Search Results (364)

Background: Smart-city road and intersection management increasingly aims to smooth bus operations and reduce stop-and-go driving, but cities often lack auditable indicators linking routine fleet data with comparable energy and environmental KPIs. Methods: This study develops a Monitoring–Reporting–Verification (MRV) workflow for daily bus records from a 2024 Polish metropolitan fleet (diesel, compressed natural gas (CNG), hybrid, and battery-electric buses). Records were quality checked, harmonized to MJ/km, aggregated to bus-month observations, and analyzed using a linear mixed-effects model with propulsion technology, season, and activity level as fixed effects and vehicle-level random intercepts. Environmental impacts were then calculated under well-to-wheel (WTW) boundaries using Environmental Footprint 3.1 (EF 3.1) impact categories, Poland’s 2024 electricity mix, and illustrative electricity-mix scenarios through 2050. Results: Relative to diesel, BEV and HEV were associated with lower adjusted energy intensity (ratios 0.272 and 0.681, respectively), whereas the CNG–diesel contrast was directionally higher but statistically inconclusive under the available CNG sample. BEV energy intensity more than doubled in winter in descriptive terms, and vehicle-specific heterogeneity remained high (ICC ≈ 0.61). The BEV climate profile improved under electricity decarbonization, while some EF categories showed mix-dependent trade-offs. The 3–10% traffic-management variants are interpreted as screening assumptions rather than measured ITS effects. Conclusions: Routine bus records can support auditable MRV and preliminary screening of fleet and corridor interventions, but causal traffic-management evaluation requires route-level trajectory, congestion, and before–after data. Full article

The transition toward sustainable aviation fuels for unmanned aerial vehicle propulsion requires alternative fuel blends that reduce emissions while maintaining stable power generation. This study investigates the combustion performance, electrical output, emission behavior, and near-field pollutant dispersion of butanol–kerosene blends in a hybrid micro-turboprop propulsion platform representative of UAV applications. Conventional kerosene and three butanol–kerosene blends, containing 10%, 20%, and 30% butanol by volume, were tested under four operating regimes ranging from idle to approximately 2.5 kW electrical load. Exhaust gas temperature, CO, NO, NOx, SO₂, electrical power output, throttle response, and pollutant dispersion behavior were evaluated experimentally, while polynomial regression was applied to quantify throttle–power relationships. The results show that the 20% butanol blend provided the most favorable overall performance. Relative to conventional kerosene, B20 achieved approximately 4.8% higher electrical power output at equivalent throttle settings, reduced fuel demand by nearly 3.9%, and decreased the throttle requirement for 2 kW electrical output by almost 5%. In terms of emissions, B20 reduced CO formation across low and intermediate operating regimes while maintaining moderate NOx levels and stable exhaust gas temperature behavior. Increasing butanol content also improved plume homogenization: the anisotropy index decreased from 2.41 for B10 to 1.96 for B20 and 1.58 for B30, while high-concentration plume regions were reduced by up to 31%. However, B30 introduced stronger evaporative cooling, ignition delay effects, and reduced mid-load responsiveness. Overall, moderate butanol blending, particularly B20, represents the most balanced solution for reducing the environmental footprint of hybrid UAV micro-turboprop propulsion without significant performance penalties. Full article

This paper arises from an ARPA-E-sponsored project seeking design opportunities to retrofit existing aircraft with hybrid electric propulsion systems. Engineers typically configure aircraft to fly a given payload over a long range, which is subject to field performance constraints. In practice, operators fly transport aircraft (civilian and military) in a manner where dispatch consciously trades payload and/or range to enable safe operations to and from short runways. This work describes a simple yet novel analytical process suitable for inclusion in conceptual design or technology portfolio trade study evaluations to assess the impacts of weight-restricted dispatch upon usable payloads. We find that options that increase low-speed thrust may maintain or improve the useful payload even if it substantially increases aircraft fixed weight. Conversely, otherwise desirable technologies that decrease low-speed thrust may severely impact the useful payload of aircraft operating to and from short runways. Full article

