Search Results (171)

This study proposes an innovative Thermodynamic Activity Controlled Homogeneous Charge Compression Ignition (TAC-HCCI) strategy for diesel–natural gas dual-fuel engines, aiming to achieve high thermal efficiency while maintaining low emissions. By employing numerical simulation methods, the effects of the intake pressure, intake temperature, EGR rate, intake valve closing timing, diesel injection timing, diesel injection pressure, and diesel injection quantity on engine combustion, energy distribution, and emission characteristics were systematically investigated. Through a comprehensive analysis of optimized operating conditions, a high-efficiency and low-emission TAC-HCCI combustion technology for dual-fuel engines was developed. The core mechanism of TAC-HCCI combustion control was elucidated through an analysis of the equivalence ratio and temperature distribution of the in-cylinder mixture. The results indicate that under the constraints of PCP ≤ 30 ± 1 MPa and RI ≤ 5 ± 0.5 MW/m², the TAC-HCCI technology achieves a gross indicated mean effective pressure (IMEPg) of 24.0 bar, a gross indicated thermal efficiency (ITEg) of up to 52.0%, and indicated specific NOx emissions (ISNOx) as low as 1.0 g/kW∙h. To achieve low combustion loss, reduced heat transfer loss, and high thermal efficiency, it is essential to ensure the complete combustion of the mixture while maintaining low combustion temperatures. Moreover, a reduced diesel injection quantity combined with a high injection pressure can effectively suppress NOx emissions. Full article

This study focuses on the optimization of valve assemblies in downhole rod pumping units (DRPUs), which remain the predominant artificial lift technology in oil production worldwide. The research addresses the critical issue of premature failures in DRPUs caused by leakage in valve pairs, i.e., a problem that accounts for approximately 15% of all failures, as identified in a statistical analysis of the 2022 operational data from the Uzen oilfield in Kazakhstan. The leakage is primarily attributed to the accumulation of mechanical impurities and paraffin deposits between the valve ball and seat, leading to concentrated surface wear and compromised sealing. To mitigate this issue, a novel valve assembly design was developed featuring a flow turbulizer positioned beneath the valve seat. The turbulizer generates controlled vortex motion in the fluid flow, which increases the rotational frequency of the valve ball during operation. This motion promotes more uniform wear across the contact surfaces and reduces the risk of localized degradation. The turbulizers were manufactured using additive FDM technology, and several design variants were tested in a full-scale laboratory setup simulating downhole conditions. Experimental results revealed that the most effective configuration was a spiral plate turbulizer with a 7.5 mm width, installed without axis deviation from the vertical, which achieved the highest ball rotation frequency and enhanced lapping effect between the ball and the seat. Subsequent field trials using valves with duralumin-based turbulizers demonstrated increased operational lifespans compared to standard valves, confirming the viability of the proposed solution. However, cases of abrasive wear were observed under conditions of high mechanical impurity concentration, indicating the need for more durable materials. To address this, the study recommends transitioning to 316 L stainless steel for turbulizer fabrication due to its superior tensile strength, corrosion resistance, and wear resistance. Implementing this design improvement can significantly reduce maintenance intervals, improve pump reliability, and lower operating costs in mature oilfields with high water cut and solid content. The findings of this research contribute to the broader efforts in petroleum engineering to enhance the longevity and performance of artificial lift systems through targeted mechanical design improvements and material innovation. Full article

The two-stage proportional valve is a key control component in heavy-duty equipment, where its signal-flow characteristics critically influence operational performance. This study proposes an innovative flow characteristic regulation method using variable-gain feedback grooves. Unlike conventional throttling notch optimization, the core mechanism actively adjusts pilot–main valve mapping through feedback groove shape and area gain adjustments to achieve the desired flow curves. This approach avoids complex throttling notch issues while retaining the valve’s high dynamics and flow capacity. Mathematical modeling elucidated the underlying mechanism. Subsequently, trapezoidal and composite feedback grooves are designed and investigated via simulation. Finally, composite feedback groove spools tailored to construction machinery operating conditions are developed. Comparative experiments demonstrate the following: (1) Pilot–main mapping inversely correlates with area gain; increasing gain enhances micro-motion control, while decreasing gain boosts flow gain for rapid actuation. (2) This method does not significantly increase pressure loss or energy consumption (measured loss: 0.88 MPa). (3) The composite groove provides segmented characteristics; its micro-motion flow gain (2.04 L/min/0.1 V) is 61.9% lower than conventional valves, significantly improving fine control. (4) Adjusting groove area gain and transition point flexibly modifies flow gain and micro-motion zone length. This method offers a new approach for high-performance valve flow regulation. Full article

