Propulsion System Design Research Articles

A Controllable Nonlinear Bistable "Fishtail" Boosting Robotic Swimmer with Excellent Maneuverability and High Energy Efficiency.

High maneuverability and energy efficiency are crucial for underwater robots to perform tasks in engineering practice. Natural evolution empowers aquatic species with skills of agile and efficient swimming, which can be deliberately employed for better robotic swimmers. A critical issue for efficient robotic swimmers is the design and control of an appropriate propulsion system. This study, therefore, presents a completely different realization of a highly flexible and controllable bistable nonlinear mechanism as a "fishtail." The mechanism combines an elastic spine and a lightweight parallel linkage mechanism. Through active control of the endpoint of the elastic spine, the compliant tail can be empowered with exceptional controllability and tunable bistability for a much more efficient and also the first-ever accurately controlled bistable elastic propulsion system. Experimental results demonstrate that the new bistable fishtail can achieve a faster speed of its size (up to an average speed of 0.8 m·s-1) with an associated higher energy efficiency (corresponding cost of transport as low as 9 J·m-1·kg-1), and greater maneuverability (with an average turning speed of up to 107°/s at a much smaller turning radius of 0.31 body length). This study will definitely provide an efficient controllable and feasible approach to the design of nonlinear compliant propulsion systems for underwater vehicles by exploring nonlinear dynamics.

Influence of hydrofoil motion patterns on the hydrodynamic performance of undulating fin for biomimetic underwater robots

The undulatory propulsion of aquatic organisms like the black ghost knifefish offers high manoeuvrability and motion stability, making it a promising model for developing advanced biomimetic underwater robots. However, these robots are frequently hindered by limitations in speed and propulsion efficiency. Inspired by the energy benefits observed in fish schooling, this study introduces a cooperative propulsion system integrating the hydrofoil with the undulating fin to enhance propulsion performance through an investigation of their interaction across various motion patterns. Specifically, we investigate the effects of static, pitching, heaving, and their combination (pitching + heaving) of the hydrofoil on the hydrodynamic performance of the undulating fin. Our results indicate that a static hydrofoil slightly increases the fin's average thrust, while pure pitching marginally reduces it. The high-speed vortices generated by the hydrofoil during pure heaving significantly suppress the fin's thrust. In contrast, the combined motion of pitching and heaving substantially enhances propulsion performance. Thus, the combined motion of the hydrofoil can better enhance the hydrodynamic performance of the undulatory propulsion robot. This study provides a theoretical foundation for the optimized design of high-speed and stable undulating fin propulsion systems, offering valuable insights for developing underwater robots with improved operational capabilities.

Effect of Nozzle Type on Combustion Characteristics of Ammonium Dinitramide-Based Energetic Propellant

The present study explores the influence of diverse nozzle geometries on the combustion characteristics of ADN-based energetic propellants. The pressure contour maps reveal a rapid initial increase in the average pressure of ADN-based propellants across the three different nozzles. Subsequently, the pressure tapers off gradually as time elapses. Notably, during the crucial initial period of 0–5 μs, the straight nozzle exhibited the most significant pressure surge at 30.2%, substantially outperforming the divergent (6.67%) and combined nozzles (15.5%). The combustion product variation curves indicate that the contents of reactants ADN and CH3OH underwent a steep decline, whereas the product N2O displayed a biphasic behavior, initially rising and subsequently declining. In contrast, the CO2 concentration remained on a steady ascent throughout the entire combustion process, which concluded within 10 μs. Our findings suggest that the straight nozzle facilitated the more expeditious generation of high-temperature and high-pressure combustion gases for ADN-based propellants, expediting reaction kinetics and enhancing combustion efficiency. This is attributed to the reduced intermittent interactions between the nozzle wall and shock waves, which are encountered in the divergent and combined nozzles. In conclusion, the superior combustion characteristics of ADN-based propellants in the straight nozzle, compared to the divergent and combined nozzles, underscore its potential in informing the design of advanced propulsion systems and guiding the development of innovative energetic propellants.

