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• Demonstrates payload range capability of a modern aircraft retrofitted with Ammonia. • Ammonia enables smaller and compact turbofan cores with engine weight reduction. • Ammonia exists as subcooled liquid under the assessed engine operating points. • Fuel conditioning is a major design driver for Ammonia operated turbofan engines. • Impacts of Ammonia as a Hydrogen carrier for civil aviation on engine and aircraft. The 2050 net zero targets for aviation to decarbonize the industry means that solutions need to be delivered that can help achieve those targets. Transitioning to zero carbon aviation fuel is an effective solution to achieve those targets. This research article aims to highlight the potential design and performance implications of using Ammonia as a zero-carbon fuel for civil aviation through a retrofit case study conducted for an Airbus A350-1000 equivalent aircraft. The impacts on both turbofan design and aircraft payload-range capability are presented. A feasibility study of using Ammonia as a Hydrogen carrier for civil aviation is also presented. The turbofan design impacts, and payload range capability are assessed using Cranfield University's in-house gas turbine performance tool TURBOMATCH and NASA FLOPS respectively. A 3-point turbofan cycle design strategy is utilized for redesigning turbofan engine cycles using Ammonia as a fuel. Ammonia fuel conditioning assessment is made using REFPROP to investigate its impact on turbofan design. Utilizing pure Ammonia as an aircraft fuel can provide significant turbofan redesign opportunities. Fuel conditioning assessment revealed that for a 430 kN thrust class engine, 2.1 MW of thermal power is required to condition Ammonia fuel at take-off. As a result, various strategies to condition the fuel and its significant impact on turbofan design are presented indicating fuel conditioning as a major design driver for Ammonia fuelled turbofan engines in the future. Although upon initial preliminary assessment, Ammonia utilized as a Hydrogen carrier showcased potential by providing additional mission range capability when compared to a pure Ammonia burning aircraft, the significant thermal energy required to crack (decompose) Ammonia into Hydrogen highlighted the challenges at aircraft mission level and Hydrogen turbofan design implications. It is found that energy requirement (power) to crack Ammonia into Hydrogen are significant which is approximately an order of magnitude higher than Ammonia fuel conditioning itself. [ABSTRACT FROM AUTHOR]

• Theoretical model for MF-PV2S aircraft engine gas exchange is established. • Prediction discrepancies of previous models are analyzed. • Modifying model zones and coefficients improve prediction accuracy. • Adaptability to varying conditions of speed, pressure, valve overlap, fuel type. • Model accuracy is validated by tracer gas method experiments. 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 b 3 , is incorporated to signify the proportion of mixed gas in the exhaust gases at a given moment. Moreover, the model characteristic coefficients b 1 and b 2 , 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. [ABSTRACT FROM AUTHOR]

[Display omitted] • A flexible oscillating hydrokinetic turbine is proposed for deep-sea conditions. • Flexible blade can passively adjust its posture to achieve suitable attack angle. • Flexible oscillating turbine offers high self-starting ability and efficiency. • The turbine can supply enough energy for Autonomous Underwater Vehicles. Harnessing the energy of deep ocean currents to power deep-sea observation equipment has emerged as a significant focus in recent years. Given the extremely low flow speeds in the deep sea, hydrokinetic turbines need to demonstrate reliable self-starting ability. A novel flexible oscillating hydrokinetic turbine is proposed in the present study to address this challenge. The advantage of the flexible oscillating hydrokinetic turbine lies in the ability to adjust the posture of the flexible blades to create optimal attack angles at different positions. Particle Image Velocimetry measurements are employed to reveal the internal flow field. The results indicate that the incoming flow through the turbine cavity induces two substantial deflections in the inflow and outflow regions, contributing to the generation of significant positive torque. The flexible blades can achieve suitable attack angles at various positions as per the expectations. Especially in the downstream region, the blades adopt a diversion state, thereby avoiding the generation of excessive negative torque. The parametric study was conducted through a water flume and a dynamic testing platform. The results indicate that when the number of blades is six and the installation angle of the blade frame is 20°, the power coefficient of the flexible oscillating hydrokinetic turbine reaches its maximum, exceeding 0.18. A full-process interdisciplinary simulation platform test showed that a flexible oscillating hydrokinetic turbine with a radius of 1 m can self-start in conditions as low as 0.1 m/s. At a flow speed of 0.5 m/s, the turbine can generate over 900 Wh of power per day, enough to power sensors or support an Autonomous Underwater Vehicle's monthly cruise. [ABSTRACT FROM AUTHOR]