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# The Rolls-Royce Trent Engine

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The Rolls-Royce Trent Engine
Michael Cervenka Technical Assistant to Director - Engineering & Technology 5 October 2000

Rolls-Royce Today World No 2 in aero-engines
World leader in marine propulsion systems Developing energy business Annual sales of over £4.5 billion Orders of over £13 billion Rolls-Royce is one of three major aero engine companies in the world, operating with a global presence. It uses its core gas turbine technology to serve the civil aerospace, defence, energy and marine sectors and currently has firm and announced orders of approximately £14 billion.

Thrust = Mass x Velocity (MV)
Newton’s 3rd Law Equilibrium Reaction Action MV Thrust = Mass x Velocity (MV) The jet engine relies on Newton’s 3rd Law, where every action has an equal and opposite reaction. An example of this is the balloon shown above. Here, gas is initially stationary inside the balloon. It is then accelerated through the the back, pushing the balloon forward. The thrust produced is equal to the mass exhausted through the back of the balloon, multiplied by the velocity, relative to the balloon.

Propeller versus Jet Propulsion
Propeller - moves LARGE MASS of air at low velocity Mvjet Mvaircraft Thrust = M(vaircraft - vjet) Thrust = m(Vaircraft - Vjet) Jet - moves small mass of gas at HIGH VELOCITY Aircraft propeller and jet engines do not store their own supply of air like the balloon. Instead, they have a steady supply of air entering the front. The thrust is achieved by accelerating this gas, so that it leaves the rear faster than it arrives at the front. The amount of thrust achieved is equal to the mass of air multiplied by the change in velocity. A propeller engine moves a large mass of air at low speed: thrust = M(vaircraft - vjet), whilst a gas turbine moves a smaller mass of air at a greater speed: thrust = m(Vaircraft - Vjet). mVjet mVaircraft

Jet Engine Layout Compressor Combustion Chamber Exhaust Nozzle
mVaircraft mVjet Shaft Turbine So how is this achieved? A jet engine mechanically compresses the air it receives through a self driven compressor, prior to the combustion stage. The expanding exhaust gases drive a turbine which drives the compressor through the shaft. These are then accelerated through the exhaust nozzle to produce thrust.

Different Jet Engine Types
Civil turbofan - Trent Military turbofan - EJ200 Modern aircraft have moved away from the turbojet, as it is too niosy and not very efficient. Modern civil and military aircraft use a variation on the turbojet, called the turbofan, or bypass engine. A large fan at the front of the engine feeds some air into the compressor, where it is conventionally combusted, whilst the rest is ducted around the outside of the engine and re-mixed with the exhaust gases at exit. The combined lower velocity and greater mass of the jet stream provides a net thrust of high propulsive efficiency (less Specific Fuel Consumption or SFC per unit thrust). The shroud of slow bypass air exhausted around the high velocity engine core exhaust also reduces the noise level. Related to the turbofan is something called the bypass ratio. This is the ratio of the mass of air going down the bypass stream divided by the mass going through the engine core. The principal difference between modern civil and military engines is this bypass ratio. On an air superiority aircraft, such as the Eurofighter, the engine (an EJ200) has a bypass ratio of only 0.3. Hence, the mass flow bypassing the engine is equal to 30% of the mass flow passing through the core. By comparison, bypass ratios on large modern civil engines can be as high as 9, with the fan providing over 80% of the total thrust.

