems, which is applied to three case studies involving air-lifted AU systems of varying scales. The findings indicate that the enhanced minimum spanning tree algorithm outperforms the conventional Prim’s algorithm, leading to an average 87% reduction in N_BEP of the optimized AIPN, compared to the AIPN of previous air-lifted AU systems while improving system stability. Consequently, the proposed optimization method for AIPN offers valuable scientific and practical insights for the engineering design of the air-lifted AU systems across diverse scales, offering transformative potential for large-scale carbon sequestration and marine productivity enhancement. Full article

Despite efforts to use ammonia as a fuel, there remain problems with low combustion speeds and high unburned ammonia (NH₃) emissions. Therefore, methods to compensate for slow combustion speeds and stabilize combustion have been studied. This study aims to analyze how increasing the compression ratio affects engine performance to enhance thermal efficiency and reduce unburned emissions in a high-pressure ammonia direct injection spark-ignited engine. In addition, by applying a high-flow-rate (HFR) injector, an improvement in the combustion of ammonia fuel and exhaust gas emissions is observed through changes in the air–fuel mixture formation of high-pressure directly injected ammonia fuel. Compared with the existing compression ratio, the incomplete combustion loss due to unburned NH₃ increases significantly, and the thermal efficiency does not increase under an increased compression ratio. When HFR injectors are applied with an increase in the compression ratio, the net work increases by 4.7%, as incomplete combustion and energy losses of fuel are reduced by reducing the amount of unburned NH₃. Full article

Nowadays, a lot of efforts are being made to increase turbine inlet temperatures (TIT), with the aim of increasing efficiency in aircraft and power generation turbines. Due to the higher temperature level, advanced cooling solutions to preserve material durability are necessary. It is essential to avoid contact between hot gases and the temperature-sensitive components, such as the stator and rotor cavity disks. Modern gas turbine performance optimization centers on reducing leakage and refining sealing systems. The interaction between the main flow and cavity flow in stator/rotor systems has a significant role in loss generation. This study employs Unsteady Reynolds-Averaged Navier–Stokes (URANS) simulations to investigate the unsteady interactions within the stator/rotor cavity of a low-pressure turbine. Numerical results are compared and validated against experimental data obtained in the cavity rig of the University of Genova. The research focuses on the effects of stator/rotor interactions, including wake ingestion from upstream rotor bars and the blocking influence of downstream potential effects on cavity sealing effectiveness. In this paper, a comparison between the zero cooling air flow rate and cavity sealing condition is shown. Special attention is given to unsteady loss mechanisms occurring downstream of the vane row and in areas where the cavity flow re-enters the main channel, showing how cooling flow rates affect these losses. From this study, it can be seen that by increasing the cooling flow rate injected into the cavity, there is an increase in the hub’s passage vortex effect and there is a more intense interaction between the main flow and the cavity flow. These results offer valuable insights into the mechanisms of interaction between the main flow and cavity flow. Full article

Background/Objectives: The aim is to bring attention to the existence of a rare type of trauma of the hand, high-pressure injection injury, that appears to be minor with negligible signs and symptoms within the first hours after the accident, but in reality, produces significant tissue destruction with severe consequences. Recognizing this type of trauma by medical personnel, understanding the mechanisms involved, and knowing the etiological and prognostic factors can lead to early treatment initiation and avoid severe mutilating sequelae. Methods: A retrospective study on 16 patients diagnosed with high-pressure injection injuries, including water, air, paint, paint mixed paint with thinner, petroleum jelly, and lime (washable paint containing calcium oxide). The patients’ epidemiological data, the time from accident to diagnosis, reasons for delayed diagnosis, treatments applied, and outcomes were recorded and evaluated. Results: All injuries occurred at the workplace due to negligence. Oil-based paint was implicated in 31.25% of cases. The most frequently affected anatomical region was the volar surface of the distal phalanx of the nondominant hand index finger. In one case, delayed presentation to medical care and diagnosis resulted in a compartment syndrome, requiring amputation. Conclusions: It is crucial to recognize and understand this type of trauma, as it constitutes an emergency due to its rapid progression. Delayed diagnosis can result in massive tissue destruction, potentially leading to the loss of limb segments and debilitating functional sequelae, which may severely impact a patient’s socio-professional life. Full article

