The RBCC , or rocket-based combined cycle propulsion system, was one of the two types of propulsion systems that may have been tested in the Boeing X-43 experimental aircraft. The RBCC, or strutjet as it is sometimes called, is a combination propulsion system that consists of a ramjet , scramjet , and ducted rocket , where all three systems use a shared flow path.
61-440: A TBCC , or turbine-based combined cycle propulsion system, is a turbine engine combined with a ramjet and scramjet . A TRCC , or turbo rocket combined cycle propulsion system, is another combination propulsion system that combines an afterburning turbine engine with a RBCC propulsion system. This spacecraft or satellite related article is a stub . You can help Misplaced Pages by expanding it . This rocketry article
122-415: A turbojet , driving the fan of a turbofan , rotor or accessory of a turboshaft , and gear reduction and propeller of a turboprop . If the engine has a power turbine added to drive an industrial generator or a helicopter rotor, the exit pressure will be as close to the entry pressure as possible with only enough energy left to overcome the pressure losses in the exhaust ducting and expel the exhaust. For
183-409: A turboprop engine there will be a particular balance between propeller power and jet thrust which gives the most economical operation. In a turbojet engine only enough pressure and energy is extracted from the flow to drive the compressor and other components. The remaining high-pressure gases are accelerated through a nozzle to provide a jet to propel an aircraft. The smaller the engine, the higher
244-420: A turbopump to permit the use of lightweight, low-pressure tanks, reducing the empty weight of the rocket. A turboprop engine is a turbine engine that drives an aircraft propeller using a reduction gear to translate high turbine section operating speed (often in the 10s of thousands) into low thousands necessary for efficient propeller operation. The benefit of using the turboprop engine is to take advantage of
305-452: A turboshaft design. They supply: Industrial gas turbines differ from aeronautical designs in that the frames, bearings, and blading are of heavier construction. They are also much more closely integrated with the devices they power—often an electric generator —and the secondary-energy equipment that is used to recover residual energy (largely heat). They range in size from portable mobile plants to large, complex systems weighing more than
366-413: A buildup on the outside of the blades. Nickel-based superalloys boast improved strength and creep resistance due to their composition and resultant microstructure . The gamma (γ) FCC nickel is alloyed with aluminum and titanium in order to precipitate a uniform dispersion of the coherent Ni 3 (Al,Ti) gamma-prime (γ') phases. The finely dispersed γ' precipitates impede dislocation motion and introduce
427-517: A few dozen hours per year—depending on the electricity demand and the generating capacity of the region. In areas with a shortage of base-load and load following power plant capacity or with low fuel costs, a gas turbine powerplant may regularly operate most hours of the day. A large single-cycle gas turbine typically produces 100 to 400 megawatts of electric power and has 35–40% thermodynamic efficiency . Industrial gas turbines that are used solely for mechanical drive or used in collaboration with
488-579: A gas turbine engine is its power to weight ratio. Since significant useful work can be generated by a relatively lightweight engine, gas turbines are perfectly suited for aircraft propulsion. Thrust bearings and journal bearings are a critical part of a design. They are hydrodynamic oil bearings or oil-cooled rolling-element bearings . Foil bearings are used in some small machines such as micro turbines and also have strong potential for use in small gas turbines/ auxiliary power units A major challenge facing turbine design, especially turbine blades ,
549-490: A hundred tonnes housed in purpose-built buildings. When the gas turbine is used solely for shaft power, its thermal efficiency is about 30%. However, it may be cheaper to buy electricity than to generate it. Therefore, many engines are used in CHP (Combined Heat and Power) configurations that can be small enough to be integrated into portable container configurations. Gas turbines can be particularly efficient when waste heat from
610-418: A lesser extent, on cars, buses, and motorcycles. A key advantage of jets and turboprops for airplane propulsion – their superior performance at high altitude compared to piston engines, particularly naturally aspirated ones – is irrelevant in most automobile applications. Their power-to-weight advantage, though less critical than for aircraft, is still important. Gas turbines offer a high-powered engine in
