ACARE 2020

The Advisory Council for Aeronautical Research in Europe (ACARE) is composed of 39 members, including representatives of the EU member states, EUROCONTROL, the European Commission, and stakeholders in the European aerospace industry. In its Strategic Research Agenda, published in 2002, ACARE set out the goals it hopes to see achieved by 2020: aircraft should consume 50 % less fuel, emit 50 % less CO2 and 80 % less NOX, and their perceived noise level should be reduced by half. For engine manufacturers this means that engines for the next generation of aircraft must cut fuel consumption by about 10%, and their successors must then reach a target of 20 % by 2020.

Afterburner

Military jet engines, in particular those designed for supersonic fighter aircraft, are equipped with an afterburner located downstream of the turbine. The afterburner can make almost double the amount of thrust available for takeoff, ascent or supersonic flight.

Bauhaus Luftfahrt

Bauhaus Luftfahrt focuses on the future of aviation. Based in Garching near Munich, this think-tank performs visionary basic research and project work. It was founded in November 2005 by EADS, Liebherr-Aerospace and MTU Aero Engines together with the Free State of Bavaria.

Claire

Clean Air Engine (Claire) is a technology program jointly developed by MTU and Bauhaus Luftfahrt which aims to drastically reduce the carbon dioxide output of aircraft engines while at the same time substantially cutting noise levels. The goal is to achieve a 30-percent reduction in CO2 emissions by 2035. All key components of the Claire program have already been tested or demonstrated proof of principle, and fulfill all expectations concerning energy efficiency and economic viability.

Combustor

A combustor or combustion chamber consists of an outer casing and a flame tube or ‘can’ in which the actual combustion takes place. Inside, the compressed air flowing into the chamber is mixed with fuel, which is then ignited and burns at a temperature of over 2000 degrees Celsius. Due to the high temperatures involved, combustors require special thermal barrier coatings.

Compressor

The task of the compressor is to ingest air and compress it before it is fed into the combustor. Compressors consist of bladed disks (rotors) that rotate at very high speed between stationary guide vanes (stators). In order to achieve a compression ratio of over 40:1, which is standard in all modern two-shaft engines, it is necessary to use multi-stage low-pressure and high-pressure compressors rotating at different speeds on dual concentric shafts. These are driven by the corresponding turbines.

Crisp

Crisp (Counter Rotating Integrated Shrouded Propfan) was a technology program set up by MTU in the mid-1980s together with the German Aerospace Center (DLR) and several other institutes. This engine concept, which was proven feasible at the time, was based on a counter-rotating fan with adjustable blades. It would have saved a considerable amount of fuel, especially on long-haul flights, but was not carried through to production maturity due to the low fuel prices of that period. The Crisp concept is now being revived and integrated into the second stage of the Claire technology program.

DECMU

DECMU stands for Digital Engine Control and Monitoring Unit and is a full-authority engine subsystem. There are normally two separate units for engine control and monitoring, but DECMU integrates both functions in a single unit.

Fan

The extremely large first rotor of the low-pressure compressor is called the fan. It accelerates the bypass stream flowing aftward and provides the engine’s main thrust. It is driven by the low-pressure turbine via the low-pressure shaft.

Geared turbofan

Geared turbofan engines consume far less fuel and generate significantly less noise than today’s engine types. They therefore have every chance of becoming the standard type for use in future short- and medium-haul aircraft. Normally, an engine’s fan, low-pressure compressor and low-pressure turbine are all rigidly connected to one shaft. In contrast, the geared fan is ‘decoupled’ from the low-pressure section by means of a reduction gear unit. This enables the low-pressure turbine and the low-pressure compressor to run at their optimum high speeds, while the fan rotates at a much lower speed (in a ratio of approx. 3:1). This results in significantly improved overall engine efficiency and greatly reduced noise levels.

Heat exchanger

A heat exchanger consists of a series of connected tubes with one fluid medium flowing inside the tubes – air in the case of aircraft engines – and a second fluid medium at a different temperature flowing along the outside of the tubes, causing energy to be transferred from the hotter medium to the cooler one. Future engines might possibly use such heat exchangers to recycle the residual energy contained in the exhaust gas stream, feeding it back into the compressed air upstream of the combustor. This would significantly increase the engine’s efficiency. This method is already being used in gas turbines, particularly in power generation plants.

Industrial gas turbines

The operating principle of an industrial gas turbine is essentially the same as that of an aero engine. However, instead of the customary low-pressure turbine used in aircraft, industrial gas turbines have a so-called power turbine. This turbine delivers the necessary power, either directly or via a gear unit, to an additional attached power unit such as a pump or generator. Nearly all industrial gas turbines of the lower and intermediate power classes are aero-engine derivatives.

Intermediate-pressure turbine

In addition to the usual high-pressure and low-pressure turbines, three-shaft engines have a third, intermediatepressure turbine which drives the intermediate-pressure compressor.

