A review of hybrid rockets: present status and future potential

This paper discusses the potential of the hybrid rocket engine as a viable and attractive mode of propulsion for both space vehicles and missiles. Research and development work on this engine in other countries is presented and evaluated. The various advantages of a hybrid engine over solid and liquid engines and its problems are highlighted. It has been argued that because of the low technology needed in the development of the hybrid system, it constitutes a cost-and-time-effective propulsion system for several applications in space programmes as well as weapon systems. In support of this conclusion, experience on the developmental studies of a variable thrust 100 kg engine is presented. Some future possibilities for hybrid propulsion systems are cited.     

Aerogel insulation systems for space launch applications

New developments in materials science in the areas of solution gelation processes and nanotechnology have led to the recent commercial production of aerogels. Concurrent with these advancements has been the development of new approaches to cryogenic thermal insulation systems. For example, thermal and physical characterizations of aerogel beads under cryogenic-vacuum conditions have been performed at the Cryogenics Test Laboratory of the NASA Kennedy Space Center. Aerogel-based insulation system demonstrations have also been conducted to improve performance for space launch applications. Subscale cryopumping experiments show the thermal insulating ability of these fully breathable nanoporous materials. For a properly executed thermal insulation system, these breathable aerogel systems are shown to not cryopump beyond the initial cooldown and thermal stabilization phase. New applications are being developed to augment the thermal protection systems of space launch vehicles, including the Space Shuttle External Tank. These applications include a cold-boundary temperature of 90 K with an ambient air environment in which both weather and flight aerodynamics are important considerations. Another application is a nitrogen-purged environment with a cold-boundary temperature of 20 K where both initial cooldown and launch ascent profiles must be considered. Experimental results and considerations for these flight system applications are discussed.     

高超声速飞行器综合热管理系统方案探讨

高超声速飞行器是当今世界航空航天领域研究的热点,由于其在飞行中遭受的热环境极其严酷,因 而可靠的综合热管理系统是安全飞行的保证。针对不同飞行任务的高超声速飞行器,分别提出了综合热管理系 统方案;对飞行时间短,飞行速度和高度变化快的飞行器,提出了以液氢燃料为主要热沉、相变蓄热材料为辅 助热沉的热管理方案;对飞行时间长,飞行马赫数高的飞行器,提出了以吸热型碳氢燃料为热沉的热管理方案; 分别探讨了两套方案涉及的关键技术,指出了未来研究工作的方向。     

Fuel‐Free Synthetic Micro‐/Nanomachines

Inspired by the swimming of natural microorganisms, synthetic micro‐/nanomachines, which convert energy into movement, are able to mimic the function of these amazing natural systems and help humanity by completing environmental and biological tasks. While offering autonomous propulsion, conventional micro‐/nanomachines usually rely on the decomposition of external chemical fuels (e.g., H₂O₂), which greatly hinders their applications in biologically relevant media. Recent developments have resulted in various micro‐/nanomotors that can be powered by biocompatible fuels. Fuel‐free synthetic micro‐/nanomotors, which can move without external chemical fuels, represent another attractive solution for practical applications owing to their biocompatibility and sustainability. Here, recent developments on fuel‐free micro‐/nanomotors (powered by various external stimuli such as light, magnetic, electric, or ultrasonic fields) are summarized, ranging from fabrication to propulsion mechanisms. The applications of these fuel‐free micro‐/nanomotors are also discussed, including nanopatterning, targeted drug/gene delivery, cell manipulation, and precision nanosurgery. With continuous innovation, future autonomous, intelligent and multifunctional fuel‐free micro‐/nanomachines are expected to have a profound impact upon diverse biomedical applications, providing unlimited opportunities beyond one's imagination.     