671-532: A recovery steam generator differ from power generating sets in that they are often smaller and feature a dual shaft design as opposed to a single shaft. The power range varies from 1 megawatt up to 50 megawatts. These engines are connected directly or via a gearbox to either a pump or compressor assembly. The majority of installations are used within the oil and gas industries. Mechanical drive applications increase efficiency by around 2%. Oil and gas platforms require these engines to drive compressors to inject gas into
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#1732788083631732-461: A second, independent turbine (known as a power turbine ) that can be connected to a fan, propeller, or electrical generator. The purpose of the gas turbine determines the design so that the most desirable split of energy between the thrust and the shaft work is achieved. The fourth step of the Brayton cycle (cooling of the working fluid) is omitted, as gas turbines are open systems that do not reuse
793-569: A threshold stress, increasing the stress required for the onset of creep. Furthermore, γ' is an ordered L1 2 phase that makes it harder for dislocations to shear past it. Further Refractory elements such as rhenium and ruthenium can be added in solid solution to improve creep strength. The addition of these elements reduces the diffusion of the gamma prime phase, thus preserving the fatigue resistance, strength, and creep resistance. The development of single crystal superalloys has led to significant improvements in creep resistance as well. Due to
854-550: A very small and light package. However, they are not as responsive and efficient as small piston engines over the wide range of RPMs and powers needed in vehicle applications. In series hybrid vehicles, as the driving electric motors are mechanically detached from the electricity generating engine, the responsiveness, poor performance at low speed and low efficiency at low output problems are much less important. The turbine can be run at optimum speed for its power output, and batteries and ultracapacitors can supply power as needed, with
915-400: Is a stub . You can help Misplaced Pages by expanding it . This aviation -related article is a stub . You can help Misplaced Pages by expanding it . Gas turbine A gas turbine or gas turbine engine is a type of continuous flow internal combustion engine . The main parts common to all gas turbine engines form the power-producing part (known as the gas generator or core) and are, in
976-477: Is a property of materials, defined as the number of cubic meters occupied by one kilogram of a particular substance. The standard unit is the meter cubed per kilogram (m /kg or m ·kg ). Sometimes specific volume is expressed in terms of the number of cubic centimeters occupied by one gram of a substance. In this case, the unit is the centimeter cubed per gram (cm /g or cm ·g ). To convert m /kg to cm /g, multiply by 1000; conversely, multiply by 0.001. Specific volume
1037-399: Is almost identical to that of water: 0.00100 m /kg. If one sets out to determine the specific volume of an ideal gas, such as super heated steam, using the equation ν = RT / P , where pressure is 2500 lbf/in , R is 0.596, temperature is 1960 °R . In that case, the specific volume would equal 0.4672 in /lb. However, if the temperature is changed to 1160 °R ,
1098-425: Is also required to drive a helicopter rotor or land-vehicle transmission ( turboshaft ), marine propeller or electrical generator (power turbine). Greater thrust-to-weight ratio for flight is achieved with the addition of an afterburner . The basic operation of the gas turbine is a Brayton cycle with air as the working fluid : atmospheric air flows through the compressor that brings it to higher pressure; energy
1159-463: Is distinguished from the Otto cycle , in that all the processes (compression, ignition combustion, exhaust), occur at the same time, continuously. In a real gas turbine, mechanical energy is changed irreversibly (due to internal friction and turbulence) into pressure and thermal energy when the gas is compressed (in either a centrifugal or axial compressor ). Heat is added in the combustion chamber and
1220-488: Is inversely proportional to density. If the density of a substance doubles, its specific volume, as expressed in the same base units, is cut in half. If the density drops to 1/10 its former value, the specific volume, as expressed in the same base units, increases by a factor of 10. The density of gases changes with even slight variations in temperature, while densities of liquid and solids, which are generally thought of as incompressible, will change very little. Specific volume
