Jet Engine Wiki
There are many types of jet engines, ranging from those with no moving parts such as pulsejets and ramjets, to those with incredibly complex high RPM parts. Below is a compiled list of engines and descriptions from wikipedia. We will be adding more engines and content to this page very soon!
Air Breathing Jet Engines
Pulse jet engines are a lightweight form of jet propulsion, but usually have a poor compression ratio, and hence give a low specific impulse.
One notable line of research of pulsejet engines includes the pulse detonation engine which involves repeated detonations in the engine, and which can potentially give high compression and good efficiency.
There are two basic types of pulsejets. The first is known as a valved or traditional pulsejet and it has a set of one-way valves through which the incoming air passes. When the air-fuel is ignited, these valves slam shut which means that the hot gases can only leave through the engine’s tailpipe, thus creating forward thrust.
The cycle frequency is primarily dependent on the length of the engine. For a small model-type engine the frequency may be around 250 pulses per second, whereas for a larger engine such as the one used on the German V-1 flying bomb, the frequency was closer to 45 pulses per second. The low-frequency sound produced resulted in the missiles being nicknamed “buzz bombs.”
The second type of pulsejet is known as the valveless pulsejet. Technically the term for this engine is the acoustic-type pulsejet, or aerodynamically valved pulsejet.
Valveless pulsejets come in a number of shapes and sizes, with different designs being suited for different functions. A typical valveless engine will have one or more intake tubes, a combustion chamber section, and one or more exhaust tube sections.
The intake tube takes in air and mixes it with fuel to combust, and also controls the expulsion of exhaust gas, like a valve, limiting the flow but not stopping it altogether. While the fuel-air mixture burns, most of the expanding gas is forced out of the exhaust pipe of the engine. Because the intake tube(s) also expel gas during the exhaust cycle of the engine, most valveless engines have the intakes facing backwards so that the thrust created adds to the overall thrust, rather than reducing it.
The combustion creates two pressure wave fronts, one traveling down the longer exhaust tube and one down the short intake tube. By properly ‘tuning’ the system (by designing the engine dimensions properly), a resonating combustion process can be achieved.
While some valveless engines are known for being extremely fuel-hungry, other designs use significantly less fuel than a valved pulsejet, and a properly designed system with advanced components and techniques can rival or exceed the fuel efficiency of small turbojet engines.
Pressure Jet Engines
The Gluhareff Pressure Jet (or tip jet) is a type of jet engine that, like a Valveless pulse jet, has no moving parts. It was invented by Eugene Michael Gluhareff, a Russian engineer who envisaged it as a power plant for personal helicopters and compact aircraft such as Microlights.
Having no moving parts, the engine works by having a coiled pipe in the combustion chamber that superheats the fuel (propane) before being injected into the air-fuel inlet. In the combustion chamber, the fuel/air mixture ignites and burns, creating thrust as it leaves through the exhaust pipe. Induction and compression of the fuel/air mixture is done both by the pressure of propane as it’s injected, along with the sound waves created by combustion acting on the intake stacks.
The engine has three intake stages, which are sized according to the sound created by the combustion process when running. This has exactly the same effect as the turbine and compressor in a turbojet, creating a vacuum that sucks in air. The intakes, along with the exhaust, are sonically tuned for maximum effectiveness. Early prototypes produced very small amounts of thrust, before Gluharev developed it from early experiments on producing thrust from using the pressurized fuel’s kinetic energy to suck in the air and compress it prior to combustion.
Pulse Detonation Engines
A pulse detonation engine, or “PDE”, is a type of propulsion system that uses detonation waves to combust the fuel and oxidizer mixture. The engine is pulsed because the mixture must be renewed in the combustion chamber between each detonation wave initiated by an ignition source. Theoretically, a PDE can operate from subsonic up to a hypersonic flight speed of roughly Mach 5. An ideal PDE design can have a thermodynamic efficiency higher than other designs like turbojets and turbofans because a detonation wave rapidly compresses the mixture and adds heat at constant volume. Consequently, moving parts like compressor spools are not necessarily required in the engine, which could significantly reduce overall weight and cost. PDEs have been considered for propulsion for over 70 years.Key issues for further development include fast and efficient mixing of the fuel and oxidizer, the prevention of autoignition, and integration with an inlet and nozzle.
