85-519: A ramjet is a form of airbreathing jet engine that requires forward motion of the engine to provide air for combustion. Ramjets work most efficiently at supersonic speeds around Mach 3 (2,300 mph; 3,700 km/h) and can operate up to Mach 6 (4,600 mph; 7,400 km/h). Ramjets can be particularly appropriate in uses requiring a compact mechanism for high-speed, such as missiles . Weapons designers are investigating ramjet technology for use in artillery shells to increase range;
170-399: A convergent–divergent nozzle . Although ramjets have been run as slow as 45 metres per second (160 km/h; 100 mph), below about Mach 0.5 (170 m/s; 610 km/h; 380 mph) they give little thrust and are highly inefficient due to their low pressure ratios. Above this speed, given sufficient initial flight velocity, a ramjet is self-sustaining. Unless the vehicle drag
255-434: A pitot -type opening for the inlet. This is followed by a widening internal passage (subsonic diffuser) to achieve a lower subsonic velocity that is required at the combustor. At low supersonic speeds a normal (planar) shock wave forms in front of the inlet. For higher supersonic speeds the pressure loss through the shock wave becomes prohibitive and a protruding spike or cone is used to produce oblique shock waves in front of
340-407: A turbine , which generates its own compressed air (i.e. ram air in a ramjet) in order to generate thrust. The diffuser converts the high velocity of the air approaching the intake into high (static) pressure required for combustion. High combustion pressures minimise entropy rise during heat addition, this minimising wasted thermal energy in the exhaust gases Subsonic and low-supersonic ramjets use
425-515: A 120 mm ramjet-assisted mortar shell is thought to be able to travel 35 km (22 mi). They have been used, though not efficiently, as tip jets on the ends of helicopter rotors. L'Autre Monde: ou les États et Empires de la Lune ( Comical History of the States and Empires of the Moon ) (1657) was the first of three satirical novels written by Cyrano de Bergerac that are considered among
510-645: A German patent application. In an additional patent application, he adapted the engine for subsonic speed. The patent was granted in 1932 (German Patent No. 554,906, 1932-11-02). In the Soviet Union, a theory of supersonic ramjet engines was presented in 1928 by Boris Stechkin . Yuri Pobedonostsev, chief of GIRD 's 3rd Brigade, carried out research. The first engine, the GIRD-04, was designed by I.A. Merkulov and tested in April 1933. To simulate supersonic flight, it
595-510: A combustor exit stagnation temperature of the order of 2,400 K (2,130 °C; 3,860 °F) for kerosene . Normally, the combustor must be capable of operating over a wide range of throttle settings, matching flight speeds and altitudes. Usually, a sheltered pilot region enables combustion to continue when the vehicle intake undergoes high yaw/pitch during turns. Other flame stabilization techniques make use of flame holders, which vary in design from combustor cans to flat plates, to shelter
680-483: A conventional rocket) there is a penalty for taking on-board air from the atmosphere. This is known as ram drag. Although the penalty is zero at static conditions, it rapidly increases with flight speed, causing the net thrust to be eroded. As flight speed builds up after take-off, the ram rise in the intake starts to have a significant effect upon nozzle pressure/temperature and intake airflow, causing nozzle gross thrust to climb more rapidly. This term now starts to offset
765-413: A fan, compresses air into a bypass duct whilst its inner portion supercharges the core compressor. The fan is often an integral part of a multi-stage core LPC. The bypass airflow either passes to a separate 'cold nozzle' or mixes with low pressure turbine exhaust gases, before expanding through a 'mixed flow nozzle'. In the 1960s there was little difference between civil and military jet engines, apart from
850-414: A final normal shock that occurs at the inlet entrance lip. The diffuser in this case consists of two parts, the supersonic diffuser, with shock waves external to the inlet, followed by the internal subsonic diffuser. At higher speeds still, part of the supersonic diffusion has to take place internally, requiring external and internal oblique shock waves. The final normal shock has to occur in the vicinity of
935-443: A high speed, high temperature jet to create thrust. While these engines are capable of giving high thrust levels, they are most efficient at very high speeds (over Mach 1), due to the low-mass-flow, high speed nature of the jet exhaust. Modern turbofans are a development of the turbojet; they are basically turbojets that include a new section called the fan stage . Rather than using all their exhaust gases to provide direct thrust like
