Aviation Propulsion Research Articles

Thermodynamic evaluation of contrail formation from a conventional jet fuel and an ammonia-based aviation propulsion system.

Condensation trail (contrail) formation in an airplane's wake requires thermodynamics supersaturation and ice nucleation to form visible ice crystals. Here, using a thermodynamic analysis, we evaluate the potential for forming contrails in a carbon-free, ammonia-powered propulsion system compared to conventional planes powered by jet fuel. The analysis calculates the moisture released by fuel into the atmosphere for each one-degree increase in air temperature due to exhaust gas. It then determines if this moisture can saturate the initially undersaturated atmosphere, maintain saturation as temperature rises, and result in supersaturation with respect to ice while leaving enough moisture for a visible cloud to form. With ammonia increases the critical temperature required for supersaturation. Although ammonia does not generate soot particles in the exhaust gas, various aerosols exist in the atmosphere through other sources that can facilitate heterogeneous ice nucleation. Hence, while ammonia's contrails might not be as dense, they can form at lower altitudes where the air is warmer and endure longer due to the increased water content, which preserves supersaturation for longer as fresh air dilutes the contrail.

Assembly method for curved porous circular workpieces based on multidimensional information fusion: Grid electrode component

To tackle the problems related to the complexities of obtaining depth information for circular workpiece with arc surface and holes, a novel vision guidance method has been introduced to precisely gauge interlayer spacing. The process includes the acquisition and preprocessing of point cloud depth information, along with matching and edge processing. The depth coordinates of the point cloud are subsequently determined. Two-dimensional image processing technology is employed to extract the coordinates of the center of the surface circular hole in the curved porous circular workpiece. The 3D coordinates are generated for guiding the assembly by integrating these datasets. Experiments on grid parts in aviation propulsion systems demonstrate that this method maintains dot matrix spacing within 0.5–1.2 mm, ensures the coaxiality of the center hole, and meets assembly standards. The results confirm the method’s effectiveness for automated assembly of curved porous round workpieces.

Rotor-Through-Coils Toroidal-Flux Reluctance E-Motor for Aviation

Electrification of aviation propulsion is in progress. New electric motor architectures — beyond axial and radial fluxes — may be required to unlock its full potential in meeting the demanding functional requirements (in terms of power, weight and efficiency) and certification requirements (from airworthiness authorities) set for airborne operating engine. This article presents a new class of toroidal-flux reluctance electric motors, where the rotor travells inside the coils — the Rotor-Through-Coils (RTC) Reluctance E-Motor. Extensive finite element magnetic model analysis was conducted (including motor operational characteristics assessment), following from an existing validated approach. The power delivered by five series-mounted motors rivales fuel-injected engines powering existing acrobat airplanes, including similar dimensions. A further important advantage will follow in a sequel publication showing the substantial advantage of this motor architecture to be entirely and effeciently air-cooled (like high pressure turbines already do in turbofans), removing the added complexity, weight, cost and certification issues implied in using onboard liquid coolants.

An efficient multi-fidelity simulation approach for performance prediction of adaptive cycle engines

Adaptive cycle engine (ACE) with multi-stream, modulated bypass ratio, and high-thrust/high-efficiency mode provides the capability of multiple mission adaptation for the next-generation aviation propulsion system. The low-fidelity zero-dimensional (0D) performance simulation method is commonly adopted in conventional engines such as turbofan and turbojet. However, it is hard to accommodate well to ACE with complex variable geometry schemes and strong interaction between components. This paper presents an efficient multi-fidelity simulation approach, often referred to as component zooming, for predicting the performance of ACE with the three-stream configuration. The one-dimensional (1D) mean-line models of the adaptive fan and low-pressure turbine (LPT) are integrated into the 0D ACE model by the iteratively-coupled method. The performance predicted by the multi-fidelity ACE models with different component zooming strategies is compared. The maximum deviations of thrust, specific fuel consumption, turbine inlet temperature, and bypass ratio between the 0D/1D Adaptive Fan/1D LPT coupled model and 0D ACE model are −10.8%, −4.4%, −5.4% (−75 K), and 1.6%, respectively, which are considerable and non-negligible for the application in the design stage of ACE. The computing time of all the multi-fidelity models is less than 2 minutes. The effects of the key aerodynamic parameters of the adaptive fan and LPT on the engine performance are also evaluated. The proposed approach provides a generic and efficient solution for multi-fidelity ACE performance prediction with acceptable computing resource requirements and time cost, which is applicable in the engine conceptual and preliminary design stage.