Different Jet Engine Types - Mechanical drive
Turboprop - AE 2100 Turboshaft - RTM322 We saw earlier how the gas turbine could be used to provide mechanical power to drive a propeller, a form which is called the turbo-prop. The example shown here is the AE2100 engine which powers the Hercules transport aircraft. The propeller acts rather like the fan on a turbofan engine, except that the effective bypass ratio is even higher with the exhaust gases providing only a small amount of residual thrust. As with the turbofan, this is achieved by enlarging the turbine, so that more power can be extracted from the exhausting gasses, in order to drive the propeller. On modern engines, the extra turbine stages are often mounted on a separate shaft. This is a concept called a free power turbine (i.e. the turbine providing the power output can rotate at its own speed). The rest of the engine then becomes a gas generator. Its sole purpose is to provide exhaust gases at the correct condition to drive the power turbine. The gas generator and free power turbine could theoretically be mounted as separate units, connected by a large pipe, although for practical reasons, it is more convenient to mount the power turbine directly behind the gas generator. This concept of using an additional turbine to extract mechanical power can be applied to other uses, and is central to Rolls-Royce’s objective of serving the civil aerospace, defence, marine and energy markets. On the top right of the picture is a turboshaft engine (in this case a schematic of the RTM322 which powers the EH101 and Apache helicopters). Below are two other applications of turboshaft engines. On the left is the Marine Trent engine, which will be used to power the Fast Ship. Five engines, each producing 40MW or over 50,000 hp will be used to propel a large catamaran cargo ship across the Atlantic at 40 knots. On the right is the Industrial Trent, providing 50MW, which can be used for power generation and oil and gas pumping. Some of the differences in designs stem from the relative importance of weight and efficiency, as well as differing emissions regulations. This will be covered in more detail later on. Marine Trent Industrial Trent

Piston Engine versus Turboprop
Air intake Compression Combustion Exhaust Intermittent Continuous Piston engine Jet engine driven propeller (Turboprop) Here we can see how the working cycle of a turboprop engine actually compares to that of a piston engine driven propeller. The inlet receives gas similar to the inlet valve on a cylinder head. The compressor increases the pressure of the gas, similar to the compression stroke of a cylinder. The combustion chamber (mixes and) ignites the gas, causing it to expand, similar to the spark induced combustion of a cylinder. The exhaust allows the expanded gas to escape, similar to the exhaust valve on a cylinder head. The gas turbine extracts energy from the exhaust gas to drive the turbine and consequently, the compressor and propeller. The simple expression ‘Suck, Squeeze, Bang and Blow’ is the best way to remember the working cycle of the gas turbine. The big difference between the 2 types of engine is that a gas turbine employs a continuous cycle, not a 4 stroke cycle, where 3 of the strokes are not actually providing power to the vehicle. This means that more fuel can be burnt in less time, creating more power for a given engine size.

Pressure and Temperature
40 Pressure (atmospheres) 1500 All these engine stages work due to the relationship between pressure, volume and temperature. The product of the pressure and volume of a gas is proportional to the temperature of that gas. The efficiency of the engine is governed by the maximum pressure and temperature achieved in the centre of the core. Advances in technology have given rise to significant increases. Improvements in compressor aerodynamics enable greater rises to be achieved with fewer components. Combustion and Turbine components now operate in environments significantly in excess of their melting temperatures, requiring extensive cooling. Improvements in materials and cooling technologies have helped to fuel the improvements in efficiency and reduction in weight. Temperature (degrees C)

Axial Compressor and Turbine Operation

Axial Compressor and Turbine Operation
Compressor Stages Turbine Stages Rotating Rotor Row Rotating Rotor Row Rotating Rotor Row Rotating Rotor Row Gas flow Airflow The compressors and turbines that we have seen so far are called axial turbines, because the flow is lined up with the axis of the engine. They are made up of a series of rotating and stationary blade rows. A pair of rows (one rotating and one stationary) make up a stage. In the case of a compressor, a rotating blade row uses the shaft power transmitted from the turbine to accelerates the flow onto stationary vanes. The vanes then convert this kinetic energy of the moving gas into pressure energy. A turbine works like a compressor in reverse. In this case, the pressure energy in the gas is converted into kinetic or motion energy in a stationary vane row. This is directed onto a rotating row of blades (in this case moving down the page), which absorb the energy to drive the compressor. Improvements in aerodynamics have enabled huge increases to the levels of work we can supply or extract using a single compressor or turbine stage. This has helped improve engine power, weight and cost. Stationary Vane Row Stationary Vane Row Stationary Nozzle Row Stationary Nozzle Row

