The use of sustainable aviation fuel (SAF) can reduce emissions, and increasing the flight ceiling is also a key objective of the poppet valves two-stroke (PV2S) aircraft engine. The high-altitude matching characteristics of the combined setup of a mechanical supercharger compressor (MSC) and turbocharger compressor (TC) and the PV2S engine remains unexplored. A 1D thermodynamic model of the PV2S engine with a combined supercharging system (CSS) was established and verified based on the high-altitude simulation tests (HAST). The results indicate that using MSC as the high-pressure stage and TC as the low-pressure stage is a more optimized solution. Adopting a 5:5 pressure ratio distribution at low altitudes and transitioning to 4:6 at high altitudes improves the efficiency of both MSC and TC while improving trapping efficiency and charging efficiency. Moderating valve overlap can enhance the effective work of TC, and pulse turbocharging improves the utilization of exhaust energy. The effective power decay of the engine using RP-3 aviation kerosene and SAF relative to sea-level decreased from 58.7 % and 58.3 % to 45.1 % and 44.6 % at 2400 r/min and 8000 m. This study provides a theoretical foundation for the matching of PV2S engine and CSS and its power recovery.

Amid environmental challenges and development pressures in high-altitude regions, sustainable engine solutions are urgently needed for both aviation and ground transportation. Altitude-induced air density reduction causes 8–13 % power loss per km of altitude and significant emissions deterioration in piston engines—problems that demand effective technical solutions. This systematic review examines two-stage turbocharging systems operating in high-altitude environments, focusing on aviation applications from moderate to near-space elevations and ground transportation in mountainous regions. The review systematically analyzes various turbocharging configurations, key parameters, matching methods, and inter-stage flow phenomena to establish a comprehensive framework for altitude-adaptive two-stage turbocharging. These systems provide notable advantages in control flexibility, altitude adaptability, and improvements in fuel economy and emission control, with optimized configurations achieving up to 95 % sea-level power restoration at 5.5 km altitude and enabling unmanned aerial vehicles to reach 20 km with pressure ratios exceeding 23. While delivering superior performance compared to single-stage alternatives, these gains come with implementation challenges including increased system cost, weight, and packaging complexity. By synthesizing previously fragmented research across system configurations, parameter optimization, and flow dynamics, this work provides both theoretical foundations and practical design guidance for sustainable high-altitude engine systems. Future development pathways include compact architectures, electrification integration, renewable fuels, and advanced propulsion systems aimed at addressing performance and environmental demands across challenging altitude profiles. This work fills critical knowledge gaps in high-altitude engine technology and supports sustainable transportation development in environmentally sensitive mountain environments.

The development of high-performance small aviation engines requires higher power-to-weight ratios, improved fuel efficiency, reduced costs, and sustainable emissions-goals unattainable with standalone piston engines or gas turbines. The combined cycle mode, integrating the piston engine's Dual cycle with the gas turbine's Brayton cycle, offers an innovative approach. This study examines a combined cycle aviation engine (CCAE) and evaluates the effects of various air distribution ratios (a) and air-fuel ratios (Abr) on performance. The research findings indicate that an a below 20 % is more advantageous for achieving a high power-to-weight ratio. Additionally, a performance simulation model for the CCAE was developed, and a testing platform was designed to validate the accuracy of the simulation model. The study further investigated the impact of different fuel and air distribution strategies on acceleration performance, high-altitude power recovery, economic performance, and emission characteristics. The results suggest that when a = 10 % and 2br = 15, the time to reach minimum takeoff power decreases by 23.9 %. In addition, HC and PM emissions are significantly reduced, with HC decreasing by over 40 % and PM by more than 30 % compared to the prototype. These findings offer valuable insights for the practical implementation of combined cycle power systems in the aviation sector.

