Search Results (56)

The development of low-emission and reliable propulsion systems is essential for extending the operational capability of unmanned aerial vehicles (UAVs). Although aviation decarbonization is widely recognized as an important objective, it must be considered within the broader context of limited renewable-energy availability. Recent system-level analyses of transportation decarbonization have shown that the allocation of renewable electricity and sustainable fuels should prioritize sectors where direct electrification is most efficient, while hard-to-electrify sectors require alternative pathways. Aviation is one of the most difficult transport sectors to electrify because of strict energy-density requirements, especially for long-endurance airborne platforms. Therefore, sustainable liquid fuels and hybrid propulsion systems should not be considered universal replacements for electrification, but rather complementary solutions for applications where batteries alone cannot provide the required endurance, payload capacity or operational flexibility. In this context, the present study focuses on alcohol–kerosene blends for hybrid UAV power systems, where liquid-fuel energy density and partial emission reduction remain relevant engineering requirements. This work provides one of the first systematic experimental evaluations of ethanol–, butanol– and octanol–kerosene blends in a micro-turboprop engine operating as part of a hybrid UAV power-generation architecture. Unlike previous studies focused mainly on micro-turbojet thrust response, the present work evaluates the coupled influence of alcohol chain length and blending ratio on exhaust gas temperature, gaseous emissions, electrical output and operational stability under multi-load conditions representative of UAV operation. Jet-A and nine alcohol–kerosene blends containing 10%, 20% and 30% ethanol, butanol or octanol by volume were tested over four operating regimes, from idle to 2500 W electrical load. The results show that ethanol blends provided the strongest CO reduction, with E30 reducing CO by 24.9% relative to Jet-A under R3, while E10 offered the most balanced behavior across the full operating range. Higher ethanol fractions improved CO suppression but introduced NOx and low-load stability penalties. Octanol blends, particularly O20, exhibited the most kerosene-like and stable response, supporting reliable power delivery with reduced operational variability. Butanol blends showed intermediate behavior without providing a dominant advantage. A multi-criteria evaluation combining emissions, EGT behavior, relative performance, operational stability and cost identified E10 as the best overall compromise for hybrid UAV use. The study demonstrates that alcohol chain length produces nonlinear system-level effects in hybrid micro-turboprop architectures and provides an experimental basis for fuel selection in low-emission UAV power systems. Full article

Integrating a heat exchanger (HEX) into the cooling duct of a high-power fuel-cell-based aircraft presents a critical trade-off between thermal performance and aerodynamic penalties. The present study addresses this challenge through the design and system-level analysis of a HEX integrated into the cooling duct. Developed as part of the Clean Aviation project FAME, the design features a rectangular inlet, a circular outlet, and a tilted HEX. The evaluation is performed using high-fidelity Large Eddy Simulations (LESs). The HEX is modeled with a porous media approach based on the Darcy–Forchheimer equation, while the simulations are carried out using a self-adapted version of the pisoFoam solver, termed pisoTempFoam, to account for heat transfer. The study reveals that while component-level design choices, such as a straight inlet and tilted HEX configuration, successfully mitigate local flow separation and duct-induced losses, a critical system-level performance issue emerges. The analysis demonstrates that the cooling duct design, when subjected to realistic operational conditions, generates the high pressure head to overcome the resistance of the HEX. The external aerodynamic analysis also indicates that the HEX resistance is a critical factor, and without overcoming it the system fails to capture the required air mass flow rate, compromising thermal management. The findings highlight the necessity to optimize the design, by an adapted duct shape or an auxiliary fan, to overcome the HEX-induced pressure drop. The porous media approach is thereby validated as an effective tool for rapid system-level design analysis, despite its inherent limitation in capturing detailed downstream turbulence. Full article

One approach to make the aviation sector climate-compatible is to minimize greenhouse gas emissions by employing electric and hybrid electric propulsion system concepts. The introduction of novel technologies introduces novel failure modes and consequently effects of failure conditions on the aircraft. This study examines the safety of distributed electrified aircraft propulsion systems and evaluates individual failure scenarios in the context of the relevant certification requirements. A comparison of the functional architectures of legacy and Electric Hybrid Propulsion Systems (EHPSs) is conducted and the existing aircraft-level requirements, that are based on experience with conventional propulsion systems, are assessed for their applicability to the certification of novel propulsion systems. Subsequently the relevant safety items from these requirements are identified in the context of a critical loss of thrust scenario. Analysis methods are assigned to these safety items in order to prove the compliance of the novel systems with the legacy certification documentation. This results in a validation concept for EHPS at the aircraft level in the context of a critical loss of thrust. In particular, the distribution of individual subsystems and components throughout the aircraft leads to reduced isolation of the respective propulsion systems and thus potential safety-critical interactions with adjacent systems. The analysis demonstrates that the use of distributed propulsion systems increases the risk of multiple failures of redundant systems and cascading failure propagation, highlighting the need to develop targeted means of prevention and the mitigation of failure conditions for these systems. Full article

