Turbofan - AbsoluteAstronomy.com

The turbofan is a type of airbreathing jet engine

Airbreathing jet engine

An airbreathing jet engine is a jet engine propelled by a jet of hot exhaust gases formed from air that is drawn into the engine via an inlet duct....

that is widely used for aircraft

Aircraft engine

An aircraft engine is the component of the propulsion system for an aircraft that generates mechanical power. Aircraft engines are almost always either lightweight piston engines or gas turbines...

propulsion. A turbofan combines two types of engines, the turbo portion which is a conventional gas turbine engine, and the fan, a propeller-like ducted fan

Ducted fan

A ducted fan is a propulsion arrangement whereby a fan, which is a type of propeller, is mounted within a cylindrical shroud or duct. The duct reduces losses in thrust from the tip vortices of the fan, and varying the cross-section of the duct allows the designer to advantageously affect the...

. The engine produces thrust through a combination of these two portions working in concert; engines that use more jet thrust

Propelling nozzle

A propelling nozzle is the component of a jet engine that operates to constrict the flow, to form an exhaust jet and to maximise the velocity of propelling gases from the engine....

relative to fan thrust are known as low bypass turbofans, while those that have considerably more fan thrust than jet are known as high bypass. Most commercial aviation jet engines in use today are of the high-bypass type, and most modern military engines are low-bypass,

The fan serves two duties. Part of the airstream from the 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 at the back of the engine. As engine noise is a function of exhaust temperature, turbofan engines are significantly quieter than a pure-jet of the same thrust. Additionally, the efficiency of propulsion is a function of the relative airspeed of the exhaust to the surrounding air; propellers are most efficient for low speed, pure jets for high speeds, and ducted fans in the middle. Turbofans are thus the most efficient engines in the range of speeds from about 500 to 1000 km/h, the speed at which most commercial aircraft operate. Turbofans retain an efficiency edge over pure jets at low supersonic

Supersonic

Supersonic speed is a rate of travel of an object that exceeds the speed of sound . For objects traveling in dry air of a temperature of 20 °C this speed is approximately 343 m/s, 1,125 ft/s, 768 mph or 1,235 km/h. Speeds greater than five times the speed of sound are often...

speeds up to roughly Mach

Mach number

Mach number is the speed of an object moving through air, or any other fluid substance, divided by the speed of sound as it is in that substance for its particular physical conditions, including those of temperature and pressure...

1.6, but have also been found to be efficient when used with continuous afterburner

AfterBurner

The AfterBurner is a lighting solution for the Game Boy Advance system that was created by Triton-Labs.Originally, portablemonopoly.net was a website created to petition Nintendo to put some kind of light in their Game Boy Advance system...

at Mach 3 and above. However, the lower exhaust speed also reduces thrust at high vehicle speeds.

The vast majority of turbofans follow the same basic design with a large fan at the front of the engine with a relatively small jet engine behind it. There have been a number of variations on this theme, however, including rear-mounted fans where they can be easily added to an existing pure-jet design, or designs that combine a low-pressure turbine and a fan stage in a single rear-mounted unit.

Introduction

Unlike a reciprocating engine, a turbojet uses continuous-flow combustion.

In a single-spool (or single-shaft) turbojet, which is the most basic form and the earliest type of turbojet to be developed, air enters an intake

Intake

An intake , or especially for aircraft inlet, is an air intake for an engine. Because the modern internal combustion engine is in essence a powerful air pump, like the exhaust system on an engine, the intake must be carefully engineered and tuned to provide the greatest efficiency and power...

before being compressed to a higher pressure by a rotating (fan-like) compressor

Axial compressor

Axial compressors are rotating, airfoil-based compressors in which the working fluid principally flows parallel to the axis of rotation. This is in contrast with other rotating compressors such as centrifugal, axi-centrifugal and mixed-flow compressors where the air may enter axially but will have...

. The compressed air passes on to a combustor, where it is mixed with a fuel (e.g. kerosene

Kerosene

Kerosene, sometimes spelled kerosine in scientific and industrial usage, also known as paraffin or paraffin oil in the United Kingdom, Hong Kong, Ireland and South Africa, is a combustible hydrocarbon liquid. The name is derived from Greek keros...

) and ignited. The hot combustion gases then enter a windmill-like turbine

Turbine

A turbine is a rotary engine that extracts energy from a fluid flow and converts it into useful work.The simplest turbines have one moving part, a rotor assembly, which is a shaft or drum with blades attached. Moving fluid acts on the blades, or the blades react to the flow, so that they move and...

, where power

Motive power

In thermodynamics, motive power is an agency, as water or steam, used to impart motion. Generally, motive power is defined as a natural agent, as water, steam, wind, electricity, etc., used to impart motion to machinery; a motor; a mover. The term may also define something, as a locomotive or a...

is extracted to drive the compressor. Although the expansion process in the turbine reduces the gas pressure (and temperature) somewhat, the remaining energy and pressure are employed to provide a high-velocity jet by passing the gas through a propelling nozzle

Nozzle

A nozzle is a device designed to control the direction or characteristics of a fluid flow as it exits an enclosed chamber or pipe via an orifice....

. This process produces a net thrust opposite to the direction of the jet flow.

After World War II, two-spool (or two-shaft) turbojets were developed to make it easier to throttle back compression systems with a high design overall pressure ratio (i.e., combustor inlet pressure/intake delivery pressure). Adopting the two-spool arrangement enables the compression system to be split in two, with a low pressure (LP) compressor supercharging a high pressure (HP) compressor. Each compressor is mounted on a separate (co-axial) shaft, driven by its own turbine (i.e. the HP turbine and LP turbine). Otherwise, a two-spool turbojet is much like a single-spool engine.

Modern turbofans evolved from the two-spool axial-flow turbojet engine, essentially by increasing the relative size of the low pressure (LP) compressor to the point where some (if not most) of the air exiting the unit actually bypasses the core (or gas-generator) stream passing through the main combustor. This bypass air either expands through a separate propelling nozzle, or is mixed with the hot gases leaving the low pressure (LP) turbine

Turbine

, before expanding through a mixed stream propelling nozzle. Owing to a lower jet velocity, a modern civil turbofan is quieter than the equivalent turbojet. Turbofans also have a better thermal efficiency, which is explained later in the article. In a turbofan, the LP compressor is often called a fan. Civil-aviation turbofans usually have a single fan stage, whereas most military-aviation turbofans (e.g. combat and trainer aircraft applications) have multistage fans. Modern military transport turbofan engines are similar to those that propel civil jetliners.

Turboprop

Turboprop

A turboprop engine is a type of turbine engine which drives an aircraft propeller using a reduction gear.The gas turbine is designed specifically for this application, with almost all of its output being used to drive the propeller...

engines are gas-turbine engines that deliver almost all of their power to a shaft to drive a propeller. Turboprops remain popular on very small or slow aircraft, such as small commuter airliners, for their fuel efficiency at lower speeds, as well as on medium military transports and patrol planes, such as the C-130 Hercules

C-130 Hercules

The Lockheed C-130 Hercules is a four-engine turboprop military transport aircraft designed and built originally by Lockheed, now Lockheed Martin. Capable of using unprepared runways for takeoffs and landings, the C-130 was originally designed as a troop, medical evacuation, and cargo transport...

and P-3 Orion

P-3 Orion

The Lockheed P-3 Orion is a four-engine turboprop anti-submarine and maritime surveillance aircraft developed for the United States Navy and introduced in the 1960s. Lockheed based it on the L-188 Electra commercial airliner. The aircraft is easily recognizable by its distinctive tail stinger or...

, for their high takeoff performance and mission endurance benefits.

If the turboprop

Turboprop

is better at moderate flight speeds and the turbojet is better at very high speeds, it might be imagined that at some speed range in the middle a mixture of the two is best. Such an engine is the turbofan (originally termed bypass turbojet by the inventors at Rolls-Royce

Rolls-Royce plc

Rolls-Royce Group plc is a global power systems company headquartered in the City of Westminster, London, United Kingdom. It is the world’s second-largest maker of aircraft engines , and also has major businesses in the marine propulsion and energy sectors. Through its defence-related activities...

). Another name sometimes used is ducted fan

Ducted fan

, though that term is also used for propellers and fans used in vertical-flight applications.

The difference between a turbofan and a propeller

Propeller (aircraft)

Aircraft propellers or airscrews convert rotary motion from piston engines or turboprops to provide propulsive force. They may be fixed or variable pitch. Early aircraft propellers were carved by hand from solid or laminated wood with later propellers being constructed from metal...