A compression ignition engine generates power by using the auto-ignition characteristics of fuel injected into the cylinder. Although it has high fuel efficiency, it discharges a lot of exhaust emissions such as NO_X and PM. Therefore, there is much ongoing research aiming to reduce the exhaust emissions by using the technologies applied in this regard, such as PCCI, HCCI, etc. However, these methods still discharge large exhaust emissions. The RCCI method, which combines the spark ignition method and compression ignition method, is attracting attention. So, in this work, the objective of this study is to numerically investigate the effect of combustion phase according to the premixed ethanol ratio based on the same total heating value in-cylinder by changing the initial air composition on the formation and oxidation of exhaust emissions in the RCCI engine. The heating value of the premixed ethanol ratio varied from 0% to 40% based on the same total lower heating value in-cylinder in steps of 10%. It was assumed that the ethanol introduced into the cylinder through the premixing chamber was evaporated, and the initial air composition in the cylinder was changed and set. It was revealed that when the premixed ratio based on the same total lower heating value was increased, the introduced fuel amount into the crevice volume with advancing the start of energizing timing was decreased, which increased the peak cylinder pressure. In addition, the ignition delay was also longer due to the low cylinder temperature by the evaporation latent heat of the ethanol, which reduced the compression loss, so the IMEP value was increased. The rich equivalence ratio had a narrow distribution in the cylinder, which caused a reduction in cylinder temperature, so the NO formation amount was reduced. The ISCO value increased the increase in premixed ethanol ratio based on the same total lower heating value in-cylinder because the flame propagation of ethanol by combustion of diesel did not work well, and the CO formed by combustion was slowly oxidized due to the cylinder’s low temperature as a result of the evaporation latent heat of ethanol. From these results, the optimal operating conditions for simultaneously reducing the exhaust emissions and improving the combustion performance were judged such that the start of energizing timing was BTDC 23 deg, and the premixed ethanol ratio based on the same total lower heating value in-cylinder was 40%. Full article

Herein, a diesel engine jet disturbance combustion system was proposed to achieve efficient and clean combustion under heavy load conditions in heavy-duty diesel engines. The key components of the combustion system were designed, and a research platform was constructed. Focusing on the internal combustion conditions of the disturbance chamber and the developmental path of high-speed jets, the design and comprehensive optimization of the jet disturbance combustion system were carried out. Following optimization, the peak internal heat release rate increased from 86 J/deg to 269 J/deg, and the cumulative heat release increased by 112 J, significantly enhancing the energy of the disturbance chamber jet. Then, considering combustion optimization and the heat transfer loss from the piston, it was determined that the optimal configuration for the disturbance chamber jet channel angles was 60 deg inter-channel angle and 10 deg channel incidence angle. This configuration allowed the disturbance chamber jet to precisely disturb the concentrated mixture area in the middle and late stages of combustion. The intervention of the disturbance chamber jet provided sufficient energy for the fuel–air mixing process and complicated the gas flow state in the main combustion chamber. Despite its low-momentum density, the residual mixture in the cylinder maintained a high mixing rate after the end of the fuel injection process. Single-cylinder engine test results showed that a diesel engine using this jet disturbance system and a 180 MPa common rail pressure fuel system achieved 52.12% thermal efficiency. Full article

The growing popularity of unconventional wells has led to increased interest in assessing and predicting their production performance. These wells, with their extended-reach structures, are able to generate and access larger reservoir volumes. Therefore, understanding the impact of a well’s lateral trajectory on its transient production performance is crucial. This study investigates the effect of lateral-trajectory undulation amplitude on flow behavior based on the experimental results obtained at the University of North Dakota using an undulated two-phase (UTP) flow loop. The experiments involved injecting an air-and-water mixture through a section with variable undulation amplitude followed by a vertical section. The results revealed that the increasing undulation amplitude resulted in lower translational velocity, frequency, and length, with consistent slug acceleration along the system profile. Additionally, the frequency of slugs decreased as they traveled through the vertical section. The measured data indicated that higher undulation amplitudes led to increased horizontal pressure losses and variability, suggesting larger instabilities. The numerical simulations predicted lower translational velocity and frequency, longer slug length, and similar vertical pressure losses when compared to the experimental results. Full article

This review addresses the current state of research into active control and suppression of vortex rope in hydroturbines under off-design operating conditions. Only active control methods that can be “switched on” when required under off-design operating conditions are considered in this work. The review focuses on air addition into the flow, as well as various auxiliary fluid jets. It includes all the best practices for vortex rope suppression in numerical and experimental studies. It can be inferred from the review that a modern flow control system should be comprehensive, designed for a specific hydroturbine geometry, and obtain feedback from the flow. Injecting ~2% of air from the impeller fairing cone appears optimal for suppressing pressure pulsations without significant efficiency loss. The cost of air injection is rarely estimated, but the use of an automatic venting system can minimize overheads and potentially improve efficiencies at low gas contents. Fluid jets ranging from 3% to 12% of the main flow rate can efficiently suppress pressure pulsations, but their high energy requirements limit their use. Azimuthal perturbation of the flow appears promising as it does not require significant energy loss, but practical implementation remains challenging as one needs to accurately know the system dynamics and be capable of real-time manipulation of the flow. Full article