International and regional decarbonisation policies are accelerating the deployment of hybrid electric propulsion systems (HEPSs) in short-sea and coastal trades, yet most existing design studies focus on ferries or tugs, rely on stylised duty cycles, and treat battery degradation only superficially. This paper proposes an integrated, data-driven framework for the design and dynamic performance optimisation of a diesel–battery HEPS for a coastal general cargo vessel operating on short-sea routes. A multi-year automatic identification system (AIS) and logbook data are processed to derive route-specific, time-resolved operating profiles, which drive a DC-based hybrid propulsion model comprising diesel generator sets, propulsion motors and a lithium-ion battery energy storage system (ESS). A degradation-aware ESS model is embedded in a life-cycle cost (LCC) formulation that explicitly accounts for battery replacement timing and residual value. The hybrid design problem is cast as a bi-level optimisation: an upper level determines engine rating and ESS capacity to minimise LCC, while fuel savings and emissions are evaluated as key parallel performance indicators, while a lower level uses dynamic programming to compute optimal power split trajectories under state-of-charge, C-rate and power constraints. A surrogate-assisted global search with Kriging and Expected Improvement is employed to manage the computational burden of repeated lower-level optimisations. Case-study results for representative coastal routes show that the optimised hybrid configurations achieve fuel savings of 16–21%, CO₂ reductions of 17–20%, and LCC reductions of 8–14% relative to a conventional mechanical baseline, outperforming a rule-based hybrid design. Sensitivity analyses with varying fuel prices and ESS costs confirm the robustness of the proposed framework and highlight the importance of explicitly coupling degradation-aware ESS. 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

The aviation sector is under increasing pressure to cut emissions, prompting strong interest in alternative propulsion systems. This study examines the potential of hybrid-electric aircraft relying on electrochemical energy storage and conversion units (EC-ESC), consisting of proton exchange membrane fuel cell systems coupled with batteries. A design space exploration framework is proposed to size and control these systems for regional aircraft, treating fuel cell system nominal power and battery C-rate as key design variables, while also accounting for in-flight degradation. A flexible degradation-aware control strategy manages power sharing within the co-design strategy, which seeks a configuration minimizing the total EC-ESC equivalent mass. The entire procedure is designed versatilely enough to be applicable for the model-based design and energy management of EC-ESC units destined for several end uses, e.g., short/medium-haul, and long-haul aircraft or automotive. Full article

This study presents an optimal strategy for hybrid electric propulsion ships with variable-speed diesel generators (VSDGs) and proton exchange membrane fuel cells (PEMFCs). With the International Maritime Organization imposing stricter environmental regulations, shipboard power systems must satisfy emission limits and operational constraints cost-effectively. To address this challenge, a Lagrangian relaxation (LR)-based optimization framework integrating unit commitment and economic dispatch is developed. Practical operational constraints reflecting realistic shipboard conditions are incorporated. The effectiveness of the proposed framework was evaluated through simulation-based case studies under various realistic operating conditions. Simulation results show that the proposed LR framework achieves lower total fuel costs than conventional priority-list methods while complying with environmental regulations under diverse operating scenarios. Full article

In this work, a dynamic polymer electrolyte membrane (PEM) fuel cell system is modelled in Modelica using the in-house developed, open-source library ThermoFluidStream. The focus lies on the fuel cell stack, the hydrogen fuel supply and the air supply. Additionally, the thermal management and the power electronics are considered in a simplified manner. Dynamic simulations are carried out for this system over an exemplary aircraft gate-to-gate mission. Simultaneously, a baseline control scheme is developed to provide the fuel cell with sufficient product gases in a suitable state regarding the temperature, pressure and relative humidity. The results indicate that the fuel cell system performs well with standard PI controllers. Only when strong dynamics occur, such as when going from taxi to take-off, does the control scheme show some weaknesses, as expected. This fuel cell system together with its control is a powerful baseline for future investigations. Full article

This paper presents the development and assessment of a 250-seat battery-electric aircraft with range extenders, designated D250-PHEP, developed within the DLR project EXACT. The concept investigates how hybrid-electric propulsion can combine the high efficiency of battery-electric operation on short routes with the range flexibility granted by gas-turbine-based range extenders. The propulsion system features four electrically driven propellers powered either by onboard batteries or by two gas turbines operating through a partially turbo-electric drive. In its base configuration, the aircraft carries a large battery enabling highly efficient hybrid operation up to 700–800 nautical miles. For improved performance at longer ranges, the design allows most battery modules to be removed, creating a mild-hybrid configuration with substantially lower mass and extended range capability. The modelling framework developed within EXACT enables a direct comparison with a turbofan and a turboprop baseline aircraft under consistent boundary conditions. The results indicate that large-scale battery-based energy storage becomes feasible once high-energy battery technology suitable for aviation reaches a pack-level specific energy of roughly 400 Wh/kg. Full article