Rail transit as a high-energy consumption field urgently requires the adoption of clean energy innovations to reduce energy consumption and accelerate the transition to new energy applications. As an energy-saving fluid machinery, the ejector exhibits significant application potential and academic value within this field. This paper reviewed the recent advances, technical challenges, research hotspots, and future development directions of ejector applications in rail transit, aiming to address gaps in existing reviews. (1) In waste heat recovery, exhaust heat is utilized for propulsion in vehicle ejector refrigeration air conditioning systems, resulting in energy consumption being reduced by 12~17%. (2) In vehicle pneumatic pressure reduction systems, the throttle valve is replaced with an ejector, leading to an output power increase of more than 13% and providing support for zero-emission new energy vehicle applications. (3) In hydrogen supply systems, hydrogen recirculation efficiency exceeding 68.5% is achieved in fuel cells using multi-nozzle ejector technology. (4) Ejector-based active flow control enables precise ± 20 N dynamic pantograph lift adjustment at 300 km/h. However, current research still faces challenges including the tendency toward subcritical mode in fixed geometry ejectors under variable operating conditions, scarcity of application data for global warming potential refrigerants, insufficient stability of hydrogen recycling under wide power output ranges, and thermodynamic irreversibility causing turbulence loss. To address these issues, future efforts should focus on developing dynamic intelligent control technology based on machine learning, designing adjustable nozzles and other structural innovations, optimizing multi-system efficiency through hybrid architectures, and investigating global warming potential refrigerants. These strategies will facilitate the evolution of ejector technology toward greater intelligence and efficiency, thereby supporting the green transformation and energy conservation objectives of rail transit. Full article

With the frequent occurrence of global floods, the demand for emergency rescue equipment has grown rapidly. The development and technological innovation of digital hydraulic drive systems (DHDSs) for emergency drainage pumps (EDPs) have become key to improving rescue efficiency. However, EDPs are prone to being affected by random and uncertain loads during operation. To achieve intelligent and efficient rescue operations, a DHDS suitable for EDPs was proposed. Firstly, the configuration and operation mode of the DHDS for EDPs were analyzed. Based on this, a multi-field coupling dynamic simulation platform for the DHDS was constructed. Secondly, the output characteristics of the system under alternating loads were simulated and analyzed. Finally, a test platform for the EDP DHDS was established, and the dynamic characteristics of the system under alternating loads were explored. The results show that as the load torque of the alternating loads increases, the amplitude of the pressure of the motor also increases, the output flow of the hydraulic-controlled proportional reversing valve (HCPRV) changes slightly, and the fluctuation range of the rotational speed of the motor increases. The fluctuation range of the pressure and the rotational speed of the motor are basically not affected by the frequency of alternating loads, but the fluctuation amplitude of the output flow of the HCPRV reduces with the increase in the frequency of alternating loads. This system can respond to changes in load relatively quickly under alternating loads and can return to a stable state in a short time. It has laudable anti-interference ability and output stability. Full article