Accidental flame initiation to propagation in pipes carrying flammable gases is a significant safety concern that can potentially result in loss of life and substantial damage to property. The understanding of flame propagation characteristics caused by methane–air mixtures within various extractive and associated process industries such as coal mining is critical in developing effective and safe fire prevention and mitigation countermeasures. The aim of this study is to investigate and visualise the fire and explosion properties of a methane–air mixture in a straight pipe with and without obstacles. The experimental setup included modular starting pipes, an array of sensors (flame, temperature, and pressure), a gas injection system, a gas analyser, data acquisition and a control system. The resulting observations indicated that the presence of obstacles within a straight pipe eventuated an increase in flame propagation speed and deflagration overpressure as well as a reduction in the elapsed time of flame propagation. The maximum flame propagation speed in the presence of an orifice with a 70% blockage ratio at multiple spots was increased around 1.7 times when compared to the pipe without obstacles for 10% methane concentration. The findings of this study will augment the body of scientific knowledge and assist extractive and associated process industries, including stakeholders in coal mining to develop better strategies for preventing or reducing the incidence of methane–air flame propagation caused by accidental fires. Full article

The effect of supersonic air temperature on the mixing characteristics of liquid hydrocarbon fuel injected into three different supersonic airflows elevated in three steps from 373 K to 673 K was investigated numerically. Compressible Reynolds-averaged Navier–Stokes (RANS) equations were solved together with species conservation equation using ANSYS Fluent for two-phase flow simulations including fuel droplet breakup and evaporation. The turbulence model needed to close the RANS equations used the Shear Stress Transport (SST) k-ω model. The Eulerian–Lagrangian model was employed to track fuel droplets in mainstream air, and the Kelvin–Helmholtz and Rayleigh–Taylor (KH-RT) models were used to simulate the droplet breakup process. Numerical solutions were validated using experimental data. The higher the air temperature, the stronger the streamwise vortices downstream of the pylon. When the air temperature was 373 K, the liquid fuel hardly evaporated, but as the air temperature increased, and the mass fraction of the vaporized fuel and the mixing efficiency increased linearly downstream of the pylon. At air temperatures of 523 K and 673 K, the mixing efficiencies were 10% and 51% at the combustor outlet, respectively. The total pressure loss decreased slightly due to droplet evaporation as the temperature increased from 373 K to 673 K. Full article

One of the promising ways to increase fuel and modern gas turbine energy efficiency is using cyclic air intercooling between the stages of high- and low-pressure compressors. For intercooling, it is possible to use cooling in the surface heat exchanger and the contact method when water is injected into the compressor air path. In the presented research on the cooling contact method, it is proposed to use a thermopressor that implements the thermo-gas-dynamic compression process, i.e., increasing the airflow pressure by evaporation of the injected liquid in the flow, which moves at near-sonic speed. The thermopressor is a multifunctional contact heat exchanger when using this air-cooling method. This provides efficient high-dispersion liquid spraying after isotherming in the high-pressure compressor, increasing the pressure and decreasing the air temperature in front of the high-pressure compressor, reducing the work on compression. Drops of water injected into the air stream in the thermopressor can significantly affect its characteristics. An increase in the amount of water increases the aerodynamic resistance of the droplets in the stream. Hence, the pressure in the flow parts of the thermopressor can significantly decrease. Therefore, the study aims to experimentally determine the optimal amount of water for water injection in the thermopressor while ensuring a positive increase in the total pressure in the thermopressor under conditions of incomplete evaporation. The experimental results of the low-consumption thermopressor (air consumption up to 0.52 kg/s) characteristics with incomplete liquid evaporation in the flowing part are presented. The research found that the relative water amount to ensure incomplete evaporation in the thermopressor flow part is from 4 to 10% (0.0175–0.0487 kg/s), without significant pressure loss due to the resistance of the dispersed flow. The relative increase in airflow pressure is from 1.01 to 1.03 (5–10 kPa). Based on experimental data, empirical equations were obtained for calculating the relative pressure increase in the thermopressor with evaporation chamber diameters of up to 50 mm (relative flow path length is from 3 to 10 and Mach number is from 0.3 to 0.8). Full article