Advanced Design of Naval Ship Propulsion Systems Utilizing Battery-Diesel Generator Hybrid Electric Propulsion Systems

As advanced sensors and weapons require high power, naval vessels have increasingly adopted electric propulsion systems. This study aims to enhance the efficiency and operability of electric propulsion systems over traditional mechanical propulsion systems by analyzing the operational profiles of modern naval vessels. Consequently, a battery-integrated generator-based electric propulsion system was selected. Considering the purpose of the vessel, a specification selection procedure was developed, leading to the design of a hybrid electric propulsion system (comprising one battery and four generators). The power management control technique of the proposed propulsion system sets the operating modes (depending on the specific fuel oil consumption of the generators) to minimize fuel consumption based on the operating load. Additionally, load distribution control rules for the generators were designed to reduce energy consumption based on the load and battery state of charge. MATLAB/Simulink was used to evaluate the proposed system, with simulation results demonstrating that it maintained the same propulsion performance as existing systems while achieving a 12-ton (22%) reduction in fuel consumption. This improvement results in cost savings and reduced carbon dioxide emissions. These findings suggest that an efficient load-sharing controller can be implemented for various vessels equipped with electric propulsion systems, tailored to their operational profiles.

Experimental study on droplet dynamics behavior and combustion characteristics of high performance green propellant in electrical ignition mode

High performance green propellant represented by ammonium dinitramide-based liquid propellant and its new ignition method are the research hotspots of space propulsion in the 21st century. Exploring the complex multi-scale physical properties of multi-component ammonium dinitramide-based liquid propellant droplets in the electrical ignition mode has wide application significance for spray, propulsion system design and combustion control. The droplet dynamics behavior and combustion characteristics of propellant droplets at different ignition voltages were studied experimentally. The droplet dynamics behavior during the evaporation process, including violent volume oscillation, approximate steady-state expansion, contraction, secondary expansion, puffing and micro-explosion, have been determined by the generation, growth, and discharge of vapor bubbles. In the initial evaporation process, the heterogeneous nucleation is dominant. As the droplet is continuously heated, homogenization nucleation gradually dominates. The main physical and chemical mechanisms of bubble evolution driven by temperature involve methanol boiling, water overheating, ammonium dinitramide decomposition and combustion reaction between vapor molecules. Increasing the ignition voltage increases the droplet dynamics behavior and the combustion, but promotes the combustion instability. Increasing the ignition voltage increases the ignition delay time, puffing delay time, droplet lifetime, maximum temperature of droplet, and reduces the ignition critical diameter. It is proposed that the method of suppressing the droplet breakup dynamics at decomposition area and enhancing the droplet breakup dynamics at the combustion area are conducive to the combustion control of the thruster in electrical ignition mode. This research provides novel insight into the study of the electrical ignition mechanism of liquid fuels.

Spray characteristics of axially-vaned slinger atomizer in air crossflow

Slinger atomizers are frequently employed to facilitate fuel spray atomization in aeroengine combustors. Unlike traditional radial slinger atomizers that induce the limited interaction between the rotating fuel and the surrounding air, this study proposes an innovative approach by incorporating axial vanes into the slinger rotor to potentially enhance fuel atomization performance. A comprehensive analysis of the spray characteristics of an axially-vaned slinger atomizer in air crossflow is numerically conducted, focusing on the effects of axial vane, rotor–stator axial clearance, and fuel inlet conditions. Results demonstrate that axially-vaned slingers outperform radial slingers by enhancing air swirl strength to disrupt the fuel jet, reducing the average droplet size by 25 % at 30000 rpm. Furthermore, positioning fuel nozzles farther from the rotor wall can mitigate the potential risk of surface thermal erosion. Fuel leakage through the rotor–stator clearance decreases from around 80 % at 10000 rpm to below 5 % at 30000 rpm and becomes negligible at 40000 rpm, thereby enhancing fuel–air mixing efficiency. Introducing supercritical fuel at the inlet facilitates its transition into a gaseous state within the slinger inner chamber, thereby markedly amplifying mixing efficiency. Nonetheless, this improvement is accompanied by a reduction in fuel flow rates. A significant aspect to consider is the heightened risk of substantial wall erosion due to pronounced leakage through the rotor–stator axial clearance. This study presents novel perspectives on improving the efficiency and ensuring the operational safety of rotary atomizers, thereby offering valuable guidance for the design of power and propulsion systems.