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#17327833424381020-462: A hot fuel-rich gas which is burnt in the ramcombustor with the compressed air supplied by the intake(s). The flow of gas improves the mixing of the fuel and air and increases total pressure recovery. In a throttleable ducted rocket, also known as a variable flow ducted rocket, a valve allows the gas generator exhaust to be throttled allowing thrust control. Unlike an LFRJ, solid propellant ramjets cannot flame out . The ducted rocket sits somewhere between
1105-447: A just a single front fan, because their additional thrust is generated by a large additional mass of air which is only moderately compressed, rather than a smaller amount of air which is greatly compressed. Military turbofans, however, have a relatively high specific thrust , to maximize the thrust for a given frontal area, jet noise being of less concern in military uses relative to civil uses. Multistage fans are normally needed to reach
1190-542: A low exhaust speed (low specific thrust – net thrust divided by airflow) to keep jet noise to a minimum and to improve fuel efficiency . Consequently, the bypass ratio (bypass flow divided by core flow) is relatively high (ratios from 4:1 up to 8:1 are common), with the Rolls-Royce Trent XWB approaching 10:1. Only a single fan stage is required, because a low specific thrust implies a low fan pressure ratio. Turbofans in civilian aircraft usually have
1275-562: A low propulsive efficiency below about Mach 2 and produce a lot of jet noise, both a result of the very high velocity of the exhaust. Modern jet propelled aircraft are powered by turbofans . These engines, with their lower exhaust velocities, produce less jet noise and use less fuel. Turbojets are still used to power medium range cruise missiles due to their high exhaust speed, low frontal area, which reduces drag, and relative simplicity, which reduces cost. Most modern jet engines are turbofans. The low pressure compressor (LPC), usually known as
1360-462: A minimum flow area known as the throat, which is followed by the subsonic diffuser. As with other jet engines, the combustor raises the air temperature by burning fuel. This takes place with a small pressure loss. The air velocity entering the combustor has to be low enough such that continuous combustion can take place in sheltered zones provided by flame holders . A ramjet combustor can safely operate at stoichiometric fuel:air ratios. This implies
1445-641: A move to large twin engine aircraft, such as the Airbus A350 or Boeing 777 , as well as allowing twin engine aircraft to operate on long overwater routes , previously the domain of 3-engine or 4-engine aircraft . Jet engines were designed to power aircraft, but have been used to power jet cars and jet boats for speed record attempts, and even for commercial uses such as by railroads for clearing snow and ice from switches in railyards (mounted in special rail cars), and by race tracks for drying off track surfaces after rain (mounted in special trucks with
1530-409: A nozzle to accelerate it to supersonic speeds and generate forward thrust . Ramjets are much less complex than turbojets or turbofans , requiring only an air intake, a combustor, and a nozzle to be built. Additionally, ramjets have little to no moving parts - liquid-fuel ramjets have only a fuel pump, whilst solid-fuel ramjets lack even this. By comparison, a turbojet uses a compressor driven by
1615-408: A portion of the engine's thrust is produced by spinning a propeller , rather than relying solely on high-speed jet exhaust. Producing thrust both ways, turboprops are occasionally referred to as a type of hybrid jet engine. They differ from turbofans in that a traditional propeller, rather than a ducted fan, provides the majority of thrust. Most turboprops use gear-reduction between the turbine and
1700-403: A pronounced large front area to accommodate a very large fan, as their design involves a much larger mass of air bypassing the core so they can benefit from these effects, while in military aircraft , where noise and efficiency are less important compared to performance and drag, a smaller amount of air typically bypasses the core. Turbofans designed for subsonic civilian aircraft also usually have
1785-582: A ramjet to function properly. His patent showed a piston internal combustion engine with added 'trumpets' as exhaust nozzles, expressing the idea that the exhaust from internal combustion engines could be directed into nozzles to create jet propulsion. The works of René Leduc were notable. Leduc's Model, the Leduc 0.10 was one of the first ramjet-powered aircraft to fly, in 1949. The Nord 1500 Griffon reached Mach 2.19 (745 m/s; 2,680 km/h) in 1958. In 1915, Hungarian inventor Albert Fonó devised
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#17327833424381870-571: A range of about 105 kilometres (65 miles). It was also used as a surface-to-surface weapon and was modified to destroy land-based radars. Using technology proven by the AQM-60, In the late 1950s and early 1960s the US produced a widespread defense system called the CIM-10 Bomarc , which was equipped with hundreds of nuclear armed ramjet missiles with a range of several hundred miles. It was powered by