1281-677: Is reducing the creep that is induced by the high temperatures and stresses that are experienced during operation. Higher operating temperatures are continuously sought in order to increase efficiency, but come at the cost of higher creep rates. Several methods have therefore been employed in an attempt to achieve optimal performance while limiting creep, with the most successful ones being high performance coatings and single crystal superalloys . These technologies work by limiting deformation that occurs by mechanisms that can be broadly classified as dislocation glide, dislocation climb and diffusional flow. Protective coatings provide thermal insulation of
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#17327880836311342-405: Is the inverse of the density of a substance; therefore, careful consideration must be taken account when dealing with situations that involve gases. Small changes in temperature will have a noticeable effect on specific volumes. The average density of human blood is 1060 kg/m . The specific volume that correlates to that density is 0.00094 m /kg. Notice that the average specific volume of blood
1403-412: Is then added by spraying fuel into the air and igniting it so that the combustion generates a high-temperature flow; this high-temperature pressurized gas enters a turbine, producing a shaft work output in the process, used to drive the compressor; the unused energy comes out in the exhaust gases that can be repurposed for external work, such as directly producing thrust in a turbojet engine , or rotating
1464-419: Is then ducted into the combustor section which can be of a annular , can , or can-annular design. In the combustor section, roughly 70% of the air from the compressor is ducted around the combustor itself for cooling purposes. The remaining roughly 30% the air is mixed with fuel and ignited by the already burning air-fuel mixture , which then expands producing power across the turbine . This expansion of
1525-475: Is used, it is possible to use exhaust air from the turbine as the primary combustion air. This effectively reduces global heat losses, although heat losses associated with the combustion exhaust remain inevitable. Closed-cycle gas turbines based on helium or supercritical carbon dioxide also hold promise for use with future high temperature solar and nuclear power generation. Gas turbines are often used on ships , locomotives , helicopters , tanks , and to
1586-968: The Airbus A400M transport, Lockheed AC-130 and the 60-year-old Tupolev Tu-95 strategic bomber. While military turboprop engines can vary, in the civilian market there are two primary engines to be found: the Pratt & Whitney Canada PT6 , a free-turbine turboshaft engine, and the Honeywell TPE331 , a fixed turbine engine (formerly designated as the Garrett AiResearch 331). Aeroderivative gas turbines are generally based on existing aircraft gas turbine engines and are smaller and lighter than industrial gas turbines. Aeroderivatives are used in electrical power generation due to their ability to be shut down and handle load changes more quickly than industrial machines. They are also used in
1647-528: The BMW 801 . This, however, also translated into poor efficiency and reliability. More advanced gas turbines (such as those found in modern jet engines or combined cycle power plants) may have 2 or 3 shafts (spools), hundreds of compressor and turbine blades, movable stator blades, and extensive external tubing for fuel, oil and air systems; they use temperature resistant alloys, and are made with tight specifications requiring precision manufacture. All this often makes
1708-401: The ideal gas law , P V = n R T {\displaystyle PV={nRT}} , and the amount of substance , n = m / M {\textstyle n=m/M} Specific volume is commonly applied to: Imagine a variable-volume, airtight chamber containing a certain number of atoms of oxygen gas. Consider the following four examples: Specific volume
1769-413: The specific volume of the gas increases, accompanied by a slight loss in pressure. During expansion through the stator and rotor passages in the turbine, irreversible energy transformation once again occurs. Fresh air is taken in, in place of the heat rejection. Air is taken in by a compressor, called a gas generator , with either an axial or centrifugal design, or a combination of the two. This air
1830-456: The active species (typically vacancies) within the alloy and reducing dislocation and vacancy creep. It has been found that a coating of 1–200 μm can decrease blade temperatures by up to 200 °C (392 °F). Bond coats are directly applied onto the surface of the substrate using pack carburization and serve the dual purpose of providing improved adherence for the TBC and oxidation resistance for