Mechanical property requirements for aero gas turbine materials

Abstract

The outstanding performance of current military and civil aero gas turbine engines is linked closely to the way in which modern design and manufacturing techniques have become totally integrated with materials designed specifically for operation within the hostile environment of a gas turbine. Advanced titanium alloys are used extensively throughout the compressor and nickel-base superalloys dominate materials application in the turbine. In spite of current achievements, the engine designer is still under severe competitive pressure to improve engine performance still further and this will inevitably lead to even more demanding material requirements. The present paper outlines the continuing trends in engine development and describes the impact these are having on materials technology in general and the mechanical property requirements of nickel-base superalloys in particular.

MST/512     

New Insight into the Development of Oxygen Carrier Materials for Chemical Looping Systems

Chemical looping combustion (CLC) and chemical looping reforming (CLR) are innovative technologies for clean and efficient hydrocarbon conversion into power, fuels, and chemicals through cyclic redox reactions. Metal oxide materials play an essential role in the chemical looping redox processes. During reduction, the oxygen carriers donate the required amount of oxygen ions for hydrocarbon conversion and product synthesis. In the oxidation step, the depleted metal oxide oxygen carriers are replenished with molecular oxygen from the air while heat is released. In recent years, there have been significant advances in oxygen carrier materials for various chemical looping applications. Among these metal oxide materials, iron-based oxygen carriers are attractive due to their high oxygen-carrying capacity, cost benefits, and versatility in applications for chemical looping reactions. Their reactivity can also be enhanced via structural design and modification. This review discusses recent advances in the development of oxygen carrier materials and the mechanisms of hydrocarbon conversion over these materials. These advances will facilitate the development of oxygen carrier materials for more efficient chemical looping technology applications.     

Layered composite thermal insulation system for nonvacuum cryogenic applications

A problem common to both space launch applications and cryogenic propulsion test facilities is providing suitable thermal insulation for complex cryogenic piping, tanks, and components that cannot be vacuum-jacketed or otherwise be broad-area-covered. To meet such requirements and provide a practical solution to the problem, a layered composite insulation system has been developed for nonvacuum applications and extreme environmental exposure conditions. Layered composite insulation system for extreme conditions (or LCX) is particularly suited for complex piping or tank systems that are difficult or practically impossible to insulate by conventional means. Consisting of several functional layers, the aerogel blanket-based system can be tailored to specific thermal and mechanical performance requirements. The operational principle of the system is layer-pairs working in combination. Each layer pair is comprised of a primary insulation layer and a compressible radiant barrier layer. Vacuum-jacketed piping systems, whether part of the ground equipment or the flight vehicle, typically include numerous terminations, disconnects, umbilical connections, or branches that must be insulated by nonvacuum means. Broad-area insulation systems, such as spray foam or rigid foam panels, are often the lightweight materials of choice for vehicle tanks, but the plumbing elements, feedthroughs, appurtenances, and structural supports all create “hot spot” areas that are not readily insulated by similar means. Finally, the design layouts of valve control skids used for launch pads and test stands can be nearly impossible to insulate because of their complexity and high density of components and instrumentation. Primary requirements for such nonvacuum thermal insulation systems include the combination of harsh conditions, including full weather exposure, vibration, and structural loads. Further requirements include reliability and the right level of system breathability for thermal cycling. The LCX system is suitable for temperatures from approximately 4 K to 400 K and can be designed to insulate liquid hydrogen, liquid nitrogen, liquid oxygen, or liquid methane equipment. Laboratory test data for thermal and mechanical performance are presented. Field demonstration cases and examples in operational cryogenic systems are also given.     

Korrosionsverhalten unterschiedlicher Aluminiumlegierungen in ethanolhaltigem Ottokraftstoff unter erhöhten Temperaturen

Corrosion behaviour of different aluminium alloys in fuels containing ethanol under increased temperatures In the face of running short the natural resources of petroleum and in consequence of the Kyoto‐Protocol, there is a change in the general political conditions. For this reason, fuel components of biogenous origin (such as ethanol or biodiesel) used as blends to conventional fuels are moving into focus. These blends can cause a change to the characteristics of the fuels. At first it was assumed, that a blend of ethanol to fuel does not have a particularly strong effect on the corrosion behaviour of lightweight construction materials. Samples made of aluminium materials with strong reference to practice, exposed to a blend of 10 % ethanol and test fluid under increased pressures and temperatures, showed at higher temperatures (T = 130 °C ‐ e.g. close to the engine used components) already after a short period strong corrosion ‐ dry corrosion. By means of the accomplished research, substantial influencing variables on the corrosion behaviour of aluminium materials in fuels blended with ethanol could be pointed out.     

