Cutting edge medical technology and smart engine maintenance
Modern high-pressure turbine blades are extremely complex, high-tech components that are subjected to huge stresses at ambient temperatures that are far in excess of the melting point of the materials used.
Yet they are required to work reliably and safely for many millions of flying kilometres. The complex cooling ducts inside the blades have much in common with the human vascular system, where endoscopy was first used over 200 years ago. Matthias Dudeck, part of the team that won the German Aviation Innovation Competition in the category “Cross Innovation” explains how pioneering work has been done to adapt this medical technology for the purpose of engine maintenance.
Reliable operation under adverse conditions
The turbine blades of a modern jet engine are subjected to extreme temperatures: the temperature of the gas flow behind the combustion chamber is 2,000°K (1,700°C), which is actually several hundred degrees hotter than the melting point of the blades. They are therefore cooled both internally and externally in order to keep them below the critical material temperature.
Impurities and foreign matter in the air flow can result in the cooling air ducts and holes in the turbine blades becoming blocked. If the original cooling air flow on and inside the blades is not restored, the blade walls can become damaged as a result of overheating. That significantly reduces the engine’s efficiency and service life. In extreme cases, engines have to be prematurely disassembled and replaced.
Removal of these impurities eliminates the need for early repairs and engine replacement, and airlines are thus able to continue to use their aircraft without any unscheduled interruptions or disruption in order to fly their passengers around the world reliably. Up to now, however, it has been necessary to remove the blades in order to do this kind of cleaning work.
Highly flexible tool for accessing locations that are difficult to reach
The turbine blades are difficult to access inside the engine, so a much smaller, more flexible tool had to be developed in order to remove the impurities from the cooling ducts and holes, given the complex geometries involved. It also has to be controlled with great precision to avoid any unwanted contact with components inside the engine. A special high-pressure cleaning head with a camera and control unit is needed in order to get an exact picture of the endoscopic work being done and monitor progress.
Exerting pressure on impurities
Within the framework of the German aerospace research programme LuFo, in an early concept phase we developed the theoretical basis for the new procedure and demonstrated the practical benefits. In a subsequent step, Rolls-Royce took the lead role in developing a tool that meets all our requirements together with our research partners Fraunhofer IPK and Schölly Fibreoptic. The system enables a water jet with a pressure of up to 500 bar – roughly four times the pressure of a standard commercially available pressure washer – to be aimed at the impurities in order to remove them, and to check the progress of the work through the in-built camera.
The particular challenges of the task were met with a unique, snake-like design made up of individual links that provides the great flexibility required to access the blades and the outstanding stability needed for the actual cleaning operation. The key to this recently patented system is that under pressure it stiffens, yet the tip remains in the same position. Thanks to this fixing of the position, depending on the design, multiple blades can be cleaned at the same time – or around 360 cooling holes at once.
The system comprises a miniaturised cleaning head with an optical unit, a complex, flexible system carrier, a control unit and control methods that prevent the device from coming into contact with internal engine parts and thus causing secondary damage. Even inspection and mounting holes only a few millimetres in size in the engine can be used as access points, thus allowing the blades to be cleaned without removing them from the engine.
The advantages of this new procedure are plain to see. As the cleaning process can be part of the regular On-Wing inspection, maintenance and life-cycle cost can be minimised while the time on-wing is increased significantly. Additionally, the number of unplanned repair work and potential service cancellations of the airline can be reduced to a minimum as well as the fuel consumption of the aircraft.
intelligent engine and automated cleaning
Supercharged by digital technology, the lines between products and services are blurring, offering Rolls-Royce a wealth of opportunities to improve what it offers its customers.
In addition to designing, testing and maintaining engines in the digital realm, the IntelligentEngine vision sets out a future in which an engine will be increasingly connected, contextually aware and intelligent, helping to deliver greater reliability and efficiency.
As part of our IntelligentEngine vision, we are already working on the further development of the system. Highly developed algorithms allow the data of our engine health monitoring centres to be analysed fully automatically in our availability centres, and engines with turbine blades that need to be cleaned can thus be identified in good time.
This data can flow into new analysis models, thus enabling the entire fleet of engines to learn from these patterns and further minimising interruptions to flying operations as a result of unscheduled maintenance.
But our vision goes beyond that. Up to now, the probe with the cleaning head has been guided manually by our highly qualified mechanics by means of video control. In future this could be done fully automatically. Thanks to the three-dimensional design data of each engine’s digital twin, the tool will know exactly the route it has to take to the turbine and be able to navigate to the turbine blades autonomously. Here, again, we are doing pioneering work: we have already carried out an initial feasibility study with very positive results.
The performance of the human vascular system is highly impressive, but it is also subject to problems that are often detected late on the basis of external symptoms. The diagnostic endoscope, the precursor of which was invented over 200 years ago, helps to detect these problems.
Since then, flexible and increasingly sophisticated and intricate optical and micro-mechanical systems have been developed that are used in applications far beyond just treatment of the vascular system and are constantly being enhanced. The method was applied to engineering over 30 years ago when the boroscope was developed.
The innovation presented here applies the progress made in medical endoscopy, in particular the controllability and miniaturisation of the instruments, to equally sensitive components in jet engines, which are difficult to access from outside the engine. Just as endoscopes are used in medicine to remove calcification from the arteries, our system is used to clean components that must be working flawlessly if the heart of the aircraft – its engine – is to remain healthy.