Multiple Shafts - Trent 95,000 lbs Thrust
LP System 1 Fan stage 5 Turbine stages >3,000 rpm IP System 8 Compressor stages 1 Turbine stage >7,500 rpm HP System 6 Compressor stages 1 Turbine stage >10,000 rpm These compressor and turbine stages are mounted in series (one behind the other) on a shaft. Most modern engines use multiple shafts to better match the requirements of the different parts of the engine. The Rolls-Royce RB211 and Trent Engines are unique in having three shafts, as shown here. In this case, only the rotating blade rows are shown, but you can see how many stages there are. The fan needs to rotate relatively slowly, due to stress limits and blade tip speed requirements. If it rotated too fast, the centrifugal loads would tear it apart and the flow at the blade tip would be highly supersonic, causing shock formations leading to significant efficiency penalties and noise. Because the fan generates so much of the thrust, a large number of turbine stages are required to power it (in this case 5). In fact, this is due to the fact that the fan is compressing a huge mass of air, whereas the turbine only has the engine core air to power it. However, you can see that it is generally much easier to extract work from a turbine than it is to supply it through a compressor, as only single turbine stages are required to power the HP and IP compressors. As the air going through the engine core is compressed, the blade height and radius reduces. In order to maintain a reasonable blade velocity with the reducing radius, the shaft rotational speed needs to increase. Thus, using three shafts ensures that each compressor and turbine stage can run closer to its ideal operating condition. This means that the engine is lighter, shorter and stronger. Also, each shaft can be scaled independently, making it simpler to build a range of engine sizes based around common technology.

Combustor Operation

Combustor Operation Primary zone Dilution zone Intermediate zone
Fuel spray nozzle

Reverse Thrust Net 25% to 30% thrust 85% thrust 15% thrust

New Product Introduction Process
Stage 1: Preliminary Concept Definition Preliminary concept defined for planning purposes Product definition stages Stage 2: Full Concept Definition Full concept defined, product launched Stage 3: Product Realisation Product developed, verified and approved Stage 4: Production Product produced and delivered to customer Capability Acquisition The product introduction process is a five stage process,the first three stages of which address product development.These stages can absorb large amounts of time, resource and non-recurring cost, so it is important that the process operates as efficiently as possible to minimise the cost to the business. It is also where many of the downstream costs are committed by virtue of the decisions made during design .Therefore good management of an efficient process will also provide the opportunity to optimise the product more effectively, to meet customer expectations product costs time to market . Each stage divides into a series of distinct activities with well defined deliverables. Progression onto the next stage is only achieved when these deliverable have been met. During Preliminary Concept Definition, one or more concepts that potentially satisfy a market opportunity or requirement are evaluated to determine the preferred solution. Functional, physical, schedule and cost targets are established and the business is able to define the capability to be acquired, either internally or externally through its supply chain. The next stage of Product Definition is Full Concept Definition, which is commenced when the market timing is correct and the necessary capabilities have been acquired. In this stage the preliminary concept is evolved into a complete conceptual definition and specification against clearly defined Customer and Business requirements. The Marketing, Manufacturing, Procurement and Customer Support functions operate concurrently with the Engineering function in Integrated Product teams, involving suppliers and partners as appropriate. The product specification that is developed defines functional and physical whole system, sub-system and component requirements, including production and maintainability requirements and costs. The Product Realisation stage is the most expensive and time consuming part of product definition. During this stage the finished conceptual definition is fully designed and verified to deliver a set of instructions for manufacture and support. It is also necessary to demonstrate that the product meets both the design intent and specification. Therefore, this stage comprises three distinct activities, design definition, design verification and formal approval. Stage 5: Customer Support Product used by customer

New Project Planning Process
BUSINESS MODEL Units sold Unit Cost Selling Price Concessions Sales Costs Development Costs Guarantee Payments Spares Turn Spares Price MARKETING MODEL Market Size Selling Price Concessions Operating Costs Payload Range Maintenance Costs Fuel Burn Commonality ENGINEERING MODEL Safety Unit Cost Weight Noise Emissions Geometry Reliability Operability Performance

