Propulsion Technology Research Articles

Rolls-Royce - 100 Years of Power

The date of December 17th 2003 is well recognised as the centenary of the first powered flight. What is less well known is that May 4th 2004 also represented another historical centenary for aerospace. On this date in 1904, the Charles Rolls and Henry Royce first met and their drive and ambition led to the formation of this world famous company. Since that day, Rolls-Royce has established itself with a reputation for excellence and innovation across a wide range of engineering products. This presentation will explore the evolution of aero-engine development at Rolls-Royce. The story starts with the highly successful Eagle and Falcon, which dominated the Allied propulsion systems of World War I. This success was followed with the Merlin, arguably the most recognised name in aerospace engines in the 1940s, before Frank Whittle’s pioneering work led to the development of the modern jet engine. Rolls-Royce is also the world leader for the unique propulsion technologies required for both supersonic and V/STOL flight and this presentation will describe design and development of these engines. The Olympus engine, which has accrued almost one million engine flying hours on Concorde and over one billion supersonic engine miles. Rolls-Royce V/STOL experience on the innovative Pegasus engine in the Harrier has also secured a position on the LiftSystemTM, the STOVL propulsion system for the Joint Strike Fighter. Today Rolls-Royce is a world leader in gas turbine technology for civil and defence aerospace, marine and energy power systems. This presentation will describe the process of developing technology once, and using it many times which has led to the development of a broad range of the latest gas turbine engines and technologies, including EJ200, F136, Adour and RTM322 for the latest military combat, trainer and helicopter aircraft. The next 100 years in gas turbine technology is certainly going to be as challenging, new and exciting as the past century. We can expect the growth of UAVs requiring More Electric, Variable Cycle and High Mach engines as well as a wealth of unique, new propulsion systems. With over 100 years success and innovation in the aerospace power business, Rolls-Royce is ideally placed to face these challenges

Indirect Optimization of Optimal Continuous Trajectory for Electric Sails With Refined Thrust Model in the Multi-Target Exploration Scenario

Electric sail-based propulsion is an innovative propellant-less propulsion technology that generates continuous thrust through the interaction between an artificial electric field and the solar wind. In an electric sail, the propulsive acceleration is adjusted by controlling the attitude of its normal plane and the coefficient determining the maximum thrust. However, the attitude adjustment speed of the electric sail is relatively small and the direction of the normal vector is constrained. Consequently, the electric sail is required to maintain a continuous propulsive acceleration vector when flying by the intermediate targets in multi-target interplanetary exploration. Therefore, an indirect optimization of three-dimensional optimal continuous interplanetary trajectory for electric sails with refined thrust model is investigated in this study. First, the optimal propulsive angles and thrust adjustment coefficient of electric sails with a refined thrust model are derived using Pontryagin's minimum principle. Second, a homotopy function is introduced in the process of trajectory optimization with an indirect method to approximate the step of the thrust adjustment coefficient to improve the accuracy of numerical integration. Additionally, the initial costates of the electric sail are transformed from the numerical simulation results of the Bezier shaping approach (BSA) and integrative Bezier shaping approach (IBSA) using the Karush-Kuhn-Tucker (KKT) condition. The numerical simulation results for the Earth-Mars rendezvous mission and the multi-target flyby mission reveal that the initial values of the costates are effective to implement an indirect optimization process of the optimal continuous trajectory for the rapid convergence of the electric sail. According to the numerical simulation results for multi-target mission, the indirect method is on average 2.5% better than the Gauss pseudospectral method (GPM) in overall index, and the calculation time is only 1.06% of GPM.

Experimental Study on the Propagation Characteristics of Rotating Detonation Wave with Liquid Hydrocarbon/High-Enthalpy Air Mixture