Development and Testing of a Gas Turbine Test Rig Setup for Demonstrating New Aviation Propulsion Concepts

To further increase efficiency and to significantly reduce climate impact in the aviation sector, new propulsion concepts must be developed. As full electrification in mid- and long-range aviation is impractical due to the low gravimetric energy density of batteries, new approaches must be developed. Therefore, the so-called hybrid electric ground demonstrator (HeBo), equipped with a Rolls Royce M250-C20B gas turbine is set up. The test rig serves as a development platform for various new gas turbine-based propulsion concepts for aviation, such as hybrid electric concepts or a novel cycle concept with steam injection to the combustor, which are described in this paper. The main focus of the work is on the experimental setup and the commissioning of the baseline test rig. This will place the test rig in the context of current research activities and serve as reference for subsequent research results.

The Effect of Film Development on Primary Breakup in a Prefilming Airblast Atomizer

Abstract Liquid fueled gas turbines are likely to remain a dominant force in aviation propulsion for the foreseeable future, and therefore understanding the atomization process is key to meeting future emissions and performance legislation. To make experiments and simulations possible, simplified geometry and boundary conditions are often used, for example, simulations of primary atomization often use a fixed film height and velocity. This paper aims to quantify the effect of a fully developed unsteady film on the atomization process. A custom Coupled Level Set & Volume of Fluid (CLSVOF) solver with adaptive meshing built in OpenFOAM v9 is used. A simulation of the atomization process in the Karlsruhe Institute of Technology atomization experiment (Warncke et al., 2017, “Experimental and Numerical Investigation of the Primary Breakup of an Airblasted Liquid Sheet,” Int. J. Multiphase Flow, 91, pp. 208–224) is presented. A precursor simulation of the film development is used to provide accurate, temporally and spatially resolved inlet boundary conditions. These results are compared to previous CLSVOF simulations from Wetherell et al. (2020, “Coupled Level Set Volume of Fluid Simulations of Prefilming Airblast Atomization With Adaptive Meshing,” ASME Paper No. GT2020-14213)” using traditional boundary conditions. The unsteady film has doubled the modal ligament length and widened the distribution, and is now in better agreement with experimental measurements. A clear correlation in both time and space is observed between the film, atomization process, and spray. The sauter mean diameter (SMD) is significantly increased, again giving better agreement with the experiment. A discussion of extracting statistical descriptions of the spray is given, outlining the unfeasible computational cost required to converge droplet diameter distributions and other high order statistics for a case such as this.

Advancements and Applications of Rim-Driven Fans in Aerial Vehicles: A Comprehensive Review

As the aviation industry seeks sustainable propulsion solutions, innovative technologies have emerged, among which rim-driven fan (RDF) systems hold notable promise. This comprehensive review paper deeply investigates RDF technology, uncovering its principles, benefits, and transformative potential for aviation propulsion. Amid escalating concerns about greenhouse gas emissions, the aviation sector’s shift towards electric propulsion has gained impetus. RDF technology has emerged as a beacon of optimism, heralding the prospect of energy-efficient and eco-conscious air travel. Navigating the slower development pace of RDF technology for aerospace applications, this paper draws insights from analogous marine technologies and relevant literature. Merging these realms, this paper meticulously examines RDF systems, spotlighting their unique attributes, with particular emphasis on the rim-driven configuration and its fundamental design principles. This review delves into the progressive strides accomplished in RDF’s evolution, encompassing the spectrum from evolving electric motor variants to intricate design considerations, strategic noise and vibration management, innovative control methodologies, advancements in bearing technology, and the strategic integration of finite element analysis (FEA) and computational fluid dynamics (CFD) for comprehensive performance optimization. In the context of aviation’s electrification journey, the exploration of RDF technology marks a pivotal inflection point. This paper concludes by succinctly encapsulating pivotal insights, accentuating RDF technology’s central role in reshaping aviation’s propulsion paradigm. As the aviation sector charts a course towards sustainable progress, the lessons gleaned from RDF technology are poised to chart the trajectory of aviation’s environmental transformation.