MRO business

MRO stands for maintenance, repair and overhaul. At MTU, the term “MRO business” is also used more specifically to designate one of the company’s two business segments, where it refers to maintenance services for commercial engines, or commercial MRO.

NEWAC

The EU recently launched a new technology program called NEWAC (New Aero Engine Core Concepts) under the leadership of MTU. The aim is to design a new core engine for use in future aircraft engines. Specific development tasks have been allocated to each of the main partners in the program, who include the major European engine manu facturers. MTU, for its part, is testing new ways of actively controlling a high-pressure compressor in flight.

NGPF

NGPF stands for Next Generation Product Family and designates the new generation of aircraft with one central aisle. It includes the successors to the Airbus A320 family and the Boeing 737.

OEM business

In the aviation industry, OEM stands for original engine manufacturer. At MTU, the term “OEM business” is used to designate one of the company’s two business segments, where it refers to the development, manufacture and assembly of (new) commercial and military engines. Spare parts for (in-service) commercial and military engines and maintenance services for military engines are also included in this business segment.

Propfan, counter-rotating

Unlike single-stage propfans, the counter-rotating propfan has two fan stages that rotate in opposite directions. This makes it much more efficient than its single-stage counterpart. The Crisp technology demonstrator developed by MTU in the 1980s already featured this counter-rotating design.

Risk- and revenue-sharing partnership

In a risk- and revenue-sharing partnership, each partner contributes a certain share of the resources needed for a specific engine program (work capacity and funding), thus carrying part of the risk. In return, each partner is entitled to a corresponding percentage of the overall sales revenue from that program.

Subsystem

A complete aircraft engine is made up of a number of subsystems. These include the high-pressure and low-pressure compressors, the combustor, the high-pressure and low-pressure turbines and the engine control system.

Thrust class

Jet engines are generally grouped into three thrust classes: engines with a thrust of between 2,500 and around 20,000 pounds, engines with a thrust of between 20,000 and approximately 50,000 pounds, and engines with a thrust ranging from 50,000 to more than 100,000 pounds. Although the official unit of force used to measure thrust is the kilonewton (kN), the English unit “pound” is still widely used in this context by the international engineering community. The abbreviation for ‘pound’ when used as a unit of force is lbf.

Turbine

In a turbine, the energy contained in the gases emerging at high pressure and velocity from the combustor is converted into mechanical energy. Like the compressor, the turbine is subdivided into a high-pressure and a low-pressure section, each of which is directly connected to the corresponding compressor via the respective shaft. The turbine has to withstand much higher stresses than the compressor, as it has to deal not only with the high gas temperatures but also with the extreme centrifugal forces of several tons acting on the outer rim of its disks.

Turbine center frame

The turbine center frame connects the high-pressure turbine to the low-pressure turbine. It has to be able to withstand the high mechanical and thermal loads. The center frame includes struts to support the shaft bearings, clad with an aerodynamic fairing, and the necessary air and oil supply lines.

Turbofan engine

The turbofan is a decisive advancement of the turbojet principle, the main difference being its enlarged first compressor stage, known as the fan. While in turbojet engines, all of the ingested air flows consecutively through the compressor, the combustor and the turbine, turbofans separate the air stream behind the fan. A fraction of the air reaches the combustor via a number of further compressor stages and is burned. The rest, however – which constitutes a much larger fraction – is channeled around the inner components. The ratio between these two airflows is known as the bypass ratio. In modern commercial engines, this ratio can be as high as 10:1. The greater the bypass ratio, the more economical, environmentally compatible and silent the engine. Turbofans are far more fuel-efficient than turbojets.

Turbojet engine

All first-generation engines work according to the turbojet principle: Air is ingested into the compressor, where it is compressed by the blades. Subsequently, it is channeled into the combustor, where fuel is injected and the mixture is burnt. The hot gases expand explosively and stream into the turbine at high velocity. The turbine consists of several turbine rotors with a multitude of blades that are forced to turn by the exhaust gas stream. The turbine drives the compressor via a shaft, and the combustion gases leave the jet nozzle. Because of their low efficiency and the large amount of noise they generate, turbojet engines are no longer produced today.

Turboprop engine

The most noticeable external feature of a turboprop is its propeller. Inside, however, the engine differs only slightly from the turbojet and the turbofan. The turbine is larger, and drives not only the compressor but also the propeller, the latter via a gear unit to reduce the speed of rotation. Consequently, more energy has to be drawn from the ex-haust gas stream in the turbine of a turboprop than in that of other engine types. Over 90 percent of the energy is required for the compressor and the propeller. Turboprop airplanes can only achieve flight speeds of up to 800 km/h and are thus slower than turbojets or turbofans, but they do have the advantage of consuming far less fuel. This predestines them for use in roles where speed is less important, such as on short-haul routes or for air freight.

Turboshaft engine

Turboshaft engines are used in helicopters and are similar to turboprops but, because the drive shaft cannot be connected in a straight line to the rotor, it is connected instead to a transmission system (gearbox), which converts the energy from the exhaust stream into the rotational motion of the rotor.