1955-523: A solid fuel ramjet (SFRJ) vehicle test in August 2022. In 2023, General Electric demonstrated a ramjet with rotating detonation combustion. It is a turbine-based combined-cycle engine that incorporates a In the late 1950s, 1960s, and early 1970s, the UK developed several ramjet missiles. The Blue Envoy project was supposed to equip the country with a long range ramjet powered air defense against bombers, but
2040-589: A solution for increasing the range of artillery , comprising a gun-launched projectile united with a ramjet propulsion unit, thus giving a long range from relatively low muzzle velocities, allowing heavy shells to be fired from relatively lightweight guns. Fonó submitted his invention to the Austro-Hungarian Army , but the proposal was rejected. After World War I, Fonó returned to the subject. In May 1928 he described an "air-jet engine" which he described as suitable for high-altitude supersonic aircraft, in
2125-413: A source of carbon dioxide in the atmosphere. Jet engines can also run on biofuels or hydrogen, although hydrogen is usually produced from fossil fuels. About 7.2% of the oil used in 2004 was consumed by jet engines. Some scientists believe that jet engines are also a source of global dimming due to the water vapour in the exhaust causing cloud formations. Nitrogen compounds are also formed during
2210-590: A special test rig on a Dornier Do 17 Z at flight speeds of up to 200 metres per second (720 km/h). Later, as petrol became scarce in Germany, tests were carried out with blocks of pressed coal dust as a fuel (see e.g. Lippisch P.13a ), which were not successful due to slow combustion. Stovepipe (flying/flaming/supersonic) was a popular name for the ramjet during the 1950s in trade magazines such as Aviation Week & Space Technology and other publications such as The Cornell Engineer. The simplicity implied by
2295-626: A specified weight and number, and to not lose more than a specified amount of thrust. The weight and numbers of birds that can be ingested without hazarding the safe flight of the aircraft are related to the engine intake area. In 2009, an Airbus A320 aircraft, US Airways Flight 1549 , ingested one Canada goose into each engine. The plane ditched in the Hudson River after taking off from LaGuardia International Airport in New York City. There were no fatalities. The incident illustrated
2380-488: A speed of Mach 3. It was used successfully in combat against multiple types of aircraft during the Falklands War . Eminent Swiss astrophysicist Fritz Zwicky was research director at Aerojet and holds many patents in jet propulsion. Patents US 5121670 and US 4722261 are for ram accelerators . The U.S. Navy would not allow Zwicky to publicly discuss his invention, US 2461797
2465-571: A take-off static thrust of 76,000 lbf (360 kN) at SLS, ISA+15 °C. Naturally, net thrust will decrease with altitude, because of the lower air density. There is also, however, a flight speed effect. Initially as the aircraft gains speed down the runway, there will be little increase in nozzle pressure and temperature, because the ram rise in the intake is very small. There will also be little change in mass flow. Consequently, nozzle gross thrust initially only increases marginally with flight speed. However, being an air breathing engine (unlike
2550-439: A tandem arrangement. Integrated boosters provide a more efficient packaging option, since the booster propellant is cast inside the otherwise empty combustor. This approach has been used on solid-fuel ramjets (SFRJ), for example 2K12 Kub , liquid, for example ASMP , and ducted rocket, for example Meteor , designs. Integrated designs are complicated by the different nozzle requirements of the boost and ramjet flight phases. Due to
2635-402: A turbojet including references to turbofans, turboprops and turboshafts: The various components named above have constraints on how they are put together to generate the most efficiency or performance. The performance and efficiency of an engine can never be taken in isolation; for example fuel/distance efficiency of a supersonic jet engine maximises at about Mach 2, whereas the drag for
Ramjet - Misplaced Pages Continue
2720-436: A turbojet, turbofan engines extract some of the power from the exhaust gases inside the engine and use it to power the fan stage. The fan stage accelerates a large volume of air through a duct, bypassing the engine core (the actual gas turbine component of the engine), and expelling it at the rear as a jet, creating thrust. A proportion of the air that comes through the fan stage enters the engine core rather than being ducted to