Digital twins for electric propulsion technologies

As the space industry is undergoing an evolution, the current approaches toward design, development, and qualification of Electric Propulsion (EP) systems largely based on empirical “trial-and-error” methodologies are falling short of addressing the emerging needs and keeping abreast of the rapid changes in market trends. Furthermore, with the proliferation of Artificial Intelligence (AI) within the space industry toward next-generation autonomous satellites and spacecrafts, the conventional EP monitoring and control strategies become inadequate and need to give way to approaches compatible with satellite-level autonomy requirements. A digital twin (DT) – a technology capable of providing an accurate dynamically adapting virtual representation of a physical asset – is a game-changing concept that catalyzes the transcendence of the EP industry past its pressing challenges today. In this paper, we aim to: (i) define the DT concept, highlighting how it surpasses traditional modelling, (ii) enumerate the DT’s breakthrough promises for the EP industry, and (iii) specify the challenges to realize practical and scalable EP DTs. Additionally, we report on the technical progress achieved and/or planned at Imperial Plasma Propulsion Laboratory to fill the foundational gaps in three building block elements of DTs, namely, (i) a cost-effective kinetic model to generate extensive high-fidelity databases for machine learning (ML), (ii) ML-enabled models for prediction and analysis of performance and operational behavior, and (iii) a DT architecture that integrates the numerical models in terms of a computing infrastructure and provides data pipelines and interfaces for the DT’s data exchanges with the real world, its dynamic updating, and uncertainty quantification.

Flow induced acoustic characteristics analysis of propulsion pump by indirect acoustic variable method and FEM

The acoustic characteristics of water-jet propulsion pumps present significant challenges, primarily due to the interaction between flow and high-speed rotating impellers wall. Notably, such complicated turbulence induced acoustic sources by brings great difficulty to identify and control. This paper firstly analyzes the flow characteristics of the propulsion pump by using the scalable Hybrid RANS-LES model. Subsequently, an indirect acoustics variable method based on Lamb vector divergence is proposed to characterize acoustic sources caused by multiscale turbulence. The effectiveness and advantages of indirect acoustics variable method are evaluated through comparison with the acoustic finite element method and experimental results. The proposed indirect acoustics variable method demonstrates the ability to accurately quantify the contribution of turbulent flow to acoustic sources. Furthermore, the intensity of acoustic sources in different flow regions can be obtained through volume integrals, which can serve as optimization parameters in the initial hydraulic design of propulsion pumps. This study provides a novel approach for predicting turbulent noise and offers guidance for the design of low-noise propulsion systems.

Design and experimental verification of propulsion system for a Mars quadcopter

Due to the Mars rotorcraft can conduct extensive surface exploration of Mars and carry sampler for collecting samples on the Martian surface, it is gradually becoming the mainstream exploration devices for Mars missions. In response to the thin atmosphere on Mars, with the flight duration and sample-carrying capacity of the quadcopter as constraints, we design the propulsion system parameters for the Mars quadcopter with the function of sampling on the Martian surface. A method for evaluating rotor performance indicators, including mass and Mach number at the tip of the blade, is proposed. Based on the evaluation index and the steady RANS method for predicting the lift and drag characteristics of the rotor, an appropriate rotor diameter for the Mars quadrotor is selected. The method combining NSGA-II and two-dimensional steady RANS is employed to optimize the airfoil of the Mars quadcopter blade under the condition of a chord length of 40 mm, a Mach number of 0.43, an angle of attack of 20°, and a Reynolds number based on chord of 6080. Experimental verification for the lift-to-drag characteristics of the single rotor is conducted in an environment simulating the atmospheric density on the Martian surface. The results show that the blade after optimization can generate a thrust of 5.95 N and consume power of 164.9 W, at the rotational speed of 3650 r/min. Based on the test bench with the function of sliding up and down for testing aerodynamic performance of quadcopter, the temperature of the motor and battery discharge characteristics of the Mars quadcopter are conducted. The results of the test show that the quadrotor can provide a thrust-to-weight ratio of 1.66 for the Mars quadcopter while meeting the design requirement of 3 min.