With the projected expansion of the general aviation sector and recent breakthroughs in sustainable aviation fuels (SAF), accurately measuring emissions from novel aircraft engines powered by SAF is paramount for evaluating the role of aviation industry in emission reduction trends and environmental consequences. Current SAF research primarily centers on low blend ratios, neglecting data on 100% SAF. This study bridges this gap by experimentally determining emissions indices for gaseous pollutants (CO, CO2, HC, NOx), total particulate matter (PM) counts and sizes, and non-volatile particulate matter (nvPM) number and mass concentrations from a heavy-fuel aircraft piston engines (HF-APE) using hydroprocessed esters and fatty acids-derived SAF (HEFA-SAF), adhering to airworthiness-standard sampling and measurement protocols. Additionally, nvPM morphology and structure are analyzed to auxiliarily assess the emission reduction. The results demonstrate that HEFA-SAF stands out for its marked reduction in both CO and HC gaseous pollutant compared to RP-3 aviation kerosene (RP3), as well as effectively reduces PM emissions compared to Diesel and RP3 across all load conditions. Notably, HEFA-SAF significantly curbs the generation of both nucleation-mode and accumulation-mode PM. Specifically, the use of HEFA-SAF leads to a 43% and 24% decrease in average nvPM number concentration, and a 65% and 53% reduction in average nvPM mass concentration respectively, compared to Diesel and RP3. At 50% load, nvPM produced by HEFA-SAF exhibits distinct nanostructural properties, characterized by fewer exposed pores and active sites within agglomerated particles. Rigorous emission testing has conclusively validated the substantial benefits of 100% HEFA-SAF in reducing emissions, offering a compelling rationale for the development of airworthiness regulations and environmental oversight frameworks designed to foster sustainable aviation practices.

Abstract Titanium alloy is vital for the propulsion system of remote-sensing spacecraft. Facing the increasing threat of space debris, exploring the dynamical properties of the new titanium materials is one of the essential technologies for spacecraft space protection. This paper presents the results of an investigation into the dynamic mechanical properties of a novel Ti-5553 β phase titanium alloy. The alloy was subjected to testing at temperatures of 25°C, 200°C, 400°C, and 600°C, and strain rates of 2000 s−1 and 4000 s−1, using two distinct experimental techniques: the split Hopkinson pressure bar (SHPB) and the Gleeble. A three-dimensional model of the SHPB experiment is established under the same conditions as the test. The findings indicate that the flow stress of the Ti-5553 β-phase titanium alloy exhibits a decline with an increase in temperature under high-temperature and high-strain-rate loading conditions. The Johnson-Cook material model of Ti-5553 titanium alloy was developed through the optimization of material parameters and subsequently applied to a three-dimensional digital simulation model. This model is capable of accurately reflecting the material’s dynamic compressive mechanical properties across a temperature range of 25 to 600°C and a strain rate range of 2000 ~ 4000 s−1. The dynamic mechanical parameters of the new Ti-5553 titanium alloy obtained in this paper can provide data support for the design of spacecraft space protection structures.

Physics-informed neural networks (PINNs) are increasingly employed for surrogate modelling of soil behaviour. Existing surrogate models for unsaturated soil only account for seepage in rigid soil, neglecting the complex coupling between deformation and seepage in unsaturated soil. This study develops a new surrogate model for hydro-mechanical coupling in unsaturated soil using the PINN approach. Dimensionless governing equations, including mass balance and force balance equations, are derived and adopted for physical constraints. With absence of explicit constitutive relations, this new surrogate model utilises sparse measured data to identify pore water pressure, effective stress and deformation in unsaturated soil. Separate neural networks are employed to facilitate efficient back-propagation for coupled problem involving multiple outputs. The newly developed model is then applied to simulate two cases with sparse measurements in unsaturated soil. The results illustrate that the newly developed surrogate model successfully learns the elasto-plastic constitutive relation of suction-induced volume change from experimental data. Meanwhile, model predictions regarding both water flow and stress distribution align within the 95 % confidence interval of theoretical values, demonstrating interpretability of PINN model. Furthermore, by adhering to physical constraints, the relative error in predicting soil deformation from neural networks significantly reduces from 49 % to less than 10 %. These findings suggest PINN model with separate networks is capable to simulate unsaturated soil considering both deformation and seepage, even with sparse measured data and incomplete physical constraints.

