Search Results (514)

The reduction of the overall emissions of the aviation sector require the improvement of the overall aircraft efficiency. In the current aircraft design, the airframe and the propulsion system are designed separately and expected to reach limits for the overall aircraft efficiency. The integration of the engine into the airframe and the implementation of boundary layer ingestion (BLI) is a promising concept to improve the overall aircraft efficiency. However, this integration alters the engine intake flow and influences the intake characteristics significantly. In this study, numerical simulations as well as water channel experiments are performed to get insights into the challenges that occur due to BLI. An actuator disc simulation is performed to validate the Froude theorem with the numerical simulations. The water channel experiments are used to perform BLI experiments for different fuselage contours and operation points of the engine. In the last step, numerical simulations of the flow into an under-wing intake are compared to an BLI intake. The studies show that the BLI can cause flow separation in different regions of the intake and the intake characteristic is altered. Full article

The rapid growth of global air traffic places the aviation industry under dual pressure: meeting increasing demand for aircraft while substantially reducing life-cycle environmental impacts. As advancements in aerodynamics, propulsion, and the adoption of lightweight composite materials continue to reduce operational fuel burn, the relative significance of manufacturing and End-of-Life phases is expected to increase. This study develops a low-fidelity aerostructural optimization framework for high aspect ratio wings that integrates life-cycle considerations into early-stage material selection. Using aluminum and carbon fiber reinforced polymers (CFRP) as reference materials, the framework quantifies trade-offs in mass savings, fuel burn, and CO₂ equivalent emissions across production, operations, and disposal phases. Results show that while CFRP offers substantial benefits in structural efficiency and operational emissions, aluminum performs more favorably in End-of-Life scenarios due to its high recyclability. The study further evaluates the potential of Sustainable Aviation Fuel (SAF) blending as a complementary decarbonization lever, revealing that moderate SAF adoption can offset part of the operational advantage of CFRP. Overall, this work demonstrates the importance of coupling material choice with life-cycle assessment in aerostructural design and outlines a pathway toward multi-objective optimization frameworks that balance performance with environmental sustainability. Full article

The open fan as a highly efficient propulsion concept is a promising approach to reduce climate-damaging emissions in aviation. However, the increased vibroacoustic emissions of the fan resulting from the open design lead to elevated cabin noise. Energy harvesting resonators can be used to leverage the piezoelectric effect and to attenuate structural vibrations caused by the acoustic loading simultaneously. To evaluate the potential of a specific configuration of energy harvesting resonators, an investigation of the dynamic interaction between the airframe and the resonators is necessary. Therefore, the eigenmodes and eigenfrequencies of a representative stiffened plate are determined experimentally using modal analysis via laser scanning vibrometry. A finite element model of the stiffened plate with the resonator idealized as a mass–spring element is implemented. The stiffness of this simplified resonator model is calibrated by correlating simulated with experimental results following a model updating approach. Finally, an optimization framework designed to determine the optimal quantity and placement of resonators using the experimentally validated model and representative loads is implemented to maximize both vibroacoustic attenuation and energy harvesting efficiency. The resulting framework serves as a generalized optimization tool capable of systematically optimizing the resonator configuration based on airframe geometry and specified vibroacoustic loading scenarios. Full article

With the tightening of international environmental requirements for civil aviation and the implementation of initiatives aimed at reducing specific greenhouse gas emissions, the transition to hybrid power plants for regional aircraft is becoming increasingly relevant. This paper proposes an approach to the integrated energy assessment of a parallel hybrid turboprop power plant at the conceptual design stage while taking the aircraft mission profile into account. The considered power plant includes a gas turbine engine, a reversible electric machine located on the same shaft as the reduction gearbox and propeller, an electrical energy storage system, and power electronics. The mission profile is represented as a sequence of segments—takeoff, climb, cruise, descent, and approach/landing. For each segment, energy balances are formulated and allowable operating ranges for the gas turbine and electric subsystems are defined. The key parameter is the hybridization factor, which determines the share of power transmitted to the propeller from the electric machine in different mission segments. The primary integrated performance metric is the energy consumption per ton-kilometer of transported payload. The analysis shows that for ranges up to 500 km, the hybrid configuration reduces specific energy consumption per ton-kilometer by up to 9%. Full article

Decarbonizing aviation requires innovative propulsion technologies and thermodynamic systems that enable efficient, sustainable energy conversion. The Institute of Thermodynamics at Leibniz University Hannover is engaged in several interdisciplinary research projects focusing on advanced, low-emission aircraft propulsion solutions. Two major areas of research are presented: high-temperature solid oxide fuel cells (SOFCs) for hybrid aircraft propulsion and thermal management systems for proton exchange membrane (PEM) fuel cell propulsion, including additively manufactured heat exchangers for aviation applications. These research activities contribute to the technological foundation of more climate-friendly aviation. Concepts are investigated through numerical simulations, experiments, and system-level analyses to develop future propulsion solutions. This paper provides a comprehensive overview of the Institute of Thermodynamics’ ongoing research and the synergies between its various fields. It offers insights into the challenges and opportunities of more sustainable aviation technologies. 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

