Search Results (131)

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

The aviation sector significantly contributes to environmental challenges, including global warming and greenhouse gas emissions, due to its reliance on fossil fuels. Fuel cells present a viable alternative to conventional propulsion systems. In the context of light aircraft applications, proton exchange membrane fuel cells (PEMFCs) have recently attracted growing interest as a substitute for internal combustion engines (ICEs). However, their performance is highly sensitive to altitude variations, primarily due to limitations in compressor efficiency and instability in cathode pressure. To address these challenges, this research presents a comprehensive numerical model that couples a PEMFC system with a dynamic air compressor model under altitude-dependent conditions ranging from 0 to 3000 m. Iso-efficiency lines were integrated into the compressor map to evaluate its behavior across varying environmental parameters. The study examines key fuel cell stack characteristics, including voltage, current, and net power output. The results indicate that, as altitude increases, ambient pressure and air density decrease, causing the compressor to work harder to maintain the required compression ratio at the cathode of the fuel cell module. This research provides a detailed prediction of compressor efficiency trends by implementing iso-efficiency lines into the compressor map, contributing to sustainable aviation and aligning with global goals for low-emission energy systems by supporting cleaner propulsion technologies for lightweight aircraft. Full article

This work studies the feasibility of integrating a hydrogen-powered propulsion system in a regional aircraft at the conceptual design level. The developed system consists of fuel cells, which will be studied at three technological levels, and batteries, also studied for four hybridization factors (X = 0, 0.05, 0.10, 0.20). Hydrogen can absorb great thermal loads since it is stored in the tank at cryogenic temperatures and is used as fuel in the fuel cells at around 80 °C. Taking advantage of this characteristic, two thermal management system (TMS) architectures were developed to ensure the proper functioning of the aircraft during the designated mission: A1, which includes a vapor compression system (VCS), and A2, which omits it for a simpler design. The models were developed in MATLAB^® and consist of different components and technologies commonly used in such systems. The analysis reveals that A2, due to the exclusion of the VCS, outperformed A1 in weight (10–23% reduction), energy consumption, and drag. A1’s TMS required significantly more energy due to the VCS compressor. Hybridization with batteries increased system weight substantially (up to 37% in A2) and had a greater impact on energy consumption in A2 due to additional fan work. Hydrogen’s heat sink capacity remained underutilized, and the hydrogen tank was deemed suitable for a non-integral fuselage design. A2 had the lowest emissions (10–20% lower than A1 for X = 0), but hybridization negated these benefits, significantly increasing emissions in pessimistic scenarios. Full article

This paper presents a robust optimization-based approach for voyage and power generation scheduling to enhance the economic efficiency and reliability of electric propulsion ships powered by polymer electrolyte membrane fuel cells (PEMFCs) and battery energy storage systems (BESSs). The scheduling method is formulated considering generation cost curves of PEMFCs with mixed-integer linear programming (MILP) and is extended to a robust optimization framework that accounts for marine environmental uncertainties. The robust optimization approach, implemented via the column-and-constraint generation (C&CG) method, ensures stable operation under various uncertainty scenarios, such as wave speed and direction influenced by wind and tidal currents. To validate the proposed method, a simulation was conducted under realistic operational conditions, followed by a case study comparing the MILP and robust optimization approaches in terms of economic efficiency and reliability. Additionally, the optimization model incorporated degradation costs associated with PEMFCs and BESSs to account for long-term operational efficiency. The case study assessed the performance of both methods under load variation scenarios across different marine environmental uncertainties. Full article

Hydrogen-powered aviation is gaining momentum as a sustainable alternative to fossil-fueled flight, yet the field faces complex technological and operational challenges. To better understand commercial innovation pathways, this study analyzes the claims sections of 166 hydrogen aviation patents issued between 2018 and 2024. Unlike prior studies that focused on patent titles or abstracts, this approach reveals the protected technical content driving commercialization. The study classifies innovations into seven domains: fuel storage, fuel delivery, fuel management, turbine enhancement, fuel cell integration, hybrid propulsion, and safety enhancement. Thematic word clouds and term co-occurrence networks based on natural language processing techniques validate these classifications and highlight core technical themes. Scientometric analyses uncover rapid patent growth, rising international participation, and strong engagement from both established aerospace firms and young companies. The findings provide stakeholders with a structured view of the innovation landscape, helping to identify technological gaps, emerging trends, and areas for strategic investment and policymaking. This claims-based method offers a scalable framework to track progress in hydrogen aviation and is adaptable to other emerging technologies. Full article