102 Million Hours of Service
RB211 & Trent operating hours August 2000 -22B million hours million hours million hours Trent million hours 4260 engines ordered engines delivered customers currently flying with RB211 or Trent engines Million hours 100 Trent 800 90 Trent 700 80 70 60 50 -535C 40 -524D -535E4 30 -524 -22 20 -524H The RB211 and its successor, the Trent, have evolved over the years to become arguably the most successful family of large commercial aero engines available today. The engine exists as eight major variants in service, together with the Trent 500 under development and the Trent 900 and 600 in the early stages of preliminary design. Over 3500 engines have been delivered and have accumulated about 102 million hours of service experience with an unrivalled record of safety whilst -535 and T800 variants are market leaders in reliability. The market share of the Trent family (including options) is presently 44% (a leading position) and is expected to rise now that the Trent 500 has been selected for the A340 and the T895 has been selected by British Airways. These achievements are to the credit of the many people that have worked on the project over 37 years since work on three shaft engines started in the Preliminary Design Dept led by Geoff Wilde. However, Geoff deserves special mention for having the foresight to propose this new engine architecture to the company in 1965, 18 months after the initial studies commenced. -524G 10 1972 1974 1976 1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 Entry into service

Why 3 Shafts? Long / Medium-Haul (40,000-100,000lbs thrust):
Short / Medium-Haul (8, ,000lbs thrust): Three-Shaft Configuration Requires high: - Overall pressure ratio - Turbine entry temperature - Bypass ratio Range Fuel consumption Acquisition Cost Maintenance Simpler engine, hence moderate: - Overall pressure ratio - Turbine entry temperature - Bypass ratio Two-Shaft Configuration In order to satisfy the civil market, Rolls-Royce has developed a clearly defined strategy, focusing on the different requirements of the long and short haul sectors. For the long haul market, the required engines must develop typically over 40,000 lbs thrust and the principal drivers are range and hence fuel consumption. This necessitates an engine with high efficiency levels, demanding high overall pressure ratios, turbine entry temperatures and bypass ratios. The optimum architecture to achieve this is a three-shaft configuration with a two-shaft gas generator, with each shaft running at its optimum speed. On a two-shaft engine, several compression stages have to driven by the LP shaft at lower rotational speeds, as dictated by the fan. However, in the three-shaft design the intermediate compressor is mounted separately and can rotate faster. Fewer compressor stages are therefore required, improving efficiency and reducing cost and engine length. This increases engine stiffness and reduces weight, as well as improving modularity of the engine design. It is therefore much simpler to scale the engine for different thrust requirements, an approach exemplified by the latest generation of Trent engines. These engines provide a wide range of thrust levels, utilising common technology, carried across the product range. For the short haul market, the required engine size is smaller and fuel consumption forms a smaller part of the overall operating costs of the engine. The principal drivers are therefore acquisition and maintenance costs. This drives to more moderate levels of overall pressure ratio, turbine entry temperature and bypass ratio. The level of pressure rise demanded from the gas generator can therefore be achieved from a single shaft, running at a higher speed than the fan which, as with the three shaft design, is mounted on its own shaft. Core technologies, such as the Fan, low NOx combustion, LP turbine, materials and controls, can be directly transferred between these two architectural configurations. In addition, compressor aerodynamic and HP turbine cooling philosophies will also be transferable.