1891-510: The addition of a ducted fan are called turbofans or (rarely) fan-jets. These engines produce nearly 80% of their thrust by the ducted fan, which can be seen from the front of the engine. They come in two types, low-bypass turbofan and high bypass , the difference being the amount of air moved by the fan, called "bypass air". These engines offer the benefit of more thrust without extra fuel consumption. Gas turbines are also used in many liquid-fuel rockets , where gas turbines are used to power
Rocket-based combined cycle - Misplaced Pages Continue
1952-401: The blade and offer oxidation and corrosion resistance. Thermal barrier coatings (TBCs) are often stabilized zirconium dioxide -based ceramics and oxidation/corrosion resistant coatings (bond coats) typically consist of aluminides or MCrAlY (where M is typically Fe and/or Cr) alloys. Using TBCs limits the temperature exposure of the superalloy substrate, thereby decreasing the diffusivity of
2013-420: The closely related form of the turbocharger . The turbocharger is basically a compact and simple free shaft radial gas turbine which is driven by the piston engine's exhaust gas . The centripetal turbine wheel drives a centrifugal compressor wheel through a common rotating shaft. This wheel supercharges the engine air intake to a degree that can be controlled by means of a wastegate or by dynamically modifying
2074-473: The compressor and the turbine with a compressed air store. In a conventional turbine, up to half the generated power is used driving the compressor. In a compressed air energy storage configuration, power is used to drive the compressor, and the compressed air is released to operate the turbine when required. Turboshaft engines are used to drive compressors in gas pumping stations and natural gas liquefaction plants. They are also used in aviation to power all but
2135-513: The compressor/shaft/turbine rotor assembly, with other moving parts in the fuel system. This, in turn, can translate into price. For instance, costing 10,000 ℛℳ for materials, the Jumo 004 proved cheaper than the Junkers 213 piston engine, which was 35,000 ℛℳ , and needed only 375 hours of lower-skill labor to complete (including manufacture, assembly, and shipping), compared to 1,400 for
2196-444: The construction of a simple gas turbine more complicated than a piston engine. Moreover, to reach optimum performance in modern gas turbine power plants the gas needs to be prepared to exact fuel specifications. Fuel gas conditioning systems treat the natural gas to reach the exact fuel specification prior to entering the turbine in terms of pressure, temperature, gas composition, and the related Wobbe index . The primary advantage of
2257-537: The direction of flow: Additional components have to be added to the gas generator to suit its application. Common to all is an air inlet but with different configurations to suit the requirements of marine use, land use or flight at speeds varying from stationary to supersonic. A propelling nozzle is added to produce thrust for flight. An extra turbine is added to drive a propeller ( turboprop ) or ducted fan ( turbofan ) to reduce fuel consumption (by increasing propulsive efficiency) at subsonic flight speeds. An extra turbine
2318-425: The early 2020s. In March 2018, GE Power achieved a 63.08% gross efficiency for its 7HA turbine. Aeroderivative gas turbines can also be used in combined cycles, leading to a higher efficiency, but it will not be as high as a specifically designed industrial gas turbine. They can also be run in a cogeneration configuration: the exhaust is used for space or water heating, or drives an absorption chiller for cooling
2379-435: The engine cycled on and off to run it only at high efficiency. The emergence of the continuously variable transmission may also alleviate the responsiveness problem. Turbines have historically been more expensive to produce than piston engines, though this is partly because piston engines have been mass-produced in huge quantities for decades, while small gas turbine engines are rarities; however, turbines are mass-produced in
2440-435: The engine's crankshaft instead of to a centrifugal compressor, thus providing additional power instead of boost. While the turbocharger is a pressure turbine, a power recovery turbine is a velocity one. Specific volume In thermodynamics , the specific volume of a substance (symbol: ν , nu ) is the quotient of the substance's volume ( V ) to its mass ( m ): It is a mass-specific intrinsic property of
2501-533: The entire engine from raw materials, including the fabrication of a centrifugal compressor wheel from plywood, epoxy and wrapped carbon fibre strands. Several small companies now manufacture small turbines and parts for the amateur. Most turbojet-powered model aircraft are now using these commercial and semi-commercial microturbines, rather than a Schreckling-like home-build. Small gas turbines are used as auxiliary power units (APUs) to supply auxiliary power to larger, mobile, machines such as an aircraft , and are