Effective thermal management is crucial for the development of future electrified aircraft propulsion systems. One of the most challenging phases is the take-off phase, which imposes particularly high demands on cooling systems. In addition, the aerodynamic drag during cruise flight has to be kept to a minimum. This study introduces a novel experimental thermal management system using a test stand with a modular air duct (TMTmad), which is designed specifically to investigate different configurations of air supply and heat exchanger in fuel cell-based electrified propulsion systems. Given the versatility of nacelle-integrated electrified propulsion architectures, this approach offers high flexibility in the design and integration of thermal management systems. This includes aspects such as the location, orientation and geometry of an air-cooled heat exchanger (HEX), as well as the inlet and outlet configurations. Moreover, the optimization of the uniform flow guidance of the duct flow within the nacelle and the integration of additional fans to ensure airflow under critical conditions can be studied. The main heat source delivers up to 6 $\mathrm{k}\mathrm{W}$ of heating power with a temperature range from −20 °C to 200 °C. The study measures the heat flux and pressure losses within these systems and includes a thorough fluid flow analysis. Furthermore, the experimental data serves as a valuable resource for validating numerical models of cooling ducts, enhancing the accuracy and reliability of future design iterations. Full article

The weight of battery modules keeps hindering them from being commercially attractive as the sole power supply for short-range electric passenger flights. Furthermore, the challenging requirements for aerospace applications limit the range of options for module elements and complicate the implementation of lightweight solutions. Hence, the objective of this study is to elaborate and evaluate concepts for battery modules to identify promising solutions for electrified aircraft propulsion systems. For that purpose, a house of quality is compiled to assess the relations between options for module elements and module requirements, as well as correlations between options. Potential concepts are elaborated by combining suitable elements. Finally, the concepts are evaluated to highlight the most preferable and compatible ones for aircraft battery modules. Full article

The decarbonization of railway transportation requires energy-efficient propulsion technologies capable of reducing fossil fuel dependence and improving the operational efficiency of rail systems. Hydrogen fuel cell (FC)–battery hybrid powertrains have emerged as a promising alternative for non-electrified high-speed railway lines due to their potential for energy-efficient operation and reduced environmental impact. However, the optimal sizing and coordinated operation of these hybrid energy sources remain a challenging problem because energy efficiency, component degradation, and system cost are strongly interrelated. This study proposes a degradation-aware mixed-integer linear programming (MILP) framework for the optimal sizing and energy management of a FC–battery hybrid propulsion system for high-speed trains. The optimization simultaneously determines the capacities of FC stacks, battery modules, and hydrogen storage while minimizing the overall lifecycle cost and improving system energy utilization. Battery and FC degradation models are incorporated into the optimization problem through linearized formulations to ensure realistic long-term operation. The proposed framework is evaluated using real operational data in the approximately 71 min high-speed rail corridor between Bursa and Osmaneli in Türkiye. Simulation results show that increasing battery capacity significantly reduces FC stress while enabling more efficient energy utilization through regenerative braking and power balancing. The results indicate that optimal battery sizing can notably improve system performance, reducing the total lifecycle cost from $1.12\times {10}^9$ USD to $5.65\times {10}^8$ USD, while decreasing the required number of fuel cell units from 31 to 18 and mitigating fuel cell degradation. The proposed approach provides an effective design tool for energy-efficient hydrogen-powered railway systems. Full article

In order to provide an innovative form of urban air mobility, a new and versatile generation of small, highly automated aircraft is currently being developed. This is made feasible by the development of new technologies such as electrified powertrains, Vertical Take-Off and Landing capabilities and distributed propulsion systems. The operation of these novel aircraft types will generate a new source of air traffic noise. In particular, the perception of noise and the annoyance caused by these aircraft and their distributed propulsion systems are likely to deviate from those of conventional aircraft and will also depend on psychoacoustic effects. Thus, the noise emission and its subjective perception will be key factors for the success of urban air mobility vehicles and their acceptance by society. In order to investigate acoustic effects that enable low-noise aircraft design, a multidisciplinary approach is applied to develop new aircraft concepts for urban air mobility. This approach includes the conceptual design of two vehicles, one vehicle with tilt-rotors and one with tiltable, ducted fans; the sizing of an electric powertrain; the design and manufacturing of a wingtip rotor; and the design and manufacturing of the low-speed ducted fans. This paper presents the design of the two vehicle architectures, including their electric powertrain, as well as the aerodynamic and acoustic performance of the rotor and fan. Full article