2805-467: Is a jet engine in which the exhaust gas which supplies jet propulsion is atmospheric air , which is taken in, compressed, heated, and expanded back to atmospheric pressure through a propelling nozzle . Compression may be provided by a gas turbine , as in the original turbojet and newer turbofan , or arise solely from the ram pressure of the vehicle's velocity, as with the ramjet and pulsejet . All practical airbreathing jet engines heat
2890-543: Is extremely high, the engine/airframe combination tends to accelerate to higher and higher flight speeds, substantially increasing the air intake temperature. As this could damage the engine and/or airframe integrity, the fuel control system must reduce fuel flow to stabilize speed and, thereby, air intake temperature. Due to the stoichiometric combustion temperature, efficiency is usually good at high speeds (around Mach 2 – Mach 3, 680–1,000 m/s, 2,500–3,700 km/h, 1,500–2,300 mph), whereas at low speeds
2975-555: Is for the Underwater Jet, a ram jet that performs in a fluid medium. Time magazine reported on Zwicky's work. The first part of a ramjet is its diffuser (compressor) in which the forward motion of the ramjet is used to raise the pressure of its working fluid (air) as required for combustion. Air is compressed, heated by combustion and expanded in a thermodynamic cycle known as the Brayton cycle , before being passed through
3060-468: Is needed to provide this thrust. Instead, the energy is taken from the central core, which gives it also a reduced exhaust speed. The average velocity of the mixed exhaust air is thus reduced (low specific thrust ) which is less wasteful of energy but reduces the top speed. Overall, a turbofan can be much more fuel efficient and quieter, and it turns out that the fan also allows greater net thrust to be available at slow speeds. Thus civil turbofans today have
3145-412: Is through ablation of the propellant by the hot compressed air from the intake(s). An aft mixer may be used to improve combustion efficiency . SFIRRs are preferred over LFRJs for some applications because of the simplicity of the fuel supply, but only when the throttling requirements are minimal, i.e. when variations in altitude or speed are limited. In a ducted rocket, a solid fuel gas generator produces
3230-475: The Bahir Dar airport; of the 104 people aboard, 35 died and 21 were injured. In another incident in 1995, a Dassault Falcon 20 crashed at a Paris airport during an emergency landing attempt after ingesting lapwings into an engine, which caused an engine failure and a fire in the airplane fuselage ; all 10 people on board were killed. Jet engines have to be designed to withstand the ingestion of birds of
3315-640: The Lockheed D-21 spy drone. In the late 1950s the US Navy introduced a system called the RIM-8 Talos , which was a long range surface-to-air missile fired from ships. It successfully shot down enemy fighters during the Vietnam War , and was the first ship-launched missile to destroy an enemy aircraft in combat. On 23 May 1968, a Talos fired from USS Long Beach shot down a Vietnamese MiG at
3400-422: The cowling or ductwork, and have increasingly utilized high-strength composite materials to achieve the required penetration resistance while keeping the weight low. In 2007 the cost of jet fuel , while highly variable from one airline to another, averaged 26.5% of total operating costs, making it the single largest operating expense for most airlines. Jet engines are usually run on fossil fuels and are thus
3485-733: The American engineer who developed it, although it was originally proposed and patented by Englishman John Barber in 1791. It is also sometimes known as the Joule cycle . The nominal net thrust quoted for a jet engine usually refers to the Sea Level Static (SLS) condition, either for the International Standard Atmosphere (ISA) or a hot day condition (e.g. ISA+10 °C). As an example, the GE90-76B has
Ramjet - Misplaced Pages Continue
3570-688: The DM-1. The world's first ramjet-powered airplane flight took place in December 1940, using two DM-2 engines on a modified Polikarpov I-15 . Merkulov designed a ramjet fighter "Samolet D" in 1941, which was never completed. Two of his DM-4 engines were installed on the Yak-7 PVRD fighter during World War II. In 1940, the Kostikov-302 experimental plane was designed, powered by a liquid fuel rocket for take-off and ramjet engines for flight. That project
3655-724: The Kawasaki Aircraft Company's facility in Gifu during the Second World War. Company officials claimed, in December 1945, that these domestic initiatives were uninfluenced by parallel German developments. One post-war U.S. intelligence assessment described the Kawasaki ram jet's centrifugal fuel disperser as the company's "most outstanding accomplishment ... eliminat[ing] a large amount of the fuel injection system normally employed." Because of excessive vibration,