Evolution of Trent Family
Boeing 777 Airbus A3XX Airbus A330 Airbus A340 Boeing 767 Boeing 747 Fan diameter - in. 110 97.5 86.3 Trent 800 Trent 8104 Trent 900 Trent 700 Trent 500 Trent 600 RB G/H-T 60,000lb 72,000lb 95,000lb 104,000lb 56,000lb 65,000lb 80,000lb Scaled core It became apparent in the late 1980’s that a large market existed for high capacity, intercontinental transports. Approximately 50% of airline business is now in this sector. The ‘big twin’ aircraft has become a large provider in the long haul as well as the medium haul market For long range aircraft, the largest single contribution to the cost of ownership is fuel, being some 40% of the total. The need to reduce fuel burn therefore is of utmost importance in the development of large thrust civil engines. The high pressure system of the -524G and H was fortunately large enough to provide the required thrust, provided a large fan was added with a new IP compressor to supercharge the HP system and new technology was used everywhere. Hence, in 1988 the Trent family of engines was launched, with take off thrust ranging from 64,000 lbf to over 100,000 lbf. The Trent 700 (67500 to lbf) was launched to power the A330 for launch customer TWA in The Trent 800 (75000 to lbf) was launched to power the B777 for launch customer Thai Airways also in 1995 and has subsequently been uprated to 95,000 lbf. Increased thrust beyond 100,000 pounds was demonstrated on the Trent 8104 which also saw the first commercial application of swept fan blade technology. At the same fan size as the Trent 700, our current most important civil engine programme is the Trent 500, where Rolls-Royce has secured a sole engine supplier deal. With over 120 confirmed launch customers of the four-engines airframe, higher production volumes than ever before will have to be achieved over the coming years. The engine is also being considered for a potential Airbus A300 replacement. Building on Trent 500 technology, the Trent 900 is offered for the Airbus A3XX programme, while the Trent 600 is aimed at future Boeing developments for the Boeing 747x and x.

Trent 700 & 800 Fan diameter increased to 2.8m (110.3in.) Five-stage LP turbine Single crystal HPT Single Crystal Uncooled IP turbine blade Fan diameter 2.47m (97.4in.) Four-stage LP turbine Phase 5 low emissions combustor 8 Stage IPC 3 Variables Trent 700 Trent 800 Area of significant commonality Area of main geometric change Compared with the -524 the overall pressure ratio of the Trent 800 increased from 34 to 41 at top of climb, bypass ratio also increased from 4 to 6 and turbine temperature increased by over 100°C. The specific fuel consumption is 6% less and the specific weight is 9% less. The specific thrust is however still higher than the -22B by 16%. This is due to increases in power derived from the engine core. There is a significant commonality between the Trent 700 and Trent 800, a feature aided by the three shaft architecture and something that was absolutely essential to enable both engines to be concurrently developed in the late 1980s and early 1990s. One of the major enhancements made on the Trent family was the introduction of the second generation super-plastically formed diffusion bonded wide chord fan blade, something that I shall cover this in more detail later. Improvements were also made to turbine blade materials, enabling the IP turbine to remain uncooled in spite of increased temperatures. The HP turbine capacity was increased to swallow the increased core mass flow. The high pressure compressor casing mount was improved to enhance tip clearance control and increase surge margin, whilst the phase five combustor offers class leading emissions.

Trent 500 Trent 500 Trent 700 Scaled IP & HP compressor
3D Aerodynamics Scaled combustor with tiled cooling HP & IP turbines have increased blade speeds High lift LP turbine blading Trent 500 Trent 700 The A /300 entered service in 1993 powered by the 34,000 lbf CFM56 engine, 2 years ahead of the B It enjoyed early market success but was insufficient on payload range and climb performance due, to non availability of a suitable engine. Many studies were conducted on advanced turbofans to no avail. Realising the threat of the B777, Airbus decided to increase the wing size and gross weight to make the aircraft fully competitive. Thrust requirements grew to 55,000/60,000 lbf which was in the range of the existing CF6-80C2 and PW4058 engines. For a while GE, who had an exclusive position on the aircraft with the CFM56, entered into an exclusive arrangement to study a new engine. However, this agreement expired in November 1996 with no agreement having been reached, leaving RR and P&W to compete for the contract. We responded very quickly with the Trent 500 in strong competition with P&W (with a derivative of the PW4058) and by mid 1997 we were selected as the sole engine supplier for the aircraft on a risk and revenue sharing basis. Our acceptance was conditional on launch aid - as was BAe’s ability to fund its share of the program. By the end of 1997 we had received firm orders for 78 aircraft from 7 airlines, surpassing the original order for the RB211 back in The order book now stands at 124 aircraft, 558 engines and 9 customers. The engine is based on the Trent 700 fan system, but with scaled Trent 800 compressors and a more advanced HP/IP turbine design. The intershaft bearing has also been reversed, so that the outer race runs at LP speed and the inner race at IP speed, to minimise hoop stresses.

