EN TR

Article

EJ200: Unbeatable Reliability

With the current programme to develop an advanced multirole fighter for the Turkish Air Force, the TF-X, Turkey has the opportunity to power this new 4.5 generation combat aircraft with an engine that is setting a new benchmark for combat performance and reliability: the EJ200. 

The EJ200 engine’s development arose from the requirement for a new propulsion system to power the multi-national Eurofighter Typhoon. The engine had to be capable of higher thrust, longer life and less complexity than prior engines. To bring this propulsion system to life, EUROJET was formed, a consortium of four major European engine companies - Rolls-Royce (UK), MTU (Germany), ITP (Spain) and Avio Aero (Italy).

Incorporating much of the advanced research carried out by Rolls-Royce on the XG-40 Advanced Core Military Engine (ACME) demonstrator, EUROJET unveiled the EJ200, a light-weight engine with high thrust and utilising state-of-the-art technology.  Over a thousand EJ200 engines have since been delivered, with a significant volume still in production. Notably the engine achieved the 500,000 Flying Hours milestone earlier this year. 

The EJ200 is the most modern combat engine in its class – with the best thrust-to-weight ratio, thrust retention and smallest fan diameter – the EJ200 sets new standards for reliability and adaptability. Engines powering the Typhoons of the UK Royal Air Force (RAF) routinely achieve a mean time between repairs of over 1,000 flying hours, while the fleet leader in the RAF has achieved over 1,700 flying hours on-wing without need for repair. This is unprecedented in combat engines where on-wing hours can often be measured in the low hundreds for previous generation engines. In recent combat sorties for the RAF, the EJ200 accumulated over 6,000 engine flying hours without a single engine rejection. The performance of the engine was so impeccable that Air Marshal Simon Bollom, Air Member for Materiel and Chief of Materiel, remarked on its performance: “We only took one spare engine, and were confident that would be enough,” citing the designs “inherent reliability.” Put simply, the engine delivered consistent, reliable performance, an outstanding availability rate, when it most mattered.

So what is it that makes the EJ200 capable of delivering this unparalleled level of performance? 

In layman terms, the EJ200, a low bypass ratio turbofan, consists of an eight-stage compression system, a single turbine each in the high-pressure and low-pressure turbine stages and thrust augmentation systems. 

Low Pressure Compressor

The EJ200 consists of a three-stage low-pressure compressor (LPC) module and a five-stage high-pressure compressor. This provides a high surge margin (pilot feedback often states it is virtually impossible to surge the engine), needs no heating devices to combat ice and has a high bird strike resistance. Each stage of the LPC is equipped with wide-chord integrated blade/disk (blisk) assemblies that are low in weight (each stage in the LPC consists of a single blisk with no removable parts) and are a major factor in the reduction of complexity easing the burden on maintenance cost and personnel. At the end of the Low Pressure Compression module, core air is compressed by a factor of 4.2.

High Pressure Compressor

Air is then directed to the High Pressure Compressor (HPC), which is again designed achieve high reliability and minimum maintenance effort.

Like the LPC, the HPC is equipped with single blisks in the first three stages. The HPC further compresses core air by a factor of 6.2, leading to air that has been compressed by a factor of 26. The fact that EJ200 achieves this in eight stages, far lesser than the nine or ten stages employed by engines of comparable performance, is testament to the efficient aerodynamic design of the blades. 

Annular Combustion Chamber

The EJ200s annular combustor receives the highly compressed air. Microspraying fuel increases combustion-efficiency and also reduces the visible emissions of oxides of nitrogen. The key factors in determining jet engine efficiency and achievable work are the temperature and pressure differences attained between the engine inlet and combustor outlet. Although the maximum temperature of air leaving the combustion chamber is classified, the outlet stator temperature is generally reported to be 200ºC higher than previous generation engines. 

Turbine Stage

Downstream of the annular combustion chamber is the High Pressure Turbine (HPT). In order to handle the large temperatures generated in the combustion chamber, the HPT uses air-cooled single-crystal blades. The HPT guide vanes utilise a special Thermal Barrier Coating which increases the life of the blade and increases the achievable operating temperature .Following the HPT is a single Low Pressure Turbine stage, again employing single crystal blades. 

Reheat Systems

EUROJET has installed an innovative three-stage thrust augmentation system to supply reheat as and when required by the pilot. Downstream from the low-pressure turbine, in the exhaust duct, are the first two stages of the thrust augmenter. The first stage consists of a radial series of burners and their associated flame cups. Subsequent to this is a stage of ‘primary vaporisers’ that spray fine mists of fuel that combust on contact with the hot exhaust air. Finally, the third stage comprises of fuel injectors located at the back of the bypass duct. These spray fuel into the cold, oxygen rich air that has passed through the duct unburned. It should be noted the dry performance of the engine is so good, pilots do not use reheat as much as other engines in this class. Operationally, this means more performance for less fuel.