Optimization of low-thrust periodic reconfiguration in Tianqin orbit

Tianqin is a project scheduled for detecting gravitational waves in space. The project requires high levels of constellation stability. This paper optimizes the Tianqin trajectory over 5 years using low-thrust maneuvers and a ‘3 months on +3 months off’ observation window scheme to improve constellation stability and reduce spacecraft fuel consumption. The result is a series of stable orbit configurations. The problem of fuel optimization is solved efficiently by combining a normalization strategy, a homotopic approach, and switching detection. Additionally, the optimization strategy quantitatively evaluates the fuel consumption required to maintain the stability of the Tianqin orbits. This evaluation provides a valuable reference for the performance design of the low-thrust propulsion system in the spacecraft.

Review of diver propulsion vehicle: A review

The ocean serves as a vital arena for resource exploitation, scientific inquiry, and strategic endeavors. Among the array of underwater propulsion technologies, diver propulsion vehicles (DPVs) stand out for their exceptional integration, concealability, and maneuverability. They hold a pivotal role in both marine scientific exploration and military operations beneath the waves, thus carrying significant research implications. However, the existing literature on DPVs remains limited, lacking comprehensive examinations of their design processes and parameters. This review systematically surveys and assesses the current landscape of DPV development and research. Three key facets—propeller design, performance assessment, and equipment engineering—are scrutinized and analyzed. By consolidating essential data from ongoing studies, this review offers valuable insights. Additionally, it forecasts potential directions and emerging focal points in the evolution of underwater propulsion for frogmen, drawing from current advancements. The objective is to furnish foundational data to support the design and study of frogman underwater propulsion systems, thereby advancing engineering applications in this domain.

Simulation of intra-chamber processes in a low-thrust rocket engine with a hydrogen-air mixture and counterflow cooling

The principles and methods of improvement of thrust, efficiency and cooling of rocket engines for space flight safety are of great interest for aerospace industry. The development of reliable and durable low-thrust rocket engines for space missions seems to be one of the important areas of development of the rocket and space industry. Issues related to the implementation of a new direction related to the design of propulsion systems for orientation systems of upper stages of launch vehicles using environmentally friendly fuel components are considered. A mathematical model is developed and numerical modelling of processes in the combustion chamber of a low-thrust rocket engine with gaseous fuel components (hydrogen and oxygen) is carried out. The model takes into account the presence of a cooling jacket. The mathematical model includes the effects of turbulence, combustion of a gaseous fuel mixture, kinetics of hydrogen combustion, and radiation. As a result of calculations, distributions of flow quantities in the combustion chamber and thermal loads on its walls are obtained. The influence of hydrogen mass flow rate on the efficiency of the working process and the dependence of thrust on hydrogen mass flow rate are discussed. The results of numerical modelling are compared with the data of a physical experiment obtained through fire tests of an engine model made of stainless steel on a three-dimensional printer.

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.

Robustness Improved Method for Deadbeat Predictive Current Control of PMLSM with Segmented Stators