, besides direct thrust, is that the intake duct of the former slows the air before it arrives at the fan

Fan (mechanical)

A mechanical fan is a machine used to create flow within a fluid, typically a gas such as air.A fan consists of a rotating arrangement of vanes or blades which act on the air. Usually, it is contained within some form of housing or case. This may direct the airflow or increase safety by preventing...

face. As both propeller and fan blades must operate at subsonic inlet velocities to be efficient, ducted fans allow efficient operation at higher vehicle speeds.

Depending on specific thrust

Specific thrust

Specific thrust is a term used in gas turbine engineering to show the relative bulk of a jet engine and is defined as the ratio: net thrust/total intake airflow.-Low specific thrust engines:...

(i.e. net thrust to intake airflow), ducted fans operate best from about 400 to 2,000 km/h (250 to 1,300 mph), which is why turbofans are the most common type of engine for aviation use today—in airliners as well as in subsonic and supersonic military fighter and trainer aircraft. It should be noted, however, that turbofans use extensive ducting to force incoming air to subsonic velocities (thus reducing shock waves throughout the engine).

Bypass ratio
Bypass ratio
The term bypass ratio relates to the design of turbofan engines, commonly used in aviation. It is defined as the ratio between the mass flow rate of air drawn in by the fan bypassing the engine core to the mass flow rate passing through the engine core....

(bypassed airflow to combustor

Combustor

A combustor is a component or area of a gas turbine, ramjet, or scramjet engine where combustion takes place. It is also known as a burner, combustion chamber or flame holder. In a gas turbine engine, the combustor or combustion chamber is fed high pressure air by the compression system. The...

airflow) is a parameter often used for classifying turbofans; when the low-bypass Conway engine entered service in 1960, no one even called it a turbofan, that term first being applied to Pratt and Whitney's JT3D with its 1-to-1 bypass.

The noise of any type of jet engine is strongly related to the velocity of the exhaust gases, typically being proportional to the eighth power of the jet velocity. High-bypass-ratio (i.e., low-specific-thrust) turbofans are relatively quiet compared to turbojets and low-bypass-ratio (i.e., high-specific-thrust) turbofans. A low-specific-thrust engine has a low jet velocity by definition, as the following approximate equation for net thrust implies:

where:

intake mass flow

fully expanded jet velocity (in the exhaust plume)

aircraft flight velocity

Rearranging the above equation, specific thrust is given by:

So for zero flight velocity, specific thrust is directly proportional to jet velocity. Relatively speaking, low-specific-thrust engines are large in diameter to accommodate the high airflow required for a given thrust.

Although jet aircraft are loud, a conventional piston engine or a turboprop

Turboprop

engine delivering the same thrust would be much louder.

Early turbofans

Early turbojet engines were very fuel-inefficient, as their overall pressure ratio and turbine inlet temperature were severely limited by the technology available at the time. The very first running turbofan was the German Daimler-Benz DB 670 (designated as the 109-007 by the RLM) which was operated on its testbed on April 1, 1943. The engine was abandoned later while the war went on and problems could not be solved. The British wartime Metrovick F.2

Metrovick F.2

The Metropolitan-Vickers F.2 was an early turbojet engine and the first British design to be based on an axial-flow compressor. It was considered too unreliable for use during the war, and never entered production...

axial flow jet was given a fan to create the first British turbofan.

Improved materials, and the introduction of twin compressors such as in the Pratt & Whitney JT3C

Pratt & Whitney JT3C

|-Specifications :-See also:-References:NotesBibliography* Francillon, René J. McDonnell Douglas Aircraft since 1920. London: Putnam, 1979. ISBN 0-370-00050-1.-External links:* * *...

engine, increased the overall pressure ratio and thus the thermodynamic

Thermodynamics

Thermodynamics is a physical science that studies the effects on material bodies, and on radiation in regions of space, of transfer of heat and of work done on or by the bodies or radiation...

efficiency of engines, but they also led to a poor propulsive efficiency, as pure turbojets have a high specific thrust/high velocity exhaust better suited to supersonic flight.

The original low-bypass turbofan engines were designed to improve propulsive efficiency by reducing the exhaust velocity to a value closer to that of the aircraft. The Rolls-Royce Conway

Rolls-Royce Conway

The Rolls-Royce RB.80 Conway was the first by-pass engine in the world to enter service. Development started at Rolls-Royce in the 1940s, but it was used only briefly in the late 1950s and early 1960s before other turbofan designs were introduced that replaced it. The Conway powered versions of...

, the first production turbofan, had a bypass ratio of 0.3, similar to the modern General Electric F404 fighter engine. Civilian turbofan engines of the 1960s, such as the Pratt & Whitney JT8D and the Rolls-Royce Spey had bypass ratios closer to 1, but were not dissimilar to their military equivalents.

The unusual General Electric CF700

General Electric CF700

|-See also:-External links:* *...

turbofan engine was developed as an aft-fan engine with a 2.0 bypass ratio. This was derived from the General Electric J85/CJ610

General Electric J85

-External links:**...

turbojet (2,850 lbf or 12,650 N) to power the larger Rockwell Sabreliner 75/80 model aircraft, as well as the Dassault Falcon 20 with about a 50% increase in thrust (4,200 lbf or 18,700 N). The CF700 was the first small turbofan in the world to be certified by the Federal Aviation Administration

Federal Aviation Administration

The Federal Aviation Administration is the national aviation authority of the United States. An agency of the United States Department of Transportation, it has authority to regulate and oversee all aspects of civil aviation in the U.S...

(FAA). There are now over 400 CF700 aircraft in operation around the world, with an experience base of over 10 million service hours. The CF700 turbofan engine was also used to train Moon-bound astronauts in Project Apollo

Project Apollo

The Apollo program was the spaceflight effort carried out by the United States' National Aeronautics and Space Administration , that landed the first humans on Earth's Moon. Conceived during the Presidency of Dwight D. Eisenhower, Apollo began in earnest after President John F...

as the powerplant for the Lunar Landing Research Vehicle.

Low-bypass turbofan

A high specific thrust/low bypass ratio turbofan normally has a multi-stage fan, developing a relatively high pressure ratio and, thus, yielding a high (mixed or cold) exhaust velocity. The core airflow needs to be large enough to give sufficient core power

Core power

Core power is a parameter used in aeroengine performance engineering to enable a comparison of the power capabilities of jet engine cores....

to drive the fan. A smaller core flow/higher bypass ratio cycle can be achieved by raising the (HP) turbine rotor inlet temperature.

Imagine a retrofit situation where a new low bypass ratio, mixed exhaust, turbofan is replacing an old turbojet, in a particular military application. Say the new engine is to have the same airflow and net thrust (i.e. same specific thrust) as the one it is replacing. A bypass flow can only be introduced if the turbine inlet temperature is allowed to increase, to compensate for a correspondingly smaller core flow. Improvements in turbine cooling/material technology would facilitate the use of a higher turbine inlet temperature, despite increases in cooling air temperature, resulting from a probable increase in overall pressure ratio.

Efficiently done, the resulting turbofan would probably operate at a higher nozzle pressure ratio than the turbojet, but with a lower exhaust temperature to retain net thrust. Since the temperature rise across the whole engine (intake to nozzle) would be lower, the (dry power) fuel flow would also be reduced, resulting in a better specific fuel consumption (SFC).

A few low-bypass ratio military turbofans (e.g. F404) have Variable Inlet Guide Vanes, with piano-style hinges, to direct air onto the first rotor stage. This improves the fan surge margin (see compressor map

Compressor map

Each compressor in a gas turbine engine has an operating map. Complete maps are either based on compressor rig test results or are predicted by a special computer program...

) in the mid-flow range. The swing wing F-111 achieved a very high range/payload capability by pioneering this, and it was also the heart of the famous F-14 Tomcat

F-14 Tomcat

The Grumman F-14 Tomcat is a supersonic, twin-engine, two-seat, variable-sweep wing fighter aircraft. The Tomcat was developed for the United States Navy's Naval Fighter Experimental program following the collapse of the F-111B project...

air superiority fighter which used the same engines in a smaller, more agile airframe to achieve efficient cruise and Mach 2 speed.