DECMU (Digital Engine Control and Monitoring Unit)

EJ200’s Digital Engine Control and Monitoring Unit (DECMU) provides carefree handling for the whole turbo-machinery, automatically activates and controls the various stages of reheat, reduces pilot workload and provides engine monitoring and executive lifing functionalities. Executive Lifing measures actual usage rather than planned mission profiles which can achieve up to 50% Life Cycle Cost savings compared to other engines without this advantage. This is key not only to achieving the unparalleled standards of reliability but also in making the engine cost effective over its performance life. Executive Lifing reduces maintenance costs, especially given that the EJ200 maintenance philosophy is a modular concept.

Performance

From the perspective of the airframer, the design of the EJ200 provides a number of advantages. The engine is compact, approximately 4 metres in length, 800mm (30 inches) in diameter and weighs around 1,000 kg. It is similar in diameter to the previous generation RB199 that powers the Panavia Tornado, yet offers 50% more thrust and manufacturing simplicity (the RB199 has the 2845 parts to the EJ200’s 1800, primarily due to the use of single piece blisks and simpler engine architecture). The EJ200 generates 60kN of dry thrust and an incredible 90kN of thrust at full reheat, offering a 9.175-to-1 power-to-weight ratio with full afterburner. This means that a twin-engine aircraft generates 180kN of thrust at full reheat, giving it the ability to hit Mach 2 at higher altitudes. Even at dry thrust, the two EJ200s pack enough power to permit the aircraft to comfortably supercruise without the need to employ reheat. Specific fuel consumption figures vary from 49 g/kNs using full reheat to a mere 21 -23 g/kNs at dry thrust. 

Also of particular significance is the low bypass ratio achieved by the EJ200. The bypass ratio is a measure of cold air flowing around the compressor and turbine stages of the engine rather than through it. Most military turbofans have a bypass ratio of 0.1 to 1, while that of the EJ200 is 0.4 to 1. This affords good subsonic performance and efficiency, while at the same time has high dry thrust that offers very good supersonic qualities and a sophisticated reheat system. The increased bypass flow provides a substantial secondary flow of air that can be employed to generate additional reheat thrust. The EJ200 is also equipped with a ‘war’ setting, which generates additional dry and reheats thrust. 

The EJ200 also effectively handles ‘thrust droop’ losses. Thrust droop is caused by gaps opening up between the tips of the turbine blades and the turbine casing at lower engine temperatures after cold start. The problem is rectified only after the engine has been running hot for a while and the gaps have been closed by expansion of rotors and casings. EUROJET has eradicated this by adopting a passive tip-clearance model using a specific selection of materials that expand and contract at different rates or different temperatures, minimising any gap that may arise between the blades and the turbine casing. All of these performance advantages will significantly complement and enhance the TFX aircraft capability. 

Wing Commander Mark Flewin, Commanding 1(F) Squadron of the RAF, describes the EJ200 quite succinctly: “It is pure performance.”

The EJ200 for T-FX

EUROJET is offering the EJ200 to Turkey for the T-FX project with the belief that the both the Turkish Air Force and Turkish industry will gain increased levels of capability and also reap further benefits as part of an overall package that is much more far reaching. The expertise of the four partner companies behind EUROJET and the EJ200 can assist Turkey to increase its level of technology knowledge in the most effective way possible utilising partnership principles and shared benefits. Rolls-Royce, in particular, has already a strong footprint in Turkey.

The EJ200 is an attractive option to several aircraft in development and naturally Turkey’s T-FX project, as it offers full capability for maximum growth and can be adapted to the particular requirements of the Turkish Air Force. Since the first production model was delivered in 2001, the EJ200 has consistently outperformed specifications and therefore has been subject to only a few upgrades and remains relatively unchanged. Despite this, EUROJET has conducted studies on an improved version, the EJ2x0, which would offer 20% dry thrust growth to 72kN and 103kN reheat capability. An even more powerful variant has also been considered. 

In addition to potential for growth and adaptability to suit a new aircraft, the partnership values that form the background to the entire EJ200 project provide the perfect basis to strengthen and establish mutually beneficial relationships. As part of these partnership principles, EUROJET fully supports a technology collaboration concept which would enhance and extend Turkey’s technological capability.

The EJ200 is in every way ideal for the T-FX project and a strong contender in the programme. Perhaps it is also the best kept secret in military propulsion – because ground-breaking reliability and performance seldom make the news.