Hydrogels have emerged as multifunctional biomaterials in cardiac surgery, offering promising solutions for myocardial regeneration, adhesion prevention, valve engineering, and localized drug and gene delivery. Their high water content, biocompatibility, and mechanical tunability enable close emulation of the cardiac extracellular matrix, supporting cellular viability and integration under dynamic physiological conditions. In myocardial repair, injectable and patch-forming hydrogels have been shown to be effective in reducing infarct size, promoting angiogenesis, and preserving contractile function. Hydrogel coatings and films have been designed as adhesion barriers to minimize pericardial adhesions after cardiotomy and improve reoperative safety. In heart valve and patch engineering, hydrogels contribute to scaffold design by providing bio-instructive, mechanically resilient, and printable matrices that are compatible with 3D fabrication. Furthermore, hydrogels serve as localized delivery platforms for small molecules, proteins, and nucleic acids, enabling sustained or stimuli-responsive release while minimizing systemic toxicity. Despite these advances, challenges such as mechanical durability, immune compatibility, and translational scalability persist. Ongoing innovations in smart polymer chemistry, hybrid composite design, and patient-specific manufacturing are addressing these limitations. This review aims to provide an integrated perspective on the application of hydrogels in cardiac surgery. The relevant literature was identified through a narrative search of PubMed, Scopus, Web of Science, Embase, and Google Scholar. Taken together, hydrogels offer a uniquely versatile and clinically translatable platform for addressing the multifaceted challenges of cardiac surgery. Hydrogels are poised to redefine clinical strategies in cardiac surgery by enabling tailored, bioresponsive, and functionally integrated therapies. Full article

Aortic stenosis is the most prevalent valvular disease globally. Transcatheter aortic valve replacement (TAVR) has become a well-established treatment for aortic stenosis, offering outcomes comparable to surgical aortic valve replacement (SAVR). Its use has expanded to include younger, lower-risk patients and those with more complex anatomies. Recent advancements in TAVR include the increased adoption of transfemoral access, prosthesis designs optimized for challenging anatomies, enhanced delivery systems with repositioning capabilities, and outer skirts to minimize paravalvular leaks. Despite these innovations, several challenges remain. This review highlights recent updates in transcatheter heart valve (THV) systems, leaflet modification devices, and the current limitations of TAVR. Full article

The introduction of transcatheter aortic valve replacement (TAVR) has revolutionized the management of aortic stenosis (AS), leading to significant improvements in patient outcomes. Over time, advancements in device technology have further optimized safety and performance of TAVR. However, as the pool of low-risk patients undergoing TAVR expands, many of whom present with concomitant coronary artery disease (CAD), new challenges have emerged. A large proportion of TAVR candidates suffer from CAD, and the clinical implications of this comorbidity remain a subject of debate. Research on the relationship between AS and CAD has yielded conflicting results, but severe CAD is generally linked to worse outcomes in AS patients. The coexistence of AS and CAD complicates diagnosis and management, requiring a comprehensive understanding of both invasive and non-invasive diagnostic techniques, along with careful revascularization strategies. This review explores the prevalence, clinical impact, and diagnostic challenges of CAD in TAVR patients, highlighting emerging methods for its assessment. Key aspects of treatment, including the timing of coronary revascularization, coronary re-access after TAVR in different settings, as well as practical tips and tricks for coronary cannulation, are also discussed. The complexity of managing AS and CAD is further intensified by the need for individualized approaches, particularly in hybrid procedures and subsequent TAVR interventions. Ongoing research and technological innovations offer promising solutions for refining the management of CAD in AS patients undergoing TAVR, with an emphasis on improving prognostic accuracy, optimizing revascularization strategies, and enhancing post-procedural care. Full article

Mitral valve disease, particularly in the context of extensive mitral annular calcification (MAC), poses significant challenges for traditional surgical management. Transcatheter mitral valve replacement (TMVR) has emerged as a promising alternative for high-risk and inoperable patients, driven by rapid advancements in valve technology, imaging techniques, and procedural strategies. Nevertheless, complications such as paravalvular leak (PVL), left ventricular outflow tract (LVOT) obstruction, and hemolysis remain obstacles to optimal outcomes, particularly in patients with complex annular anatomy. We present the case of an 89-year-old female with severe mitral stenosis and MAC who developed acute hemolytic anemia following experimental TMVR using the Edwards SAPIEN S3 valve. This case serves as a platform to explore recent advances in TMVR, including novel device platforms, enhanced imaging modalities for pre-procedural planning, innovative deployment strategies, and emerging adjunctive techniques aimed at reducing complications. Through this case, we underscore persistent challenges and emphasize the importance of meticulous patient selection and vigilant follow-up. Despite substantial progress, TMVR in the setting of MAC remains high-risk, demanding continued innovation in valve design, refined patient stratification, and improved peri-procedural management to enhance outcomes and mitigate risks such as hemolysis. Full article