3740-476: The UK and Hans von Ohain in Germany , developed the turbojet concept independently into practical engines during the late 1930s. Turbojets consist of an inlet, a compressor , a combustor, a turbine (that drives the compressor) and a propelling nozzle. The compressed air is heated in the combustor and passes through the turbine, then expands in the nozzle to produce a high speed propelling jet Turbojets have
3825-618: The air by burning fuel. Alternatively a heat exchanger may be used, as in a nuclear-powered jet engine. Most modern jet engines are turbofans, which are more fuel efficient than turbojets because the thrust supplied by the gas turbine is augmented by bypass air passing through a ducted fan . The original air-breathing gas turbine jet engine was the turbojet . It was a concept brought to life by two engineers, Frank Whittle in England UK and Hans von Ohain in Germany . The turbojet compresses and heats air and then exhausts it as
3910-421: The booster is mounted immediately aft of the ramjet, e.g. Sea Dart , or wraparound where multiple boosters are attached around the outside of the ramjet, e.g. 2K11 Krug . The choice of booster arrangement is usually driven by the size of the launch platform. A tandem booster increases the length of the system, whereas wraparound boosters increase the diameter. Wraparound boosters typically generate higher drag than
3995-495: The booster's higher thrust levels, a differently shaped nozzle is required for optimum thrust compared to that required for the lower thrust ramjet sustainer. This is usually achieved via a separate nozzle, which is ejected after booster burnout. However, designs such as Meteor feature nozzleless boosters. This offers the advantages of elimination of the hazard to launch aircraft from the boost debris, simplicity, reliability, and reduced mass and cost, although this must be traded against
4080-399: The bypass air is introduced, and many other factors. An example is design of the air intake. The thermodynamics of a typical air-breathing jet engine are modeled approximately by a Brayton Cycle which is a thermodynamic cycle that describes the workings of the gas turbine engine, which is the basis of the airbreathing jet engine and others. It is named after George Brayton (1830–1892),
4165-454: The case. These high energy parts can cut fuel and control lines, and can penetrate the cabin. Although fuel and control lines are usually duplicated for reliability, the crash of United Airlines Flight 232 was caused when hydraulic fluid lines for all three independent hydraulic systems were simultaneously severed by shrapnel from an uncontained engine failure. Prior to the United 232 crash,
4250-455: The compressed air bottle from which it is inflated, which is mounted lengthwise in the tank. This offers a lower-cost approach than a regulated LFRJ requiring a pump system to supply the fuel. A ramjet generates no static thrust and needs a booster to achieve a forward velocity high enough for efficient operation of the intake system. The first ramjet-powered missiles used external boosters, usually solid-propellant rockets, either in tandem, where
4335-426: The engine casing. To do this the engine has to be designed to pass blade containment tests as specified by certification authorities. Bird ingestion is the term used when birds enter the intake of a jet engine. It is a common aircraft safety hazard and has caused fatal accidents. In 1988 an Ethiopian Airlines Boeing 737 ingested pigeons into both engines during take-off and then crashed in an attempt to return to
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#17327833424384420-635: The engine was only intended for use in rocket, or catapult-launched pilotless aircraft. Preparations for flight testing ended with the Japanese surrender in August 1945. In 1936, Hellmuth Walter constructed a test engine powered by natural gas . Theoretical work was carried out at BMW , Junkers , and DFL . In 1941, Eugen Sänger of DFL proposed a ramjet engine with a high combustion chamber temperature. He constructed large ramjet pipes with 500 millimetres (20 in) and 1,000 millimetres (39 in) diameter and carried out combustion tests on lorries and on
4505-457: The exhaust is extracted to spin the rotating shaft, which is used to power machinery rather than a propeller, they therefore generate little to no jet thrust and are often used to power helicopters . A propfan engine (also called "unducted fan", "open rotor", or "ultra-high bypass") is a jet engine that uses its gas generator to power an exposed fan, similar to turboprop engines. Like turboprop engines, propfans generate most of their thrust from
4590-428: The fan gives higher thrust at low speeds. The lower exhaust speed also gives much lower jet noise. The comparatively large frontal fan has several effects. Compared to a turbojet of identical thrust, a turbofan has a much larger air mass flow rate and the flow through the bypass duct generates a significant fraction of the thrust. The additional duct air has not been ignited, which gives it a slow speed, but no extra fuel