Afterburning turbofan

Since the 1970s, most jet fighter

Fighter aircraft

A fighter aircraft is a military aircraft designed primarily for air-to-air combat with other aircraft, as opposed to a bomber, which is designed primarily to attack ground targets...

engines have been low/medium bypass turbofans with a mixed exhaust, afterburner

AfterBurner

and variable area final nozzle. An afterburner is a combustor located downstream of the turbine blades and directly upstream of the nozzle, which burns fuel from afterburner-specific fuel injectors. When lit, prodigious amounts of fuel are burnt in the afterburner, raising the temperature of exhaust gases by a significant degree, resulting in a higher exhaust velocity/engine specific thrust. The variable geometry nozzle must open to a larger throat area to accommodate the extra volume flow when the afterburner is lit. Afterburning is often designed to give a significant thrust boost for take off, transonic acceleration and combat maneuvers, but is very fuel intensive. Consequently afterburning can only be used for short portions of a mission.

Unlike the main combustor, where the downstream turbine blades must not be damaged by high temperatures, an afterburner can operate at the ideal maximum (stoichiometric) temperature (i.e. about 2100K/3780Ra/3320F). At a fixed total applied fuel:air ratio, the total fuel flow for a given fan airflow will be the same, regardless of the dry specific thrust of the engine. However, a high specific thrust turbofan will, by definition, have a higher nozzle pressure ratio, resulting in a higher afterburning net thrust and, therefore, a lower afterburning specific fuel consumption. However, high specific thrust engines have a high dry SFC. The situation is reversed for a medium specific thrust afterburning turbofan: i.e. poor afterburning SFC/good dry SFC. The former engine is suitable for a combat aircraft which must remain in afterburning combat for a fairly long period, but only has to fight fairly close to the airfield (e.g. cross border skirmishes) The latter engine is better for an aircraft that has to fly some distance, or loiter for a long time, before going into combat. However, the pilot can only afford to stay in afterburning for a short period, before aircraft fuel reserves become dangerously low.

Modern low-bypass military turbofans include the Pratt & Whitney F119

Pratt & Whitney F119

|-See also:-External links:* *...

, the Eurojet EJ200

Eurojet EJ200

|-See also:-External links:* * * * *...

, the General Electric F110

General Electric F110

-External links:* - The F110 Engine Family* - F110-GE-100 Gallery* - F110* - General Electric F110...

, the Klimov RD-33

Klimov RD-33

|- Specifications :thrust=49.4 kN Dry, 81.4 - 88.4 kN Afterburning. -See also:- External links :* * * * * * * * * *...

, and the Saturn AL-31, all of which feature a mixed exhaust, afterburner and variable area propelling nozzle.

High-bypass turbofan

The low specific thrust/high bypass ratio turbofans used in today's civil jetliners (and some military transport aircraft) evolved from the high specific thrust/low bypass ratio turbofans used in such [production] aircraft back in the 1960s.

Low specific thrust is achieved by replacing the multi-stage fan with a single stage unit. Unlike some military engines, modern civil turbofans do not have any stationary inlet guide vanes in front of the fan rotor. The fan is scaled to achieve the desired net thrust.

The core (or gas generator) of the engine must generate sufficient core power to at least drive the fan at its design flow and pressure ratio. Through improvements in turbine cooling/material technology, a higher (HP) turbine rotor inlet temperature can be used, thus facilitating a smaller (and lighter) core and (potentially) improving the core thermal efficiency. Reducing the core mass flow tends to increase the load on the LP turbine, so this unit may require additional stages to reduce the average stage loading and to maintain LP turbine efficiency. Reducing core flow also increases bypass ratio (5:1, or more, is now common).

Further improvements in core thermal efficiency can be achieved by raising the overall pressure ratio of the core. Improved blade aerodynamics reduces the number of extra compressor stages required. With multiple compressors (i.e. LPC, IPC, HPC) dramatic increases in overall pressure ratio have become possible. Variable geometry (i.e. stators) enable high pressure ratio compressors to work surge-free at all throttle settings.

The first high-bypass turbofan engine was the General Electric TF39

General Electric TF39

|-See also:-External links:*...

, designed in mid 1960s to power the Lockheed

Lockheed Corporation

The Lockheed Corporation was an American aerospace company. Lockheed was founded in 1912 and later merged with Martin Marietta to form Lockheed Martin in 1995.-Origins:...

C-5 Galaxy

The Lockheed C-5 Galaxy is a large military transport aircraft built by Lockheed. It provides the United States Air Force with a heavy intercontinental-range strategic airlift capability, one that can carry outsize and oversize cargos, including all air-certifiable cargo. The Galaxy has many...

military transport aircraft. The civil General Electric CF6

General Electric CF6

The General Electric CF6 is a family of high-bypass turbofan engines produced by GE Aviation. A development of the first high-power high-bypass jet engine available, the TF39, the CF6 powers a wide variety of civilian airliners. The basic engine core formed the basis for the LM2500, LM5000, and...

engine used a derived design. Other high-bypass turbofans are the Pratt & Whitney JT9D

Pratt & Whitney JT9D

-Bibliography:* Gunston, Bill. World Encyclopedia of Aero Engines. Cambridge, England. Patrick Stephens Limited, 1989. ISBN 1-85260-163-9-External links:*...

, the three-shaft Rolls-Royce RB211

Rolls-Royce RB211

The Rolls-Royce RB211 is a family of high-bypass turbofan engines made by Rolls-Royce plc and capable of generating 37,400 to 60,600 pounds-force thrust. Originally developed for the Lockheed L-1011 , it entered service in 1972 and was the only engine to power this aircraft type...

and the CFM International CFM56

CFM International CFM56

The CFM International CFM56 series is a family of high-bypass turbofan aircraft engines made by CFM International , with a thrust range of . CFMI is a 50–50 joint-owned company of SNECMA, France and GE Aviation , USA. Both companies are responsible for producing components and each has its own...

. More recent large high-bypass turbofans include the Pratt & Whitney PW4000

Pratt & Whitney PW4000

|-See also:-External links:* * *...

, the three-shaft Rolls-Royce Trent

Rolls-Royce Trent

Rolls-Royce Trent is the name given to a family of high bypass turbofan aircraft engines manufactured by Rolls-Royce plc. All are developments of the RB211 with thrust ratings of . Versions of the Trent are in service on the Airbus A330, A340, A380, Boeing 777, and 787, and variants are in...

, the General Electric GE90

General Electric GE90

General Electric GE90 is a family of high-bypass turbofan aircraft engines built by GE Aviation for the Boeing 777, with thrust ratings ranging from 74,000 to 115,000 lbf . It was first introduced in November 1995 on British Airways' 777s, and is available only on the 777...

/GEnx and the GP7000, produced jointly by GE and P&W.

High-bypass turbofan engines are generally quieter than the earlier low bypass ratio civil engines. This is not so much due to the higher bypass ratio as to the use of a low pressure ratio, single stage fan which significantly reduces specific thrust and, thereby, jet velocity. The combination of a higher overall pressure ratio and turbine inlet temperature improves thermal efficiency. This, together with a lower specific thrust (better propulsive efficiency), leads to a lower specific fuel consumption.

For reasons of fuel economy, and also of reduced noise, almost all of today's jet airliners are powered by high-bypass turbofans. Although modern combat aircraft tend to use low bypass ratio turbofans, military transport aircraft (e.g. C-17

C-17 Globemaster III

The Boeing C-17 Globemaster III is a large military transport aircraft. Developed for the United States Air Force from the 1980s to the early 1990s by McDonnell Douglas, the C-17 is used for rapid strategic airlift of troops and cargo to main operating bases or forward operating bases throughout...

) mainly use high bypass ratio turbofans (or turboprops) for fuel efficiency.

Because of the implied low mean jet velocity, a high bypass ratio/low specific thrust turbofan has a high thrust lapse rate (with rising flight speed). Consequently the engine must be over-sized to give sufficient thrust during climb/cruise at high flight speeds (e.g. Mach 0.83). Because of the high thrust lapse rate, the static (i.e. Mach 0) thrust is relatively high. This enables heavily laden, wide body aircraft to accelerate quickly during take-off and consequently lift-off within a reasonable runway length.

The turbofans on twin engined airliners are further over-sized to cope with losing one engine during take-off, which reduces the aircraft's net thrust by 50%. Modern twin engined airliners normally climb very steeply immediately after take-off. If one engine is lost, the climb-out is much shallower, but sufficient to clear obstacles in the flightpath.

The Soviet Union's engine technology was less advanced than the West's and its first wide-body aircraft, the Ilyushin Il-86

Ilyushin Il-86

The Ilyushin Il-86 is a medium-range wide-body jet airliner. It was the USSR's first wide-body and the world's second four-engined wide-body...

