Green Engines

The International Civil Aviation Organisation (ICAO) has warned that the aviation industry needs to prepare for severe disruptions as a result of climate change and that it needs to make full use of clean technology and policy tools in order to reduce its carbon footprint. ICAO’s 2016 Environmental Report says that changes to the atmosphere brought about by rising global temperatures caused by greenhouse gas emissions, will affect airplane’s ability to fly, while rising sea levels will affect airports. Impacts will include higher winds impeding the ability of aircraft to takeoff and an increase in-flight turbulence, icing and engine-threatening dust storms. With such environmental concerns, there are various organisations across continents working on sustainable alternatives.

The Air Transport Action Group (ATAG), a not-for-profit association, has stated that worldwide, flights produced 781 million tonnes of CO₂ in 2015, while over all humans produced 36 billion tonnes. The global aviation industry produces around two per cent of all human-induced CO₂ emissions. Aviation is responsible for 12 per cent of CO₂ emissions from all transport sources compared to 74 per cent from road transport. Around 80 per cent of aviation CO₂ emissions are from flights of over 1,500 km for which there is no practical alternative mode of transport.

Reductions in fuel burn

The Sustainable and Green Engine (SAGE) ITD of Clean Sky demonstrates five engine technologies contributing towards the Advisory Council for Aeronautic Research in Europe (ACARE) environmental targets. There are six engine projects contained in the programme. Each one targets specific technologies and market sectors, led by a member of the European engines industry.

Open rotor technologies offer the potential for significant reduction in fuel burn and CO₂ emissions relative to turbofan engines of equivalent thrust. Higher propulsive efficiencies are achieved for turbofans by increasing the bypass ratio through increase in fan diameter, but there is a diminishing return to this improvement as nacelle diameters and consequently weight and drag increase. Open rotor engines remove this limitation by operating the propeller blades without a surrounding nacelle, thus enabling ultrahigh bypass ratios to be achieved.

Further improvements in propulsive efficiency can be gained in open rotor engines by using a second row of propeller blades rotating in opposite direction to the front row to remove the spin from the column of air to give a more direct thrust. The technical challenges of counter-rotating open rotor engines are many, but are principally reduction of the noise created by the propeller blades to counter the loss of attenuation provided by a turbofan nacelle.

Open rotor engine

Turbofans are isolated from the airframe by the nacelle, but the airflow through open rotor propellers interacts with the supporting airframe structure and so the installation impacts on the engine system noise and efficiency.

Rolls-Royce has developed open rotor propeller design to minimise noise and has demonstrated the effectiveness of these designs through scaled rig testing in the FP7 DREAM programme. The SAGE1 project is planned to acquire technology for the propulsion system, increasing the Technology Readiness Level (TRL) to TRL 5. Collaborating in the SAGE1 project under Rolls-Royce leadership are Volvo Aero Corporation and ITP. Further Partners will be selected as the project progresses.

Large 3 shaft demonstrator

The SAGE3 project is focused on low pressure system and external technologies. Rolls-Royce has been developing composite fan technologies in the Framework Programme 6 (FP6) VITAL and ELF programmes, but the technology requires engine demonstration to achieve Technology Readiness Level 6, the environment in which it will operate. The SAGE3 project will include an engine demonstration (the Advanced Low Pressure System, or ALPS, demonstrator) to provide this verification.

Further technology demonstration in the SAGE3 project will focus on advanced externals, with engine demonstration opportunities offered to advanced systems to reduce the weight of the installations. These lightweight integrated sub-systems will focus on utilisation of composite and other lightweight materials, on improved integration of externals with the engine structure and extension of existing lightweight solutions to higher temperature applications. Low pressure turbine technologies will be developed and demonstrated by ITP and compressor intercase technologies by Volvo Aero.

WITH AIR TRAVEL EXPECTED TO DOUBLE BY 2035, WE WILL NEED A WAY TO NOT ONLY CONNECT URBAN CENTRES, BUT ALSO PROTECT THE PLANET

The basis for the engine demonstration will be a Trent 1000 engine and planned testing includes a full range of aerodynamic and noise tests on indoor and outdoor test stands and in flight. Rig testing is planned for components where either this will provide full validation such as for the intercase technologies or where a limited engine dataset will verify the results of a more complete rig test survey. Collaborating in the SAGE3 project under Rolls-Royce leadership are Volvo Aero Corporation, ITP, FACC and University of Rapperswil.

Lean burn demonstrator

The SAGE6 project is focused on delivering a lean burn combustion system demonstrator engine. The aim is to demonstrate a lean burn whole engine system to a TRL6 maturity level, suitable for incorporation into civil aerospace applications in the 30,000lb to 100,000 plus thrust classes. SAGE6 is continuing on from previous demonstrator programmes such as ANTLE/POA, E3E and EFE. The SAGE6 project will include an engine demonstration (Advanced Low Emission Combustion, or ALECSYS demonstrator) to provide this verification.

Further technology demonstration in the SAGE6 project will focus on lean burn combustion technology, advanced engine health monitoring, advanced cooling technologies, advanced fuel heat management and improved manufacturing capabilities. Current TRL levels of the various subsystems vary, but are typically at TRL3-4. Whilst existing demonstrator platforms (rigs and engines) will be sufficient to develop the system to TRL5, additional capability in the form of a ground demonstrator will be required. This vehicle will encompass the entire lean burn system including the combustor, fuel supply and control system, sensing technologies and the associated externals and installation hardware and represents a significant set of modifications to the architecture of the Trent 1000 donor engine. Collaboration in the SAGE6 project under Rolls-Royce leadership is through partners selected through the Clean Sky Call for Proposal process as the project progresses.

PurePower and quieter airports

Pratt & Whitney’s new PurePower Geared Turbofan (GTF) engine is another engine that is designed to address environmental concerns. The engine reduces its noise footprint by 75 per cent, while also delivering a 16 per cent improvement in fuel efficiency and reducing NOx emissions by 50 per cent to the regulatory limit.

Pratt & Whitney states “If every airplane departing LaGuardia was powered by a Geared Turbofan engine, about 500,000 few airport neighbours would be impacted by noise from takeoff and landing.” This engine not only leads to quieter neighborhoods near airports – it’s a key to the health of future cities and skies, too. As our population grows and urbanises and with air travel expected to double by 2035, we will need a way to not only connect urban centres, but also protect the planet. One way to do that is through green aviation technology like the Geared Turbofan engine.”

Pratt & Whitney and its parent company, Fortune 45 manufacturer United Technologies Corporation, are investing heavily in alternative fuels and leading-edge technologies such additive manufacturing and nanomaterials to make even greener, quieter engines.

LEAP’s revolutionary technology

Similarly, the next-generation LEAP engine offered by CFM International (a 50/50 company between Safran Aircraft Engines and GE), features a revolutionary new technology. The fan blades and cases on this engine are made of a 3D woven composite using the Resin Transfer Molding (RTM) process, to sufficiently decrease engine weight, which in turn reduces fuel consumption and NOx (oxides of nitrogen) emissions.