To date, no practical PDE has been put into production, but several testbed engines have been built and one was successfully integrated into a low-speed demonstration aircraft that flew in sustained PDE powered flight in 2008. In June 2008, the Defense Advanced Research Projects Agency (DARPA) unveiled Blackswift which was intended to use this technology to reach speeds of up to Mach 6. However the project was cancelled soon afterward, in October 2008.
A ramjet, sometimes referred to as a stovepipe jet, or an athodyd, is a form of airbreathing jet engine using the engine’s forward motion to compress incoming air, without a rotary compressor. Ramjets cannot produce thrust at zero airspeed and thus cannot move an aircraft from a standstill. Ramjets require considerable forward speed to operate well, and as a class work most efficiently at speeds around Mach 3. This type of jet can operate up to speeds of Mach 6.
Ramjets can be particularly useful in applications requiring a small and simple engine for high speed use, such as missiles, while weapon designers are looking to use ramjet technology in artillery shells to give added range: it is anticipated that a 120-mm mortar shell, if assisted by a ramjet, could attain a range of 22 mi (35 km). They have also been used successfully, though not efficiently, as tip jets on helicopter rotors.
Ramjets are frequently confused with pulsejets, which use an intermittent combustion, but ramjets employ a continuous combustion process, and are a quite distinct type of jet engine.
A scramjet (supersonic combustion ramjet) is a variant of a ramjet airbreathing jet engine in which combustion takes place in supersonic airflow. As in ramjets, a scramjet relies on high vehicle speed to forcefully compress and decelerate the incoming air before combustion (hence ramjet), but whereas a ramjet decelerates the air to subsonic velocities before combustion, airflow in a scramjet is supersonic throughout the entire engine. This allows the scramjet to efficiently operate at extremely high speeds: theoretical projections place the top speed of a scramjet between Mach 12 and Mach 24, which is near orbital velocity. The fastest air-breathing aircraft is a SCRAM jet design, the NASA X-43A which reached Mach 9.8. For comparison, the second fastestair-breathing aircraft, the manned SR-71 Blackbird, has a cruising speed of Mach 3.2.
The scramjet is composed of three basic components: a converging inlet, where incoming air is compressed and decelerated; a combustor, where gaseous fuel is burned with atmospheric oxygen to produce heat; and a diverging nozzle, where the heated air is accelerated to produce thrust. Unlike a typical jet engine, such as a turbojet or turbofan engine, a scramjet does not use rotating, fan-like components to compress the air; rather, the achievable speed of the aircraft moving through the atmosphere causes the air to compress within the inlet. As such, no moving parts are needed in a scramjet, which greatly simplifies both the design and operation of the engine. In comparison, typical turbojet engines require inlet fans, multiple stages of rotating compressor fans, and multiple rotating turbine stages, all of which add weight, complexity, and a greater number of failure points to the engine. It is this simplicity that allows scramjets to operate at such high velocities, as the conditions encountered in hypersonic flight severely hamper the operation of conventional turbomachinery.
Due to the nature of their design, scramjet operation is limited to near-hypersonic velocities. As they lack mechanical compressors, scramjets require the high kinetic energy of a hypersonic flow to compress the incoming air to operational conditions. Thus, a scramjet-powered vehicle must be accelerated to the required velocity by some other means of propulsion, such as turbojet, railgun, or rocket engines. In the flight of the experimental scramjet-powered Boeing X-51A, the test craft was lifted to flight altitude by aBoeing B-52 Stratofortress before being released and accelerated by a detachable rocket to near Mach 4.5.
While scramjets are conceptually simple, actual implementation is limited by extreme technical challenges. Hypersonic flight within the atmosphere generates immense drag, and temperatures found on the aircraft and within the engine can be much greater than that of the surrounding air. Maintaining combustion in the supersonic flow presents additional challenges, as the fuel must be injected, mixed, ignited, and burned within milliseconds. While scramjet technology has been under development since the 1950s, only very recently have scramjets successfully achieved powered flight.