This paper reviews selected biofuels that are currently in use, as well as fuels considered promising, for powering compression-ignition (CI) engines, including Common Rail systems. The review focuses on fuel properties, production pathways, operational compatibility, and the effects on engine performance and exhaust emissions. The objective is to systematize the current state of knowledge on biodiesel, hydrotreated vegetable oil (HVO), biomass-to-liquid (BtL), F-34, and sustainable aviation fuel (SAF), and to identify their key advantages, implementation constraints, and research gaps relevant to transport and power-generation applications. The paper compiles and compares published studies on fuel production routes and on the consequences of fuel use in CI engines with respect to performance and pollutant emissions. As an outcome, the available evidence is synthesized, fuels with the highest implementation potential are indicated in the context of emission reduction while maintaining required operational functionality, and priority areas for further research are highlighted, including the still insufficiently characterized effects of SAF on CI engine operation and emissions. 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

Contrail emissions are aviation’s largest non-CO₂ contribution to global climate change. According to the Schmidt–Appleman criterion, potential future aircraft propulsion systems may enhance contrail formation relative to conventional engines through three mechanisms: (1) increased overall efficiency, (2) the use of hydrogen as fuel, and (3) external cooling in low-temperature fuel cell propulsion systems, which is the most critical factor. This paper presents the thermodynamic background and a system concept for contrail prevention applicable to conventional gas turbines, hydrogen combustion, and fuel cell propulsion systems. First, it is shown that fuel cell propulsion and hydrogen combustion exhibit equivalent thermodynamic contrail propensity when fuel cell exhaust is mixed with cooling air, analogous to core–bypass mixing in a conventional turbofan engines. Second, contrail mitigation via controlled condensation of exhaust water vapor is analyzed. It is demonstrated that the required cooling for LT-PEM fuel cell systems is 3–5 times lower than for turbofan engines, due to the already extensive thermal management in fuel cells. Since contrail avoidance is only necessary in ice supersaturated regions, a control scheme is proposed that limits condensation to the minimum required amount of water, thereby significantly reducing the overall drag impact. Avoiding contrail formation could provide a substantial climate benefit for future propulsion architectures. Full article

The fast growth of the aviation sector has intensified the need for sustainable alternatives to conventional fossil-based jet fuels. Sustainable aviation fuel (SAF) has emerged as one of the most promising strategies to reduce greenhouse gas emissions while remaining compatible with existing aviation infrastructure. Among the different feedstocks explored for SAF production, lipid-based resources such as vegetable oils, animal fats, and waste cooking oil have received considerable attention due to their high content of triglycerides and free fatty acids. Additionally, the increasing generation of plastic waste has stimulated interest in its catalytic valorization as an alternative carbon source for hydrocarbon fuel production. This mini-review summarizes recent advances in catalytic pathways for producing jet-fuel-range hydrocarbons (C₈–C₁₆) from lipid-based feedstocks and polyolefins. Particular emphasis is given on hydroprocessing reactions, including deoxygenation, cracking, and isomerization, which are essential to adjust fuel properties and meet aviation specifications. In this context, bifunctional heterogeneous catalysts play a crucial role, particularly regarding the influence of the metal phase and catalyst support on catalytic activity and stability. Different support classes, including metal oxides, mesoporous silicas, and zeolites, are discussed. Carbon-based materials, especially carbon nanotubes (CNT), are also highlighted due to their outstanding chemical and textural properties. Full article

Unconventional aircraft configurations are considered as potential solutions to achieve the ambitious emission reduction goals in aviation. However, the identification, selection, and synergetic combination of promising technologies remain a highly vague and uncertain process. This has been addressed in the framework for the advanced morphological approach (FAMA), which represents a structured design process for the generation and evaluation of unconventional aircraft configurations. It implies the decomposition of the task into subproblems, their analysis and the synthesis of concepts in a solution space. This general workflow has been further developed and adapted on three levels in aircraft design: (1) the qualitative idea generation; (2) the semi-quantitative concept selection from the generated ideas; and (3) the probabilistic estimation of design parameters and figures of merit for the most promising concepts from the previous level. The current paper focuses on the overview of the finalized methodology as well as levels one and two, while level three will be presented in more detail in future work. The first level is demonstrated on the concept generation for regional aerial transportation. The second level results in the percentual performance comparisons of promising technologies for the design of an energy-efficient long-range aircraft. Full article

