A ramjet, sometimes referred to as a stovepipe jet, is a form of jet engine that contains no major moving parts. specific --->A jet engine is a Reaction engine that discharges a fast moving jet of Fluid to The Moving Parts was a late 1970s Boston-based Rock music band Unlike most other airbreathing jet engines, ramjets have no rotary compressor at the inlet, instead, the forward motion of the engine itself 'rams' the air through the engine. Ramjets therefore require forward motion through the air to produce thrust.
Ramjets can be particularly useful in applications requiring a small and simple engine for high speed use; such as missiles. A missile (see also pronunciation differences) is a self-propelled explosive Projectile used as a weapon towards a target They have also been used successfully, though not efficiently, as tip jets on helicopter rotors. Tip jet refers to the jet Nozzles located at the tip of some Helicopter rotor blades History Since 400 AD Chinese children have played with bamboo flying toys. [1]
Ramjets require considerable forward speed to operate well, and as a class work most efficiently at speeds around Mach 3, and this type of jet can operate up to speeds of at least Mach 5.
Ramjets employ a continuous combustion process, but are frequently confused with pulsejets, which use an intermittent combustion, but these are a quite distinct type. A pulse jet engine (or pulsejet) is a very simple form of Internal combustion engine based Jet engine where combustion occurs in Pulses
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History
The idea of the ramjet (not to be confused with the Pulse jet engine of V-1 flying bomb fame) was patented as early as 1908 by the French engineer René Lorin, who considered them for subsonic flight. A pulse jet engine (or pulsejet) is a very simple form of Internal combustion engine based Jet engine where combustion occurs in Pulses The Fieseler Fi 103, better known as V-1 (German Vergeltungswaffe 1 was an early Cruise missile used during World War Two René Lorin (1877 - 1933 a graduate of the Ecole Centrale Paris, invented the Ramjet, which he patented in 1908 he patented a subsonic ramjet design and had not
Albert Fonó In 1915 he devised a solution for increasing the range of artillery, comprising a gun-luanched projectile which was to be united with a ramjet propulsion unit. Albert Fonó (1881 Budapest - 1972 Budapest) was a Hungarian Mechanical engineer who was one of the early pioneers of Turbojet This was to make it possible to obtain a long range with low initial 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. [1]In 1928 the Hungarian Albert Fonó applied for, and in 1932, obtained, a German patent on supersonic ramjets. Albert Fonó (1881 Budapest - 1972 Budapest) was a Hungarian Mechanical engineer who was one of the early pioneers of Turbojet
In the Soviet Union, the GIRD-08 ramjet engine was built by Yuri Pobedonostsev and test fired in 1933. The Union of Soviet Socialist Republics (USSR was a constitutionally Socialist state that existed in Eurasia from 1922 to 1991 Russian Group of Study of Reactive Motion (in Russian: Группа изучения реактивного движения (ГИРД transliterated GIRD) was a
In France the works of René Leduc were notable, as was that of William Avery in the United States. This article is about the country For a topic outline on this subject see List of basic France topics. William H Avery ( July 25, 1912 &ndash June 26, 2004) was an influential Aeronautics Engineer. The United States of America —commonly referred to as the Leduc's Model 010 was the first-ever ramjet-powered aircraft to fly, in 1949. Year 1949 ( MCMXLIX) was a Common year starting on Saturday (link will display the full calendar of the Gregorian calendar.
Design
A ramjet is designed around its inlet. An object moving at high speed through air generates a high pressure region in front and a low pressure region to the rear. A ramjet uses this high pressure in front of the engine to force air through the tube, where it is heated by combusting some of it with fuel. It is then passed through a nozzle to accelerate it to supersonic speeds. This acceleration gives the ramjet forward thrust. Thrust is a reaction force described quantitatively by Newton 's Second and Third Laws.
A ramjet is sometimes referred to as a 'flying stovepipe', a very simple device comprising an air intake, a combustor, and a nozzle. A nozzle is a mechanical device or Orifice designed to control the characteristics of a Fluid flow as it exits (or enters an enclosed chamber or Pipe. Normally the only moving parts are those within the turbopump, which pumps the fuel to the combustor in a liquid-fuel ramjet. As the name suggests a turbopump comprises basically two main components a rotodynamic Pump and a driving Turbine, both mounted on the same shaft Solid-fuel ramjets are even simpler.