Rotating detonation engines (RDEs) are a promising propulsion technology featuring high thermal efficiency and a simple structure. To adapt the practical engineering applications of ramjet RDEs, rotating detonation combustion using a liquid hydrocarbon and pure air mixture will be required. This paper presents an experimental study on the propagation characteristics of rotating detonation waves with a liquid hydrocarbon and high-enthalpy air mixture in a hollow cylindrical chamber. The parameters, such as the equivalence ratio and inlet mass flux, are considered in this experiment. The frequency and the propagation velocity of rotating detonation combustion are analyzed under typical operations. The experimental results show that the peak pressure and propagation velocity of the rotating detonation wave are close to the C-J theoretical values under the inlet mass flux of 400 kg/(m2s). Both the propagation velocity and peak pressure of the rotating detonation wave decrease as the mass flux and equivalence ratio are reduced while the number of detonation wavefronts increases. Detonation wave instability tends to occur when the inlet mass flux decreases. There is a transition progress from thermo-acoustic combustion to rotating detonation combustion in the experiment under the condition of mass flux 350 kg/(m2s) and the equivalent ratio 0.8. The static pressure in the chamber is higher during detonation combustion than during thermo-acoustic combustion. These experimental results provide evidence that rotating detonation waves have the potential to significantly improve propulsion performance. The findings can serve as a valuable reference for the practical engineering application of rotating detonation engines.

NTPSS-vPower: A model for system simulation of a nuclear thermal propulsion system

Nuclear thermal propulsion (NTP) with a large specific impulse and a high thrust-to-weight ratio is one of the preferred propulsion technologies for realizing mankind’s vision of interstellar exploration. The system analysis of NTP, which is a crucial part of the system design, is used to evaluate the system response during operation. This work developed the NTPSS-vPower model on the vPower simulation platform for system simulation of a typical NTP system. Specifically, a properties model considering the thermal dissociation of high-temperature hydrogen, a point neutron kinetics model, a hybrid model of two-dimensional heat transfer and one-dimensional fluid flow of the core, and simplified models of the nozzle, turbine, and pump are developed. The differences of crucial parameters between steady-state simulation results and published design data are within 5%. Furthermore, NTPSS-vPower is used to simulate four typical events to predict the transient behavior of the system, which provides a reference for subsequent system analyses and experimental studies.

Significant Development Potential of the Solid Oxide Fuel Cell for the Technical Progress of the Marine Main Propulsion Plant in the Context of Energy Conservation and Emission Reduction

The International Maritime Organization (IMO) has proposed a series of strict pollutant emission regulations and carbon emission reduction targets, and the shipping industry is seeking new types of the marine main propulsion plant with advantages of high-efficiency and low-emission. Among the possible alternatives, the marine electric propulsion technology whose electric power source is fuel cell has gained sufficient attentions. At present, the worldwide research of the marine applications for fuel cell supplying propulsion power focuses more on the proton exchange membrane fuel cell (PEMFC) with low power instead of other types of fuel cell, and a series of research projects have achieved concrete results such as the industrialized marine fuel cell system or practical demonstration application. But the development trends of the application of the marine fuel cell supplying propulsion power are from the small boat to the great ship, from the navigating zone with low environmental complexity such as coastal water, inland waters to the ocean with complex navigation conditions. Thus, the power demand of the marine fuel cell in the future will show steady growth, which will create more development opportunities for the solid oxide fuel cell (SOFC) with the advantages of higher power, greater efficiency, long life span and fuel diversity. Although some challenges exist, the solid oxide fuel cell with significant development potential can certainly lead the technical progress of the marine main propulsion plant in the context of energy conservation and emission reduction.

Relationship between Corona Discharge Thrust and Applied Voltage’s Polarity

The thrust from corona discharge might be a promising propulsion technology in future aviation due to its advantage of not requiring mechanical moving parts. Although the thrust from corona discharge has been researched by many scholars, the effect of the applied voltage’s polarity on the thrust has received little attention. This polarity effect might be very important for some special electrohydrodynamic thrusters. This paper firstly built a test platform to reveal the effect of the applied voltage’s polarity on both the thrust and the corona current from a pair of symmetrically distributed needle electrodes. Then the applied voltage’s polarity on the electrical field distribution between a pair of needle-plate electrodes was simulated. Finally, the relationship between the space ions at the tip of the needle electrode and the thrust are discussed. The results show that a negative needle electrode with a smaller curvature radius has a stronger thrust than a positive one with a larger curvature radius, and a stronger thrust corresponds to a higher corona current. The local electric field is enhanced by the space ions at the tip of a negative needle electrode, while it is weakened by a positive needle electrode. This results in the polarity of thrust.