Rocket-based combined cycle - Misplaced Pages Continue
2562-407: The exhaust gases, or from ducted fans connected to the gas turbines. Jet engines that produce thrust from the direct impulse of exhaust gases are often called turbojets . While still in service with many militaries and civilian operators, turbojets have mostly been phased out in favor of the turbofan engine due to the turbojet's low fuel efficiency, and high noise. Those that generate thrust with
2623-550: The hobby of engine collecting. In its most extreme form, amateurs have even rebuilt engines beyond professional repair and then used them to compete for the land speed record. The simplest form of self-constructed gas turbine employs an automotive turbocharger as the core component. A combustion chamber is fabricated and plumbed between the compressor and turbine sections. More sophisticated turbojets are also built, where their thrust and light weight are sufficient to power large model aircraft. The Schreckling design constructs
2684-435: The inlet air and increase the power output, technology known as turbine inlet air cooling . Another significant advantage is their ability to be turned on and off within minutes, supplying power during peak, or unscheduled, demand. Since single cycle (gas turbine only) power plants are less efficient than combined cycle plants, they are usually used as peaking power plants , which operate anywhere from several hours per day to
2745-448: The inverse of the specific volume; therefore, substance X has a density of 1.522 g/cm and substance Y has a density of 2.673 g/cm . With this information, the specific gravities of each substance relative to one another can be found. The specific gravity of substance X with respect to Y is 0.569, while the specific gravity of Y with respect to X is 1.756. Therefore, substance X will not sink if placed on Y. The specific volume of
2806-617: The lack of grain boundaries, single crystals eliminate Coble creep and consequently deform by fewer modes – decreasing the creep rate. Although single crystals have lower creep at high temperatures, they have significantly lower yield stresses at room temperature where strength is determined by the Hall-Petch relationship. Care needs to be taken in order to optimize the design parameters to limit high temperature creep while not decreasing low temperature yield strength. Airbreathing jet engines are gas turbines optimized to produce thrust from
2867-550: The marine industry to reduce weight. Common types include the General Electric LM2500 , General Electric LM6000 , and aeroderivative versions of the Pratt & Whitney PW4000 , Pratt & Whitney FT4 and Rolls-Royce RB211 . Increasing numbers of gas turbines are being used or even constructed by amateurs. In its most straightforward form, these are commercial turbines acquired through military surplus or scrapyard sales, then operated for display as part of
2928-400: The mixture then leaves the combustor section and has its velocity increased across the turbine section to strike the turbine blades, spinning the disc they are attached to, thus creating useful power. Of the power produced, 60-70% is solely used to power the gas generator. The remaining power is used to power what the engine is being used for, typically an aviation application, being thrust in
2989-467: The pioneer of modern Micro-Jets, Kurt Schreckling , produced one of the world's first Micro-Turbines, the FD3/67. This engine can produce up to 22 newtons of thrust, and can be built by most mechanically minded people with basic engineering tools, such as a metal lathe . Evolved from piston engine turbochargers , aircraft APUs or small jet engines , microturbines are 25 to 500 kilowatt turbines
3050-474: The purpose of using pulverized coal or finely ground biomass (such as sawdust) as a fuel. In the indirect system, a heat exchanger is used and only clean air with no combustion products travels through the power turbine. The thermal efficiency is lower in the indirect type of external combustion; however, the turbine blades are not subjected to combustion products and much lower quality (and therefore cheaper) fuels are able to be used. When external combustion
3111-670: The rotation rate of the shaft must be to attain the required blade tip speed. Blade-tip speed determines the maximum pressure ratios that can be obtained by the turbine and the compressor. This, in turn, limits the maximum power and efficiency that can be obtained by the engine. In order for tip speed to remain constant, if the diameter of a rotor is reduced by half, the rotational speed must double. For example, large jet engines operate around 10,000–25,000 rpm, while micro turbines spin as fast as 500,000 rpm. Mechanically, gas turbines can be considerably less complex than Reciprocating engines . Simple turbines might have one main moving part,
