Aircraft Propulsion Research Articles

Analysis and Verification of cooling structure of superconducting motors for electrical aircraft propulsion

Analysis and Verification of cooling structure of superconducting motors for electrical aircraft propulsion

Study on Coordination of Different Types of DC Superconducting Current Limiter and DC Circuit Breaker for Electric Propulsion Aircraft

Study on Coordination of Different Types of DC Superconducting Current Limiter and DC Circuit Breaker for Electric Propulsion Aircraft

Thermal control of a hydrogen-powered uncrewed aerial vehicle for crossing the Atlantic Ocean

The Drone Mermoz project aims to evaluate the feasibility of an uncrewed aircraft system powered by a hydrogen fuel cell, designed to traverse the Atlantic Ocean. The aircraft must complete a journey of 3000 km with a minimum endurance of 36 hours. In addition to ensuring sufficient onboard energy, a critical requirement is the stable operation of the entire propulsion system throughout the journey.This paper outlines the developmental stages, theoretical modeling, and experimental testing of a thermal management system designed for a long-range uncrewed aircraft system equipped with hydrogen fuel cell-based propulsion. The 4-meter, sub-25 kg aircraft is engineered to undertake a 3000 km journey from Dakar, Senegal to Natal, Brazil.A critical challenge in developing this hydrogen-powered drone is designing an efficient thermal management system to ensure continuous ventilation of the fuselage. While one side of the system involves the fuel cell generating electricity for aircraft propulsion, the other side must effectively dissipate a substantial amount of heat to ensure the stable operation of the entire system.

Research on optimization of the synthesis endo-tetrahydrodicyclopentadiene from dicyclopentadiene

Endo-tetrahydrodicyclopentadiene (endo-THDCPD) serves as a crucial precursor in the synthesis of exo-tetrahydrodicyclopentadiene (exo-THDCPD), the primary component of JP-10 , a single-component hydrocarbon fuel utilized for high-performance cruise missiles, rockets, and supersonic aircraft propulsion. Endo-THDCPD was synthesized through the hydrogenation reaction of dicyclopentadiene (DCPD) using a Pd/C catalyst. In this study, optimal conditions for the hydrogenation process have been thoroughly investigated. Specifically, the reaction is carried out in n-hexane solvent at a reaction temperature of 90 °C, a total H2 pressure of 0.5 MPa, a reaction time of 4 hours, and a catalyst/DCPD mass ratio of 10%.

Initial Comparison of analytical methods for noise prediction of future electric aircraft powertrains

Increasing requirements regarding greenhouse gas emissions produced in the aviation sector require new technologies for aircraft propulsion systems. A suitable technology for a more sustainable and low emission aircraft is the electrification of the powertrain. The noise emission by electric machines becomes an important contribution to the overall aircraft noise, especially since future aircraft will need high-power density electric machines that pose additional challenges regarding design and manufacturing. Electric machines with power densities of 10 kW/kg and higher are currently not available for detailed measurements, to get a first impression of the dominating noise sources of electric motors, models for predicting the noise emission are necessary. Compared to numerical methods, analytical models offer a fast estimation of the noise generated by electric motors. In this paper, analytical models for noise prediction generated by electric motors suitable for aircraft propulsion systems are presented. The most advanced model includes the calculation of the excitation forces acting on the stator due to the magnetic flux density that is coupled with a sound radiation analysis of the outer surface of the motor. By varying the basic parameters for each model under investigation, the noise radiation of a permanent magnet synchronous electric motor is assessed.

Predicting noise for full-scale distributed propulsion aircraft by synthesizing subscale data with existing prediction tools

Future projections of the economic impact of Urban Air Mobility (UAM) or Advanced Air Mobility (AAM) are bold with global GDP increases ranging from billions to trillions over the next few decades. While the potential opportunities are vast, there will be a paradigm shift in the sheer volume of flights at lower altitudes near populated communities. While there is still debate on the initial markets, there is a strong consensus that these aircraft must not appreciably contribute to the existing soundscape and ideally would be imperceptible in most cases. The novel designs of many distributed propulsion aircraft are challenging the existing noise prediction tools that were primarily built around propellers, jet aircraft, and rotorcraft. This paper will present a summary of recent research efforts on synthesizing subscale experimental acoustics measurement data with noise propagation tools to compute community noise exposure on the ground for different full-scale vehicle configurations and flight profiles. The benefits, drawbacks, and limitations of each data source will be discussed along with suggestions for how to improve the prediction methods and models by synthesizing multiple data sets.