By way of contrast, a turbojet uses a gas turbine driven fan to compress the air further. TurboJET (噴射飛航 is the brand name for the operations of the Hong Kong -based Shun Tak-China Travel Ship Management Limited (信德中旅船務管理有限公司 A gas compressor is a mechanical device that increases the Pressure of a Gas by reducing its Volume. This gives greater efficiency and far more power at low speeds, where the ram effect is weak, but is also more complex, heavier and more expensive, and the temperature limits of the turbine section limits the top speed and thrust at high speed. A turbine is a rotary Engine that extracts Energy from a Fluid flow
Inlet
Ramjets try to exploit the very high dynamic pressure within the air approaching the intake lip. In Fluid dynamics dynamic pressure (indicated with q, or Q, and sometimes called velocity pressure) is the quantity defined by An efficient intake will recover much of the freestream stagnation pressure, which is used to support the combustion and expansion process in the nozzle. In Fluid dynamics, stagnation pressure is the Pressure at a Stagnation point in a fluid flow where the kinetic energy is converted into pressure energy
Most ramjets operate at supersonic flight speeds and use one or more conical (or oblique) shock waves, terminated by a strong normal shock, to slowdown the airflow to a subsonic velocity at the exit of the intake. For other uses see Supersonic. The term supersonic is used to define a speed that is over the Speed of sound ( Mach 1 A cone is a three-dimensional Geometric shape that tapers smoothly from a flat round base to a point called the apex or vertex For the music album by Converter see Shock Front For the 1977 horror film see Shock Waves A shock wave (also called Further diffusion is then required to get the air velocity down to level suitable for the combustor.
Subsonic ramjets don't need such a sophisticated inlet since the airflow is already subsonic and a simple hole is usually used. This would also work at slightly supersonic speeds, as the air will choke at the inlet, but this is inefficient.
Combustor
Since there is no downstream turbine, a ramjet combustor can safely operate at stoichiometric fuel:air ratios, which implies a combustor exit stagnation temperature of the order of 2400 K for kerosene. Stoichiometry (sometimes called reaction stoichiometry to distinguish it from composition stoichiometry is the Calculation of Quantitative (measurable Stagnation temperature is the Temperature at a Stagnation point in a fluid flow Normally the combustor must be capable of operating over a wide range of throttle settings, for a range of flight speeds/altitudes. Usually a sheltered pilot region enables combustion to continue when the vehicle intake undergoes high yaw/pitch, during turns. Flight dynamics is the science of air and space vehicle orientation and control in three dimensions Other flame stabilization techniques make use of flame holders, which vary in design from combustor cans to simple flat plates, to shelter the flame and improve fuel mixing. Overfuelling the combustor can cause the normal shock within a supersonic intake system to be pushed forward beyond the intake lip, resulting in a substantial drop in engine airflow and net thrust.
Nozzles
The nozzle is a critical part of a ramjet design, since it accelerates exhaust flow to produce thrust. A nozzle is a mechanical device or Orifice designed to control the characteristics of a Fluid flow as it exits (or enters an enclosed chamber or Pipe.
For a ramjet operating at a subsonic flight Mach number, exhaust flow is accelerated through a converging nozzle. A nozzle is a mechanical device or Orifice designed to control the characteristics of a Fluid flow as it exits (or enters an enclosed chamber or Pipe. For a supersonic flight Mach number, acceleration is typically achieved via a convergent-divergent nozzle. A de Laval Nozzle (or convergent-divergent nozzle, CD nozzle or con-di nozzle) is a tube that is pinched in the middle making an hourglass-shape
Performance and control
Ramjets have been run from as low as 45 m/s (100 mph)[2] upwards. Below about Mach 0. 5 they give little thrust and are highly inefficient due to their low pressure ratios.