高温合金材料在大型现代化舰船动力的应用

本文根据现代化舰船动力装置不同部件的工作条件,归纳了船用大型柴油机、燃气轮机、核反应堆动力装置及舰船动力装置用高温螺栓等部位应用前景极好的高温合金材料。     

Multidisciplinary approach to materials selection for bipropellant thrusters using ablative and radiative cooling

Reduction of costs is a main consideration in every space mission, and propulsion system is an important subsystem of those missions where orbital maneuvers are considered. Lighter propulsions with higher performance are necessary to reduce the mission costs. Bipropellant propulsions have been widely used in launch vehicles and upper-stages as well as deorbit modules because of better performances in comparison with other propulsion systems. Unfortunately heat transfer and thermal control limit bipropellant propulsion performance and maximum performance cannot be achieved. Well-known cooling methods such as regenerative and film cooling increase the cost using extra equipment and high temperature materials. In this paper, a new approach for cooling is presented based on combined ablative and radiative cooling. Governing equations are derived for two or three layers of thermal protection system (TPS) to optimize the TPS mass. The first layer is used as an ablative layer to control the temperature where the second and third layers are used as an insulator to control the heat fluxes. Proposed cooling method has been applied for two real bipropellant thrusters. According to the results, the presented algorithm can suitably predict the heat fluxes and satisfy the wall temperature constraint. Then, the algorithm has been used to minimize the wall temperatures as low as possible and replace high temperature materials (platinum alloy) with common materials (composite or steel). It is shown that selection of TPS materials affects the TPS mass and Isp simultaneously, but conversely. Best solution should be derived by trading off between structure temperature (cost), Isp (performance), and TPS thicknesses (geometry). Multidisciplinary approach to TPS and structure material selection of a bipropellant thruster is presented for a case study. It has been shown that mass and performance penalties of using TPS are acceptable, considering the advantages of using steel alloy instead of platinum alloy.     

Production of Nanoscale Detonation Carbon using a Pulse Gas-Detonation Device

Combustion and thermal decomposition of hydrocarbon fuels are used to produce different forms of carbon. Combustion in the detonation mode is of particular interest, as nanocarbon obtained under these conditions differs in properties from products synthesized by other techniques. A pulsed gas-detonation device designed on the basis of a CCDS2000 detonation spraying facility opens up new possibilities for manufacturing of nanocarbon. The device operates in a flow mode of gas supply into the reactor at the atmospheric pressure, which ensures high productivity and industrial safety of this method. Using detonation of acetylene-oxygen mixtures rich in acetylene, nanoscale carbon was obtained with particle morphology depending on the ratio of the components in the gaseous mixture.     

Laser ignition in internal-combustion engines: Sparkless initiation

Laser ignition has been implemented in a single-cylinder internal combustion engine fueled by gasoline. Indicator diagrams (cylinder pressure versus crank angle) were obtained for laser ignition with nano- and microsecond pulses of an Nd:YAG laser. The maximum power of microsecond pulses was below critical for spark initiation, while the radiation wavelength was outside the spectral range of optical absorption by hydrocarbon fuels. Apparently, the ignition starts due to radiation absorption by the oil residues or carbon deposit in the combustion chamber, so that the ability of engine to operate is retained. This initiation of spark-free ignition shows the possibility of using compact semiconductor quantum-cascade lasers operating at wavelengths of about 3.4 μm (for which the optical absorption by fuel mixtures is high) in ignition systems of internal combustion engines.     