Prognostics and Health Management for Electrified Aircraft Propulsion: State of the Art and Challenges

Abstract In recent years, the aviation industry has witnessed a transformative wave of innovation in electrified aircraft propulsion (EAP), driven by sustainability and efficiency goals. Integration of novel electrical subsystems, including high-voltage power electronics, motors/generators, and energy storage devices, has introduced intricate complexities. In this context, an intensified focus on Prognostics and Health Management (PHM) is imperative, considering the heightened reliability needs in a transportation propulsion application. This paper analyzes the current state-of-the-art in PHM applicable to various EAP systems and components crucial for the functioning of electric aircraft. Typical fault modes and fault management strategies are analyzed at various levels of systems hierarchy. An integral aspect of our investigation involves the identification of critical gaps within existing PHM frameworks, guiding the research agenda for enhanced reliability and performance. Moreover, the distributed nature and complexity of EAP systems underscore the importance of Model-Based Systems Engineering (MBSE). We advocate for the exploration of MBSE not only to inform the design of PHM solutions but also to facilitate certification and Verification and Validation activities. Additionally, the paper offers insights into existing tools and simulation software capable of integrating traditional gas turbine modules with electric subsystems, as well as simulating various faulty conditions in EAP relevant to PHM development. Key gaps in these tools are emphasized, drawing attention to areas that require further refinement and development. This comprehensive exploration aims to pave the way for future advancements in PHM tailored for the unique challenges posed by EAP systems.

Multidimensional Taxonomies for Research, Development, and Implementation of Electric Aircraft Ecosystem

The electrification of aviation represents a significant technological frontier, promising substantial advancements in sustainable transportation. This paper presents a comprehensive set of taxonomies that systematically categorize and analyze the multifaceted aspects of electric aviation, with a particular focus on machine-related components and systems. It provides detailed classifications of electric aircraft propulsion systems, power management architectures, and energy storage technologies, offering insight into their design, functionality, and integration challenges. The paper explores the ecosystem of electric aviation, including key stakeholders, use cases, and enabling technologies, which are vital for coordinating machine development strategies and fostering sustainable growth. The creation of business models that cater to the dynamic nature of the industry, emphasizing the role of innovative machine designs in shaping market adoption are discussed in the paper. The study highlights the importance of electric aviation for regional development, outlining predictive models for regional market development that consider machine capabilities and infrastructure requirements.

Net-Zero Greenhouse Gas Emission Electrified Aircraft Propulsion for Large Commercial Transport

Until recently, electrified aircraft propulsion (EAP) technology development has been driven by the dual objectives of reducing greenhouse gas (GHG) emissions and addressing the depletion of fossil fuels. However, the increasing severity of climate change, posing a significant threat to all life forms, has resulted in the global consensus of achieving net-zero GHG emissions by 2050. This major shift has alerted the aviation electrification industry to consider the following: What is the clear path forward for EAP technology development to support the net-zero GHG goals for large commercial transport aviation? The purpose of this paper is to answer this question. After identifying four types of GHG emissions that should be used as metrics to measure the effectiveness of each technology for GHG reduction, the paper presents three significant categories of GHG reduction efforts regarding the engine, evaluates the potential of EAP technologies within each category as well as combinations of technologies among the different categories using the identified metrics, and thus determines the path forward to support the net-zero GHG objective. Specifically, the paper underscores the need for the aviation electrification industry to adapt, adjust, and integrate its EAP technology development into the emerging new engine classes. These innovations and collaborations are crucial to accelerate net-zero GHG efforts effectively.

Reversionary Control Modes for the Mitigation of Failures in a Partially Turboelectric Aircraft Propulsion System

Abstract In support of emission and fuel burn reduction goals, the aviation industry is actively pursuing the advancement of electrified aircraft propulsion (EAP) technology. This includes turboelectric and hybrid electric propulsion designs that combine gas turbine engine and electrical system hardware. Such architectures exhibit a high degree of coupling between subsystems. This drives the need for system-level control strategies to ensure the safe, coordinated, and efficient operation of all subsystems. The design and certification of any aircraft propulsion system requires that all potential subsystem failures are identified, and the hazards posed by these failures are appropriately mitigated. This requirement is particularly challenging for EAP systems due to their integrated nature. One approach to assist in EAP failure mitigation is the inclusion of automated reconfiguration capabilities within the propulsion control system. Such control modes, referred to as reversionary control modes, are designed to automatically detect failures and activate backup control modes upon failure detection. This paper covers the design and evaluation of reversionary control mode logic developed for a partially turboelectric propulsion concept. Test results from a real-time hardware-in-the-loop evaluation of the concept are also presented and discussed. The results show that the developed reversionary control logic can successfully detect and mitigate subsystem failures in a representative environment that includes actual electrical system hardware.