Non-linear and multi-domain modelling of a free piston engine with linear electric machine

In the current technological era, with the rapid advances in low-carbon power generation solutions, there has been renewed interest in the Free Piston Engine (FPE) as a viable thermal propulsion technology. However, describing and capturing the intrinsic non-linear dynamics of the FPE is computationally challenging and, understandably, is generally characterised by a simplified linear description, which may inherently omit the dominant dynamics.Consequently, this study considers the non-linear and multi-directional nature of the coupled translation loads during motoring and power generation. Thus, presenting a non-linear and multi-domain description of the FPE. The proposed model was implemented in an opposed-piston free-piston engine configuration and validated during motoring and generating against experimental data captured from a prototype with identical parameters. The simulation results strongly correlate to the experimental data with similar translator displacement, in-cylinder pressure and bounce chamber pressure traces. Furthermore, the study demonstrated that the proposed modelling approach captured the dominant dynamics of the FPE and proved satisfactory accuracy and performance. In addition to validating the proposed modelling approach, this paper concludes with a simulation study that demonstrates the embedding of a novel surrogate Chemical Kinetics (CK) description of the hydrous ethanol auto-ignition process and the resultant influence on the FPE dynamics, most importantly, on gaseous emission formation.Therefore, this paper aims to extend the current knowledge in this novel and emerging technology by considering the characteristic non-linearity and multi-directional nature of its coupling with multi-physical domains such as mechanical, chemical and electrical.

First Example of 1,2,5-Oxadiazole-Based Hypergolic Ionic Liquids: a New Class of Potential Energetic Fuels.

The development of liquid energetic fuels with improved properties is important topic in space propulsion technologies. In this manuscript, a series of energetic ionic liquids incorporating a 1,2,5-oxadiazole ring and nitrate, dicyanamide or dinitramide anion was synthesized and their physicochemical properties were evaluated. The synthesized compounds were fully characterized and were found to have good thermal stabilities (up to 219 °C) and experimental densities (1.21-1.47 g cm-3). Advantageously, 1,2,5-oxadiazole-based ionic liquids have high combined nitrogen-oxygen contents (up to 64.4%), while their detonation velocities are on the level of known explosive TNT, and combustion performance exceeds those of benchmark 2-hydroxyethylhydrazinium nitrate. Considering the established hypergolicity with H2O2 in the presence of a catalyst, and insensitivity to impact, synthesized ionic liquids have strong application potential as energetic fuels for space technologies.

Comparative Analysis of Hybrid-Electric Regional Aircraft with Tube-and-Wing and Box-Wing Airframes: A Performance Study

The continuously expanding transport aviation sector has a significant impact on climate change, and measures must be taken to limit its environmental impact. The study of advanced airframes, which may increase the lift-to-drag ratio and structural efficiency, and the development of innovative high-efficient powertrains, could be a way to achieve air transport decarbonization. This paper explores this broad topic by proposing a classical performance comparison between an aircraft with a traditional tube-and-wing (TW) airframe and a corresponding one with an advanced box-wing (BW) lifting architecture, both equipped with a parallel hybrid-electric powertrain. In fact, the propulsion technologies selected for this comparative study are consistent with the 2035 forecast, and both aircraft concepts are designed to belong to the regional transport category. The comparison between TW and BW is conducted on a conceptual and multi-disciplinary level, offering an analysis of the competitive benefits and limitations in terms of the aerodynamic, structural, and propulsive performance of the two configurations. The metrics selected to make the comparison are related to aircraft performance, such as the structural weight, the block fuel, or the energy required to accomplish the assigned mission. The outcomes obtained highlight the potential of BW airframes coupled with hybrid-electric powertrains to reduce fuel consumption, and hence the related greenhouse gas emissions, because of improvements introduced by this advanced architecture in both the aircraft’s empty weight and energy efficiency.