Fuel cells, propulsion systems, and reaction control systems (RCSs) are just a few of the space applications that depend on pressure vessels (PVs) to safely hold high-pressure fluids while enduring extreme environmental conditions both during launch and in orbit. Under these challenging circumstances, PVs must be lightweight while retaining structural integrity in order to increase the efficiency and lower the launch costs. PVs have significant challenges in space conditions, such as extreme vibrations during launch, the complete vacuum of space, and sudden temperature changes based on their location within the satellite and orbit types. Determining the operational temperature limits and endurance of PVs in space applications requires assessing the combined effects of these factors. As the main propellant for satellites and rockets, hydrogen has great promise for use in future space missions. This study aimed to assess the structural integrity and determine the thermal operating limits of different types of hydrogen pressure vessels using finite element analysis (FEA) with Ansys 2019 R3 Workbench. The impact of extreme space conditions on the performances of various kinds of hydrogen pressure vessels was analyzed numerically in this work. This study determined the safe operating temperature ranges for Type 4, Type 3, and Type 1 PVs at an operating hydrogen storage pressure of 35 MPa in an absolute vacuum. Additionally, the dynamic performance was assessed through modal and random vibration analyses. Various aspects of Ansys Workbench were explored, including the influence of the mesh element size, composite modeling methods, and their combined impact on the result accuracy. In terms of the survival temperature limits, the Type 4 PVs, which consisted of a Nylon 6 liner and a carbon fiber-reinforced epoxy (CFRE) prepreg composite shell, offered the optimal balance between the weight (56.2 kg) and a relatively narrow operating temperature range of 10–100 °C. The Type 3 PVs, which featured an Aluminum 6061-T6 liner, provided a broader operational temperature range of 0–145 °C but at a higher weight of 63.7 kg. Meanwhile, the Type 1 PVs demonstrated a superior cryogenic performance, with an operating range of −55–54 °C, though they were nearly twice as heavy as the Type 4 PVs, with a weight of 106 kg. The absolute vacuum environment had a negligible effect on the mechanical performance of all the PVs. Additionally, all the analyzed PV types maintained structural integrity and safety under launch-induced vibration loads. This study provided critical insights for selecting the most suitable pressure vessel type for space applications by considering operational temperature constraints and weight limitations, thereby ensuring an optimal mechanical–thermal performance and structural efficiency. Full article

Unmanned aerial vehicles, known today as drones, in the beginning, were small-dimension research models powered by small electric motors fed from electrical batteries. The propulsion system for these drones had to be adapted to the specific applications along their development. Electric and hybrid-electric propulsion drones represent a rapidly developing field in the aerospace industry. Electric drones are those with purely electric propulsion fed from batteries, while hybrid-electric ones have a hybrid propulsion system combining a thermal engine and an electric motor. Another class of hybrid-electric drones includes those with an electric propulsion system fed from fuel cells and batteries. This paper proposes the configuration of an electric propulsion system with a hybrid power source for a transport drone, as well as an analysis of the special electrical components onboard an electric drone, such as batteries, fuel cells, and electric motors. In the final part of the paper, this propulsion system is modeled and analyzed in Matlab/Simulink version 2021a. Design software and simulation tools specifically developed for hybrid-electric drones are essential for ensuring the accuracy and efficiency of these processes. Electric drones have the advantage of zero emissions, but at present, the batteries are still too heavy for aviation applications. By using hydrogen fuel cells as the main power source, it is possible to considerably reduce the power source weight. This is an important advantage of the system proposed in this work. Using hydrogen fuel cells in aircraft and drone propulsion is an important trend in the scientific world. This technology seems to be mature enough to be implemented in aviation. From a technical point of view, these kinds of systems are already feasible. Their usefulness and reliability have to be proven in time. Full article