, was powered by low-bypass engines. The Yakovlev Yak-42

Yakovlev Yak-42

The Yakovlev Yak-42 is a 100/120-seat three-engined mid-range passenger jet. It was designed as a replacement for several obsolete Aeroflot jets as a mid-range passenger jet...

, a medium-range, rear-engined aircraft seating up to 120 passengers introduced in 1980 was the first Soviet aircraft to use high-bypass engines.

Turbofan configurations

Turbofan engines come in a variety of engine configurations. For a given engine cycle (i.e. same airflow, bypass ratio, fan pressure ratio, overall pressure ratio and HP turbine rotor inlet temperature), the choice of turbofan configuration has little impact upon the design point performance (e.g. net thrust, SFC), as long as overall component performance is maintained. Off-design performance and stability is, however, affected by engine configuration.

As the design overall pressure ratio of an engine cycle increases, it becomes more difficult to throttle the compression system, without encountering an instability known as compressor surge. This occurs when some of the compressor aerofoils stall (like the wings of an aircraft) causing a violent change in the direction of the airflow. However, compressor stall can be avoided, at throttled conditions, by progressively:

1) opening interstage/intercompressor blow-off valves (inefficient)

and/or

2) closing variable stators within the compressor

Most modern American civil turbofans employ a relatively high pressure ratio High Pressure (HP) Compressor, with many rows of variable stators to control surge margin at part-throttle. In the three-spool RB211

Rolls-Royce RB211

/Trent

Rolls-Royce Trent

the core compression system is split into two, with the IP compressor, which supercharges the HP compressor, being on a different coaxial shaft and driven by a separate (IP) turbine. As the HP Compressor has a modest pressure ratio it can be throttled-back surge-free, without employing variable geometry. However, because a shallow IP compressor working line is inevitable, the IPC has one stage of variable geometry on all variants except the -535, which has none.

Single shaft turbofan

Although far from common, the Single Shaft Turbofan is probably the simplest configuration, comprising a fan and high pressure compressor driven by a single turbine unit, all on the same shaft. The SNECMA M53

SNECMA M53

-External links:* *...

, which powers Mirage fighter aircraft, is an example of a Single Shaft Turbofan. Despite the simplicity of the turbomachinery configuration, the M53 requires a variable area mixer to facilitate part-throttle operation.

Aft-fan turbofan

One of the earliest turbofans was a derivative of the General Electric J79 turbojet, known as the CJ805-23

General Electric CJ805

|-See also:-External links:* * *...

, which featured an integrated aft fan/low pressure (LP) turbine unit located in the turbojet exhaust jetpipe. Hot gas from the turbojet turbine exhaust expanded through the LP turbine, the fan blades being a radial extension of the turbine blades. This aft-fan configuration was later exploited in the General Electric GE-36

General Electric GE-36

-External links:* * , Flight International, June 12, 2007....

UDF (propfan) Demonstrator of the early 80's. One of the problems with the aft fan configuration is hot gas leakage from the LP turbine to the fan.

Basic two spool

Many turbofans have the Basic Two Spool configuration where both the fan and LP turbine (i.e. LP spool) are mounted on a second (LP) shaft, running concentrically with the HP spool (i.e. HP compressor driven by HP turbine). The BR710

Rolls-Royce BR700

-External links:* * *...

is typical of this configuration. At the smaller thrust sizes, instead of all-axial blading, the HP compressor configuration may be axial-centrifugal (e.g. General Electric CFE738), double-centrifugal or even diagonal/centrifugal (e.g. Pratt & Whitney Canada PW600

Pratt & Whitney Canada PW600

-External links:*...

Boosted two spool

Higher overall pressure ratios can be achieved by either raising the HP compressor pressure ratio or adding an Intermediate Pressure (IP) Compressor between the fan and HP compressor, to supercharge or boost the latter unit helping to raise the overall pressure ratio

Overall pressure ratio

In aeronautical engineering, the term overall pressure ratio is defined as the ratio of the stagnation pressure as measured at the front and rear of the compressor of a gas turbine engine...

of the engine cycle to the very high levels employed today (i.e. greater than 40:1, typically). All of the large American turbofans (e.g. General Electric CF6

General Electric CF6

, GE90 and GEnx plus Pratt & Whitney JT9D

Pratt & Whitney JT9D

-Bibliography:* Gunston, Bill. World Encyclopedia of Aero Engines. Cambridge, England. Patrick Stephens Limited, 1989. ISBN 1-85260-163-9-External links:*...

and PW4000

Pratt & Whitney PW4000

|-See also:-External links:* * *...

) feature an IP compressor mounted on the LP shaft and driven, like the fan, by the LP turbine, the mechanical speed of which is dictated by the tip speed and diameter of the fan. The Rolls Royce BR715 is a non american example of this. The high bypass ratios (i.e. fan duct flow/core flow) used in modern civil turbofans tends to reduce the relative diameter of the attached IP compressor, causing its mean tip speed to decrease. Consequently more IPC stages are required to develop the necessary IPC pressure rise.

Three spool

Rolls-Royce chose a three spool configuration for their large civil turbofans (i.e. the RB211

Rolls-Royce RB211

and Trent

Rolls-Royce Trent

families), where the Intermediate Pressure (IP) compressor is mounted on a separate (IP) shaft, running concentrically with the LP and HP shafts, and is driven by a separate IP turbine.

Ivchenko Design Bureau chose the same configuration for their Lotarev D-36 engine, followed by Lotarev/Progress D-18T and Progress D-436

Progress D-436

|-See also:-Bibliography:* Ivchenko-Progress D-436 , Aero-engines - Turbofan.Jane's. http://www.janes.com/articles/Janes-Aero-Engines/Ivchenko-Progress-D-436-Ukraine.html. Retrieved Aug 12 2009....

.

The Turbo-Union RB199

Turbo-Union RB199

|-See also:-External links:*...

military turbofan also has a three spool configuration, as does the Russian military Kuznetsov NK-321.

Geared fan

As bypass ratio increases, the mean radius ratio of the fan and LP turbine increases. Consequently, if the fan is to rotate at its optimum blade speed the LP turbine blading will spin slowly, so additional LPT stages will be required, to extract sufficient energy to drive the fan. Introducing a (planetary) reduction gearbox

Epicyclic gearing

Epicyclic gearing or planetary gearing is a gear system consisting of one or more outer gears, or planet gears, revolving about a central, or sun gear. Typically, the planet gears are mounted on a movable arm or carrier which itself may rotate relative to the sun gear...

, with a suitable gear ratio, between the LP shaft and the fan enables both the fan and LP turbine to operate at their optimum speeds. Typical of this configuration are the long-established Honeywell TFE731

Honeywell TFE731

|-See also:-External links:*...

, the Honeywell ALF 502

Honeywell ALF 502

|-See also:-References:Bibliography-External links:* *...

/507, and the recent Pratt & Whitney PW1000G

Pratt & Whitney PW1000G

|-See also:-External links:* * * * * * * *...

Military turbofans

Most of the configurations discussed above are used in civil turbofans, while modern military turbofans (e.g. SNECMA M88

SNECMA M88

|-See also:-External links:* * Snecma M88's pdf* *...

) are usually Basic Two Spool.

High Pressure Turbine

Most civil turbofans use a high efficiency, 2-stage HP turbine to drive the HP compressor. The CFM56 uses an alternative approach: a single stage, high-work unit. While this approach is probably less efficient, there are savings on cooling air, weight and cost. In the RB211

Rolls-Royce RB211

and Trent

Rolls-Royce Trent

series, Rolls-Royce split the two stages into two discrete units; one on the HP shaft driving the HP compressor; the other on the IP shaft driving the IP (Intermediate Pressure) Compressor. Modern military turbofans tend to use single stage HP turbines.

Low Pressure Turbine

Modern civil turbofans have multi-stage LP turbines (e.g. 3, 4, 5, 6, 7). The number of stages required depends on the engine cycle bypass ratio and how much supercharging (i.e. IP compression) is on the LP shaft, behind the fan. A geared fan may reduce the number of required LPT stages in some applications. Because of the much lower bypass ratios employed, military turbofans only require one or two LP turbine stages.