This paper investigates the feasibility of an interior permanent magnet (IPM) rotor for 1 MW-class high-speed permanent magnet synchronous machines (PMSMs) in a hybrid propulsion system of electrified aviation. A double-layer IPM machine and a surface-mounted PM (SPM) benchmark machine with Halbach-array PMs, which are typically employed in aviation applications; are designed using the same design specifications, the same stator, double-three-phase winding layout, physical air-gap length, outer and inner diameters of rotor; and the same materials. The rotor robustness of the IPM machine using high-strength iron material has been verified through mechanical strength analysis with an outstanding safety factor margin. The electromagnetic performances of IPM and SPM benchmark machines are compared. It is found that the IPM design can achieve similar high torque/power density and high efficiency to the SPM benchmark machine, using 48% less rare-earth PM materials and a simpler rotor structure without a carbon fiber sleeve for easy manufacturing. The investigation confirms the feasibility of IPM topology for MW-class high-speed aviation propulsion machines for lower cost and more sustainable purposes. Full article

An efficient thermal management system (TMS) is essential for ensuring hybrid-electric aircraft (HEA) can handle the significant heat rejection required by electrified propulsion. This paper presents a system-level analysis of a compact P2PL TMS for a 1.4 MW battery generating a 70 kW heat load. A modular modeling method was used to size the key components, and then dynamic simulations were conducted under varying environmental conditions. The results indicate that a compact TMS weighing 22 kg can be developed, with a condenser heat transfer area of 26.20 m² and operating with a refrigerant mass flow rate of 0.56 kg/s while maintaining low pump power consumption at 22 W. This system can successfully regulate a battery’s temperature so that it remains below 40 °C in both standard (15 °C) and cold (−20 °C) environments. Pressure analysis confirmed the system’s flexibility and its ability to control battery temperature between 27 °C and 38 °C by adjusting the working pressure (6–8 bar). Furthermore, under hot day conditions (40 °C), battery temperature can be maintained at 47.6 °C. Even under extreme conditions (50 °C), the TMS limits the temperature to 57.45 °C, ensuring it stays within the safe operating range. Full article

A promising approach to advancing sustainable urban mobility is the increased use of light electric vehicles, such as e-cycles and their cargo-carrying variants: e-cargo cycles. These micromobility vehicles fall between e-cycles and conventional vehicles in terms of transport capacity, range, and cost. A key advantage of e-cargo cycles over their non-electrified counterparts is the electric powertrain, which enables them to carry heavier payloads, travel longer distances, and reduce driver fatigue. Since the primary use of e-cargo cycles is urban parchment deliveries, trip efficiency plays a critical role in their effectiveness within urban logistics. This efficiency is influenced by factors such as travel distance, traffic density, and the weight and volume of the delivery payload. While higher delivery capacity generally enhances efficiency, studies have shown that as the drop size increases, the efficiency of e-cargo cycle delivery trips tends to decline. A practical way to address this limitation is the use of cargo attachments, such as trailers. These micromobility solutions are already widely implemented globally and significantly enhance transport capacity. This paper reports the process of designing and testing the control algorithm of an electrical system for an experimental attachment demonstrator that can be used to convert most cycle vehicles into cargo variants. The system integrates two 250 W BLDC hub motors, two 576 Wh lithium-ion batteries, dual load-cell sensing in the coupling element, and an STM32-based controller to provide independent propulsion and synchronization with the leading cycle. The force-based control strategy enables automatic adaptation to varying payloads typically encountered in urban logistics, which is supported by the variable storage volume capable of transporting payloads of up to 200 kg. Full article