The design of double-wall structures must minimize the impact on engine performance while simultaneously ensuring effective cooling. Current research on cooling efficiency, which considers parameters such as blowing ratio, as well as studies on aerodynamic flow losses, do not adequately meet the design requirements for doublewall structures in engine environments. This paper presents an entropy-based cooling effectiveness (ECE) metric that integrates the cooling performance of double-wall structures with the associated system losses in the engine. This metric serves as an effective tool for comparing the design levels of various cooling structures under engine operating conditions. Simulation results indicate that external cooling structures with a small blowing ratio and internal cooling structures characterized by weak impingement and a high heat transfer area are pivotal in enhancing the low-entropy generation design of double-wall structures. A novel double-wall structure is proposed, which features V-shaped fins and small-blowing-ratio film-cooling holes (VF-SF). Experimental tests were conducted in a high-temperature wind tunnel, comparing the conventional 121 structure with the newly proposed VF-SF structure. The research findings revealed significant improvements in both overall cooling efficiency (phi) and ECE with the VF-SF design. Under comparable engine conditions, specifically with a bleed air ratio of 3.8 %, the VF-SF structure exhibited a 76 % increase in phi and an 84 % enhancement in ECE, marking a substantial advancement in low entropy generation design. These results offer critical insights for optimizing the design of double-wall structures within engine system environments and highlight the considerable potential for enhanced thermal management in aircraft engines.

The use of sustainable aviation fuel (SAF) in heavy-fuel aircraft piston engines (HF-APE) has significant implications for reducing carbon emissions in general aviation. However, current research on the combustion characteristics of SAF in HF-APE primarily focuses on ground conditions, and a comprehensive understanding of high-altitude combustion has yet to be fully developed. This study examines the high-altitude performance and combustion characteristics of a HF-APE using conventional fuels and HEFA-SAF through experiments conducted in a high-altitude environmental simulation. The power and fuel consumption performance, as well as the in-cylinder combustion process of diesel, RP-3 kerosene (RP-3), and SAF at altitudes ranging from 0 to 5500 m, are compared and analyzed.The experimental results reveal a consistent trend of power loss for all three fuels (diesel, RP-3, and SAF) at varying altitudes. At an altitude of 5500 m, power losses compared to sea level are 23.4% for diesel, 22.8% for RP-3, and 22.1% for SAF. The specific fuel consumption (SFC) increases significantly at low speeds but varies little at high speeds, with RP-3 and SAF exhibiting an SFC 8.3% higher than that of diesel at low speeds. The in-cylinder pressure and heat release rate (HRR) trends are similar under varying loads, with RP-3 and SAF exhibiting longer ignition delay times (IDTs) compared to diesel, but higher HRR peaks under highload conditions. The high-altitude environment causes a reduction in peak pressure and HRR for all fuels, while also prolonging ignition delay and combustion duration. Specifically, at an altitude of 5500 m, peak pressure and HRR are reduced by an average of 12% to 23%. HEFA-SAF demonstrates enhanced power performance and lowtemperature fluidity in high-altitude environments, providing a crucial experimental foundation for the use of SAF in general aviation and unmanned aerial vehicle propulsion.

The in-cylinder gas exchange process is crucial to the power performance of two-stroke aircraft piston engines, which is easily influenced by complex factors such as high-altitude performance variation and in-cylinder flow characteristics. This paper reviews the development history and characteristics of gas exchange types, as well as the current state of theory and the validation methods of gas exchange technology, while also discusses the trends of cutting-edge technologies in the field. This paper provides a theoretical foundation for the optimization and engineering design of gas exchange systems and, more importantly, points out that the innovation of gas exchange types, the modification of theoretical models, and the technology of variable airflow organization are the key future research directions in this field.