Cycle improvements

Consider a mixed turbofan with a fixed bypass ratio and airflow. Increasing the overall pressure ratio of the compression system raises the combustor entry temperature. Therefore, at a fixed fuel flow there is an increase in (HP) turbine rotor inlet temperature. Although the higher temperature rise across the compression system implies a larger temperature drop over the turbine system, the mixed nozzle temperature is unaffected, because the same amount of heat is being added to the system. There is, however, a rise in nozzle pressure, because overall pressure ratio increases faster than the turbine expansion ratio, causing an increase in the hot mixer entry pressure. Consequently, net thrust increases, whilst specific fuel consumption (fuel flow/net thrust) decreases. A similar trend occurs with unmixed turbofans.

So turbofans can be made more fuel efficient by raising overall pressure ratio and turbine rotor inlet temperature in unison. However, better turbine materials and/or improved vane/blade cooling are required to cope with increases in both turbine rotor inlet temperature and compressor delivery temperature. Increasing the latter may require better compressor materials.

Overall pressure ratio can be increased by improving fan (or) LP compressor pressure ratio and/or HP compressor pressure ratio. If the latter is held constant, the increase in (HP) compressor delivery temperature (from raising overall pressure ratio) implies an increase in HP mechanical speed. However, stressing considerations might limit this parameter, implying, despite an increase in overall pressure ratio, a reduction in HP compressor pressure ratio.

According to simple theory, if the ratio turbine rotor inlet temperature/(HP) compressor delivery temperature is maintained, the HP turbine throat area can be retained. However, this assumes that cycle improvements are obtained, whilst retaining the datum (HP) compressor exit flow function (non-dimensional flow). In practise, changes to the non-dimensional speed of the (HP) compressor and cooling bleed extraction would probably make this assumption invalid, making some adjustment to HP turbine throat area unavoidable. This means the HP turbine nozzle guide vanes would have to be different from the original! In all probability, the downstream LP turbine nozzle guide vanes would have to be changed anyway.

Thrust growth

Thrust growth is obtained by increasing core power

Core power

Core power is a parameter used in aeroengine performance engineering to enable a comparison of the power capabilities of jet engine cores....

. There are two basic routes available:

a) hot route: increase HP turbine rotor inlet temperature

b) cold route: increase core mass flow

Both routes require an increase in the combustor fuel flow and, therefore, the heat energy added to the core stream.

The hot route may require changes in turbine blade/vane materials and/or better blade/vane cooling. The cold route can be obtained by one of the following:

adding T-stage
T-stage
T-stages are the small compressor stages, featured on some turbofan engines, that are mounted on the low pressure shaft directly behind the fan....

s to the LP/IP compression
adding a zero-stage
Zero-stage
Jet engines are often uprated by adding a zero-stage to the front of a compressor. At a given core size, adding a stage to the front of the compressor not only increases the cycle overall pressure ratio, but increases the core mass flow....

to the HP compression
improving the compression process, without adding stages (e.g. higher fan hub pressure ratio)

all of which increase both overall pressure ratio and core airflow.

Alternatively, the core size

Core size

Core size is a parameter used in aeroengine performance engineering to enable a size comparison between jet engine cores.The alternative core power parameter is more difficult to compute, but has the advantage that it takes into account not only the basic flow size of the device, but also the...

can be increased, to raise core airflow, without changing overall pressure ratio. This route is expensive, since a new (upflowed) turbine system (and possibly a larger IP compressor) is also required.

Changes must also be made to the fan to absorb the extra core power. On a civil engine, jet noise considerations mean that any significant increase in Take-off thrust must be accompanied by a corresponding increase in fan mass flow (to maintain a T/O specific thrust of about 30 lbf/lb/s), usually by increasing fan diameter. On military engines, the fan pressure ratio would probably be increased to improve specific thrust, jet noise not normally being an important factor.

Technical discussion

Specific Thrust (net thrust/intake airflow) is an important parameter for turbofans and jet engines in general. Imagine a fan (driven by an appropriately sized electric motor) operating within a pipe, which is connected to a propelling nozzle. It is fairly obvious, the higher the Fan Pressure Ratio (fan discharge pressure/fan inlet pressure), the higher the jet velocity and the corresponding specific thrust. Now imagine we replace this set-up with an equivalent turbofan - same airflow and same fan pressure ratio. Obviously, the core of the turbofan must produce sufficient power to drive the fan via the Low Pressure (LP) Turbine. If we choose a low (HP) Turbine Inlet Temperature for the gas generator, the core airflow needs to be relatively high to compensate. The corresponding bypass ratio is therefore relatively low. If we raise the Turbine Inlet Temperature, the core airflow can be smaller, thus increasing bypass ratio. Raising turbine inlet temperature tends to increase thermal efficiency and, therefore, improve fuel efficiency.
Naturally, as altitude increases there is a decrease in air density and, therefore, the net thrust of an engine. There is also a flight speed effect, termed Thrust Lapse Rate. Consider the approximate equation for net thrust again:

With a high specific thrust (e.g. fighter) engine, the jet velocity is relatively high, so intuitively one can see that increases in flight velocity have less of an impact upon net thrust than a medium specific thrust (e.g. trainer) engine, where the jet velocity is lower. The impact of thrust lapse rate upon a low specific thrust (e.g. civil) engine is even more severe. At high flight speeds, high specific thrust engines can pick-up net thrust through the ram rise in the intake, but this effect tends to diminish at supersonic speeds because of shock wave losses.
Thrust growth on civil turbofans is usually obtained by increasing fan airflow, thus preventing the jet noise becoming too high. However, the larger fan airflow requires more power from the core. This can be achieved by raising the Overall Pressure Ratio (combustor inlet pressure/intake delivery pressure) to induce more airflow into the core and by increasing turbine inlet temperature. Together, these parameters tend to increase core thermal efficiency and improve fuel efficiency.
Some high bypass ratio civil turbofans use an extremely low area ratio (less than 1.01), convergent-divergent, nozzle on the bypass (or mixed exhaust) stream, to control the fan working line. The nozzle acts as if it has variable geometry. At low flight speeds the nozzle is unchoked (less than a Mach Number of unity), so the exhaust gas speeds up as it approaches the throat and then slows down slightly as it reaches the divergent section. Consequently, the nozzle exit area controls the fan match and, being larger than the throat, pulls the fan working line slightly away from surge. At higher flight speeds, the ram rise in the intake increases nozzle pressure ratio to the point where the throat becomes choked (M=1.0). Under these circumstances, the throat area dictates the fan match and, being smaller than the exit, pushes the fan working line slightly towards surge. This is not a problem, since fan surge margin is much better at high flight speeds.
The off-design behaviour of turbofans is illustrated under compressor map
Compressor map
Each compressor in a gas turbine engine has an operating map. Complete maps are either based on compressor rig test results or are predicted by a special computer program...

and turbine map
Turbine map
Each turbine in a gas turbine engine has an operating map. Complete maps are either based on turbine rig test results or are predicted by a special computer program. Alternatively, the map of a similar turbine can be suitably scaled.-Description:...

.
Because modern civil turbofans operate at low specific thrust, they only require a single fan stage to develop the required fan pressure ratio. The desired overall pressure ratio for the engine cycle is usually achieved by multiple axial stages on the core compression. Rolls-Royce tend to split the core compression into two with an intermediate pressure (IP) supercharging the HP compressor, both units being driven by turbines with a single stage, mounted on separate shafts. Consequently, the HP compressor need only develop a modest pressure ratio (e.g.~4.5:1). US civil engines use much higher HP compressor pressure ratios (e.g. ~23:1 on the General Electric GE90
General Electric GE90
General Electric GE90 is a family of high-bypass turbofan aircraft engines built by GE Aviation for the Boeing 777, with thrust ratings ranging from 74,000 to 115,000 lbf . It was first introduced in November 1995 on British Airways' 777s, and is available only on the 777...

) and tend to be driven by a two stage HP turbine. Even so, there are usually a few IP axial stages mounted on the LP shaft, behind the fan, to further supercharge the core compression system. Civil engines have multi-stage LP turbines, the number of stages being determined by the bypass ratio, the amount of IP compression on the LP shaft and the LP turbine blade speed.
Because military engines usually have to be able to fly very fast at Sea Level, the limit on HP compressor delivery temperature is reached at a fairly modest design overall pressure ratio, compared with that of a civil engine. Also the fan pressure ratio is relatively high, to achieve a medium to high specific thrust. Consequently, modern military turbofans usually only have 5 or 6 HP compressor stages and only require a single stage HP turbine. Low bypass ratio military turbofans usually have one LP turbine stage, but higher bypass ratio engines need two stages. In theory, by adding IP compressor stages, a modern military turbofan HP compressor could be used in a civil turbofan derivative, but the core would tend to be too small for high thrust applications.