The decarbonization of regional passenger rail transport is one of the key challenges for the sustainable transformation of the transport sector in Poland. While railway transportation remains one of the least carbon-intensive modes of transport, significant emission disparities persist between electrified and non-electrified lines, where diesel traction is still prevalent. This article presents a comparative analysis of various propulsion technologies—diesel, hybrid, battery-electric and hydrogen fuel-cell—taking into account both local (TTW) and total (WTW) greenhouse gas emissions. The study incorporates Poland’s current energy mix and proposes a methodological framework to assess emissions at the line level. It highlights the risks of focusing exclusively on in situ zero-emission technologies and calls for a more flexible, efficiency-based approach to fleet modernization. The analysis demonstrates that hybrid and optimized combustion-based systems can provide substantial emission reductions in the short term, especially in rural and transitional regions. The paper also critically discusses transport funding policies, pointing to discrepancies between incentives for private electric mobility and the lack of support for public transport solutions that could effectively counter mobility exclusion. The presented methodology and conclusions provide a basis for further research on transport decarbonization strategies tailored to national and regional contexts. Full article

Aquaculture lagoons must reconcile visitor access with biodiversity protection. This study integrates results of a large survey of the attitudes of tour operators with field observations of fish populations to test whether operator choices can align tourism and conservation. Using data from 801 guided-tour participants in Taiwan’s Cigu Lagoon, a sequential experience hierarchy was validated whereby environmental knowledge enhanced attitudes, strengthened perceived guide professionalism, induced flow, and ultimately increased conservation intention (R² = 0.523). Experiential service quality exerted stronger effects than functional quality (β = 0.287 vs. 0.156; both p < 0.001). Parallel underwater monitoring indicated that electric, low-vibration motors were associated with richer fish assemblages and larger fish body sizes; fish abundance is 61% higher and mean body length 38% greater, with community composition differing significantly by motor type (PERMANOVA, p < 0.001). Together, these results link training and technology adoption to measurable ecological gains and pro-conservation motivation, indicating that electrified propulsion and interpretive practice are mutually reinforcing levers for biodiversity-positive tourism. The framework offers directly actionable criteria—motor choice, guide development, and safety/facility context—for transitioning small-scale fisheries and recreation toward low-impact marine experiences. Full article

Aviation is under increasing pressure to reduce carbon emissions in conventional transports and support the growth of low-altitude operations such as long-endurance eVTOLs. Hybrid-electric propulsion addresses these challenges by integrating the high specific energy of fuels or hydrogen with the controllability and efficiency of electrified powertrains. At present, the field of hybrid-electric aircraft is developing rapidly. To systematically study hybrid-electric propulsion control in aviation, this review focuses on practical aspects of system development, including propulsion architectures, system- and component-level modeling approaches, and energy management strategies. Key technologies in the future are examined, with emphasis on aircraft power-demand prediction, multi-timescale control, and thermal integrated energy management. This review aims to serve as a reference for configuration design, modeling and control simulation, as well as energy management strategy design of hybrid-electric propulsion systems. Building on this reference role, the review presents a coherent guidance scheme from architectures through modeling to energy-management control, with a practical roadmap toward flight-ready deployment. Full article

Since 1 January 2024, newly produced heavy-duty trailers are subject to the assessment of their performance regarding CO₂ and fuel consumption according to Implementing Regulation (EU) 2022/1362. The method is based on the already established approach for the CO₂ and energy consumption evaluation of trucks and buses, i.e., applying a combination of component testing and vehicle simulation using the software VECTO (Vehicle Energy Consumption calculation TOol). For the evaluation of trailers, generic conventional towing vehicles in combination with the specific CO₂ and fuel consumption-relevant properties of the trailer, such as mass, aerodynamics, rolling resistance etc., are simulated in the “VECTO Trailer” software. The corresponding results are used in the European HDV CO₂ standards with which manufacturers must comply to avoid penalty payments (2030: −10% for semitrailers and −7.5% for trailers compared with the baseline year 2025). Methodology and legislation are currently being extended to also cover the effects of electrified trailers (trailers with an electrified axle and/or electrically supplied auxiliaries) on CO₂, electrical energy consumption, and electric range extension (special use case in combination with a battery-electric towing vehicle). This publication gives an overview of the developed regulatory framework and methods to be implemented in a future extension of VECTO Trailer as well as a comparison of different e-trailer configurations and usage scenarios regarding their impact on CO₂, energy consumption, and electric range by applying the developed methods in a preliminary potential analysis. Results from this analysis indicate that e-trailers that use small batteries (5–50 kWh) to power electric refrigeration units achieve a CO₂ reduction of 5–10%, depending primarily on battery capacity. In contrast, e-trailers designed for propulsion support with larger batteries (50–500 kWh) and e-axle(s) (50–500 kW) demonstrate a reduction potential of up to 40%, largely determined by battery capacity and e-axle rating. Despite their reduction potential, market acceptance of e-trailers remains uncertain as the higher number of trailers compared with towing vehicles could lead to slow adoption, especially of the more expensive configurations. 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