The Oxford Science Lecture Series

DR JULIA KING

Director of Marine Power, Rolls-Royce plc

"Powering a better world: clean, versatile gas-turbine power for the 21st century"

University Museum, Oxford, 2nd March 2001

 This lecture, the 17th in the Oxford Science Lectures series, was given by Dr. Julia King, expert on metal fatigue and turbo-efficiency and currently a director of Marine Power in Rolls-Royce. The meeting was held jointly with Zonta UK, who generously sponsored the event as part of a weekend reunion programme.

The invention of the gas-turbine engine by Frank Whittle in 1941 brought about a major revolution in the already expanding aviation industry. Compared to the limitations associated with the relatively low speeds and distance ranges of craft with propeller-driven petrol engines, the turbine offered much higher speeds and greater distances in planes of comparable size and load. This leap forward in attainable efficiency promised long-haul flights and economic air-travel, converting "aerodromes" into "airports" and offering accessible worldwide travel for business, commerce and pleasure, and eventually leading to the realisation of rockets, satellites and space exploration.

The thrust supplied by an aircraft engine depends upon the mass of air it can move and the velocity it can impart to it. A turbine, whose duty cycle is continuous whereas that of a combustion engine is intermittent (according to the number of its pistons), can expel air at substantially greater velocities than propeller blades can turn it, so it achieves very considerable extra thrust without requiring the aircraft to be any larger or heavier. The energy for the thrust is supplied by compressing and heating the air that is drawn into the turbine and then expelling it.

For all sorts of reasons - economic, ecological, safety, comfort, to name but a few - the various elements of a gas turbine need to be streamlined in design and optimised in performance, deriving maximum power per unit of combustion fuel whilst achieving minimum noise and minimal output of harmful gases. Dr. King dwelt on aspects of turbine development and design bearing on efficiency and safety.

She described the recent introduction by Rolls-Royce of honeycomb structures for the blades of intake fans in order to obtain better performance and reduced metal fatigue without increasing the mass of the blades, and the use of a Ti/superplastic alloy whose bonding onto the fan has to be carried out in clean-room conditions. She referred to the different features of the turbine and to specific innovations to meet a variety of challenges: compressor optimization (demonstrated by academic computational fluid dynamics) to minimise energy losses as the gas is transferred; problems of igniting gas travelling at 30 to 40 m/s, and how the flow is slowed down at that stage; that a turbine works best when the temperature of the gas is evenly distributed within it, requiring causes for uneven temperature distribution to be addressed and rectified. She explained why the crystalline structure of conventional materials is important, and how alloys made with single-crystal structures can withstand higher temperatures and are also more robust. Efficient cooling of the turbine is crucial to the durability of the engine, and she described how newly-developed ceramic coatings applied to the metal/hot gas surfaces permit higher operating temperatures - though presenting other challenges because the ceramic coating has a lower thermal expansion than the metal it shields.

In ecological terms, unburned hydrocarbons are serious. CO emissions have been substantially reduced in recent years, but fractions of harmful nitrous oxides in exhaust gases remain way too high (some 60% of the levels measured in 1970) and their reduction is now of high priority. Combustors have been shown to operate more cleanly under different mechanisms of fuel injection, depending on whether an aircraft is taxiing or cruising.

The safety aspects of modern aicraft which Dr. King included in her talk referred to the performance of turbine engines when struck by foreign objects (such as birds or hail), or when challenged by extremes of weather. Illustrating some vivid examples of the stringent tests carried out in simulators, she assured the audience of the ability of Rolls-Royce engines to withstand lashing rainstorms, to re-ignite within 90 seconds if the temperature suddenly fell to - 40, and to be unaffected if a fan blade became damaged through an encounter with a large bird. It was a little ironic to reflect that the same creatures whose perfection of natural flight helped pioneer aircraft design should constitute such a physical danger.

Dr. King also sketched the uses of gas-turbines in marine engines and power stations, emphasising the similarities of the basic turbine operations but highlighting essential differences. Marine turbines have no fans for air intake, but employ additional gear-trains. Diesel-fuelled power-station turbines have (perforce) managed to reduce nitrous oxide emissions to acceptably low levels (less than 10% of those measured in 1970) by operating the combustor within a very narrow band of temperatures and employing multiple fuel-injection stages. Noise minimisation is also of particular importance for the latter.

The AWiSE Committee was later invited to a reception in which Zonta UK presented Amelia Earhart Research awards to successful applicants working aerospace-related research. The recipients - three young women from overseas, training for research degrees in the UK - gave 5-minute overviews of their different research, managing to impart huge enthusiasm for the behaviour of holes in the structure of aircraft materials, for aerials that unfold correctly on rockets and satellites, and for robotic control software.

Zonta is a world-wide service organisation of executives in business and the professions, working to improve the status of women. Members are not necessarily involved in professions allied to the aerospace industry, and at the present reunion few in fact were. However, thanks to Dr. King's lucid explanations everyone went away substantially better informed, and intrigued by the diverse opportunities for research by women in the engineering sciences.

Last modified 21 March 2001.