Airflow Simulation in a Turbofan Engine: A Study of Flow Behavior

The efficient functioning of modern turbofan engines relies heavily on a deep understanding of airflow dynamics within critical components. This research paper presents a comprehensive investigation into airflow simulation within a turbofan engine, employing advanced computational techniques. The study focuses on flow behavior and makes use of SolidWorks for 3D modeling and ANSYS for simulation. The investigation centers on analyzing key flow parameters such as velocity, pressure, and temperature. The methodology involves creating an accurate 3D model of the turbofan engine excluding the compressor, combustion chamber, and turbine using SolidWorks to capture fine geometry and details. Subsequently, ANSYS is utilized to simulate the airflow within the turbofan engine, simulating realistic conditions and enabling the detailed analysis of flow behavior. The results of this study advance knowledge of turbofan engine technology and lay the groundwork for additional study and advancement in the area of aviation propulsion systems. In response to the evolving requirements of the aviation sector, the knowledge acquired from this research will serve as a priceless asset in the development of engines that are characterized by enhanced dependability, a reduced ecological footprint, and heightened fuel efficiency.

Cooling performance of droplet-shaped Kagome truss structure combined with jet array impingement composite cooling structure

Gas turbine is one of the most efficiency conversion equipment of heat into power, which is widely used in aviation propulsion and power generation. With the gas inlet temperature of gas turbine skyrocketing recently, gas turbine can achieve higher efficiency but the super high temperature far exceeds the bearable temperature limits of blade material. This causes a great threaten in lifespan of turbine blades and making advanced and efficient cooling structures for blades essential. To enhance the cooling effectiveness of middle chord region of gas turbine blade, a novel droplet-shaped Kagome truss structure (DKTS) is proposed and investigated through experimental and numerical analysis. Subsequently, within jet impingement channel, DKTS is compared against circular pin-fins (CPF), droplet-shaped pin-fins (DPF), and circular Kagome truss structures (CKTS) for fluid flow and heat transfer performance. The experimental method is used to study effects on cooling characteristics between DKTS and CKTS under different operating conditions. The numerical method is used to study effects on cooling characteristics among CPF, DPF, CKTS and DKTS, and to study influences of investigated parameters on cooling performance of DKTS. Experimental results show that under equivalent windward areas, both heat transfer efficiency and flow performance of DKTS are better than those of CKTS. The results of numerical simulations indicate that at the same porosity across jet Reynolds numbers ranging 5000–50000, DKTS increases thermal-hydraulic performance by 11.1%–17.5% relative to CKTS. Moreover, DPF and DKTS reduce flow resistance and augment heat transfer capabilities as compared to CPF and CKTS. This shows that turbulators with droplet-shaped rods have better thermal-hydraulic performance. Finally, the effects of differing jet Reynolds numbers, diameter, tail angles, and inclination angles on fluid flow and heat transfer characteristics of DKTS are conducted. These results may provide a reference for further optimization researches or industrial applications of DKTS.

On the Potentials of the Integration of Pressure Gain Combustion with a Hybrid Electric Propulsion System

As the issue of pollutant emissions from aviation propulsion escalates, research into alternative powertrains is gaining momentum. Two promising technologies are the Hybrid Electric Propulsion System (HEPS) and Pressure Gain Combustion (PGC). HEPS is expected to reduce pollutant emissions by decreasing fuel consumption, whereas PGC uses detonation in the combustor to increase the thermal efficiency of engines by elevating the total pressure during combustion. This study extensively explores the integration of these two emerging technologies, thoroughly assessing the advantages that arise from their combination. First, the renowned turboprop engine PW127 is benchmarked and modeled using Gasturb software. The model is integrated into Simulink using the T-MATS tool, with HEPS and pressure gain components added to analyze the thermodynamics of various configurations under different pressure gain values and HEPS parameters. The analysis, conducted up to the cruise phase of the baseline aircraft, reveals that applying pressure gain combustion through Rotating Detonation Combustion (RDC) results in a more significant increase in efficiency and decrease in fuel consumption compared to HEPS with conventional gas turbines. However, HEPS helps maintain a more uniform combustor inlet condition and reduces the Turbine Inlet Temperature (TIT) at the takeoff phase, where the highest TIT otherwise occurs. The results suggest that integrating HEPS with PGC can be beneficial in maintaining optimal combustor conditions and mitigating turbine efficiency degradation.