21世纪世界航空动力技术发展趋势与展望

21世纪的世界航空动力技术将继续加速发展，有可能出现革命性变化。传统的燃气涡轮发动机仍具有巨大的发展潜力；随着超燃冲压发动机以及涡轮和火箭基组合循环发动机的应用，高超声速飞行将成为现实，并有可能迎来以高超声速空天往返飞行为标志的新的航空时代；脉冲爆震发动机、超微型发动机等新概念发动机必将登上历史舞台；新能源航空发动机将占据一席之地；航空动力技术将继续在人类科技发展和社会进步中占据重要的地位。     

Study on the effect of exhaust gas-based fuel preheating device on ethanol–diesel blends operation in a compression ignition engine

Rapid depletion of fossil fuels and stringent emission regulations compel the scientific community to search for alternative energy sources for the internal combustion engines. Among many alternative biofuels, ethanol is getting worldwide attention for compression ignition engine either in the form of partial substitute or complete replacement for diesel fuel. Ethanol fuel has certain undesirable properties like poor flammability limit which results in cold starting issues and higher hydrocarbon emission which restricts their use in compression ignition engine. This issue can be easily overcome by preheating of ethanol fuel before it gets admitted inside the engine cylinder. In the present study, a standard preheating device is designed and fabricated in accordance with engine specifications and simulations were carried out under various operating conditions to evaluate its performance. Furthermore, experimental investigations were carried out in a compression ignition engine fueled with ethanol blends of 20 and 30% with diesel by volume and the fuel blends were preheated using burned exhaust gases. In addition, a comparative study has been carried out for preheated and non-preheated blends of E20 (20% of ethanol and 80% of diesel) and E30 with baseline diesel. The experimental results show that the preheated E20 (20% of ethanol and 80% of diesel) blend has higher brake thermal efficiency of 36.28% with a significant reduction in brake specific fuel consumption when compared with all the other blends. Moreover, the preheated E20 blend reduces the carbon monoxide, unburned hydrocarbon and smoke emissions by 49, 48 and 10%, respectively. However, the NOx emission is increased by 6% as compared to the non-preheating effect. It is also noted that the preheating of ethanol blends produced better combustion results with a significant reduction in the ignition delay period. Hence, it can be concluded that the ethanol fuel can be effectively used in a diesel engine by means of preheating using exhaust gases and could be a viable option for diesel engine applications.     

微电推进系统研制及应用现状

200kg以下的微小卫星的轨道维持、姿态控制、阻尼补偿、编队飞行等任务对微电推进技术及产品提出了明确的应用需求,不同类型的微电推进在不同功率范围内有着各自的优势.本文对中国微小卫星12U立方星LPPT-5脉冲等离子体电推进系统、150kg小卫星LPPT-25脉冲等离子体电推进系统、6U立方星LVAT-1真空弧电推进系统...     

A redox-stable efficient anode for solid-oxide fuel cells

Solid-oxide fuel cells (SOFCs) promise high efficiencies in a range of fuels. Unlike lower temperature variants, carbon monoxide is a fuel rather than a poison, and so hydrocarbon fuels can be used directly, through internal reforming or even direct oxidation. This provides a key entry strategy for fuel-cell technology into the current energy economy. Present development is mainly based on the yttria-stabilized zirconia (YSZ) electrolyte. The most commonly used anode materials are Ni/YSZ cermets, which display excellent catalytic properties for fuel oxidation and good current collection, but do exhibit disadvantages, such as low tolerance to sulphur and carbon deposition when using hydrocarbon fuels, and poor redox cycling causing volume instability. Here, we report a nickel-free SOFC anode, La0.75Sr0.25Cr0.5Mn0.5O3, with comparable electrochemical performance to Ni/YSZ cermets. The electrode polarization resistance approaches 0.2 Omega cm2 at 900 degrees C in 97% H2/3% H2O. Very good performance is achieved for methane oxidation without using excess steam. The anode is stable in both fuel and air conditions, and shows stable electrode performance in methane. Thus both redox stability and operation in low steam hydrocarbons have been demonstrated, overcoming two of the major limitations of the current generation of nickel zirconia cermet SOFC anodes.     