Material Strength Specific Strength Temperature Titanium Alloy
Nickel Alloy Steel Aluminium Alloy Temperature

Engine Materials Titanium Nickel Steel Aluminium Composites
Engine material usage has changed significantly over the latter part of the last century. Titanium and Nickel now dominate. The increased temperature limits of advanced Titanium alloys has enabled its use in significant parts of the HP compressor, giving rise to current engine usage by weight of over 30%. Considerable effort has also been directed at Nickel alloy development, with its very high temperature capabilities making it the most suitable material for all the hot end engine components. Nickel usage in engine by weight now exceeds 40%. Steel is still used for shafts and bearing structures, due principally to its ductility. Aluminium and composites form a relatively small part of the engine’s weight, generally due to poor temperature limits. Future advances may see the use of metal matrix composites in compressors discs to significantly reduce weight, whilst in the longer term, ceramic matrix composites in turbines have the potential to withstand even higher temperatures.

Fan Blade Technology + 4% efficiency Clappered Wide-chord fan
Having broadly covered the RB211 and Trent engine family development programmes, I am now going to explore in more detail some of the specific technologies that have being applied to our latest generation of engines. One of the most significant advances made by Rolls-Royce was the introduction of the hollow, wide chord fan blade on the -535E4 in And subsequently on the -524 and the V2500. Previous fan blades of solid titanium construction were restricted in chord by a limit on blade weight, necessary to enable successful containment in the event of failure. These relatively narrow blades were aeroelastically unstable, requiring a snubber or damper to prevent flutter, thereby reducing blade efficiency and capacity. The introduction of the hollow blade reduced the weight and increased the stiffness, whilst removal of the snubber also helped to reduce engine noise. + 4% efficiency

Wide-chord Fan Technology
Honeycomb construction 1st generation: 1984 2nd generation: 1995 DB/SPF construction Following the introduction of the first generation hollow blade, with an internal titanium honeycomb structure, the Trent engine family now incorporates a second generation fan blade manufactured using the diffusion bonded, super-plastically formed process. This results in internal webs joining the two outer skins and running in a radial direction to help absorb the centrifugal stresses. The diffusion bonding of the web to the outer skins is done is a super clean environment and results in a join with similar properties to the parent material. This advanced process increases the strength of the internal stiffening structure, allowing the blade weight and manufacturing costs to be reduced. Further savings are possible in the containment structure and fan disc. Rolls-Royce is the undisputed leader on wide chord fan technology and we are working on a third generation swept blade to improve high speed efficiency, possibly coupled with lower tip speed to reduce noise. The manufacturing method will however remain essentially the same.

Fan Section

Swept Fans

Compressor Aerodynamics
The earliest versions of the RB211 had a pressure ratio of 25, compared to a pressure ratio of over 40 on the Trent 800. This increase has been made possible through improvements in materials, enabling higher gas temperatures and speeds as well as significant gains in aerodynamic understanding. In particular, the use of computational fluid dynamics to model the airflow around compressor aerofoils has enabled significant increases in the pressure rise achieved through a single stage, reducing engine length, parts count and cost. Early modelling centred on steady or time averaged calculations on a single blade row. However, we are now beginning to simulate the unsteady interactions between neighbouring blade rows, in this case on a rotor row and two adjacent stator rows.