Centrifugal impellers (CIs) boast advantages such as compact structure, lightweight characteristics, and high single-stage pressure ratio. These benefits make them essential across sectors such as aerospace, energy and power, and automotive. The manufacturing process of impellers plays a crucial role in determining their aerodynamic performance and production costs. It demands attention to diverse processing methods, the distinctive features of free-form surface and thin-walled blades, and factors affecting manufacturing accuracy and efficiency. Consequently, the manufacturing technologies for impeller machining have become the focal point of current research. The 5-axis milling manufacturing process for CIs has been extensively analyzed and reviewed. This thorough review scrutinizes and contrasts the attributes of 5-axis end milling and flank milling methods, covering processing principles, unique characteristics, and the implications of tool geometry. Regarding these two milling methods, the paper summarizes the current research findings on milling strategies for free-form surface blade fabrication and the evaluation and management of errors and deformations in the machining of thin-walled blades. Moreover, it delves into the challenges and innovative technological solutions in tool-path planning and deformation control within 5-axis milling. This paper aims to furnish technical guidance for the manufacture of CIs, thereby charting a path towards the realization of high-performance and cost-efficient CIs.

Real-time precise orbit and clock products are prerequisites for Real-Time Precise Point Positioning (RT-PPP) and its related applications, such as time synchronization and disaster monitoring. While real-time products have achieved relatively high accuracy, occasional outliers and accuracy degradation significantly restricts the application of RT-PPP in safety-critical fields. Sub-meter anomalies or larger are typically manageable, as users can easily detect and exclude them through outlier detection in the preprocessing stage before positioning. However, handling small-scale anomalies solely with user-side data and algorithms poses challenges, which also affect the accuracy and reliability of positioning solutions. To address this, we propose a quality monitoring method for real-time precise satellite orbit and clock products. The method utilizes a quality monitoring network of well-distributed stations to validate real-time products continuously. The product quality monitoring server-side calculates both pseudorange and carrier-phase Quality Indicator (QI) for each satellite by using real-time statistics of residuals from quality monitoring network stations, supplemented by product error empirical models. Furthermore, the isolation Forest (iForest) algorithm is employed to detect outliers prior to real-time residual statistics, mitigating the impact of monitoring network or communication link failures on QI while slightly increasing the computational load. QI are broadcasted to users, aiding them in excluding satellites with lower accuracy or reducing the weighting of these satellites in the positioning solution. We conducted a 1 month quality monitoring of Centre National d’Etudes Spatiales real-time orbit and clock products in January 2023, using 30 continuous stations of the Crustal Movement Observation Network of China. The results indicate that the pseudorange QI is greater than 1 m, which can adequately bound the product errors but still exhibit considerable redundancy. In contrast, the carrier-phase QI is within 15 cm, significantly reducing redundancies. The carrier-phase QI can instantly and accurately reflect the accuracy changes of satellite orbit and clock products and bound more than 99.93

Under the demand of global aviation carbon reduction, the multi-fuel poppet valves two-stroke (MF-PV2S) aircraft engine exhibits advantages such as lower lubricant consumption and the flexibility to high-altitude valve timing adjustment, which position it to play a more significant role in general aviation aircraft and unmanned aerial vehicle propulsion systems. High-altitude gas exchange performance is a critical factor in the thermal efficiency and power characteristics of two-stroke aircraft engines. However, the applicability and accuracy of existing models in predicting the gas exchange process for PV2S engines remain insufficiently discussed. Recognizing discrepancies in the predictions of PV2S gas exchange processes by existing models, a theoretical model applicable to high-altitude gas exchange in an MF-PV2S aircraft engine is established. The modified model adjusts the exhaust composition during the second and third phases of the scavenging process, and a novel model characteristic coefficient, designated as b3, is incorporated to signify the proportion of mixed gas in the exhaust gases at a given moment. Moreover, the model characteristic coefficients b1 and b2, are determined with nonlinearity, based on appropriate relationships that account for the characteristics of the PV2S gas exchange process. The model calculates gas exchange characteristics under different operating conditions and fuels, comparing these results with simulations and tracer gas-based experiments. The findings demonstrate that the model successfully captures the characteristics of early appearance and prolonged duration of fresh charge loss during PV2S gas exchange, significantly enhancing the predictive accuracy. Through adjustments of model coefficients based on specific conditions, the model predicts and describes the variation process of PV2S gas exchange performance parameters under different conditions, including various speeds, different intake-exhaust pressure differences at different altitudes, valve overlaps, and fuel types. The maximum relative errors between model predictions and experimental trapping efficiency, delivery ratio and charging efficiency are 2.58 %, 4.33 %, and 3.89 % respectively. The model can be used for rapid and accurate prediction of gas exchange characteristics under different conditions for the MF-PV2S aircraft engine. Also, it serves as an alternative model of three-dimensional simulation models that can be coupled into the one-dimensional thermodynamic cycle simulation.