Energy-Efficient Control of a Gas Turbine Power Generation System

Gas turbines are used in the energy sectors as propulsion and power generation technologies. Despite technological advances in power generation and the emergence of numerous energy resources, gas turbine technology remains important due to its flexibility in load demand following, dynamical behavior, and the ability to work on different fuels with minor design changes. However, there would be no ambitious progress for gas turbines without reliable modeling and simulation. This paper describes a novel approach for modeling, identifying, and controlling a running gas turbine power plant. A simplified nonlinear model structure composed of s-domain transfer functions and nonlinear blocks represented by rate limiters, saturations, and look-up tables has been proposed. The model parameters have been optimized to fit real-world data. The verified model was then used to design a multiple PI/PD control to regulate the gas turbine via the inlet guide vane and fuel vales. The aim is to raise and stabilize the compressor’s differential pressure or pressure ratio, as well as raise the set-point of the temperature exhausted from the combustion turbine; as a result, energy efficiency has been improved by an average of 237.16 MWh saving in energy (or 8.96% reduction in fuel consumption) for a load range of 120 MW to 240 MW.

Design Investigation of Potential Long-Range Hydrogen Combustion Blended Wing Body Aircraft with Future Technologies

Present work investigates the potential of a long-range commercial blended wing body configuration powered by hydrogen combustion engines with future airframe and propulsion technologies. Future technologies include advanced materials, load alleviation techniques, boundary layer ingestion, and ultra-high bypass ratio engines. The hydrogen combustion configuration was compared to the configuration powered by kerosene with respect to geometric properties, performance characteristics, energy demand, equivalent CO2 emissions, and Direct Operating Costs. In addition, technology sensitivity studies were performed to assess the potential influence of each technology on the configuration. A multi-fidelity sizing methodology using low- and mid-fidelity methods for rapid configuration sizing was created to assess the configuration and perform robust analyses and multi-disciplinary optimizations. To assess potential uncertainties of the fidelity of aerodynamic analysis tools, high-fidelity aerodynamic analysis and optimization framework MACH-Aero was used for additional verification. Comparison of hydrogen and kerosene blended wing body aircraft showed a potential reduction of equivalent CO2 emission by 15% and 81% for blue and green hydrogen compared to the kerosene blended wing body and by 44% and 88% with respect to a conventional B777-300ER aircraft. Advancements in future technologies also significantly affect the geometric layout of aircraft. Boundary layer ingestion and ultra-high bypass ratio engines demonstrated the highest potential for fuel reduction, although both technologies conflict with each other. However, operating costs of hydrogen aircraft could establish a significant problem if pessimistic and base hydrogen price scenarios are achieved for blue and green hydrogen respectively. Finally, configurational problems featured by classical blended wing body aircraft are magnified for the hydrogen case due to the significant volume requirements to store hydrogen fuel.

Advanced Electric Propulsion Concepts for Fast Missions to the Outer Solar System and Beyond

Electric Propulsion (EP) comprises all types of space propulsion in which a certain amount of propellant is ionized and then accelerated by electric or magnetic fields, or both. This propulsion technology allows for much higher specific impulses (Isp > 2,000 s) than conventional chemical propulsion (Isp < 500 s), resulting in a major reduction of the propellant mass or a considerably higher final speed for a certain space mission. Hence, EP can enable very challenging space missions as DAWN has clearly shown. Furthermore, an EP system coupled with an advanced nuclear reactor could enable fast manned missions to Mars (one-way travel times less than 4 months). This propulsion technology can be scaled up to even higher specific impulses (Isp > 5,000s). However, the power needed for the same thrust is also increasing. An Oberth maneuver performed very close to the Sun could provide the additional power to a high-Isp Solar Electric Propulsion (SEP) system in order to reach the needed delta-v for challenging interstellar precursor missions. A breakthrough in power source specific mass is needed in order to enable missions with ultra-high specific impulses (> 10,000 s); this breakthrough could be realized having the power source not on board, as with Laser-powered Electric Propulsion (LEP), where the needed power is beamed to the spacecraft from an external laser source. In this case the on-board power source is limited to a light-weight photovoltaic receiver/converter. The development of ultra-high Isp ion thrusters powered by an external laser source could enable the most challenging interstellar precursor missions up to the Oort Cloud and beyond. This paper gives an update on the status of these advanced propulsion concepts, and provides some examples of interstellar precursor missions enabled by advanced EP systems which could be launched before 2040. Keywords: Interstellar, Electric Propulsion, Oberth, Laser

Investigation the performance of the recompression Brayton cycle with different N2O-based binary mixtures for a nuclear power spacecraft