Recent developments in blade technology

The turbine

Turbine

blades in a turbofan engine are subject to high heat and stress, and require special fabrication. New material construction methods and material science have allowed blades, which were originally polycrystalline

Polycrystalline

Polycrystalline materials are solids that are composed of many crystallites of varying size and orientation. The variation in direction can be random or directed, possibly due to growth and processing conditions. Fiber texture is an example of the latter.Almost all common metals, and many ceramics...

(regular metal), to be made from lined up metallic crystals and more recently mono-crystalline (i.e. single crystal) blades, which can operate at higher temperatures with less distortion.

Nickel-based superalloys are used for HP turbine blades in almost all modern jet engines. The temperature capabilities of turbine blades have increased mainly through four approaches: the manufacturing (casting) process, cooling path design, thermal barrier coating (TBC), and alloy

Alloy

An alloy is a mixture or metallic solid solution composed of two or more elements. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may or may not be homogeneous in distribution, depending on thermal history...

development.

Although turbine blade (and vane) materials have improved over the years, much of the increase in (HP) turbine inlet temperatures is due to improvements in blade/vane cooling technology. Relatively cool air is bled from the compression system, bypassing the combustion process, and enters the hollow blade or vane. After picking up heat from the blade/vane, the cooling air is dumped into the main gas stream. If the local gas temperatures are low enough, downstream blades/vanes are uncooled and not adversely affected.

Strictly speaking, cycle-wise the HP Turbine Rotor Inlet Temperature (after the temperature drop across the HPT stator) is more important than the (HP) turbine inlet temperature. Although some modern military and civil engines have peak RITs of the order of 1560 °C (2,840 °F), such temperatures are only experienced for a short time (during take-off) on civil engines.

Turbofan engine manufacturers

The turbofan engine market is dominated by General Electric, Rolls-Royce plc

Rolls-Royce plc

and Pratt & Whitney

Pratt & Whitney

Pratt & Whitney is a U.S.-based aerospace manufacturer with global service operations. It is a subsidiary of United Technologies Corporation . Pratt & Whitney's aircraft engines are widely used in both civil aviation and military aviation. Its headquarters are in East Hartford, Connecticut, USA...

, in order of market share. GE and SNECMA

Snecma

Snecma is a major French manufacturer of engines for commercial and military aircraft, and for space vehicles. The name is an acronym for Société Nationale d'Étude et de Construction de Moteurs d'Aviation .In 2005, the Snecma group, which included Snecma ,...

of France have a joint venture, CFM International

CFM International

CFM International is a joint venture between GE Aviation, a division of General Electric of the United States and Snecma, a division of Safran of France...

which, as the 3rd largest manufacturer in terms of market share, fits between Rolls-Royce and Pratt & Whitney. Rolls-Royce and Pratt & Whitney also have a joint venture, International Aero Engines

International Aero Engines

IAE International Aero Engines AG is a Zürich-registered joint venture manufacturing company formed in 1983.- Ownership :Current shareholders are:* Pratt & Whitney of the United States * MTU Aero Engines of Germany...

, specializing in engines for the Airbus A320

Airbus A320 family

The Airbus A320 family is a family of short- to medium-range, narrow-body, commercial passenger jet airliners manufactured by Airbus Industrie.Airbus was originally a consortium of European aerospace companies, and is now fully owned by EADS. Airbus's name has been Airbus SAS since 2001...

family, whilst finally, Pratt & Whitney and General Electric have a joint venture, Engine Alliance

Engine Alliance

The Engine Alliance is a 50/50 joint venture between General Electric and Pratt & Whitney formed in August 1996 to develop, manufacture, sell, and support a family of modern technology aircraft engines for new high-capacity, long-range aircraft.The main application for such an engine, the GP7200,...

marketing a range of engines for aircraft such as the Airbus A380

Airbus A380

The Airbus A380 is a double-deck, wide-body, four-engine jet airliner manufactured by the European corporation Airbus, a subsidiary of EADS. It is the largest passenger airliner in the world. Due to its size, many airports had to modify and improve facilities to accommodate it...

General Electric

GE Aviation, part of the General Electric

General Electric

General Electric Company , or GE, is an American multinational conglomerate corporation incorporated in Schenectady, New York and headquartered in Fairfield, Connecticut, United States...

Conglomerate, currently has the largest share of the turbofan engine market. Some of their engine models include the CF6 (available on the Boeing 767

Boeing 767

The Boeing 767 is a mid-size, wide-body twin-engine jet airliner built by Boeing Commercial Airplanes. It was the manufacturer's first wide-body twinjet and its first airliner with a two-crew glass cockpit. The aircraft features two turbofan engines, a supercritical wing, and a conventional tail...

, Boeing 747

Boeing 747

The Boeing 747 is a wide-body commercial airliner and cargo transport, often referred to by its original nickname, Jumbo Jet, or Queen of the Skies. It is among the world's most recognizable aircraft, and was the first wide-body ever produced...

, Airbus A330

Airbus A330

The Airbus A330 is a wide-body twin-engine jet airliner made by Airbus, a division of EADS. Versions of the A330 have a range of and can accommodate up to 335 passengers in a two-class layout or carry of cargo....

and more), GE90 (only the Boeing 777

Boeing 777

The Boeing 777 is a long-range, wide-body twin-engine jet airliner manufactured by Boeing Commercial Airplanes. It is the world's largest twinjet and is commonly referred to as the "Triple Seven". The aircraft has seating for over 300 passengers and has a range from , depending on model...

) and GEnx

General Electric GEnx

The General Electric GEnx is an advanced dual rotor, axial flow, high-bypass turbofan jet engine in production by GE Aviation for the Boeing 787 and 747-8...

(developed for the Boeing 747-8

Boeing 747-8

The Boeing 747-8 is a wide-body jet airliner developed by Boeing Commercial Airplanes. Officially announced in 2005, the 747-8 is the fourth-generation Boeing 747 version, with lengthened fuselage, redesigned wings and improved efficiency...

& Boeing 787 Dreamliner and proposed for the Airbus A350

Airbus A350

The Airbus A350 is a family of long-range, wide-body jet airliners under development by European aircraft manufacturer Airbus.A consortium originally comprising European aerospace companies from the UK, France, Spain and West Germany, Airbus is now fully owned by EADS and since 2001 has been known...

, currently in development) engines. On the military side, GE engines power many U.S. military aircraft, including the F110

General Electric F110

-External links:* - The F110 Engine Family* - F110-GE-100 Gallery* - F110* - General Electric F110...

, powering 80% of the US Air Force's F-16 Fighting Falcon

F-16 Fighting Falcon

The General Dynamics F-16 Fighting Falcon is a multirole jet fighter aircraft originally developed by General Dynamics for the United States Air Force . Designed as an air superiority day fighter, it evolved into a successful all-weather multirole aircraft. Over 4,400 aircraft have been built since...

s, and the F404 and F414

General Electric F414

The General Electric F414 is an afterburning turbofan engine in the 22,000 lbf thrust class produced by GE Aviation. The F414 was developed from GE's widely-used F404 turbofan for use in the Boeing F/A-18E/F Super Hornet.-Origin:...

engines, which power the Navy's F/A-18 Hornet

F/A-18 Hornet

The McDonnell Douglas F/A-18 Hornet is a supersonic, all-weather carrier-capable multirole fighter jet, designed to dogfight and attack ground targets . Designed by McDonnell Douglas and Northrop, the F/A-18 was derived from the latter's YF-17 in the 1970s for use by the United States Navy and...

and Super Hornet

F/A-18E/F Super Hornet

The Boeing F/A-18E/F Super Hornet is a twin-engine carrier-based multirole fighter aircraft. The F/A-18E single-seat variant and F/A-18F tandem-seat variant are larger and more advanced derivatives of the F/A-18C and D Hornet. The Super Hornet has an internal 20 mm gun and can carry air-to-air...

. Rolls-Royce and General Electric are jointly developing the F136

General Electric/Rolls-Royce F136

The General Electric/Rolls-Royce F136 is an advanced turbofan engine being developed by General Electric and Rolls-Royce plc for the Lockheed Martin F-35 Lightning II.-Development:...

engine to power the Joint Strike Fighter.