The in-cylinder combustion process is a focus on research on heavy fuel aviation piston engine (HF-APE), which is quite significant because of its strong correction with engine's power and economic performance, as well as the level of emissions. This study reviews the representative combustion types of HF-APE in recent years, and comprehensively analyzes their aviation adaptability from various aspects. A review was conducted from the perspective of visualization measurement, combustion analysis, and high-altitude simulation technologies, all of which are the crucial methods to study the HF-APE combustion process. A comparative study was investigated on the combustion characteristics and aviation adaptability under different fuels. To meet the requirements of airworthiness regulations and the development of general aviation for more energy saving and environmental protection, further summarizing the progress as well as predicting the trends of HF-APE combustion technologies, are expected to be promoted due to their valuable scientific significance and engineering applications.

Filaments with multi‐materials, complex structures, and sophisticated functions are of great importance to wearable electronics, flexible actuators, and sensors. Direct ink writing (DIW) is mainly adopted to fabricate functional filaments. However, finely regulating the filament's structure is difficult due to the unmovable and static extruding nozzle parts. Here, a dynamically adjustable DIW platform is presented with a movable needle in a Y‐shaped microfluidic nozzle, enabling precise subvoxel control over the structure of the inner layer to print dual‐material and multi‐structure filaments. The position, proportion, and shape of the filaments’ inner layer can be precisely manipulated by adjusting the extruding pressure and the motion of the needle's position in the microfluidic nozzle. Therefore, filaments with various complex structures can be fabricated. Via the printing platform, wavy inner structures are manufactured for stretchable conductance‐stable and triboelectric nanogenerator fibers to realize energy harvesting and self‐powered sensing. Such subvoxel‐controlled microfluidic printing significantly increases the complexity of dual‐material filaments to provide potential applications for flexible electronics.

The poppet valves two-stroke (PV2S) aircraft engine fueled with sustainable aviation fuel is a promising option for general aviation and unmanned aerial vehicle propulsion due to its high power-to-weight ratio, uniform torque output, and flexible valve timings. However, its high-altitude gas exchange performance remains unexplored, presenting new opportunities for optimization through artificial intelligence (AI) technology. This study uses validated 1D + 3D models to evaluate the high-altitude gas exchange performance of PV2S aircraft engines. The valve timings of the PV2S engine exhibit considerable flexibility, thus the Latin hypercube design of experiments (DoE) methodology is employed to fit a response surface model. A genetic algorithm (GA) is applied to iteratively optimize valve timings for varying altitudes. The optimization process reveals that increasing the intake duration while decreasing the exhaust duration and valve overlap angles can significantly enhance high altitude gas exchange performance. The optimal valve overlap angle emerged as 93 degrees CA at sea level and 82 degrees CA at 4000 m altitude. The effects of operating parameters, including engine speed, load, and exhaust back pressure, on the gas exchange process at varying altitudes are further investigated. The higher engine speed increases trapping efficiency but decreases the delivery ratio and charging efficiency at various altitudes. This effect is especially pronounced at elevated altitudes. The increase in exhaust back pressure will significantly reduce the delivery ratio and increase the trapping efficiency. This study demonstrates that integrating DoE with AI algorithms can enhance the high-altitude performance of aircraft engines, serving as a valuable reference for further optimization efforts.