Trent 500 Tiled Combustor Cold supporting wall Cast tile Thermal barrier coating Tiles reduce wall cooling air requirements making more air available for NOx reduction A significant cost reduction relative to conventional machined combustors is also achieved Large primary zone volume for altitude re-light Small total volume for NOx control The first combustion chamber to enter service in the RB211 was the ‘Package 1’ annular combustor, which suffered numerous life problems, suffered from poor low speed efficiency and emitted ‘white smoke’ on take off during cold days (unburnt fuel). Its durability problems were however fixed over time. The Phase 2 combustor was introduced in 1983 on the -524 and -535 with better efficiency, smoke and durability but was marginal in NOx emissions. In 1986 NOx was recognised as a problem and the regulatory authorities (ICAO) imposed a limit which was just above the that of the -524H. Consequently the Phase 2 combustor was subject to a great deal of redesign to reduce the NOx whilst giving acceptable smoke. However, this was inadequate for future engines. Thus, the Phase 5 combustor was launched as a research programme in 1988 and was rapidly developed as a low emissions combustor to enter service in the Trent 700 in 1995. It employs more and better fuel injectors, a leaner primary zone and a lower residence time to reduce NOx. In addition to the Trent engines, all new -535’s and -524’s have been fitted with the Phase 5 combustor, which meets the CAEP 2 regulation limit to be imposed in the near future. It is also the standard for the BR710, BR715 and EJ200 engine and will be fitted to the Adour 900 and is the ‘best in class’ of modern civil aero engine combustors. The Trent 500 engine will feature a further refinement to this design, called a tiled combustor. This uses cast tiles, which are bolted to a supporting wall. The tiles have a thermal barrier coating and the reduction in required cooling air enables more air to be used for mixing in the combustion process. This improves the temperature profile, further reducing NOx. Large airspray injectors for improved mixing and smoke control

Improvements in Materials
Realising an acceptable turbine blade life was a significant challenge, due to high centrifugal stress levels and surrounding gas temperatures. One of the significant contributors to achieving this goal has been the introduction of advanced casting techniques. In 1977, equiaxed cast turbine blades were introduced on the RB This manufacturing process offered much more design flexibility for the internal cooling configuration, compared to previous extruded blades. However, the resulting material structure had a large number of grain boundaries, with a random crystal orientation. In 1979, the directionally solidified cast blades were introduced on the -22B and 535E4, following development on the High Temperature Demonstrator Unit. The crystals are grown up the blade in order to align the maximum strength capability with the direction of centrifugal stress. There are significantly fewer grain boundaries and they are all close to the radial direction. The original DS blade has achieved a life of over 20,000 hours and remains in service today. Single crystal blades were first introduced on the RB in They are based on the directionally solidified casting process, but separate out a single crystal, which is then grown radially from the blade root. The resulting structure has no grain boundaries and, as with the DS casting process, the crystal is aligned with the radial centrifugal stresses. All the Trent family of engines incorporate second generation single crystal materials, and we are currently developing a third generation, to further increase the alloy’s temperature capability. Equiaxed Crystal Structure Directionally Solidified Structure Single Crystal

Turbine Cooling Cooling air Single pass Multi-pass Thermal Barrier
Alongside these advances in materials, significant improvements have been made to the cooling configurations. The early extruded and cast equiaxed blades introduced in the 1970s on the -22B and early -524s had single pass cooling configurations like the one shown. The air had a relatively short path inside the blade before being exhausted through dust holes and film cooling holes, limiting its potential to absorb heat through contact with the metal. The latest generation RB211 and Trent blades use a multi-pass configuration, where the flow passes through a long passage before being exhausted. This maximises the heat pick-up of the cooling air, enabling increases to the main stream gas temperatures and reductions in required cooling flow. These advantages combine to improve the engine efficiency. One further addition has been the use of thermal barrier coatings. These use high temperature ceramics to provide an insulating layer around the metal, reducing its surface temperatures and heat input. This correspondingly reduces the amount of heat that needs to be absorbed by the cooling flow, further enhancing the cooling efficiency. The combined effect of the improvements in materials and cooling technology has enabled the turbine inlet temperatures to be raised from 1660K on the early cast equiaxed blades to 1840K on the Trent 800. The corresponding component life has also been increased. Cooling air Single pass Multi-pass Thermal Barrier Coating