Effect of Microstructure on Impact Resistance and Machinability of TiAl Alloys for Jet Engine Turbine Blade Applications

The impact resistance and machinability of TiAl alloys, which are used for jet engine turbine blades, are critical for ensuring reliability and reducing manufacturing costs. This study investigated the effects of the microstructure on these properties using Ti–Al–Cr ternary alloys via Charpy impact tests at room temperature and 700 °C and performing cutting tests using a face mill with cemented carbide tools. As a result, it was confirmed that six types of typical microstructures of TiAl alloys, namely, fine FL, coarse FL, L + γ, γ, γ + β, and L + γ + β, could be formed by varying the Al and Cr concentrations and heat-treatment conditions. Impact resistance and machinability are each the exact opposite trends to the other, with coarse FL having the best impact resistance but poor machinability. Meanwhile, γ has the best machinability but the weakest impact resistance. L + γ has no major drawbacks, including creep strength. As the microstructure of TiAl4822, currently used in LEAP (leading edge aviation propulsion) engine blades, is almost a γ single-phase microstructure, we assumed that manufacturers chose this microstructure to improve machinability and thus reduce the cost. However, because the γ microstructure has the lowest impact resistance, caution should be exercised when applying it to other engines with different operating environment. On the other hand, the microstructure containing the β phase is inferior in all aspects, including creep strength. Thus, it is questionable to use TiAl-forged materials with a residual β phase in small-sized products that can be manufactured by casting.

Overview of Autoignition and Flame Propagation Properties for Ammonia Combustion

With the increasingly stringent CO2 emission, next-generation propulsion systems with chemical reaction combustion involved need to operate with carbon-free fuels, such as ammonia or hydrogen. During the past few decades, intensive research has been conducted on ammonia combustion, which is growingly regarded as a potential alternative fuel to be applied in gas turbines for power generation and aviation propulsion systems to reduce the CO2 footprint and increase carbon-free fuel flexibility. Two major technical challenges with applying such fuel in practical engines are poor ignition and flame propagation behaviors. The present work provides a technical review by presenting state-of-the-art advances in ammonia combustion science and technology by clarifying the fundamental combustion properties and the corresponding enhancement strategies. Experimental techniques applied to measuring the ignition delay time are first introduced and overviewed, along with passive and active means to accelerate them. Then, the laminar burning velocities of ammonia-based dual-fuel combustion at varying operating conditions and their temperature and pressure dependences are described. This is followed by the spin-off applications of ammonia-fueled detonation engines. Finally, we show the prospects and challenges of ammonia combustion and suggest critical topics in aerospace and power generation applications that could benefit from further investigations.

Design of an aircraft generator with radial force control.

With the increasing electrical energy demands in aviation propulsion systems, the increase in the onboard generators' power density is inevitable. During the flight, forces coming from the gearbox or gyroscopic forces generated by flight manoeuvres like take-off and landing can act on the generators' bearings, which can lead to wear and fatigue in the bearings. Utilizing the radial force control concept in the electrical machine can relieve loads from the bearings that not only minimize the bearing losses but also increase bearing life. The objective of the MAGLEV project (Measurement and Analysis of Generator bearing Loads and Efficiency with Validation) is to study, demonstrate, and test a new class of high-speed generators with radial force control. In this paper, design steps of this type of generator and its test rig are presented and the measurement methodology used for radial force control is explained. The concept is developed in an electrical machine and is validated on a test rig by measuring required parameters like shaft displacement, vibrations and bearing temperature. Additionally, the friction moment of each generator's bearings is measured and validated in a separate test rig under comparable conditions to the bearing loads in the generator. Therefore, a novel approach to determine precisely the bearing friction in a radial load unit, rotatably supported by an additional needle bearing is used, which shows a good agreement with the calculated friction. Furthermore, new calculation methods for the operating behavior of cylindrical roller bearings with clearance are presented, which are utilized in the generator test rig.