Above this speed, given sufficient initial flight velocity, a ramjet will be self-sustaining. Indeed, unless the vehicle drag is extremely high, the engine/airframe combination will tend to accelerate to higher and higher flight speeds, substantially increasing the air intake temperature. In Fluid dynamics, drag (sometimes called fluid resistance) is the force that resists the movement of a Solid object through a Fluid (a As this could have a detrimental effect on the integrity of the engine and/or airframe, the fuel control system must reduce engine fuel flow to stabilize the flight Mach number and, thereby, air intake temperature to sensible levels. Mach number (\mathrm{Ma} or M (generally ˈmɑːk sometimes /ˈmɑːx/ or /ˈmæk/ is the speed of an object moving through air or any Fluid
Due to the stoichiometric combustion temperature, efficiency is usually good at high speeds (Mach 2-3), whereas at low speeds the relatively poor compression ratio means that ramjets are outperformed by turbojets or even rockets. TurboJET (噴射飛航 is the brand name for the operations of the Hong Kong -based Shun Tak-China Travel Ship Management Limited (信德中旅船務管理有限公司 A rocket or rocket vehicle is a Missile, Aircraft or other Vehicle which obtains Thrust by the reaction of the
Ramjet Types
Ramjets can be classified according to the type of fuel, liquid or solid, and the booster. [3]
In a liquid fuel ramjet (LFRJ) hydrocarbon fuel (typically) is injected into the combustor ahead of a flameholder which stabilises the flame resulting from the combustion of the fuel with the compressed air from the intake(s). A means of pressurising and supplying the fuel to the ramcombustor is required which can be complicated and expensive. Aerospatiale-Celerg have designed an LFRJ where the fuel is forced into the injectors by an elastomer bladder which inflates progressively along the length of the fuel tank. Aérospatiale was a French Aerospace manufacturer that primarily built both civilian and military Aircraft and Rockets The company was created in 1970 Initially the bladder forms a close-fitting sheath around the compressed air bottle from which it is inflated, which is mounted lengthwise in the tank. [4] This offers a lower cost approach than a regulated LFRJ requiring a turbopump and associated hardware to supply the fuel. [5]
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 the booster is mounted immediately aft of the ramjet, e. g. Sea Dart, or wraparound where multiple boosters are attached alongside the outside of the ramjet e. Sea Dart or Guided Weapon System (GWS 30 is a British Surface-to-air missile system designed by Hawker Siddeley Dynamics and built by g. SA-4 Ganef. The choice of booster arrangement is usually driven by the size of the launch platform. A tandem booster increases the overall length of the system whereas wraparound boosters increase the overall diameter. Wraparound boosters will usually generate higher drag than 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, for example SA-6 Gainful, liquid, for example ASMP, and ducted rocket, for example Meteor, designs. The Air-Sol Moyenne Portée ( ASMP; medium-range air to surface missile) is a French air-launched nuclear Missile. Meteor is an active radar guided beyond-visual-range air to air Missile (BVRAAM being developed by MBDA to equip the Eurofighter Integrated designs are complicated by the different nozzle requirements of the boost and ramjet phases of flight. Due to the higher thrust levels of the booster a different 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 ejected boost nozzle debris, simplicity, reliability, and reduced mass and cost[6], although this must be traded against the reduction in performance compared with that provided by a dedicated booster nozzle.
Integral rocket ramjet/ducted rocket
These are a slight variation on the ramjet where the supersonic exhaust from a rocket combustion process is used to compress and react with the incoming air in the main combustion chamber. Air-augmented rockets (also known as rocket-ejector ramrocket ducted rocket integral rocket/ramjets or ejector ramjets use the supersonic exhaust of some kind of rocket engine to further 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 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 Mach number are limited.
In a ducted rocket a solid fuel gas generator produces 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 (TDR), also known as a Variable Flow Ducted Rocket (VFDR), a valve allows the gas generator exhaust to be throttled allowing control of the thrust. Unlike an LFRJ solid propellant ramjets cannot flameout. A flameout refers to the failure of a Jet engine caused by the extinction of the flame in the Combustion chamber. The ducted rocket sits somewhere between the simplicity of the SFRJ and the unlimited throttleability of the LFRJ.