Permanent magnet linear synchronous motors (PMLSMs) with stator segmented structures are widely used in the design of high-power propulsion systems. However, due to the inherent delay and segmented structure of the systems, there are parameter disturbances in the inductance and flux linkage of the motors. This makes the deadbeat predictive current control (DPCC) algorithm for a current loop less robust in the control system, leading to a decrease in control performance. Compensation methods such as compensation by observer and online estimation of parameters, are problematic to apply in practice due to the difficulty of parameter adjustment and the high complexity of the algorithm. In this paper, a robustness-improved incremental DPCC (RII-DPCC) method—which uses incremental DPCC (I-DPCC) to eliminate flux linkage parameters—is proposed. The stability of the current loop was evaluated through zero-pole analysis of the discrete transfer function. Current feedforward was introduced to improve the stability of I-DPCC. The inductance stability range of I-DPCC was increased from 0.8–1.25 times to 0–2 times the actual value, and the theoretical stability range was increased more than 4 times, effectively improving the robustness of the predictive model to flux linkage and inductance parameters. Finally, the effectiveness of the proposed method was verified through numerical simulation and experiment.

Flame transfer functions of asymmetric conical and V-shaped flames

Transfer functions of asymmetric flames subjected to incident flow perturbations are explored using the classical kinematic model, the G-equation, parameterized by flame tip angle α, flame-base incline angle β, and eccentricity e. With perturbations of various frequencies, we analyze perturbed asymmetric flames and derive analytical formulations of Flame Transfer Functions (FTF) for various flame conditions. It is observed that the gain of the asymmetric conical flame is increased compared to the symmetric case. Meanwhile, the amplification effect of the V-shaped flame is considerably suppressed as the flame becomes asymmetric. That means with a proper asymmetric geometry setting, the V-shaped flame no longer tends to amplify the perturbation and in other words becomes less susceptible to combustion instability. These findings have significant value for the future design and optimization of propulsion systems, where improving flame stability and reducing thermoacoustic instabilities are critical. Subsequently, a numerical study is conducted to verify the FTF results and examine the response of asymmetric flames under various perturbation levels. It has been demonstrated that the asymmetric conical flame is minimally affected by the amplitude of these perturbations, and the asymmetric V-shaped flame is highly sensitive to the convective amplitudes.

Design and Simulation of a Fuel Cell-based Hybrid Underwater Vehicle Propulsion System in Matlab/Simulink

Remotely Operated Vehicles (ROVs) and Autonomous Underwater Vehicles (AUVs) have many applications in underwater missions. A recurring issue is managing the power source of the vehicle, especially air-independent propulsion sources, such as batteries, accumulators, and fuel cells, to increase diving depth, underwater endurance, and range. The current article proposes the use of both fuel cells and batteries simultaneously. The subject of the study is Pluto Plus ROVs, which are mine sweeping and counter-terrorism underwater vehicles. The considered system is simulated in Matlab/Simulink. The result was a block diagram that simulates a hybrid propulsion system for submersibles in general and serves as the basis for improving the propulsion system for Pluto Plus ROVs.

Rocket Dynamics of Capped Nanotubes: A Molecular Dynamics Study.

The study of nanoparticle motion has fundamental relevance in a wide range of nanotechnology-based fields. Molecular dynamics simulations offer a powerful tool to elucidate the dynamics of complex systems and derive theoretical models that facilitate the invention and optimization of novel devices. This research contributes to this ongoing effort by investigating the motion of one-end capped carbon nanotubes within an aqueous environment through extensive molecular dynamics simulations. By exposing the carbon nanotubes to localized heating, propelled motion with velocities reaching up to ≈0.08 nm ps-1 was observed. Through systematic exploration of various parameters such as temperature, nanotube diameter, and size, we were able to elucidate the underlying mechanisms driving propulsion. Our findings demonstrate that the propulsive motion predominantly arises from a rocket-like mechanism facilitated by the progressive evaporation of water molecules entrapped within the carbon nanotube. Therefore, this study focuses on the complex interplay between nanoscale geometry, environmental conditions, and propulsion mechanisms in capped nanotubes, providing relevant insights into the design and optimization of nanoscale propulsion systems with various applications in nanotechnology and beyond.