Intelligent sliding mode fault-tolerant control of aviation propulsion motor system based on adaptive chaotic gray wolf optimization

In order to solve the problem of motor fault caused by extreme low temperature and vibration in the high altitude of aviation propulsion motor, using the intelligent sliding mode fault-tolerant control, a speed controller based on variable exponential power reaching law and an extended sliding mode disturbance observer is designed; furthermore, the parameters are optimized by the adaptive chaotic gray wolf optimization algorithm. In addition, a second-order nonsingular terminal sliding mode observer and a frequency adaptive complex coefficient filter are designed. First, variable exponential power reaching law is helpful to eliminate the speed tracking error and buffeting for the speed controller, the external disturbance can be estimated and compensated using the extended sliding mode disturbance observer, and adaptive chaotic gray wolf optimization algorithm can enhance the accuracy of parameters. Second, for the sake of making the aviation propulsion motor run smoothly in the case of speed sensor fault, second-order nonsingular terminal sliding mode observer is designed to estimate the speed and position of aviation propulsion motor, and adaptive complex coefficient filter is designed to improve the estimation accuracy. Finally, based on MATLAB/Simulink simulation and STM32 motor series experiments, the effectiveness of the proposed observer and controller algorithm is verified.

Design and Analysis of Cryogenic Cooling System for Electric Propulsion System Using Liquid Hydrogen

As the demand for eco-friendly energy increases, hydrogen energy and liquid hydrogen storage technologies are being developed as an alternative. Hydrogen has a lower liquefaction point and higher thermal conductivity than nitrogen or neon used in general cryogenic systems. Therefore, the application of hydrogen to cryogenic systems can increase efficiency and stability. This paper describes the design and analysis of a cryogenic cooling system for an electric propulsion system using liquid hydrogen as a refrigerant and energy source. The proposed aviation propulsion system (APS) consists of a hydrogen fuel cell, a battery, a power distribution system, and a motor. For a lab-scale 5 kW superconducting motor using a 2G high-temperature superconducting (HTS) wire, the HTS motor and cooling system were analyzed for electromagnetic and thermal characteristics using a finite element method-based analysis program. The liquid hydrogen-based cooling system consists of a pre-cooling system, a hydrogen liquefaction system, and an HTS coil cooling system. Based on the thermal load analysis results of the HTS coil, the target temperature for hydrogen gas pre-cooling, the number of buffer layers, and the cryo-cooler capacity were selected to minimize the thermal load of the hydrogen liquefaction system. As a result, the hydrogen was stably liquefied, and the temperature of the HTS coil corresponding to the thermal load of the designed lab-scale HTS motor was maintained at 30 K.

Remaining useful life prediction for equipment based on RF-BiLSTM

The prediction technology of remaining useful life has received a lot attention to ensure the reliability and stability of complex mechanical equipment. Due to the large-scale, non-linear, and high-dimensional characteristics of monitoring data, machine learning does not need an exact physical model and prior expert knowledge. It has robust data processing ability, which shows a broad prospect in the field of life prediction of complex mechanical and electrical equipment. Therefore, a remaining useful life prediction algorithm based on Random Forest and Bi-directional Long Short-Term Memory (RF-BiLSTM) is proposed. In the RF-BiLSTM algorithm, RF is utilized to extract health indicators that reflect the life of the equipment. On this basis, a BiLSTM neural network is used to predict the residual life of the device. The effectiveness and advanced performance of RF-BiLSTM are verified in commercial modular aviation propulsion system datasets. The experimental results show that the RMSE of the RF-BiLSTM is 0.3892, which is 47.96%, 84.81%, 38.89%, and 86.53% lower than that of LSTM, SVR, XGBoost, and AdaBoost, respectively. It is verified that RF-BiLSTM can effectively improve the prediction accuracy of the remaining useful life of complex mechanical and electrical equipment, and it has certain application value.