Proton exchange membrane fuel cells (PEMFCs) offer a promising zero-emission power solution for maritime transportation, yet thermal management remains challenging due to localized overheating and non-uniform temperature distribution. To address the trade-off between pressure drop and thermal performance in marine PEMFC cooling plates, this study developed and systematically evaluated six flow channel configurations through CFD simulations. Parametric analysis coupled with orthogonal experimental design was employed to explore the effects of secondary flow channel number (N), angle (α), width (d), and spacing (L). The results demonstrated that Type B (parallel flow with secondary channels) reduced the pressure drop by 28.2% while achieving the highest cooling efficiency coefficient (2.66 × 10⁴) compared to conventional configuration. Range analysis further ranked parameter sensitivity and identified optimal parameter combinations for distinct optimization objectives: thermal performance (N = 7, α = 30°, d = 0.5 mm, and L = 2.5 mm), pressure drop (N = 8, α = 75°, d = 1.5 mm, and L = 2.5 mm), and cooling efficiency (N = 8, α = 90°, d = 1.5 mm, and L = 2.5 mm). These findings provide practical guidelines for designing cooling plates that address thermal-hydraulic requirements in marine PEMFC systems, advancing their viability for maritime propulsion applications. Full article

The potential of utilizing the rejected heat of a fuel cell system to improve the aircraft propulsive efficiency is discussed for various flight conditions. The thermodynamic background of the process and the connection of power consumption in the fan of the ducted propulsor and fuel cell heat are given, and a link between these two components is presented. A concept that goes beyond the known ram heat exchanger is discussed, which outlines the potential benefits of integrating a fan upstream of the heat exchanger. The influence of the fan pressure ratio, flight speed, and altitude, as well as the temperature level of the available fuel cell heat on the propulsive efficiency, is presented. A correlation between the fan pressure ratio, flight speed, and exchangeable fuel cell heat is established, providing a simplified computational approach for evaluating feasible operating conditions within this process. This paper identifies the challenges of heat exchanger integration at International Standard Atmosphere sea level conditions and its benefits for cruise flight conditions. The results show that for a flight Mach number of 0.8 and a fan pressure ratio of 1.5 at a cruising altitude of 11,000 m, the propulsion efficiency increases by approximately 8 percentage points compared to a ducted propulsor without heat utilization. Under sea-level conditions, the concept does not offer any performance advantages over a ducted propulsor. Instead, it exhibits either comparable or reduced propulsive efficiency. Full article

With the increasing severity of global environmental issues and the pressure from the strict pollutant emission regulations proposed by the International Maritime Organization (IMO), the shipping industry is seeking new types of marine power systems that can replace traditional propulsion systems. Marine fuel cells, as an emerging energy technology, only emit water vapor or a small amount of carbon dioxide during operation, and have received widespread attention in recent years. However, research on their application in the shipping industry is relatively limited. Therefore, this paper collects relevant reports and literature on the use of fuel cells on ships over the past few decades, and conducts a thorough study of typical fuel cell-powered vessels. It summarizes and proposes current design schemes and optimization measures for marine fuel cell power systems, providing directions for further improving battery performance, reducing carbon emissions, and minimizing environmental pollution. Additionally, this paper compares and analyzes marine fuel cells with those used in automotive, aviation, and locomotive applications, offering insights and guidance for the development of marine fuel cells. Although hydrogen fuel cell technology has made significant progress in recent years, issues still exist regarding hydrogen production, storage, and related safety and standardization concerns. In terms of comprehensive performance and economics, it still cannot effectively compete with traditional internal combustion engines. However, with the continued rapid development of fuel cell technology, marine fuel cells are expected to become a key driver for promoting green shipping and achieving carbon neutrality goals. Full article

The power to weight ratio of power plants is an important consideration, especially in the design of Unmanned Aircraft System (UAS). In this paper, a UAS with an MTOW of 35.3 kg, equipped with a fuel cell as a prime power supply to provide electrical power to the propulsion system, is considered. A pressure vessel design that can estimate and determine the total size and weight of the combined power plant of a fuel cell stack with hydrogen and air/oxygen vessels and the propulsion system of the UAS for high-altitude operation is proposed. Two scenarios are adopted to determine the size and weight of the pressure vessels required to supply oxygen to the fuel cell stack. Different types of stainless-steel materials are used in the design of the pressure vessel in order to find an appropriate material that provides low size and weight advantages. Also, the design of a hydrogen pressure vessel and mass estimation are also considered. The estimated sizes and weights of the hydrogen and oxygen vessels of the power plant and propulsion system in this research offer a maximum of four hours of flying time for the UAS mission; this is based on a Horizon (H-1000) Proton Exchange Membrane (PEM) stack. Full article