A Comparison of Model Predictive Control Architectures for Application to Electrified Aircraft Propulsion Systems

Abstract As electrified aircraft propulsion (EAP) systems continue to mature, more sophisticated hardware and software are being developed to balance operations among electric machines and gas-turbine engines. In hybrid-electric propulsion systems, the increased complexity resulting from integrating turbine-engine shafts with electric machines necessitates control methodologies to account for various physical domains. Ideal controllers for hybrid-electric engines manage systems, subsystems, and their interactions in a coordinated fashion, able to account for safety and performance goals while being computationally efficient. In a previous work, linear model predictive control (MPC) schemes were implemented in centralized and distributed frameworks on a nonlinear turbofan engine model as a proof of concept. However, these schemes were not evaluated for computational complexity, prompting further study. The research presented here develops hierarchical MPC schemes to reduce the computational burden of the previous MPC schemes. A two-tier framework is implemented, where a slower sampling MPC controls electric machines and determines fan-speed tracking goals for a faster sampling controller, which is either a MPC or a proportional-integral (PI) controller. The proposed designs are compared to the centralized MPC investigated previously, and performance is measured via fan speed tracking error, energy storage state-of-charge, and computation time. Results reveal that the hierarchical MPC scheme employing a lower-level PI controller improves computation time while maintaining comparable tracking and state-of-charge regulation to the centralized scheme.

Impact of Future Low-Emissions Combustor Technology on Acoustic Scaling Laws

A first-of-its-kind examination of broadband noise associated with a far-term advanced low-emission aerocombustor concept is presented. Because of design trends and expected cycle changes for future aircraft propulsion systems, noise generated by sources in the combustor are expected to become of increasing significance for airport-community noise. The paper assesses the impact on legacy semi-empirical noise-prediction methods from the expected radical departures from current combustor operating conditions and designs, such as fuel/air distribution and flame anchoring techniques. Such methods are essential in system-level noise assessments at the preliminary design stage for advanced air transports to assure that overall environmental goals are met. Detailed unsteady pressure measurements, obtained in a fundamental combustion noise experiment using a combustor rig at relevant pressures and temperatures are analyzed. In addition to an advanced far-term low-emissions concept, a reference configuration with the test section arranged to model a modern combustor sector was also studied. For the test rig in the current-generation configuration, the measured broadband acoustic data are reasonably well described by the acoustic-power scaling laws used in legacy semi-empirical noise-prediction methods. For the future-advanced configuration, the legacy scaling laws, with some notable exceptions, provide correct trends, but with much less accuracy.

Performance and optimization evaluation for integration of sCO2 power system into the aircraft propulsion system

The aviation industry accounts for part of the CO2 emissions contributing to climate change. The industry has established a target to reduce 2050 net aviation carbon emissions by 50 % relative to 2005 levels. With this in mind, waste heat recovery is a key pathway to achieve reduced emissions and improve system efficiency. The waste heat may potentially be converted to electric power using a supercritical CO2 Brayton power cycle. The sCO2 power system offers the advantage of compactness owing to the high working fluid density, which is an important consideration for aircraft performance. The present work focuses on the integration of the sCO2 power system into the aircraft propulsion system and evaluation of its performance. Detailed optimization of the sCO2 waste heat system will be evaluated with a focus on cycle efficiency and net power under different operating conditions, including ground, takeoff, climb, cruise, and landing operations. The study is divided into two parts with two different turbofan engines, one with a nominal thrust of 30 kN and the other with a nominal thrust of 9 kN. The first part shows the effect and operation of the waste heat recovery unit under the different operating conditions. The second part is focused on cycle optimization and performance evaluation. The results demonstrate the potential of waste heat recovery during a range of operational conditions. The sCO2 cycle efficiency can reach between 25 and 39 % (depending on aircraft engine) with net power output in the range of 100 to 260 kW.