Prediction of Aero-Engine Remaining Useful Life Combined with Fault Information

Since the fault information of an aero-engine is very important for the remaining useful life of an aero-engine, the paper proposes to combine the fault information for the remaining useful life prediction of an aero-engine. Firstly, we preprocessed the signals of the dataset. Next, the preprocessed signals were used to train a CNN (convolutional neural network)-based fault diagnosis model and obtain fault features from the model. Then, we combined BIGRU (bidirectional gated recurrent unit) and the fault features to predict the remaining useful life of the aero-engine. We used the CMAPSS (commercial modular aviation propulsion system simulation) dataset to verify the effectiveness of the proposed method. After that, comparison experiments with different parameters, structures, and models were conducted in the paper.

Design of an aircraft generator with radial force control

With the increasing electrical energy demands in aviation propulsion systems, the increase in the onboard generators’ power density is inevitable. During the flight, forces coming from the gearbox or gyroscopic forces generated by flight manoeuvres like take-off and landing can act on the generators' bearings, which can lead to wear and fatigue in the bearings. Utilizing the radial force control concept in the electrical machine can relieve loads from the bearings that not only minimize the bearing losses but also increase bearing life. The objective of the MAGLEV project (Measurement and Analysis of Generator bearing Loads and Efficiency with Validation) is to study, demonstrate, and test a new class of high-speed generators with radial force control. In this paper, design steps of this type of generator and its test rig are presented and the measurement methodology used for radial force control is explained. The concept is developed in an electrical machine and is validated on a test rig by measuring required parameters like shaft displacement, vibrations and bearing temperature. Additionally, the friction moment of each generator’s bearings is measured and validated in a separate test rig under comparable conditions to the bearing loads in the generator. Therefore, a novel approach to determine precisely the bearing friction in a radial load unit, rotatably supported by an additional needle bearing is used, which shows a good agreement with the calculated friction. Furthermore, new calculation methods for the operating behavior of cylindrical roller bearings with clearance are presented, which are utilized in the generator test rig.

Comparison of phase-change-heat-pump cooling and liquid cooling for PEM fuel cells for MW-level aviation propulsion

Proton exchange membrane fuel cells (PEMFCs) are seen a key player in the sustainable and clean aviation transition. They can supply the main mega-watt (MW) level electric power aboard with many advantages. To notably increase their system specific power, a new phase-change-heat-pump (PCHP) cooling strategy is proposed and compared with the conventional liquid cooling through a model-based study. The comparison is carried out in terms of the induced drag power on a PEMFC-jet hybrid engine layout. The results reveal a drag reduction of 1.528 MW under the PCHP cooling, which accounts for about 16% of the aircraft's net cruise power. This saving is mainly from the minimized capacity of the heat exchanger between the PEMFCs and ambient. Besides, the ramjet effect also contributes significantly in the drag reduction. Last but not least, the optimal operating current density of the PEMFCs under PCHP cooling is brought up by about 26.5%.

Design of an aircraft generator with radial force control

With the increasing electrical energy demands in aviation propulsion systems, the increase in the onboard generators’ power density is inevitable. During the flight, forces coming from the gearbox or gyroscopic forces generated by flight manoeuvres like take-off and landing can act on the generators' bearings, which can lead to wear and fatigue in the bearings. Utilizing the radial force control concept in the electrical machine can relieve loads from the bearings that not only minimize the bearing losses but also increase bearing life. The objective of the MAGLEV project (Measurement and Analysis of Generator bearing Loads and Efficiency with Validation) is to study, demonstrate, and test a new class of high-speed generators with radial force control. In this paper, design steps of this type of generator and its test rig are presented and the measurement methodology used for radial force control is explained. The concept is developed in an electrical machine and is validated on a test rig by measuring required parameters like shaft displacement, vibrations and bearing temperature. Additionally, the friction moment of each generator’s bearings is measured and validated in a separate test rig under comparable conditions to the bearing loads in the generator. Therefore, a novel approach to determine precisely the bearing friction in a radial load unit, rotatably supported by an additional needle bearing is used, which shows a good agreement with the calculated friction. Furthermore, new calculation methods for the operating behavior of cylindrical roller bearings with clearance are presented, which are utilized in the generator test rig.