CFM International

CFM International is a joint venture between GE Aviation, a division of General Electric of the United States and Snecma, a division of Safran of France...

is a joint venture between GE Aircraft Engines and SNECMA

Snecma

of France.
They have created the very successful CFM56

CFM International CFM56

series, used on Boeing 737

Boeing 737

The Boeing 737 is a short- to medium-range, twin-engine narrow-body jet airliner. Originally developed as a shorter, lower-cost twin-engine airliner derived from Boeing's 707 and 727, the 737 has developed into a family of nine passenger models with a capacity of 85 to 215 passengers...

, Airbus A340

Airbus A340

The Airbus A340 is a long-range four-engine wide-body commercial passenger jet airliner. Developed by Airbus Industrie,A consortium of European aerospace companies, Airbus is now fully owned by EADS and since 2001 has been known as Airbus SAS. a consortium of European aerospace companies, which is...

, and Airbus A320 family

Airbus A320 family

aircraft.

Rolls-Royce

Rolls-Royce plc

is the second largest manufacturer of turbofans and is most noted for their RB211

Rolls-Royce RB211

and Trent

Rolls-Royce Trent

series, as well as their joint venture engines for the Airbus A320

Airbus A320 family

and McDonnell Douglas MD-90

McDonnell Douglas MD-90

The McDonnell Douglas MD-90 is a twin-engine, short- to medium-range, single-aisle commercial jet aircraft. The MD-90 was developed from the MD-80 series. Differences from the MD-80 include more fuel efficient International Aero Engines V2500 engines and a longer fuselage...

families (IAE V2500

International Aero Engines V2500

The IAE V2500 is a two-shaft high-bypass turbofan engine which powers the Airbus A320 family , and the McDonnell Douglas MD-90. International Aero Engines is a consortium backed by four aero-engine manufacturers, formed in 1983 to produce the engine...

with Pratt & Whitney and others), the Panavia Tornado

Panavia Tornado

The Panavia Tornado is a family of twin-engine, variable-sweep wing combat aircraft, which was jointly developed and manufactured by the United Kingdom, West Germany and Italy...

(Turbo-Union RB199

Turbo-Union RB199

|-See also:-External links:*...

) and the Boeing 717

Boeing 717

The Boeing 717 is a twin-engine, single-aisle jet airliner, developed for the 100-seat market. The airliner was designed and marketed by McDonnell Douglas as the MD-95, a third-generation derivative of the DC-9. Capable of seating of up to 117 passengers, the 717 has maximum range of...

(BR700

Rolls-Royce BR700

-External links:* * *...

). The Rolls-Royce AE 3007 was developed by Allison Engine Company

Allison Engine Company

The Allison Engine Company was a U.S. aircraft engine manufacturer. In 1929, shortly after the death of James Allison, the company was purchased by the Fisher brothers. Fisher sold the company to General Motors, who owned it for most of its history...

before its acquisition by Rolls-Royce, powers several Embraer

Embraer

Embraer S.A. is a Brazilian aerospace conglomerate that produces commercial, military, and executive aircraft and provides aeronautical services....

regional jets. Rolls-Royce Trent 970s were the first engines to power the new Airbus A380. The famous thrust vectoring

Thrust vectoring

Thrust vectoring, also thrust vector control or TVC, is the ability of an aircraft, rocket or other vehicle to manipulate the direction of the thrust from its engine or motor in order to control the attitude or angular velocity of the vehicle....

Pegasus

Rolls-Royce Pegasus

The Rolls-Royce Pegasus is a turbofan engine originally designed by Bristol Siddeley, and now manufactured by Rolls-Royce plc. This engine is able to direct thrust downwards which can then be swivelled to power a jet aircraft forward. Lightly loaded, it can also manoeuvre like a helicopter,...

engine is the primary powerplant of the Harrier "Jump Jet" and its derivatives.

Pratt & Whitney

is third behind GE and Rolls-Royce in market share. The JT9D

Pratt & Whitney JT9D

-Bibliography:* Gunston, Bill. World Encyclopedia of Aero Engines. Cambridge, England. Patrick Stephens Limited, 1989. ISBN 1-85260-163-9-External links:*...

has the distinction of being chosen by Boeing

Boeing

The Boeing Company is an American multinational aerospace and defense corporation, founded in 1916 by William E. Boeing in Seattle, Washington. Boeing has expanded over the years, merging with McDonnell Douglas in 1997. Boeing Corporate headquarters has been in Chicago, Illinois since 2001...

to power the original Boeing 747

Boeing 747

"Jumbo jet". The PW4000

Pratt & Whitney PW4000

|-See also:-External links:* * *...

series is the successor to the JT9D, and powers some Airbus A310

Airbus A310

The Airbus A310 is a medium- to long-range twin-engine widebody jet airliner. Launched in July 1978, it was the second aircraft created by Airbus Industrie,a consortium of European aerospace companies, Airbus is now fully owned by EADS and since 2001 has been known as Airbus SAS. the consortium of...

, Airbus A300

Airbus A300

The Airbus A300 is a short- to medium-range widebody jet airliner. Launched in 1972 as the world's first twin-engined widebody, it was the first product of Airbus Industrie, a consortium of European aerospace companies, wholly owned today by EADS...

, Boeing 747, Boeing 767, Boeing 777, Airbus A330 and MD-11

McDonnell Douglas MD-11

The McDonnell Douglas MD-11 is a three-engine medium- to long-range widebody jet airliner, manufactured by McDonnell Douglas and, later, by Boeing Commercial Airplanes. Based on the DC-10, it features a stretched fuselage, increased wingspan with winglets, refined airfoils on the wing and smaller...

aircraft. The PW4000 is certified for 180-minute ETOPS when used in twinjets. The first family has a 94 inches (2.4 m) fan diameter and is designed to power the Boeing 767, Boeing 747, MD-11, and the Airbus A300. The second family is the 100 inch (2.5 m) fan engine developed specifically for the Airbus A330 twinjet, and the third family has a diameter of 112 inches (2.8 m) designed to power Boeing 777. The Pratt & Whitney F119 and its derivative, the F135, power the United States Air Force's F-22 Raptor

F-22 Raptor

The Lockheed Martin/Boeing F-22 Raptor is a single-seat, twin-engine fifth-generation supermaneuverable fighter aircraft that uses stealth technology. It was designed primarily as an air superiority fighter, but has additional capabilities that include ground attack, electronic warfare, and signals...

and the international F-35 Lightning II

F-35 Lightning II

The Lockheed Martin F-35 Lightning II is a family of single-seat, single-engine, fifth generation multirole fighters under development to perform ground attack, reconnaissance, and air defense missions with stealth capability...

, respectively. Rolls-Royce are responsible for the lift fan which will provide the F-35B variants with a STOVL

STOVL

STOVL is an acronym for short take off and vertical landing.This is the ability of some aircraft to take off from a short runway or take off vertically if it does not have a very heavy payload and land vertically...

capability. The F100

Pratt & Whitney F100

-External links:* * *...

engine was first used on the F-15 Eagle

F-15 Eagle

The McDonnell Douglas F-15 Eagle is a twin-engine, all-weather tactical fighter designed by McDonnell Douglas to gain and maintain air superiority in aerial combat. It is considered among the most successful modern fighters with over 100 aerial combat victories with no losses in dogfights...

and F-16 Fighting Falcon

F-16 Fighting Falcon

. Newer Eagles and Falcons also come with GE F110 as an option, and the two are in competition.

Aviadvigatel

Aviadvigatel OJSC is a developer and builder of aero-engines for Ilyushin Il-76MF, Ilyushin Il-96, Tupolev Tu-204, Tupolev Tu-214, and other aircraft...

(Russian:Авиационный Двиѓатель) is a Russian manufacturer of aircraft engine

Aircraft engine

An aircraft engine is the component of the propulsion system for an aircraft that generates mechanical power. Aircraft engines are almost always either lightweight piston engines or gas turbines...

s that succeeded the Soviet Soloviev Design Bureau. The company currently offers several versions of the Aviadvigatel PS-90

Aviadvigatel PS-90

|-See also:-External links:**...

engine that powers Ilyushin Il-96

Ilyushin Il-96

The Ilyushin Il-96 is a four-engined long-haul widebody airliner designed by Ilyushin in the Soviet Union and manufactured by the Voronezh Aircraft Production Association in Voronezh, Russia...

-300/400/400T, Tupolev Tu-204

Tupolev Tu-204

The Tupolev Tu-204 is a twin-engined medium-range jet airliner capable of carrying 210 passengers, designed by Tupolev and produced by Aviastar SP and Kazan Aircraft Production Association. First introduced in 1989, it is considered to be broadly equivalent to the Boeing 757 and has competitive...