Performance Estimation of Fixed-Wing UAV Propulsion Systems

The evaluation of propulsion systems used in UAVs is of paramount importance to enhance the flight endurance, increase the flight control performance, and minimize the power consumption. This evaluation, however, is typically performed experimentally after the preliminary hardware design of the UAV is completed, which tends to be expensive and time-consuming. In this paper, a comprehensive theoretical UAV propulsion system assessment is proposed to assess both static and dynamic performance characteristics via an integrated simulation model. The approach encompasses the electromechanical dynamics of both the motor and its controller. The proposed analytical model estimates the propeller and motor combination performance with the overarching goal of enhancing the overall efficiency of the aircraft propulsion system before expensive costs are incurred. The model embraces an advanced blade element momentum theory underpinned by the development of a novel mechanism to predict the propeller performance under low Reynolds number conditions. The propeller model utilizes XFOIL and various factors, including post-stall effects, 3D correction, Reynolds number fluctuations, and tip loss corrections to predict the corresponding aerodynamic loads. Computational fluid dynamics are used to corroborate the dynamic formulations followed by extensive experimental tests to validate the proposed estimation methodology.

Economic Aspects of Aircraft Propulsion Electrification

Aircraft propulsion electrification is currently being considered by industry and academia as one of the most promising strategies to reduce air transport emissions and increase overall efficiency levels. In the past decade, several papers were published on this subject, with the majority indicating encouraging fuel burn benefits versus conventional, fossil-fuel-based propulsion systems when future technologies, novel aircraft configurations, and synergistic propulsive-airframe integration are employed. However, a much smaller effort has been applied to the economic aspects of hybrid and fully electric propulsion, which are crucial for a successful product introduction. The present paper describes the modeling of a baseline general-aviation-type aircraft and its propulsion system retrofit with electrified architectures, exploring different electrification strategies for a fixed airframe design. Analyses are performed at the aircraft level, comparing recurring and cash operating costs for several cost and durability scenarios. While considerable CO2 reductions may be achieved in some electrification strategies, aircraft performance is significantly penalized, and important improvements in economic figures of merit are needed in order to make electrified propulsion cost-competitive. Electrified architectures tend to increase costs: turboelectric increases recurring equipment costs, while hybrid-electric increases recurring and direct maintenance costs, especially at higher degrees of energy hybridization.

A Jacobi-Ritz Approach for Aeroelastic Analysis of Swept Distributed Propulsion Aircraft Wing

Abstract This paper presents a Jacobi-Ritz approach for conducting flutter and divergence analysis of a complex distributed propulsion aircraft wing like NASA X-57. The general orthogonal Jacobi polynomials are used to approximate the bending displacement and torsional rotation angle in the Ritz method based structural and aeroelastic analysis. The Jacobi polynomials satisfy the orthogonality condition using weight functions which are easily modified to satisfy different essential and natural boundary conditions. Compared to simple polynomials, Jacobi polynomials can eliminate the well-known ill-conditioning numerical issues when considering higher-order polynomials. The Jacobi-Ritz method is also found to alleviate mode switching often encountered in tracking the changes of modes with the varying airspeed. The Jacobi-Ritz method is later used to investigate the flutter and divergence speeds under distributed propulsor mass and their locations, nonuniform aerodynamic model in the presence of multiple propulsors, and the sweep angle. Results show that placing the distributed propulsors on the wing's leading edge increases the flutter speed even though the bending and torsion modal frequencies are decreased compared to those of the wing without propulsors. The presence of pods for the middle high-lift motors causes an extra aerodynamic moment which reduces the flutter speed. Parametric studies also show that the divergence speed is lower than the flutter speed for a uniform and straight distributed propulsor wing. Using swept-back wing configuration and placing the tip propulsor near the wing's leading edge can help to increase both flutter and divergence speeds.

Ground test protection strategy for the 100 kW series hybrid electric propulsion system

With the goal of lower emissions, hybrid electric propulsion (HEP) aircraft is considered to be a promising solution, with the advantages of being more environmentally friendly and efficient. Moreover, superior reliability and good safety of the HEP systems is vital to ensure a safe flight. For this purpose, this article presents several successful case studies on overspeed, overvoltage/overcurrent, and communication protection with the combination of theory and experimental data. Given the practical application capability of fault protection, this article established a 100 kW HEP platform and designed an effective system level fault protection architecture, which consists of physical layer, decision layer and execution layer. Experimental studies have been conducted on the turboshaft engine overspeed, electrical architecture overvoltage/overcurrent, communication faults to verify the effectiveness of the proposed fault protection scheme. The test results have shown that the proposed strategy can effectively deal with various fault situations mentioned above to prevent the entire HEP aircraft system from becoming paralyzed, thus improving the reliability and safety of the system.