The imperative for small aviation engines lies in the pursuit of heightened power-to-weight ratios and thermal efficiencies. Relying solely on piston engines and gas turbines is insufficient to concurrently meet these evolving performance demands. This paper introduces the concept of a combined cycle aviation engine (CCAE), amalgamating the cycle modes of piston engines and gas turbines. The CCAE achieves flexible control over turbine operating states and engine performance through the adjustment of the energy distribution between these two cycles. The air diversion strategy (alpha) and the burner's fuel supply strategy (Ab) are identified as the key determinants of system performance. To comprehensively investigate the impact of alpha and Ab on CCAE's performance, this paper constructs a theoretical model, a simulation model, and a test bench. The simulation model's accuracy is validated through test data, and the air-fuel ratio range for burner stable combustion is explored. The simulation results indicate a reduction of 50 % in the fluctuation of turbine speed within a single cycle. Under high-altitude conditions, CCAE's intake mass flow rate, power, and efficiency are notably enhanced when compared to conventional turbocharged piston engines. These findings contribute valuable insights that can inform the application of CCAE within the aviation domain.

Laser powder bed fusion (L-PBF) technology is an appropriate scheme for producing intricate components with complex internal structures, such as the intricate flow channel networks in aircraft hydraulic manifolds. However, it is an enormous challenge to fabricate circular channels without support structures that exhibit low shape deviation and high surface quality through L-PBF. This study introduces an innovative annular gradient-forming process that divides the circular flow channel into three sections, namely the inner layer, the transition layer, and the substrate, sequentially from the inside to the outside along the radial direction. Throughout the L-PBF process, the laser energy density is incrementally increased for the inner layer, transition layer, and substrate. The research focuses on manufacturing Ti6Al4V (TC4) circular channels with a diameter of 10 mm, exploring various process parameters to achieve low surface roughness, high dimensional accuracy, and low porosity through the annular gradient process. The effectiveness of the proposed annular gradient process and its parameters is validated through the fabrication and testing of circular channels with diameters of 8 mm, 10 mm, and 12 mm. The results demonstrate that the root mean square deviation (RMS) of the horizontal circular channels using the annular gradient process is reduced by over 80%, and the surface roughness Ra is reduced by over 50%. Furthermore, the channels also have better mechanical properties.

Limited by the poor transient response performance of turbochargers, the dynamic performance of aviation piston engines tends to deteriorate. In a bid to enhance the turbocharger's acceleration capabilities, this study scrutinizes various factors impacting its performance. Based on the operational principles and transient response process of the turbocharger, three types of inertia—namely, aerodynamic inertia (ADI), thermal inertia (TI), and mechanical inertia (MI) — are identified and addressed for design. To begin, this paper pioneers the innovative definition of a method for evaluating the transient response performance of the turbocharger. This method incorporates the introduction of an ADI parameter, inspired by the definition of MI. Subsequently, a thin-walled volute design with a low Biot number and a lightweight turbine impeller is introduced to reduce the turbocharger's TI and MI. The simulation results of the flow field distribution within the volute and diffuser demonstrate the comprehensive design method's effectiveness in improving gas pressure and temperature distributions in these components. Notably, the pressure distribution fluctuation in the constant moment-of-momentum volute (CMV) is 62.8% lower than that in the constant velocity moment volute (CVMV). The low-TI thin-walled volute not only enhances the turbocharger's response speed but also reduces its weight by approximately 40%. The impact of three types of inertia on the engine's response speed is quantified as follows: ADI (94%) > MI (5%) > TI (1%). This conclusion has been verified through test results of both the turbocharger and the engine. This design method not only significantly improves the turbocharger's response performance but also offers valuable insights for the optimal design of other blade mechanical systems.