The development of space power supply and space propulsion technology based on solar and chemical energy has approached the limit state. Large-scale space missions such as solar system marginal exploration, deep space orbit transfer and manned deep space exploration have put forward higher requirements for highly reliable, sustainable and high-power power sources. With the potential development of compact components, the S-CO2 recompression Brayton cycle has attracted much attention to improve the key technologies of nuclear power spacecraft and reduce the system mass and research and development cost. To weaken the constraint of the critical point of the supercritical working medium on the minimum cycle conditions, the additional gas mixed with pure N2O as the working medium can change the critical point properties to improve the cycle efficiency. At this present study stage, there is no specific standard for selecting the appropriate binary mixture components to improve the cycle efficiency. This study analyzed the physical properties of N2O-based binary mixtures and adopted them as a criterion to judge whether the N2O-based binary mixture can improve the cycle efficiency. Finally, according to the analysis results obtained and specific system environment requirements, several factors have been identified the selection criteria for N2O-based binary mixtures. The conclusion of this work is that the working medium with a more significant entropy difference, a higher specific heat capacity for the compressor close to the minimum cycle temperature in a specific temperature range and a lower maximum enthalpy of the N2O-based binary mixtures can obtain a higher cycle efficiency. Moreover, the substances reduce the critical temperature under that of N2O; in this scenario, the thermal performance is improved compared with pure S-N2O.

Preliminary sizing and study of a hybrid rocket based combined cycle

This study investigates the feasibility and performance of a missile propelled by a Hybrid Rocket-Based Combined Cycle (HRBCC) engine, which combines hybrid rocket and air-breathing engines. The HRBCC engine could enable intra and extra-atmospheric hypersonic flight in the future. Using a hybrid rocket engine could bring several advantages as reduced costs, increased reliability and simplicity. This research presents the unique feature of the hybrid rocket engine developed by HyPrSpace and explains its benefits for the conception of a HRBCC system. The performance of the missile was studied in two operational modes: pure rocket and ramjet. The results were then used to develop an in-house code that compared the trajectory of different missiles. Our findings indicate that HRBCC engines provide several advantages over other propulsive technologies and can meet the requirements of various military applications.

Overview and preliminary results of the Scalability Investigation of hybrid Electric concepts for Next-generation Aircraft (SIENA) project

This paper presents an overview and preliminary system architecture evaluation results of the project SIENA developed under the European Union Clean Sky 2 Program Thematic Topics. The ambition of the project is to accelerate the development of novel aircraft propulsion technologies by identification of technologies that are scalable across different aircraft categories. One of the main tasks within this process is the aircraft-level evaluation of the various system architecture and technology options. For this, a conceptual aircraft design software developed at Politecnico di Milano, and an aircraft on-board systems design and analysis method developed at Collins Aerospace Applied Research and Technology are combined. Utilizing these joint capabilities, the paper presents system architecture performance studies for two aircraft categories, a regional turboprop (ATR 72) and a short/medium-range turbofan (A320neo). The studies compare novel propulsion system concepts, for which kerosene is replaced with hydrogen as the main energy source on board, against traditional reference systems. In this context, two future technology scenarios are considered reflecting conservative and optimistic assumptions, respectively.

Analysis on the working mode of electric propulsion system

At present, the electromagnetic propulsion technology and the electrostatic propulsion technology are more mature than before. With the increase of available power on the spacecraft, the performance can be better improved. This paper mainly reviews the electric propulsion technology for long-term space travel. It can be concluded that, compared to traditional chemical rocket systems, electric propulsion systems are more suitable for long-term space missions and have the ability to transport relatively heavy objects in space.

Enhanced Decomposition of Ammonium Perchlorate-Ethyl Cellulose-Molybdenum Disulfide Nanocomposites.