, Tu-214 series and the Ilyushin Il-76

Ilyushin Il-76

The Ilyushin Il-76 is a multi-purpose four-engined strategic airlifter designed by Ilyushin design bureau. It was first planned as a commercial freighter in 1967. Intended as a replacement for the Antonov An-12, the Il-76 was designed for delivering heavy machinery to remote, poorly-serviced areas...

-MD-90. The company is also developing the new Aviadvigatel PD-14

Aviadvigatel PD-14

The PD-14 is a next generation turbofan engine being developed by Aviadvigatel to become one of the alternative power plants for the MS-21 twin-jet passenger aircraft. The PD-14 was announced in early 2010 with its development cost estimated at RUR 35 billion...

engine for the new Russian MS-21 airliner.

Ivchenko-Progress

Ivchenko-Progress is the Ukrainian aircraft engine company that succeeded the Soviet Ivchenko Design Bureau. Some of their engine models include Progress D-436

Progress D-436

|-See also:-Bibliography:* Ivchenko-Progress D-436 , Aero-engines - Turbofan.Jane's. http://www.janes.com/articles/Janes-Aero-Engines/Ivchenko-Progress-D-436-Ukraine.html. Retrieved Aug 12 2009....

available on the Antonov An-72/74

Antonov An-72

The Antonov An-72 is a transport aircraft developed by Antonov in the former Soviet Union. It was designed as a STOL transport and intended as a replacement for the Antonov An-26, but variants have found success as commercial freighters.The An-72 gets its nickname, Cheburashka, from the large...

, Yakovlev Yak-42

Yakovlev Yak-42

The Yakovlev Yak-42 is a 100/120-seat three-engined mid-range passenger jet. It was designed as a replacement for several obsolete Aeroflot jets as a mid-range passenger jet...

, Beriev Be-200

Beriev Be-200

The Beriev Be-200 Altair is a multipurpose amphibious aircraft designed by the Beriev Aircraft Company and manufactured by Irkut. Marketed as being designed for fire fighting, search and rescue, maritime patrol, cargo, and passenger transportation, it has a capacity of 12 tonnes of water, or up...

, Antonov An-148

Antonov An-148

The Antonov An-148 Antonov Design Bureau from Kiev, Ukraine, is a regional jet aircraft designed by the Ukrainian Antonov Design Bureau and produced by Ukraine's Kiev Aviation Plant AVIANT and Russia's Voronezh Aircraft Production Association. Development of the plane was started in the 1990s,...

and Tupolev Tu-334

Tupolev Tu-334

-See also:-References:* Gordon, Yefim; Rigamant, Vladimir . OKB Tupolev: A History of the Design Bureau and its Aircraft. Hinckley, England: Midland Publishing. ISBN 1-85780-214-4....

and Progress D-18T

Ivchenko-Progress D-18

|-See also:-External links:*...

that powers two of the world largest airplanes, Antonov An-124

Antonov An-124

The Antonov An-124 Ruslan is a strategic airlift jet aircraft. It was designed by the Ukrainian SSR's Antonov design bureau, then part of the Soviet Union. It is the world's largest ever serially-manufactured cargo airplane and world's second largest operating cargo aircraft...

and Antonov An-225

Antonov An-225

The Antonov An-225 Mriya is a strategic airlift cargo aircraft, designed by the Antonov Design Bureau in the 1980s. It is the world's heaviest aircraft. The design, built in order to transport the Buran orbiter, was an enlargement of the successful An-124 Ruslan...

Extreme bypass jet engines

In the 1970s Rolls-Royce/SNECMA tested a M45SD-02 turbofan fitted with variable pitch fan blades to improve handling at ultra low fan pressure ratios and to provide thrust reverse down to zero aircraft speed. The engine was aimed at ultra quiet STOL

STOL

STOL is an acronym for short take-off and landing, a term used to describe aircraft with very short runway requirements.-Definitions:There is no one accepted definition of STOL and many different definitions have been used by different authorities and nations at various times and for a myriad of...

aircraft operating from city centre airports.

In a bid for increased efficiency with speed, a development of the turbofan and turboprop known as a propfan

Propfan

A propfan was first defined as a small diameter, highly loaded multiple bladed variable pitch propulsor having swept blades with thin advanced airfoil sections, integrated with a nacelle contoured to retard the airflow through the blades thereby reducing compressibility losses and designed to...

engine was created that had an unducted fan. The fan blades are situated outside of the duct, so that it appears like a turboprop with wide scimitar-like blades. Both General Electric and Pratt & Whitney/Allison demonstrated propfan engines in the 1980s. Excessive cabin noise and relatively cheap jet fuel prevented the engines being put into service.

Terminology

Afterburner

AfterBurner

: extra combustor immediately upstream of final nozzle (also called reheat)
Average stage loading: constant * (delta temperature)/[(blade speed) * (blade speed) * (number of stages)]
Bypass: airstream that completely bypasses the core compression system, combustor and turbine system
Bypass ratio

Bypass ratio

The term bypass ratio relates to the design of turbofan engines, commonly used in aviation. It is defined as the ratio between the mass flow rate of air drawn in by the fan bypassing the engine core to the mass flow rate passing through the engine core....

: bypass airflow /core compression inlet airflow
Core: turbomachinery handling the airstream that passes through the combustor.
Core power

Core power

Core power is a parameter used in aeroengine performance engineering to enable a comparison of the power capabilities of jet engine cores....

: residual shaft power from ideal turbine expansion to ambient pressure after deducting core compression power
Core thermal efficiency: core power/power equivalent of fuel flow
Dry: afterburner (if fitted) not lit
EGT: Exhaust Gas Temperature
EPR: Engine Pressure Ratio
Fan: turbofan LP compressor
Fan pressure ratio: fan outlet total pressure/intake delivery total pressure
Flex temp

Flex temp

Flex temp is a technique used to reduce engine wear in large airliners by performing take-off at less than full power.For Airbus and Fokker aircraft the technique is known as flex temp or just flex...

: use of artificially high apparent air temperature to reduce engine wear
Gas generator: engine core
HPC: high pressure compressor
HP compressor: high pressure compressor
HPT: high pressure turbine
HP turbine: high pressure turbine
Intake ram drag: penalty associated with jet engines picking up air from the atmosphere (conventional rocket motors do not have this drag term, because the oxidiser travels with the vehicle)
IEPR: Integrated Engine Pressure Ratio
IPC: intermediate pressure compressor
IP compressor: intermediate pressure compressor
IPT: intermediate pressure turbine
IP turbine: intermediate pressure turbine
LPC: low pressure compressor
LP compressor: low pressure compressor
LPT: low pressure turbine
LP turbine: low pressure turbine
Net thrust: nozzle total gross thrust - intake ram drag (excluding nacelle drag, etc., this is the basic thrust acting on the airframe)
Overall pressure ratio: combustor inlet total pressure/intake delivery total pressure
Overall thermal efficiency: thermal efficiency * propulsive efficiency
Propulsive efficiency

Propulsive efficiency

In aircraft and rocket design, overall propulsive efficiency \eta is the efficiency, in percent, with which the energy contained in a vehicle's propellant is converted into useful energy, to replace losses due to air drag, gravity, and acceleration. It can also be stated as the proportion of the...

: propulsive power/rate of production of propulsive kinetic energy (maximum propulsive efficiency occurs when jet velocity equals flight velocity, which implies zero net thrust!)
SFC: Specific fuel consumption
Specific fuel consumption: total fuel flow/net thrust (proportional to flight velocity/overall thermal efficiency)
Static pressure: normal meaning of pressure. Excludes any kinetic energy effects
Specific thrust

Specific thrust

Specific thrust is a term used in gas turbine engineering to show the relative bulk of a jet engine and is defined as the ratio: net thrust/total intake airflow.-Low specific thrust engines:...

: net thrust/intake airflow
Thermal efficiency

Thermal efficiency

In thermodynamics, the thermal efficiency is a dimensionless performance measure of a device that uses thermal energy, such as an internal combustion engine, a boiler, a furnace, or a refrigerator for example.-Overview:...

: rate of production of propulsive kinetic energy/fuel power
Total fuel flow: combustor (plus any afterburner) fuel flow rate (e.g. lb/s or g/s)
Total pressure: static pressure plus kinetic energy term
Turbine rotor inlet temperature: gas absolute mean temperature at principal (e.g. HP) turbine rotor entry

External links

Wikibooks: Jet

propulsion

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