Amid the rapid growth of the aviation sector, carbon reduction presents a significant challenge for airlines. This study investigates the structural characteristics and dynamic evolution of carbon emission efficiency among 18 global airlines from 2015 to 2021 using a two-stage super-efficient slack-based measure model (SBM) and an SBM-based Hicks–Moorsteen productivity index, incorporating absolute β-convergence tests. Key findings include the following: (1) The overall mean static efficiency of the airlines ranged from 0.225 (American Airlines) to 0.662 (Singapore Airlines), with an industry-wide average of 0.44. (2) Dynamic productivity change also exhibited significant variation: the overall mean superefficient SBM-based Hicks–Moorsteen (HM) productivity index was 0.962, but it dropped sharply to 0.526 in 2019–2020 due to the COVID-19 pandemic. After 2020, several airlines demonstrated significant recovery, with Emirates and Singapore Airlines achieving dynamic productivity change indices above 1.5. (3) In 16 out of 18 airlines, operational efficiency exceeded production efficiency, highlighting the importance of technological improvements in production. (4) Limited technological progress was identified as the main factor behind efficiency declines, while absolute β-convergence indicated that inefficient airlines are gradually catching up with efficient peers. These findings provide insights for airlines and policymakers in designing targeted carbon reduction strategies and promoting sustainable aviation development. The empirical scope of this study is limited to 18 major global airlines over the period 2015–2021. Due to data availability constraints, the sample does not fully cover all regions or low-cost carriers. The Hicks–Moorsteen index and its EC/TC components are used for interpretative and heuristic purposes only and should not be understood as a strict mathematical decomposition within the two-stage network SBM framework. Full article

As aviation faces growing pressure to reduce its climate impact, the exFAN project investigates a hydrogen fuel cell aircraft concept equipped with a heat recuperation system that reuses waste thermal energy to improve efficiency and lower fuel demand. This study compares the exFAN configuration with five major propulsion pathways, kerosene, bio-fuel, e-fuel, hydrogen combustion, and standard fuel cell systems, through an integrated well-to-wake (WTT + TTW) assessment including both CO₂ and non-CO₂ effects. The exFAN results are preliminary and based on analytical estimations regarding potential efficiency gains and fuel savings, providing an indicative view of hydrogen aviation’s lowest achievable climate footprint. Full article

In this paper, a new hybrid prediction method is proposed for estimating remaining useful life, emissions, and performance parameters using experimental data obtained from a micro-turbojet engine. Experiments were conducted under various rotational speed conditions, yielding a total of 342 measurement points. Turbine speed, exhaust gas temperature, fuel flow rate, and thrust were considered as input variables in the study. Thermal efficiency, total power, CO₂, and NO₂ were considered as output variables. The experimental findings showed that thermal efficiency varied between 0.49% and 7.1%, total power between 0.266 and 13.94 kW, and CO₂ emissions by volume between 0.317% and 2.183%. The proposed RL-MH-LR-CBR approach combines the advantages of multiple methods. In this method, the interpretable formulation of linear regression serves as the foundation. Additionally, in the adaptive meta-heuristic optimization process, a hyper-heuristic selection mechanism based on the UCB1-based multi-arm bandit approach is used to select the optimal algorithm from among the meta-heuristic methods. Finally, the CatBoost-based residual error learning component aims to capture non-linear patterns that cannot be explained by the linear model. The method was compared with 14 different methods on both the NASA C-MAPSS FD001 dataset and real engine data. The results demonstrate that the proposed framework exhibits more balanced, stable, and higher generalization capabilities compared to classical regression models and powerful AI methods, particularly in non-linear, noisy, and heterogeneous outputs. In the real engine dataset, the proposed method produced R² values of 0.968 for CO₂ and 0.936 for NO₂, while the predictive performance was even stronger for thermal efficiency and total power, with corresponding R² values of 0.998 and 0.995, respectively. Additionally, the method demonstrated a clear advantage in hard-to-model outputs by reducing the error level to 0.061 in NO₂ predictions. These findings demonstrate that the proposed approach is not limited to micro-turbojet-engines. The developed method provides a robust decision support framework that is applicable, scalable, and generalizable to predictive maintenance, emissions monitoring, energy systems, aviation analytics, and other highly dynamic engineering problems. Full article

The future of low-emission aviation lies in electric aircraft propulsion systems based on fuel cells. One of the challenge lies in designing and testing critical components, such as heat exchangers, and studying their impact on system-level performance and power densities. This paper presents the design and experimental characterization of a compact TPMS gyroid-pipe heat exchanger with embedded coolant channels. Thermal–hydraulic performance is quantified using heat transfer rates and pressure drop measurements. Three design variants of the gyroid pipe are prototyped and experiments are performed for a range of mass flow rates and temperatures. The results are presented in terms of heat exchanger characteristics and the design operating points are determined. A comparison is made between the gyroid-pipe design and a conventional louvered-fin-plate heat exchanger. The results show that the louvered-fin-plate design outperforms the gyroid-pipe design, mainly due to higher pressure loss. Additional design variants of the gyroid-pipe heat exchanger, in which the TPMS curvatures are stretched along the air length, improve the thermal and hydraulic performance. The gyroid-pipe heat exchanger design is beneficial as its volumetric and gravimetric power densities are higher than those of a conventional heat exchanger. This is important for reducing the mass of the system and ensuring the feasibility of a fuel cell system in aviation. Full article