4675-440: The first science fiction stories. Arthur C Clarke credited this book with conceiving the ramjet, and as the first fictional example of rocket-powered space flight. The ramjet was designed in 1913 by French inventor René Lorin , who was granted a patent (FR290356) for his device. He could not test his invention due to the unavailability of adequate equipment since there was no way at the time for an aircraft to go fast enough for
4760-429: The first generation of turbofan airliners used low-bypass engines, their high noise levels and fuel consumption mean they have fallen out of favor for large aircraft. High bypass engines have a much larger fan stage, and provide most of their thrust from the ducted air of the fan; the engine core provides power to the fan stage, and only a proportion of the overall thrust comes from the engine core exhaust stream. Over
4845-520: The first turbofan engines produced, and provide the majority of their thrust from the hot core exhaust gases, while the fan stage only supplements this. These engines are still commonly seen on military fighter aircraft , because they have a smaller frontal area which creates less ram drag at supersonic speeds leaving more of the thrust produced by the engine to propel the aircraft. Their comparatively high noise levels and subsonic fuel consumption are deemed acceptable in such an application, whereas although
4930-427: The flame and improve fuel mixing. Over-fuelling the combustor can cause the final (normal) shock in the diffuser to be pushed forward beyond the intake lip, resulting in a substantial drop in airflow and thrust. The propelling nozzle is a critical part of a ramjet design, since it accelerates exhaust flow to produce thrust. Subsonic ramjets accelerate exhaust flow with a nozzle . Supersonic flight typically requires
5015-427: The flight. Re-lights are usually successful after flame-outs but with considerable loss of altitude. It was the case of British Airways Flight 9 which flew through volcanic dust at 37,000 ft. All 4 engines flamed out and re-light attempts were successful at about 13,000 ft. One class of failure that has caused accidents is the uncontained failure, where rotating parts of the engine break off and exit through
5100-417: The fuel to the ramcombustor is required, which can be complicated and expensive. This propulsion system was first perfected by Yvonne Brill during her work at Marquardt Corporation . Aérospatiale-Celerg designed an LFRJ where the fuel is forced into the injectors by an elastomer bladder that inflates progressively along the length of the fuel tank. Initially, the bladder forms a close-fitting sheath around
5185-407: The greatest risk of a bird ingestion is during takeoff and landing and during low level flying. If a jet plane is flying through air contaminated with volcanic ash , there is risk that ingested ash will cause erosion damage to the compressor blades, blockage of fuel nozzle air holes and blockage of the turbine cooling passages. Some of these effects may cause the engine to surge or flame-out during
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#17327833424385270-426: The hazards of ingesting birds beyond the "designed-for" limit. The outcome of an ingestion event and whether it causes an accident, be it on a small fast plane, such as military jet fighters , or a large transport, depends on the number and weight of birds and where they strike the fan blade span or the nose cone. Core damage usually results with impacts near the blade root or on the nose cone. Few birds fly high, so
5355-425: The incoming air is slowed to subsonic velocities for combustion. In addition, the combustion chamber's inlet temperature increases to very high values, approaching the dissociation limit at some limiting Mach number. Ramjet diffusers slow the incoming air to a subsonic velocity before it enters the combustor. Scramjets are similar to ramjets, but the air flows through the combustor at supersonic speed. This increases
5440-535: The jet exhaust blowing onto the track surface). Airbreathing jet engines are nearly always internal combustion engines that obtain propulsion from the combustion of fuel inside the engine. Oxygen present in the atmosphere is used to oxidise a fuel source, typically a hydrocarbon-based jet fuel . The burning mixture expands greatly in volume, driving heated air through a propelling nozzle . Gas turbine powered jet engines: Ram powered jet engine: Pulsed combustion jet engine: Two engineers, Frank Whittle in
5525-511: The last several decades, there has been a move towards very high bypass engines, which use fans far larger than the engine core itself, which is typically a modern, high efficiency two or three-spool design. This high efficiency and power is what allows such large fans to be viable, and the increased thrust available (up to 75,000 lbs per engine in engines such as the Rolls-Royce Trent XWB or General Electric GENx ), have allowed