Trajectory/propulsion integrated design optimization of the manned lunar lander propelled by hybrid rocket motors using analytical target cascading

Lunar missions are currently experiencing a significant surge in popularity, presenting expansive opportunities for further exploration and development. To thoroughly explore the design margins and potential of lunar landers, and to foster the development of overall designs driven by comprehensive performance objectives, it is crucial to conduct optimization design considering the coupling between key disciplines such as trajectory and propulsion. Considering the significant increase in computational complexity caused by conducting trajectory/propulsion integrated design optimization, the analytical target cascading method is employed to hierarchically decompose and coordinate optimization of the complex systems. This article presents a phased soft-landing strategy on the manned lunar lander propelled by hybrid rocket motors, utilizing powered explicit guidance and Apollo powered descent guidance, and proceeds with the trajectory/propulsion integrated design optimization involving diverse grain shapes and feed systems. This optimization process is separately undertaken utilizing multidisciplinary feasible method and analytical target cascading method. The analysis reveals that integrating trajectory and propulsion considerations into the optimization process facilitates a 5 % reduction in the overall mass relative to optimizations constrained solely by velocity increment and lack comprehensive trajectory design considerations. This highlights the profound impact of trajectory requirements on propulsion system design and the advantages of powered explicit guidance laws in minimizing fuel consumption. Crucially, the use of analytical target cascading achieves the better optimization results, and significantly reduces subsystem evaluation times, enhancing operational efficiency by 48 %, demonstrating the advantage in handling complex, large-scale systems. On another level, with different β values, the Mean Relative Error of the target values for the three schemes obtained by the analytical target cascading method is 0.0016, indicating good stability and strong robustness. The practical exploration in this article provides methods and frameworks for high-performance optimization design of complex aerospace mission profiles in the future.

Design and performance analysis of a compact dual-motor underwater vector propulsion system

Vector propulsion systems enhance the limited three-dimensional motion capabilities of conventional systems at low speeds. However, their requirement for multiple prime movers increases the underwater robot’s power capacity, impacts its size and mass and compromises long endurance capabilities. To solve this problem, a compact dual-motor underwater vector propulsion system is proposed in this paper. It employs a nozzle, adjustable in a two-dimensional plane, to produce an adjusting force, and a propeller, perpendicular to this plane, for main thrust, achieving three-dimensional motion. The innovation lies in a dual-shaft motor with each shaft featuring a one-way bearing. The synchronized direction of rotation of the two one-way bearings is opposite. This configuration enables the motor to drive the propeller during forward rotation and the nozzle during reverse rotation, achieving a two-in-one drive motor and reducing prime movers. Additionally, using nozzles for attitude regulation overcomes the limitation of conventional propulsion systems. An analytical model defines mechanical output characteristics. Computational fluid dynamics analyze hydrodynamic characteristics. The prototype’s underwater experiments confirm its ability to generate main thrust and a two-dimensional planar adjusting force, enabling three-dimensional motion.

Experimental design and testing of a pneumatic propulsion system for maritime transportation

Although the transportation sector is the backbone of economic exchange and social growth, it remains a major contributor to pollution and adverse emissions. Maritime transportation is a booming sector in coastal cities such as Dubai and the United Arab Emirates. Apart from being a tourist attraction, it also relieves a small portion of transportation congestion. Conventional boats use engines that operate on diesel and are thus responsible for air and waterborne pollution that severely harms marine wildlife and raises the concentrations of poisonous and carcinogenic materials in the water. In this paper, an alternative propulsion method is proposed in the form of a pneumatically powered boat. The system is powered by an air motor-mounted propeller fed by an onboard compressed air tank(s). In contrast to typical propulsion systems, compressed air systems offer effective, clean, and sustainable propulsion systems. The system performance was analyzed and compared with that of an electrical propulsion system powered by electrochemical batteries. In addition, a life cycle analysis was conducted to quantify any reduction in carbon dioxide emissions due to the utilization of the pneumatic system. The experimental results proved that compressed air is an effective alternative to electrical motors in terms of eco-friendliness, effectiveness, and sustainability. The pneumatic system provided a 6% extra propulsion force and a carbon footprint saving of 307 kgCO2/year over their electrical counterparts. Pneumatic systems offer a real advantage over other propulsion methods for ferryboat applications, which are defined by a constant trip length and path.