Flight speed
Ramjets generally give little or no thrust below about half the speed of sound, and they are inefficient (less than 600 seconds) until the airspeed exceeds 1000 km/h (600 mph) due to low compression ratios. Sound is a vibration that travels through an elastic medium as a Wave. Specific impulse (usually abbreviated I sp is a way to describe the efficiency of rocket and jet engines 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). In Aerodynamics, the flight envelope or performance envelope of an Aircraft refers to the capabilities of a design in terms of speed and altitude However, ramjets generally outperform gas turbine based jet engine designs and work best at supersonic speeds (Mach 2-4)[7]. For other uses see Supersonic. The term supersonic is used to define a speed that is over the Speed of sound ( Mach 1 Mach number (\mathrm{Ma} or M (generally ˈmɑːk sometimes /ˈmɑːx/ or /ˈmæk/ is the speed of an object moving through air or any Fluid Although inefficient at slower speeds they are more fuel-efficient than rockets over their entire useful working range up to at least Mach 5. A rocket or rocket vehicle is a Missile, Aircraft or other Vehicle which obtains Thrust by the reaction of the 5.
Ramjets top speed is limited by disassociation to about Mach 5. 5.
Related engines
Air turbo ramjet
Another example of this is the Air Turbo Ramjet (ATR) which operates as a conventional turbojet at subsonic speeds and a fan assisted ramjet at speeds below Mach 6.
Scramjets
Ramjets always slow the incoming air to a subsonic velocity within the combustor. A scramjet ( s upersonic c ombustion ramjet) is a variation of a Ramjet with the distinction being that some or all of the combustion process Scramjets, or "supersonic combustion ramjet" are similar to ramjets, but the air goes through the entire engine at supersonic speeds, eliminating the creation of a strong shock wave in the intake. A scramjet ( s upersonic c ombustion ramjet) is a variation of a Ramjet with the distinction being that some or all of the combustion process This increases the stagnation pressure recovered from the freestream and improves net thrust. Owing to the hypersonic (rather than supersonic) flight speeds experienced, scramjet air intake temperatures are too high for burning kerosene, so hydrogen is normally used as the fuel. In Aerodynamics, hypersonic speeds are speeds that are highly Supersonic. 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. Although scramjet engines have been studied for many decades it is only recently that small experimental units have been flight tested and then only very briefly (e. g. the Boeing X-43). The X-43 is an unmanned experimental Hypersonic Aircraft design with multiple planned scale variations meant to test different [8]
Precooled engines
A variant of the pure ramjet is the 'combined cycle' engine, intended to overcome the limitations of the pure ramjet. One example of this is the SABRE engine; this uses a precooler, behind which is ramjet and turbine machinery. SABRE (Synergic Air Breathing Engine is a design for a Hypersonic hydrogen-fueled air breathing combined cycle Rocket engine / Turbojet engine
The ATREX engine developed in Japan is an experimental implementation of this concept. The ATREX engine (Air Turbo Ramjet Engine with eXpander cycle developed in Japan is an experimental precooled Jet engine that works as a Turbojet at low It uses liquid hydrogen fuel in a fairly exotic single-fan arrangement. The liquid hydrogen fuel is pumped through a heat exchanger in the air-intake, simultaneously heating the liquid hydrogen, and cooling the incoming air. A heat exchanger is a device built for efficient Heat transfer from one medium to another whether the media are separated by a solid wall so that they never mix or the media This cooling of the incoming air is critical to achieving a reasonable efficiency. The hydrogen then continues through a second heat exchanger position after the combustion section, where the hot exhaust is used to further heat the hydrogen, turning it into a very high pressure gas. This gas is then passed through the tips of the fan providing driving power to the fan at sub-sonic speeds. After mixing with the air it's then combusted in the combustion chamber.
Nuclear powered ramjets
During the Cold War the United States designed and ground-tested a nuclear-powered ramjet called Project Pluto. Project Pluto was a United States government program to develop Nuclear powered Ramjet engines for use in Cruise missiles Two experimental engines Cold War is the state of conflict tension and competition that existed between the United States and the Soviet Union (USSR and their respective allies from the Project Pluto was a United States government program to develop Nuclear powered Ramjet engines for use in Cruise missiles Two experimental engines This system used no combustion - a nuclear reactor heated the air instead. This article is a subarticle of Nuclear power. A nuclear reactor is a device in which Nuclear chain reactions are initiated controlled The project was ultimately canceled because ICBMs seemed to serve the purpose better, and because a low-flying missile would have been highly radioactive. Radioactive decay is the process in which an unstable Atomic nucleus loses energy by emitting ionizing particles and Radiation.