Research and development of ultra-high temperature materials in Japan

Abstract

Gas turbines for aircraft engine and power generation are typical fields of application of high temperature materials. Nickel-based superalloys are excellent and most useful materials for these applications and have been well developed especially with the outstanding progress of jet engines. In future, from a view point of global environmental problems, there will be strong demands for special materials for high temperature and high efficiency gas turbines for power generation. However, the temperature capability of the superalloys will saturate to some limit because of their melting points which are lower than 1400°C. So-called ultra-high temperature materials, such as intermetallic compounds, refractory metals and alloys, ceramics, and various composite materials are expected to surpass the temperature capability of the superalloys, although these materials have several problems such as difficulty of processing, lack of ductility and toughness or the poor resistance to oxidation and hot-corrosion. In this paper, present and future prospects of R&D of these ultra-high temperature materials have been briefly reviewed.     

Thermal Analysis of Thermal Protection System of Test Launch Vehicle

In this paper, a thermal analysis of the thermal protection system (TPS) of test launch vehicle (TLV) is explained. TLV is heated during the flight due to engine exhaust plume gas by thermal radiation and a TPS is needed to protect the vehicle from the heating. The thermal analysis of the TPS is conducted to predict the heat flux from plume gas and temperature of the TPS during the flight. To simplify the thermal analysis, plume gas radiation and radiative properties are assumed to be surface radiation and constants, respectively. Thermal conductivity, emissivity and absorptivity of the TPS material are measured. Proper plume conditions are determined from the preliminary analysis and then the heat flux and temperature of the TPS are calculated.     

Investigation of a Bird Strike Incident of a Military Gas Turbine Engine

This paper investigates a bird strike incident of a military gas turbine engine. The jet pipe temperature of the engine shoot up and rotor speed reduced suddenly during takeoff roll. Long flame was noticed from the engine and aircraft crashed at runway end. Forensic analysis of remnants collected from flow passages confirmed the bird ingestion. Blockage of flow passages due to the presence of bird has led to engine surge and high gas temperature resulting in extensive damage of low pressure turbine module. The paper also proposes remedial measures to avoid such bird strikes during flight.     

Reducing uncertainty in fatigue life limits of turbine engine alloys

In probabilistic design of materials for fracture-critical components in modern military turbine engines, a typical maximum design target risk (DTR) is 5 × 10⁻⁸ component failures/engine flight hour. This metric underscores the essential role of safety in a design process that simultaneously strives to achieve performance, efficiency, reliability, and affordability throughout the life cycle of the engine. Traditionally, the design and life management approaches for engine materials have typically relied on extensive testing programs to produce large databases of fatigue data, from which statistically based life limits are derived by extrapolation from the mean fatigue behavior. However, we have found that the statistical behavior of fatigue lifetimes under a given test condition often exhibits a bimodal form, and that the trends in mean vs. minimum fatigue lifetime typically respond differently to loading or to microstructural variables. Under such circumstances, the underlying life-limiting mechanisms appear to exhibit a probabilistic microstructural hierarchy in fatigue resistance that is controlled by susceptibility of local microstructural neighborhoods to early damage and the growth of small cracks. These findings suggest that significant opportunities may exist for reductions in uncertainty in materials life-cycle prediction and management, if such hierarchies can be understood and controlled. This paper explores the potential implications of these findings, and a number of possible approaches are suggested for incorporating the insights of life-limiting fatigue into methods of integrated computational materials engineering (ICME) to support optimized life-cycle design of materials and components in turbine engines. Benefits of this approach appear to include substantial improvements in model accuracy, coupled with reduced requirements for materials testing, potentially leading to a significant reduction in the time and cost to develop, validate, transition, and implement new, more fatigue resistant alloys.