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DEVILS advocate: an alternative take on VHBR engine cooling

Very High Bypass Ratio engines with high-power gearboxes place enormous demands on oil lubrication systems to cope with the cooling requirements associated with the loading and temperatures of these fuel-efficient engines. To keep Europe's aeroengine design and manufacturing capability at the forefront of global competitiveness it is imperative to apply innovative R&D to push oil lubrication and engine heat management technology to new levels of optimisation – which is why Clean Sky's DEVILS project has been developing a radical new approach, using a system that varies the oil flow according to the different phases of flight.

Very High Bypass Ratio Engines are conservative in terms of fuel consumption, but generate searing heat in the process, placing exceptional demands on engine lubrication systems to keep things running smoothly and prevent overheating. 

"Normally aircraft engines are fitted with an oil lubrication system whose function is to lubricate all the components and to remove heat" explains Giuliano Di Paola, Chief Technical Officer at Napoli-based Protom Group S.p.A. "But today's engines are fitted with oil lubrication systems that have not evolved much in the past 30 or 40 years. When engines run at minimum, at low speeds, or even when engines run at high speed, the oil pump gives you more oil flow than what is needed, so today's systems are not optimised" says Di Paola. 

Di Paola's team have been coordinating the DEVILS (Development of Very High Bypass Ratio Engines Innovative Lubrication System) project which kicked off in February 2017 and runs until May 2020, supported with the collaborative talents of Abete S.r.l; TAT Technologies Ltd; Euro.Soft S.r.l; Univeristà di Napoli ‘Federico II’; and Centro Nazionale delle Ricerche (CNR). The project’s objectives are to research, develop and validate the robustness of an innovative variable flow oil pump to be integrated in a high performance aircraft lubrication system architecture with the aim of reducing fuel and oil consumption. The project also seeks to research, implement and validate smart fault detection and health monitoring algorithms to assist the system in reducing oil low flow rate needs and prognostic functions.

To accomplish this the DEVILS consortium is confronting these interconnected challenges with the development of a model based systems engineering tool to aid evaluation and selection of candidate VHBR system architectures; development of methods and techniques required to achieve variable flows that allow oil feed and scavenge systems to be optimized around the flight envelope; demonstration of an intelligent variable flow oil system and advanced control scheme showing how operations can be optimised across a range of simulated flight conditions; and finally, research into autonomous fault detection and correction for future oil systems.

What is particularly unique in the consortium's approach is the idea of constantly varying the flow of oil in alignment with each successive phase of flight – because, of course, take-off and climb segments of a flight are clearly more demanding on the engines than cruising or descent. This means that carefully matching the oil flow to the status of the flight phase can reduce the amount of oil used and can result in lower fuel-burn too.

"Varying the flow of oil in an oil lubrication system makes it possible to use just the quantity of oil that you need each time during a flight” says Di Paola. ‘With today's systems, when the engine runs at maximum, since the pump is geared, the oil gives you more flow than what you need. With our new pump you'll be able to adjust the quantity of oil you need for each flight phase, so it is an optimisation and you will use less oil than today's systems. This has an impact in terms of environment, because you have less oil, so less weight and also there is a reduction of engine fuel consumption with the consequent reduction of CO2 emissions. In terms of impact on fuel consumption and consequently on the emissions of CO2 we expect a 15 to 20% reduction".

In April 2018, the DEVILS consortium passed an important project milestone with the freezing of the oil lubrication system architecture and the geometry of the variable flow rate pump. "We are sizing the complete system based on some requirements that have been given by Rolls-Royce, based on an actual engine" says Di Paola.

"We have already done some thermo-fluid-dynamic analysis, and with this kind of technology using a variable oil flow control pump it is possible to achieve some of the following benefits, such as the possibility to vary the flow rate of oil, adding a fixed speed of the pump or maybe compensate for viscosity variation, so there are some benefits in terms of features that will be demonstrated by analysis" says Di Paola. "There is going to be a big demonstration planned at the end of the project. The objective is to set up a complete demonstrator in the laboratory to construct a complete oil lubrication system with an oil pump and with heat exchangers and oil tanks, as well as associated equipment, in order to assess some of the benefits we expect”

The pump will be equipped with internal sensors in order to add some inputs to the methodologies. The sensors will detect pressure, temperature and vibration and based on these parameters Protom is developing some methodologies so as to monitor wear on the internal components of the pump.

"If this technology is proved to be viable I think there will be a need to completely modernise all engine oil lubrication systems, which means there will be a need to manufacture these systems, which would generate new jobs in Europe" says Di Paola.