Propulsive efficiency
Performance Trends Straight jet Low bypass Medium bypass High bypass 50 40 %sfc improvement (bare engine) Propulsive efficiency 30 Cycle efficiency 20 Thermal efficiency 10 Component efficiency In drawing this talk to a close I would just like to reflect on the progress made over 50 years of gas turbine development. Since the Avon entered service in the Comet IV in 1958, specific fuel consumption has been halved, making a major contribution to aircraft economy, particularly on long range routes. In the 26 years since the RB211-22C entered service, there has been a 15% improvement with the largest contributions coming from component efficiency improvements and overall cycle benefits. On the other hand, propulsive efficiency has not changed significantly, getting lower in the RB211 and early Trents and improving again in the Trent This is because the penalties of nacelle drag and weight offset the fundamental benefits - a point that GE missed on the GE90. However, the demand for lower noise is now tending to drive the choice of specific thrust rather than TET and payload range, where installed drag and weight tend to offset the benefits of low specific thrust. As we look to the future, the opportunities open to the engine manufacturer to improve performance are reducing and the challenge will be at the airframer to look to more adventurous aircraft designs to enhance performance. Datum Avon 1958 Conway 1960 Spey 1963 -22B 1973 -524B4/D4 1981 -535E4 1983 -524G/H 1988 RB211 Trent

Electric Engine Concepts
Air for pressurisation/cabin conditioning supplied by dedicated system Generator on fan shaft provides power to airframe under both normal and emergency conditions Internal active magnetic bearings and motor/generators replace conventional bearings, oil system and gearboxes (typical all shafts) Pylon/aircraft mounted engine systems controller connected to engine via digital highway New Engine Architecture with reduced parts count, weight, advanced cooling, aerodynamics and lifing All engine accessories electrically driven A step change in engine performance is expected by the application of ‘more electric’ technologies. This type of engine would do away with the conventional lubrication system and replace it with oil-less magnetic bearings. A generator directly on the fan shaft will produce power to the airframe systems. An airframe-integrated system where all flight control actuators are electric can lead to a reduction In specific fuel consumption of as much as 15%. More weight can be saved by avoiding the need for a separate emergency generator system when using the wind-milling power of the large fan to provide power through the on-shaft generator. On this concept engine, a distributed control system can be used where local ‘black boxes’ are coupled through digital technology with pylon mounted systems away form the actual engine. Although the engine shown here is a civil variant, these type of technologies can equally be applied to military aircraft.

Compressor Weight Reduction
Conventional disk & blades Blisk - up to 30% weight saving Bling - Ti MMC - up to 70% weight saving

Metal Matrix Composites
Specific Strength Titanium Metal Matrix Composite Titanium Alloy Nickel Superalloy Temperature (degrees C)

Future Emissions Improvements
Pilot Main Double-annular combustor Pilot Main Pre-mixed double-annular combustor

Future Aircraft Configurations
Large diameter duct Gas generator Contra-rotating turbine Contra-rotating fan Flying wing The blended wing body concept is currently being studied on both sides of the Atlantic as a radical move away from the current cylindrical fuselage configuration with two or four under-wing engines. The inherent benefits of the flying wing are large due to the lower drag and increased lift of the blended fuselage. From a propulsion point of view it also allows us to consider new possibilities. The configuration shown here with the engines mounted on top of the fuselage effectively shields the ground from the engine noise source. Contra-rotating aft fan designs can then become a distinct possibility. Combining these concepts with all-electric technologies can produce an aircraft with a fuel consumption 45% lower than the current level of technology at significantly reduced operating cost. Whether the airframe manufacturers and airlines will pursue this option will depend on the future economic and political climate that influences the market rather than the technical feasibility of the concept. Blended wing aircraft may offer up to 30% reduction in fuel consumption - 40% if combined with electric engine concepts

Conclusion The three-shaft concept is now recognised as a world leader
Customer-focused competitive technology is critical to its success Success is a tribute to many generations of people The RB211 & Trent family has a long and secure future To conclude: There is no doubt that the three shaft concept is now accepted as the world leader - some 35 years after the initial work started. The future focus will be as much on reducing unit cost through fewer components and improving in service diagnostic capability, as it will be on enhancing performance and reliability. This is particularly important as we take an increased commercial responsibility for the life cycle costs of an engine through ‘power by the hour’ type agreements. I would like to pay tribute to the many generations of people, particularly the engineers, who have contributed towards the success of the 3 shaft engine. I am sure that the RB211 and Trent engines have a very long and secure future Thank you for listening.

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