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#17327880836313172-483: The same air. Gas turbines are used to power aircraft, trains, ships, electrical generators, pumps, gas compressors, and tanks . In an ideal gas turbine, gases undergo four thermodynamic processes: an isentropic compression, an isobaric (constant pressure) combustion, an isentropic expansion and isobaric heat rejection. Together, these make up the Brayton cycle , also known as the "constant pressure cycle" . It
3233-545: The size of a refrigerator . Microturbines have around 15% efficiencies without a recuperator , 20 to 30% with one and they can reach 85% combined thermal-electrical efficiency in cogeneration . Most gas turbines are internal combustion engines but it is also possible to manufacture an external combustion gas turbine which is, effectively, a turbine version of a hot air engine . Those systems are usually indicated as EFGT (Externally Fired Gas Turbine) or IFGT (Indirectly Fired Gas Turbine). External combustion has been used for
3294-503: The smallest modern helicopters, and function as an auxiliary power unit in large commercial aircraft. A primary shaft carries the compressor and its turbine which, together with a combustor, is called a Gas Generator . A separately spinning power-turbine is usually used to drive the rotor on helicopters. Allowing the gas generator and power turbine/rotor to spin at their own speeds allows more flexibility in their design. Also known as miniature gas turbines or micro-jets. With this in mind
3355-412: The specific volume of the super heated steam would have changed to 0.2765 in /lb, which is a 59% overall change. Knowing the specific volumes of two or more substances allows one to find useful information for certain applications. For a substance X with a specific volume of 0.657 cm /g and a substance Y with a specific volume 0.374 cm /g, the density of each substance can be found by taking
3416-433: The substance. It is the reciprocal of density ρ ( rho ) and it is also related to the molar volume and molar mass : The standard unit of specific volume is cubic meters per kilogram (m /kg), but other units include ft /lb, ft /slug, or mL/g. Specific volume for an ideal gas is related to the molar gas constant ( R ) and the gas's temperature ( T ), pressure ( P ), and molar mass ( M ): It's based on
3477-511: The substrate. The Al from the bond coats forms Al 2 O 3 on the TBC-bond coat interface which provides the oxidation resistance, but also results in the formation of an undesirable interdiffusion (ID) zone between itself and the substrate. The oxidation resistance outweighs the drawbacks associated with the ID zone as it increases the lifetime of the blade and limits the efficiency losses caused by
3538-595: The turbine engines high power-to-weight ratio to drive a propeller, thus allowing a more powerful, but also smaller engine to be used. Turboprop engines are used on a wide range of business aircraft such as the Pilatus PC-12 , commuter aircraft such as the Beechcraft 1900 , and small cargo aircraft such as the Cessna 208 Caravan or De Havilland Canada Dash 8 , and large aircraft (typically military) such as
3599-463: The turbine housing's geometry (as in a variable geometry turbocharger ). It mainly serves as a power recovery device which converts a great deal of otherwise wasted thermal and kinetic energy into engine boost. Turbo-compound engines (actually employed on some semi-trailer trucks ) are fitted with blow down turbines which are similar in design and appearance to a turbocharger except for the turbine shaft being mechanically or hydraulically connected to
3660-480: The turbine is recovered by a heat recovery steam generator (HRSG) to power a conventional steam turbine in a combined cycle configuration. The 605 MW General Electric 9HA achieved a 62.22% efficiency rate with temperatures as high as 1,540 °C (2,800 °F). For 2018, GE offers its 826 MW HA at over 64% efficiency in combined cycle due to advances in additive manufacturing and combustion breakthroughs, up from 63.7% in 2017 orders and on track to achieve 65% by
3721-498: The wells to force oil up via another bore, or to compress the gas for transportation. They are also often used to provide power for the platform. These platforms do not need to use the engine in collaboration with a CHP system due to getting the gas at an extremely reduced cost (often free from burn off gas). The same companies use pump sets to drive the fluids to land and across pipelines in various intervals. One modern development seeks to improve efficiency in another way, by separating
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