This study presents an AI-driven energy management system (EMS) for a hybrid electric flying car, integrating multiple power sources—including solid-state batteries, Li-ion batteries, fuel cells, solar panels, and wind turbines—to optimize power distribution across various flight phases. The proposed EMS dynamically adjusts power allocation during takeoff, cruise, landing, and ground operations, ensuring optimal energy utilization while minimizing losses. A MATLAB-based simulation framework is developed to evaluate key performance metrics, including power demand, state of charge (SOC), system efficiency, and energy recovery through regenerative braking. The findings show that by optimizing renewable energy collecting, minimizing battery depletion, and dynamically controlling power sources, AI-based predictive control dramatically improves energy efficiency. While carbon footprint assessment emphasizes the environmental advantages of using renewable energy sources, SOC analysis demonstrates that regenerative braking prolongs battery life and lowers overall energy use. AI-optimized energy distribution also lowers overall operating costs while increasing reliability, according to life-cycle cost assessment (LCA), which assesses the economic sustainability of important components. Sensitivity analysis under sensor noise and environmental disturbances further validates system robustness, demonstrating that efficiency remains above 84% even under adverse conditions. These findings suggest that AI-enhanced hybrid propulsion can significantly improve the sustainability, economic feasibility, and real-world performance of future flying car systems, paving the way for intelligent, low-emission aerial transportation. Full article

Hydrogen fuel cell systems are a viable option for electrified aero engines due to their efficiency and environmental benefits. However, integrating these systems presents challenges, notably in terms of overall system weight and thermal management. Heat exchangers are crucial for the effective thermal management system of electric propulsion systems in commercial electrified aviation. This paper provides a comprehensive review of various heat exchanger types and evaluates their potential applications within these systems. Selection criteria are established based on the specific requirements for air and hydrogen heat exchangers in electrified aircraft. The study highlights the differences in weighting criteria for these two types of heat exchangers and applies a weighted point rating system to assess their performance. Results indicate that extended surface, microchannel, and printed circuit heat exchangers exhibit significant promise for aviation applications. The paper also identifies key design challenges and research needs, particularly in enhancing net heat dissipation, increasing compactness, improving reliability, and ensuring effective integration with aircraft systems. Full article

The use of novel technologies for low-emission and more efficient aviation requires not only the achievement of a given technology readiness level, but also their integration into aircraft concepts. Furthermore, the assessment of unconventional configurations requires robustness considerations already in the conceptual aircraft design phase. In this context, the next developmental milestone of the Advanced Morphological Approach (AMA) as a conceptual aircraft design method is presented by introducing design parameter uncertainties for disruptive technologies. The purpose of this work is the integration verification of Bayesian networks (BNs) into the AMA process for semi-quantitative system modeling and uncertainty propagation. This allowed for the visualization of uncertainties in the solution space, and therefore the depiction and initial estimation of configuration robustness. The verification is demonstrated on an existing conceptual design use case of a regional aircraft for 50 passengers, similar to the ATR 42-600. It investigated hybrid-electric and fuel-cell-based hybrid propulsion systems for 2030, 2040, and 2050 as potential years of entry into service. A BN-based system model has been developed by verifying its quality, adding parameter uncertainty and three energy price scenarios. The executed Bayesian inference propagated the uncertainties through the system and allowed for the visualization of a solution space. The presented uncertainties for the mission energy, mission energy price, and emission criteria for each design solution yield a more reliable basis for robustness analysis and decision-making. Full article

To enable climate-neutral aviation, improving the energy efficiency of aircraft is essential. The research project Synergies of Highly Integrated Transport Aircraft investigates cross-disciplinary synergies in aircraft and propulsion technologies to achieve energy savings. This study examines a fuel cell electric powered configuration with distributed electric propulsion. For this, a reverse-engineered ATR 72-500 serves as a reference model for calibrating the methods and ensuring accurate performance modeling. A baseline configuration featuring a state-of-the-art turboprop engine with the same entry-into-service is also introduced for a meaningful performance comparison. The analysis uses an enhanced version of the Stanford University Aerospace Vehicle Environment (SUAVE), a Python-based aircraft design environment that allows for novel energy network architectures. This paper details the preliminary aircraft design process, including calibration, presents the resulting aircraft configurations, and examines the integration of a fuel cell-electric energy network. The results provide a foundation for higher fidelity studies and performance comparisons, offering insights into the trade-offs associated with hydrogen-based propulsion systems. All fundamental equations and methodologies are explicitly presented, ensuring transparency, clarity, and reproducibility. This comprehensive disclosure allows the broader scientific community to utilize and refine these findings, facilitating further progress in hydrogen-powered aviation technologies. Full article