Ammonium perchlorate (AP) is commonly used in propulsion technology. Recent studies have demonstrated that two-dimensional (2D) nanomaterials such as graphene (Gr) and hexagonal boron nitride (hBN) dispersed with nitrocellulose (NC) can conformally coat the surface of AP particles and enhance the reactivity of AP. In this work, the effectiveness of ethyl cellulose (EC) as an alternative to NC was studied. Using a similar encapsulation procedure as in recent work, Gr and hBN dispersed with EC were used to synthesize the composite materials Gr-EC-AP and hBN-EC-AP. Additionally, EC was used because the polymer can be used to disperse other 2D nanomaterials, specifically molybdenum disulfide (MoS2), which has semiconducting properties. While Gr and hBN dispersed in EC had a minimal effect on the reactivity of AP, MoS2 dispersed in EC significantly enhanced the decomposition behavior of AP compared to the control and other 2D nanomaterials, as evidenced by a pronounced low-temperature decomposition event (LTD) centered at 300 °C and then complete high-temperature decomposition (HTD) below 400 °C. Moreover, thermogravimetric analysis (TGA) showed a 5% mass loss temperature (Td5%) of 291 °C for the MoS2-coated AP, which was 17 °C lower than the AP control. The kinetic parameters for the three encapsulated AP samples were calculated using the Kissinger equation and confirmed a lower activation energy pathway for the MoS2 (86 kJ/mol) composite compared to pure AP (137 kJ/mol). This unique behavior of MoS2 is likely due to enhanced oxidation-reduction of AP during the initial stages of the reaction via a transition metal-catalyzed pathway. Density functional theory (DFT) calculations showed that the interactions between AP and MoS2 were stronger than AP on the Gr or hBN surfaces. Overall, this study complements previous work on NC-wrapped AP composites and demonstrates the unique roles of the disperagent and 2D nanomaterial in tuning the thermal decomposition of AP.

Reverse engineering of stakeholder preferences – A multi-criteria assessment of the German passenger car sector

Germany is a frontrunner in setting frameworks for the transition to a low-carbon system. The mobility sector plays a significant role in this shift, affecting different people and groups on multiple levels. Without acceptance from these stakeholders, emission targets are out of reach. This research analyzes how the heterogeneous preferences of various stakeholders align with the transformation of the mobility sector, looking at the extent to which the German transformation paths are supported and where stakeholders are located.Under the research objective of comparing stakeholders' preferences to identify which car segments require additional support for a successful climate transition, a status quo of stakeholders and car performance criteria is the foundation for the analysis. Stakeholders' hidden preferences hinder the derivation of criteria weightings from stakeholders; therefore, a ranking from observed preferences is used. This study's inverse multi-criteria decision analysis means that weightings can be predicted and used together with a recalibrated performance matrix to explore future preferences toward car segments.Results show that stakeholders prefer medium-sized cars, with the trend pointing towards the increased potential for alternative propulsion technologies and electrified vehicles. These insights can guide the improved targeting of policy supporting the energy and mobility transformation. Additionally, the method proposed in this work can fully handle subjective approaches while incorporating a priori information. A software implementation of the proposed method completes this work and is made publicly available.

A Simulation Framework for Aircraft Take-Off Considering Ground Effect Aerodynamics in Conceptual Design

The development of novel aircraft concepts and propulsion technologies requires up-to-date physics-based methods and tools for conceptual aircraft design. In this context, a simulation model for the take-off manoeuvre is proposed in this article, to be employed in the conceptual design phase for aircraft whether of traditional or innovative configuration. The model is capable of evaluating the longitudinal dynamics, both translational and rotational, of the aircraft considered as a rigid body, and influenced by the aerodynamic effects introduced by the presence of the ground. The ground effect, indeed, induces variations in the aerodynamic forces depending on the distance and the attitude of the lifting surfaces from the ground, which may significantly influence the aeromechanical characteristics of the aircraft during the evolution of the take-off manoeuvre. The simulation model is based on the numerical solution of the equations of the dynamics of the rigid aircraft in the longitudinal plane and integrates a vortex lattice aerodynamic solver to evaluate the aerodynamic and aeromechanical characteristics of the aircraft considering the ground effect in each time-step. The proposed approach is configuration independent, as it can model the geometry, evaluate the aerodynamics, and simulate the dynamics of aircraft with any lifting architecture; furthermore, the simulation model is fast and flexible, making it effective for the conceptual phase of aircraft design. The paper proposes the description of the take-off manoeuvre of two aircraft with different airframes: one with a conventional tube-and-wing architecture and one with a box-wing lifting system. The results proposed highlight the potential of the simulation model to detect aeromechanic and dynamic differences during the development of the manoeuvre for different aircraft configurations, and to assess the significance of considering ground effect aerodynamics.

Propulsion Technology of the Future - Quo Vadis?

Propulsion Technology of the Future - Quo Vadis?