This study documents the design, development, and evaluation of a purpose-built aerial firefighting fleet optimized for diverse wildfire suppression environments as part of the COLOSSUS project’s X-Challenge. The multidisciplinary effort encompassed aerodynamic design, propulsion system, systems integration, cost estimation, simulation, design of experiments, and fleet optimization. Key technical advancements include a conceptual hybrid electric Vertical Takeoff and Landing (eVTOL) aircraft design, and the integration of a series hybrid propulsion model into the System of Systems Inverse Design (SoSID) simulation toolkit, in which evaluation takes place at fleet level. Simulation results indicate that the proposed aircraft achieves competitive or superior effectiveness across all test scenarios, with the series hybrid configuration offering notable endurance and tactical adaptability. Full article

Aviation demand is projected to surpass 8 billion passengers per year by 2040, increasing the climate burden of kerosene-fueled propulsion. Conventional engines emit CO₂ and non-CO₂ species such as nitrogen oxides and soot, which significantly contribute to global warming. Hydrogen-based propulsion combining Solid Oxide Fuel Cells (SOFCs) with a Gas Turbine (SOFC–GT) can offer a carbon-neutral alternative with the potential for higher efficiencies than current turbofan and turboprop systems. In an SOFC–GT concept, waste heat from the SOFC is recovered in the turbine cycle, while the electrical output drives an electric motor, forming a hybrid turbomachinery–electric powertrain. Achieving SOFC operating temperatures of 650–800 °C at cruise conditions represents a key thermodynamic challenge, as compressor outlet conditions are insufficient. Two architectures are analyzed: direct coupling, where SOFC requirements define turbomachinery operation, and indirect coupling, which introduces air bypasses to increase flexibility. The results show that direct coupling enables higher cycle efficiency, whereas indirect coupling improves off-design operability at the expense of performance. Cross-validation of independent simulation frameworks strengthens the reliability of the findings and provides a foundation for evaluating SOFC–GT propulsion feasibility. Full article

Maritime transport is under increasing pressure to cut greenhouse gas and pollutant emissions to meet global decarbonization goals and tighter environmental standards. Ship electric propulsion systems offer a promising solution for short-range maritime operations, particularly for small vessels and coastal activities. Full-electric vessels can significantly reduce operational emissions; however, a key challenge is the extensive charging time for onboard energy storage, which can affect operational continuity and logistical efficiency. This study examines mission planning and energy management for a hybrid multi-source electric mail boat operating in the Aeolian archipelago. It evaluates the viability and performance of a daily inter-island route powered by a high-temperature methanol fuel cell, batteries, and photovoltaic panels. A routing and simulation framework was developed to model the boat’s itinerary among seven islands, accounting for realistic navigation speeds, scheduled stops, solar energy availability, and battery state-of-charge constraints. The study analyzes distance, travel time, energy consumption, solar power generation, and fuel–electric usage with high temporal resolution, enabling detailed analysis of power flows during sailing and docking. Several operational strategies were assessed, including periods of increased speed supported by battery assistance and fuel–electric cell output, combined with coordinated energy management to keep battery levels above a lower acceptable threshold while completing the route in a single day. The methodology provides a practical tool for planning low-emission island networks and supports the integration of innovative energy systems into small electric workboats operating in specific maritime regions. Full article

Maneuverability and performance of UAVs are strongly influenced by the adopted propulsion layout. Electrification has enabled modern UAVs to achieve unprecedented maneuverability, including hovering and VTOL (Vertical Take Off and Landing) capabilities, allowing the adoption of complex propulsion layouts otherwise impossible to manage with conventional fossil powered machines. Despite significant advancements in lithium-based cell technologies, the energy densities achieved by current storage systems remain insufficient to ensure extended operational autonomy. Hybrid systems represent an effective compromise, combining the high energy density of conventional fuels with agile power management of electric storage systems. In this work, the authors investigate the design, modelling, and control of an innovative autonomous compound helicopter equipped with a hybrid propulsion system. For this purpose, a comprehensive digital twin has been developed, capable of simulating the interactions among the vehicle, propulsion system, and energy management systems under a predefined mission profile. Full article

Sustainability is one of the guiding principles of the aviation industry. In the coming years, new sustainable aircraft concepts and propulsion technologies are expected to be developed and scaled up. One of the most promising solutions is the development of battery-powered aircraft. This paper aims to present the key concepts associated with these new aircraft designs. The first part of the paper provides an overview of the key advantages of battery-powered aircraft. It also identifies limitations that these designs will need to overcome to be scaled up. The second part focuses on the two main types of battery-powered aircraft. The difference between all-electric aircraft (AEA) and hybrid-electric aircraft is explained. The main advantages and limitations of each type are also discussed. The third part of the paper analyses the impact of introducing battery-powered aircraft on different aviation markets. Due to its relevance, the analysis of a new business model—Innovative Air Mobility (IAM)—is detailed. The development of battery-powered aircraft is discussed as a key driver for this business model. Full article