Transcatheter aortic valve replacement (TAVR) was first introduced as a minimally invasive treatment for patients with severe aortic stenosis (AS) who are at high or intermediate surgical risk. Recently, its application has expanded to include younger and lower-risk patients, establishing TAVR as a less invasive alternative to surgical aortic valve replacement (SAVR) across the entire surgical spectrum. The expanding utilization of TAVR has driven significant advancements that have greatly enhanced its safety and effectiveness, resulting in a substantial reduction in complications such as paravalvular leak, conduction abnormalities, and periprocedural strokes. Numerous trials have demonstrated the potential superiority of TAVR over conventional surgery in achieving favorable clinical outcomes. Furthermore, the increasing number of long-term trials has provided valuable insight into TAVR outcomes in previously under-studied populations, including patients with complex anatomies. However, significant challenges remain, particularly in ensuring the long-term durability of transcatheter valves, with younger patients likely to outlive their bioprosthetic valves. Consequently, the focus is shifting towards lifetime management strategies, including considerations for coronary re-access, the risk of coronary obstruction, and prosthesis–patient mismatch. This review explores key developments in the field, including TAVR for aortic regurgitation and bicuspid anatomy, the emerging role of TAVR in moderate and asymptomatic AS, and innovations in valve design and procedural planning. We also examine novel imaging tools, adjunctive technologies, and strategies to address coronary access and re-intervention. As long-term data accumulate, these evolving trends will shape the future of TAVR and its role in managing aortic valve disease across increasingly complex clinical scenarios. Full article

Plateau hypoxia represents a type of hypobaric hypoxia caused by reduced atmospheric pressure at high altitudes. Pressurization therapy is one of the most effective methods for alleviating acute high-altitude sickness. This study focuses on the development of an advanced control system for a vehicle-mounted mild hyperbaric chamber (MHBC) designed for the prevention and treatment of plateau hypoxia. Conventional control methods struggle to cope with the high complexity and inherent uncertainties associated with MHBC control tasks, thereby motivating the exploration of sequential decision-making approaches such as reinforcement learning. Nevertheless, the application of sequential decision-making in MHBC control encounters several challenges, including data inefficiency and non-stationary dynamics. The system’s low tolerance for trial-and-error may lead to component damage or unsafe operating conditions, and anomalies such as valve failure can emerge during long-term operation, compromising system stability. To address these challenges, this study proposes a decision-time learning and planning integrated framework for MHBC control. Specifically, an innovative latent model embedding decision-time learning is designed for system identification, separately managing system uncertainties to fine-tune the model output. Furthermore, a decision-time planning algorithm is developed and the planning process is further guided by incorporating a value network and an enhanced online policy. Experimental results demonstrate that the proposed decision-time learning and planning integrated approaches achieve notable performance in MHBC control. Full article

This study presents an innovative hybrid geothermal air conditioning system that combines conventional air-based heat exchange with ground heat exchange technology. The system features a ground heat exchanger placed downstream from the outdoor unit heat exchanger, requiring minimal modifications to conventional air conditioners through the addition of bypass flow paths and a four-way valve. This design ensures that the ground heat exchanger consistently operates after the outdoor unit heat exchanger in both cooling and heating modes. The researchers evaluated the proposed system’s performance through both computational simulation (1D-CAE) and experimental testing. Simulation results demonstrated significant efficiency improvements, with the hybrid system achieving a coefficient of performance (COP) of 4.51 compared to just 1.24 for conventional air conditioners under extreme temperature conditions (38 °C). The experimental validation with a shallow-buried (20 cm) ground heat exchanger confirmed an approximately 20% COP improvement across various ambient temperatures. The main advantages of this hybrid system over conventional geothermal systems include reduced installation costs due to shorter borehole lengths, separate air conditioning units and underground piping, and compatibility with existing control systems. The design addresses skilled labor shortages while enabling large-scale demonstration operations with minimal initial investment. Future work will focus on optimizing the burial depth and conducting long-term durability testing to advance practical implementation. Full article