5610-479: The name came from a comparison with the turbojet engine which employs relatively complex and expensive spinning turbomachinery. The US Navy developed a series of air-to-air missiles under the name of " Gorgon " using different propulsion mechanisms, including ramjet propulsion on the Gorgon IV. The ramjet Gorgon IVs, made by Glenn Martin , were tested in 1948 and 1949 at Naval Air Station Point Mugu . The ramjet
5695-424: The pressure has decreased, and the engine has lost all thrust. The compressor blades will then usually come out of stall, and re-pressurize the engine. If conditions are not corrected, the cycle will usually repeat. This is called surge . Depending on the engine this can be highly damaging to the engine and creates worrying vibrations for the crew. Fan, compressor or turbine blade failures have to be contained within
5780-574: The pressure recovered from the streaming air and improves net thrust. Thermal choking of the exhaust is avoided by having a relatively high supersonic air velocity at combustor entry. Fuel injection is often into a sheltered region below a step in the combustor wall. The Boeing X-43 was a small experimental ramjet that achieved Mach 5 (1,700 m/s; 6,100 km/h) for 200 seconds on the X-51A Waverider . Airbreathing jet engine An airbreathing jet engine (or ducted jet engine )
5865-487: The probability of a simultaneous failure of all three hydraulic systems was considered as high as a billion-to-one. However, the statistical models used to come up with this figure did not account for the fact that the number-two engine was mounted at the tail close to all the hydraulic lines, nor the possibility that an engine failure would release many fragments in many directions. Since then, more modern aircraft engine designs have focused on keeping shrapnel from penetrating
5950-538: The propeller and not the exhaust jet. The primary difference between turboprop and propfan design is that the propeller blades on a propfan are highly swept to allow them to operate at speeds around Mach 0.8, which is competitive with modern commercial turbofans. These engines have the fuel efficiency advantages of turboprops with the performance capability of commercial turbofans. While significant research and testing (including flight testing) has been conducted on propfans, none have entered production. Major components of
6035-501: The propeller. ( Geared turbofans also feature gear reduction, but they are less common.) The hot-jet exhaust is an important minority of thrust, and maximum thrust is obtained by matching the two thrust contributions. Turboprops generally have better performance than turbojets or turbofans at low speeds where propeller efficiency is high, but become increasingly noisy and inefficient at high speeds. Turboshaft engines are very similar to turboprops, differing in that nearly all energy in
6120-503: The rear, and is thus compressed and heated; some of the energy is extracted to power the compressors and fans, while the remainder is exhausted at the rear. This high-speed, hot-gas exhaust blends with the low speed, cool-air exhaust from the fan stage, and both contribute to the overall thrust of the engine. Depending on what proportion of cool air is bypassed around the engine core, a turbofan can be called low-bypass , high-bypass , or very-high-bypass engines. Low bypass engines were
6205-437: The reduction in performance of a dedicated booster nozzle. A slight variation on the ramjet uses the supersonic exhaust from a rocket combustion process to compress and react with the incoming air in the main combustion chamber. This has the advantage of giving thrust even at zero speed. In a solid fuel integrated rocket ramjet (SFIRR), the solid fuel is cast along the outer wall of the ramcombustor. In this case, fuel injection
6290-616: The relatively high fan pressure ratio needed for high specific thrust. Although high turbine inlet temperatures are often employed, the bypass ratio tends to be low, usually significantly less than 2.0. Turboprop engines are jet engine derivatives, still gas turbines, that extract work from the hot-exhaust jet to turn a rotating shaft, which is then used to produce thrust by some other means. While not strictly jet engines in that they rely on an auxiliary mechanism to produce thrust, turboprops are very similar to other turbine-based jet engines, and are often described as such. In turboprop engines,
6375-429: The relatively low pressure means the ramjets are outperformed by turbojets and rockets . Ramjets can be classified according to the type of fuel, either liquid or solid; and the booster. In a liquid fuel ramjet (LFRJ), hydrocarbon fuel (typically) is injected into the combustor ahead of a flameholder. The flameholder stabilises the flame with the compressed air from the intake(s). A means of pressurizing and supplying