J58
The SR-71's Pratt & Whitney J58 engines act as turbojet-assisted ramjets at high-speeds (Mach 3. WikipediaWikiProject Aircraft. Please see WikipediaWikiProject Aircraft/page content for recommended layout WikipediaWikiProject Aircraft. Please see WikipediaWikiProject Aircraft/page content for recommended layout 2).
Ionospheric ramjet
The upper atmosphere above about 100km contains monatomic oxygen that has been produced by the sun through photochemistry. A concept was created by NASA for recombining this thin gas back to diatomic molecules at orbital speeds to power a ramjet. [9]
Bussard ramjet
The Bussard ramjet is a space drive that fuses interstellar wind and exhausts it at high speed from the rear of the vehicle. The Bussard ramjet is a theoretical method of Spacecraft propulsion proposed in 1960 by the physicist Robert W
References
- ^ Here Comes the Flying Stovepipe. TIME. Time (trademarked in capitals as TIME) is a weekly American Newsmagazine, similar to Newsweek and Retrieved on 2008-03-09. 2008 ( MMVIII) is the current year in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common Events 590 - Bahram Chobin is crowned as king Barham VI of Persia.
- ^ RAMJET PRIMER
- ^ "A Century of Ramjet Propulsion Technology Evolution", AIAA Journal of Propulsion and Power, Vol. 20, No. 1, January - February 2004
- ^ "Aerospatiale studies low-cost ramjet", Flight International, 13 - 19 December 1995
- ^ "Hughes homes in on missile pact", Flight International, 11 - 17 September 1996
- ^ Procinsky, I. M. , McHale, C. A. , "Nozzleless Boosters for Integral-Rocket-Ramjet Missile Systems, Paper 80-1277, AIAA/SAE/ASME 16th Joint Propulsion Conference, 30th June to 2nd July 1980
- ^ 11.6 Performance of Jet Engines
- ^ "Boeing: History -- Chronology 2002-2004"
- ^ PRELIMINARY SURVEY OF PROPULSION USING CHEMICAL ENERGY STORED IN THE UPPER ATMOSPHERE By Lionel V, Baldwin and Perry L. Blackshear
Aircraft using ramjets
- Hiller Hornet (a ramjet powered helicopter)
- Leduc experimental aircraft
- Lockheed D-21
- Lockheed X-7
- Nord 1500 Griffon
- Republic XF-103
- SR-71 Blackbird (Turbojet engines that function as ramjets at mach 1+ speeds. WikipediaWikiProject Aircraft. Please see WikipediaWikiProject Aircraft/page content for recommended layout WikipediaWikiProject Aircraft. Please see WikipediaWikiProject Aircraft/page content for recommended layout The Lockheed X-7 (dubbed the "Flying Stove Pipe" was an unmanned test bed for Ramjet engines and Missile guidance technology The Nord 1500 Griffon was the prototype of a Ramjet -powered Fighter aircraft designed and built in the mid-1950s by French state-owned aircraft manufacturer WikipediaWikiProject Aircraft. Please see WikipediaWikiProject Aircraft/page content for recommended layout WikipediaWikiProject Aircraft. Please see WikipediaWikiProject Aircraft/page content for recommended layout )
Missiles using ramjets
See also
- Ram accelerator
- Aircraft engines
- Scramjet
- Jet Engine Performance
- Jet aircraft
- Jetboat
- Turbofan
- Turbojet
- Turboprop
- Turboshaft
- Jet engine
- Spacecraft propulsion
- Supercharger
- Turbocharger
- Gas turbine
- Bussard ramjet
- Kurt Schreckling who built practical jet engines for model aircraft
External links
- The Boeing Logbook: 2002 - 2004
- Ramjet Performance Primer
- GIRD-08 information
- Design notes on a ramjet powered helicopter
Dictionary
ramjet
-noun
- (aviation) A jet engine in which forward motion forces air into an inlet, compressing it (as opposed to having a pump type device compressing the air for combustion with fuel), and where combustion is subsonic.
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