Hydrogen-powered aircraft constitute a transformative innovation in aviation, motivated by the imperative for sustainable and environmentally friendly transportation solutions. This paper aims to concentrate on the design of hydrogen powertrains employing a system approach to propose representative design models for distribution and propulsion systems. Initially, the requirements for powertrain design are formalized, and a use-case-driven analysis is conducted to determine the functional and physical architectures. Subsequently, for each component pertinent to preliminary design, an analytical model is proposed for multidisciplinary analysis and optimization for powertrain sizing. A double-wall pipe model, incorporating foam and vacuum multi-layer insulation, was developed. The internal and outer pipes sizing were performed in accordance with standards for hydrogen piping design. Valves sizing is also considered in the present study, following current standards and using data available in the literature. Furthermore, models for booster pumps to compensate pressure drop and high-pressure pumps to elevate pressure at the combustion chamber entrance are proposed. Heat exchanger and evaporator models are also included and connected to a burning hydrogen engine in the sizing process. An optimal liner pipe diameter was identified, which minimizes distribution systems weight. We also expect a reduction in engine length and weight while maintaining equivalent thrust. Full article

Background and Clinical Significance: Papillary Fibroelastoma is a benign primary cardiac tumor, commonly located in a valvular position, predominantly on the aortic valve. Case Presentation: We present a 73-year-old male patient with a medical history of chronic lymphatic leukemia, kidney failure, diabetes, and obstructive sleep apnea. In a routinely performed echocardiogram an abnormal structure in the left ventricle was found. The patient presented completely asymptomatically at the time of examination. A cardiac magnetic resonance-scan provided further information about the size and localization of the tumor in the left ventricle, which seemed to be attached to a papillary muscle and was about 1.6 cm in diameter. Due to visible scarring of the myocardia, which was identified in the scan, a cardiac catheter examination was performed. A coronary artery disease was detected with a severe stenosis in three vessels. During an elective bypass-operation, the removal of the structure was performed with an approach through the left atrium, passing the mitral valve using a valve sizer for better exposure. The tumor of 1 cm presented macroscopically with an anemone-like shape. The histopathological examination confirmed the intraoperative assumption of a papillary fibroelastoma, found in an aberrant location. Conclusions: Unexpectedly challenging surgical removals of structures in the left ventricle require innovative techniques with available instruments for better exposure. Full article

Background/Objectives: Aortic valve stenosis (AS) is a prevalent cardiovascular condition among elderly patients frequently treated with Transcatheter Aortic Valve Implantation (TAVI). Traditional hemodynamic monitoring during TAVI relies on invasive methods. The ClearSight^® Finger Cuff system offers a non-invasive alternative for continuous hemodynamic monitoring. To compare the reliability and feasibility of non-invasive hemodynamic monitoring with traditional invasive hemodynamic monitoring during TAVI procedures. Methods: In this prospective observational study, patients undergoing elective TAVI were recruited from two tertiary hospitals between March and August 2023. Invasive hemodynamic measurements were obtained using arterial and pigtail catheters, with a subset undergoing right heart catheterization. Non-invasive measurements were captured using the ClearSight^® system. Data on baseline characteristics, procedural details, and 30-day follow-up outcomes were collected. Results: The study cohort comprised 50 patients (median age 82 years (IQR 78.0, 85.8), 50% female). Non-invasive measurements of cardiac output (CO), cardiac index (CI), and stroke volume (SV) were consistently lower than invasive measurements (CO: 4.1 vs. 4.8 L/min, p = 0.03; CI: 2.2 vs. 2.7 L/min/m², p = 0.01, SV: 66 vs. 77 mL, p = 0.25). Non-invasive blood pressure readings were lower than invasive radial and aortic measurements before and after TAVI. Correlation of non- and invasive measurements was low but similar before and after TAVI (Mean percentage error of 52%). Conclusions: The ClearSight^® system provided lower absolute values for all evaluated hemodynamic parameters as well as low correlation compared to traditional methods pre- as well as post-interventional. Full article