6460-539: The same engines as the AQM-60, but with improved materials to endure longer flight times. The system was withdrawn in the 1970s as the threat from bombers subsided. In April 2020, the U.S. Department of Defense and the Norwegian Ministry of Defense jointly announced their partnership to develop advanced technologies applicable to long range high-speed and hypersonic weapons. The Tactical High-speed Offensive Ramjet for Extended Range (THOR-ER) program completed
6545-1080: The simplicity of the SFRJ and LFRJ's unlimited speed control. Ramjets generally give little or no thrust below about half the speed of sound , and they are inefficient ( specific impulse of less than 600 seconds) until the airspeed exceeds 1,000 kilometres per hour (280 m/s; 620 mph) due to low compression ratios. Even above the minimum speed, a wide flight envelope (range of flight conditions), such as low to high speeds and low to high altitudes, can force significant design compromises, and they tend to work best optimised for one designed speed and altitude (point designs). However, ramjets generally outperform gas turbine-based jet engine designs and work best at supersonic speeds (Mach 2–4). Although inefficient at slower speeds, they are more fuel-efficient than rockets over their entire useful working range up to at least Mach 6 (2,000 m/s; 7,400 km/h). The performance of conventional ramjets falls off above Mach 6 due to dissociation and pressure loss caused by shock as
6630-427: The still increasing ram drag, eventually causing net thrust to start to increase. In some engines, the net thrust at say Mach 1.0, sea level can even be slightly greater than the static thrust. Above Mach 1.0, with a subsonic inlet design, shock losses tend to decrease net thrust, however a suitably designed supersonic inlet can give a lower reduction in intake pressure recovery, allowing net thrust to continue to climb in
6715-400: The supersonic regime. Jet engines are usually very reliable and have a very good safety record. However, failures do sometimes occur. In some cases in jet engines the conditions in the engine due to airflow entering the engine or other variations can cause the compressor blades to stall . When this occurs the pressure in the engine blows out past the blades, and the stall is maintained until
6800-613: The system was cancelled. It was replaced by a shorter range ramjet missile system called the Bloodhound . The system was designed as a second line of defense in case attackers were able to bypass the fleet of defending English Electric Lightning fighters. In the 1960s the Royal Navy developed and deployed a ramjet powered surface to air missile for ships called the Sea Dart . It had a range of 65–130 kilometres (40–80 mi) and
6885-411: The use of afterburning in some (supersonic) applications. Today, turbofans are used for airliners because they have an exhaust speed that is better matched to the subsonic flight speed of the airliner. At airliner flight speeds, the exhaust speed from a turbojet engine is excessively high and wastes energy. The lower exhaust speed from a turbofan gives better fuel consumption. The increased airflow from
6970-435: The vehicle carrying it is increasing as a square law and has much extra drag in the transonic region. The highest fuel efficiency for the overall vehicle is thus typically around Mach 0.85. For the engine optimisation for its intended use, important here is air intake design, overall size, number of compressor stages (sets of blades), fuel type, number of exhaust stages, metallurgy of components, amount of bypass air used, where
7055-639: Was cancelled in 1944. In 1947, Mstislav Keldysh proposed a long-range antipodal bomber , similar to the Sänger-Bredt bomber , but powered by ramjet instead of rocket. In 1954, NPO Lavochkin and the Keldysh Institute began development of a Mach 3 ramjet-powered cruise missile, Burya . This project competed with the R-7 ICBM developed by Sergei Korolev , but was cancelled in 1957. Several ram jets were designed, built, and ground-tested at
7140-689: Was designed at the University of Southern California and manufactured by the Marquardt Aircraft Company . The engine was 2.1 metres (7 ft) long and 510 millimetres (20 in) in diameter and was positioned below the missile. In the early 1950s the US developed a Mach 4+ ramjet under the Lockheed X-7 program. This was developed into the Lockheed AQM-60 Kingfisher . Further development resulted in
7225-462: Was fed by air compressed to 200 bar , and was fueled with hydrogen. The GIRD-08 phosphorus-fueled ramjet was tested by firing it from an artillery cannon. These shells may have been the first jet-powered projectiles to break the speed of sound . In 1939, Merkulov did further ramjet tests using a two-stage rocket , the R-3. He developed the first ramjet engine for use as an auxiliary motor of an aircraft,
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