The turbojet is the oldest kind of general-purpose airbreathing jet engine. Two engineers, Frank Whittle in the United Kingdom and Hans von Ohain in Germany, developed the concept independently into practical engines during the late 1930s.
Turbojets consist of an air inlet, an air compressor, a combustion chamber, a gas turbine (that drives the air compressor) and a nozzle. The air is compressed into the chamber, heated and expanded by the fuel combustion and then allowed to expand out through the turbine into the nozzle where it is accelerated to high speed to provide propulsion.
Turbojets are quite inefficient if flown below about Mach 2and very noisy. Most modern aircraft use turbofans instead for economic reasons. Turbojets are still very common in medium range cruise missiles,due to their high exhaust speed, low frontal area and relative simplicity.
A turboshaft engine is a form of gas turbine which is optimized to produce shaft power, rather than jet thrust. In concept, turboshaft engines are very similar to turbojets, with additional turbine expansion to extract heat energy from the exhaust and convert it into output shaft power.
Turboshaft engines are commonly used in applications which require a sustained high power output, high reliability, small size, and light weight. These include helicopters, auxiliary power units, boats and ships, tanks, hovercraft, and stationary equipment.
The turbofan is a type of airbreathing jet engine that is very typically employed for aircraft propulsion, that is based around a gas turbine engine. Turbofans provide thrust using a combination of a ducted fan and a jet exhaust nozzle. Part of the airstream from the ducted fan passes through the core, providing oxygen to burn fuel to create power. However, the rest of the air flow bypasses the engine core and mixes with the faster stream from the core, significantly reducing exhaust noise. The substantially slower bypass airflow produces thrust more efficiently than the high-speed air from the core, and this reduces the specific fuel consumption. In other words, for many jet applications (not all), turbofans were a step forward in fuel efficiency from turbojets.
A few designs work slightly differently, having the fan blades as a radial extension of an aft-mounted low-pressure turbine unit.
Turbofans have a net exhaust speed that is much lower than that of a turbojet. This makes them much more efficient at subsonic speeds than turbojets, and somewhat more efficient at supersonic speeds up to roughly Mach 1.6, but have also been found to be efficient when used with continuous afterburner at Mach 3 and above. However, the lower exhaust speed also reduces thrust at high vehicle speeds.
All currently manufactured commercial jet aircraft use turbofans, which are more efficient and quieter than turbojets. Turbofans are also used in many military jet aircraft, such as the Sukhoi Su-35, McDonnell Douglas F-15 Eagle, Mikoyan MiG-31, Mikoyan MiG-29 and others. Turbofans are also used in unmanned aerial vehicles such as the RQ-4 Global Hawk.
Tesla Turbine Engines
The Tesla turbine is a bladeless centripetal flow turbine patented by Nikola Tesla in 1913. It is referred to as a bladeless turbine because it uses the boundary layer effect and not a fluid impinging upon the blades as in a conventional turbine. The Tesla turbine is also known as the boundary layer turbine, cohesion-type turbine, and Prandtl layer turbine (after Ludwig Prandtl). Bioengineering researchers have referred to it as a multiple disk centrifugal pump. One of Tesla’s desires for implementation of this turbine was for geothermal power, which was described in “Our Future Motive Power“.
A rocket engine, or simply “rocket”, is a jet engine that uses only propellant mass for forming its high speed propulsive jet. Rocket engines are reaction engines and obtain thrust in accordance with Newton’s third law. Since they need no external material to form their jet, rocket engines can be used for spacecraft propulsion as well as terrestrial uses, such as missiles. Most rocket engines are internal combustion engines, although non combusting forms also exist.
Rocket engines as a group have the highest exhaust velocities, are by far the lightest, but are the least propellant efficient of all types of jet engines.
Fuel / Oxidizer Types
Liquid Fueled Rocket
Hybrid Fuel Rocket