Characterisation of Large-Sized REBaCuO Bulks for Application in Flux Modulation Machines.

High temperature superconductors (HTSs) are enablers of extensive electrification for aircraft propulsion. Indeed, if used in electrical machines, HTS materials can drastically improve their performance in terms of the power-to-weight ratio. Among the different topologies of superconducting electrical machines, a flux modulation machine based on HTS bulks is of interest for its compactness and light weight. Such a machine is proposed in the FROST (Flux-barrier Rotating Superconducting Topology) project led by Airbus to develop new technologies as part of their decarbonization goals driven by international policies. The rotor of the machine will house large ring-segment-shaped HTS bulks in order to increase the output power. However, the properties of those bulks are scarcely known and have barely been investigated in the literature. In this context, the present work aims to fill out partially this scarcity within the framework of FROST. Thus, a thorough characterisation of the performances and homogeneity of 11 large REBaCuO bulks was carried out. Ten of the bulks are to be utilized in the machine prototype, originally keeping the eleventh bulk as a spare. A first set of characterisation was conducted on the eleven bulks. For this set, the trapped field mapping and the critical current were estimated. Then, a series of in-depth characterisations on the eleventh bulk followed. It included critical current measurement, X-ray diffraction, and scanning electron microscopy on different millimetre-size samples cut out from the bulk at various locations. The X-ray diffraction and scanning electron microscopy showed weakly oxygenated regions inside the bulk explaining the local drop or loss in superconducting properties. The objective was to determine the causes of the inhomogeneities found in the trapped field measured on all the bulks, sacrificing one of them, here the spare one. To help obtain a clearer picture, a numerical model was then elaborated to reproduce the field map of the eleventh bulk using the experimental data obtained from the characterisation of its various small samples. It is concluded that further characterisations, including the statistics on various bulks, are still needed to understand the underlying reasons for inhomogeneity in the trapped field. Nonetheless, all the bulks presented enough current density to be usable in the construction of the proposed machine.

Liquid Cooling of Fuel Cell Powered Aircraft: The Effect of Coolants on Thermal Management

Abstract Electric propulsors powered by Proton Exchange Membrane Fuel Cells (PEMFCs) offer a net zero solution to aircraft propulsion. Heat generated by the PEMFCs can be transferred to atmospheric air via a liquid cooling system; however, the cooling system results in parasitic power and adds mass to the propulsion system, thereby affecting system specific power. The design of the cooling system is sensitive to the choice of liquid coolant and so informed coolant selection is required if associated parasitic power and mass are to be minimized. Two approaches to selection of coolants for PEMFC-powered aircraft are presented in this paper for operating temperatures in the range 80-200°C (this covers low, intermediate, and high temperature PEMFCs). The first approach uses a Figure of Merit (FoM) alongside minimum and maximum operating temperature requirements. The FoM supports the selection of coolants that minimize pumping power and mass while maximizing heat transfer rate. The second approach uses a cooling system model to select ȜPareto efficientȝ coolants. A hybrid-electric aircraft using a PEMFC stack is used as a representative case study for the two approaches. Hydrocarbon-based coolants are shown to be favorable for the case study considered here (aromatics for PEMFCs operating at <130°C and aliphatics for PEMFCs operating at >130°C). As the PEMFC operating temperature increases, the parasitic power and mass of the TMS decreases. Operating at elevated temperatures is therefore beneficial for liquid cooled PEMFC-powered aircraft. Nevertheless, there are diminishing performance gains at higher operating temperatures.

Multifidelity & multi-objective Bayesian optimization of hydrogen-air injectors for aircraft propulsion

The use of hydrogen as a fuel is a promising way to reduce the emissions of civil aviation but it requires the development of wholly new injectors for the combustion chamber. Thanks to the increase in available computing power, the application of optimization techniques combined with CFD computations is now possible to develop these injectors. Among the optimization approaches, Bayesian optimization is particularly relevant when the objective functions and constraints of the optimization problem are expensive to evaluate which is the case in CFD-based optimization. Besides, the use of a multifidelity strategy allows to reduce the simulation cost of the Bayesian method. Therefore, this paper investigates the application of a multifidelity and multi-objective Bayesian approach to improve the performances of a laboratory swirl injector using hydrogen and operating in conditions close to industrial targets. This optimization study combines LES simulations as high-fidelity model with 2D RANS simulations as low-fidelity.