No doubt, aircraft provide a fast, efficient and reliable mode of transport with no comparable alternative for long distance travel. But that comes with a price tag. There are so many aspects that add up to the cost of air travel, foremost being the price of aviation turbine fuel, which in some parts of the world accounts for over 40 per cent of an airline’s operating costs. If one has to keep costs down, improve aircraft efficiency and at the same time be environmentally responsible, then the aircraft manufacturer first and the operator later will have to initiate measures for optimum performance.

At the core of it all is the engine which is the heart of an airplane. From 1903, when Charlie Taylor built an inline aeroengine for the Wright Flyer, till date aeroengines have undergone a sea change, adding more power, thrust, reliability, efficiency, etc. Today’s aircraft are designed for over 15 per cent improvement in fuel burn than comparable aircraft of a decade ago, delivering 40 per cent lower emissions than aircraft previously designed. And contributing significantly to this is the engine. On a per flight per passenger basis, efficiency is expected to continue to improve through 2050 with engine being pivotal to the development.

Overall, fuel efficiency of an aircraft can be improved through a variety of means such as efficient engines, new fuels, improved aircraft efficiency, improved efficiency in operations and optimised air traffic management. Engine manufacturers are under constant pressure to develop engines which give the lowest fuel burn, fuel continuing to be prohibitive pricewise.

Huge Investments

Aeroengine manufacturers have been investing heavily in effecting improvements in the engines. There is a neck-and-neck race amongst engine manufacturers to out-perform the other and one of the yardsticks of a good engine is its fuel efficiency.

Engine manufacturers invest in technology to provide clean, quiet, affordable, reliable and efficient power. This is a continuous process and regular investments are made to maintain and improve the overall performance of in-service and in-production aircraft. Philippe Fonta, Head of Environmental Policy, Airbus Engineering’s Centre of Competence Power Plant, mentions that multiple engine upgrade programmes have been achieved in the last decade that delivered up to two per cent fuel burn improvement (for example CFM56-5B Tech insertion, V2500 Select One, Trent 700 EP, GE90-115B Mat’y, etc). There are further improvements on that and some engines claim up to 20 per cent less fuel burn.

As far as new products are concerned, engines and auxiliary power units (APUs) for new aircraft designs are expected to provide a minimum of 15 per cent fuel savings with regard to the aircraft they replace. Some project and/or development aircraft from business aeroplanes through regional and long-range aircraft worldwide are expected to bring significant benefits when they enter into revenue service in the near future. Engine technologies, e.g. materials, coatings, combustion, sensors, cooling etc are modelled, tested and implemented as soon as they become mature.

These technologies have a positive impact on thermal efficiency, higher operating pressure ratios are targeted to improve combustion and some engine cycle refinements are envisaged. All this must be balanced with the potential risks of increased maintenance costs and weight and/or drag due to engine complexity in an overall context of maximum reliability.

Transmissive Efficiency. Through new components and advanced engine architecture.

Propulsive Efficiency. Engine architectures are evolving for example advanced turbofan, some different concepts are emerging such as advanced geared turbofans, open-rotors, hybrids, etc, each with their own multi-generation product development plans. In order to achieve the optimum improvements, massive investments have to be made in research programmes and public/private partnerships are therefore essential.

These investments are urgent considering that air traffic worldwide is increasing so rapidly that global carbon dioxide emissions from aviation, which now represent just two to three per cent of all CO₂ pollution, could jump as much as 500 per cent by 2050.

Adding Gear

Pratt & Whitney, a division of United Technologies, tried a radical approach for making turbofan engines more efficient—adding a gear. The resulting fan-drive gear system engine, more than a decade in the making, can cut fuel use by up to 16 per cent. Pratt & Whitney says the PurePower line of engines will be able to cut carrier operating costs by 20 per cent or about $1.7 million per plane per year, dampen noise levels by half and cut CO₂ emissions by 3,600 tonnes a year.

How does the gear improve efficiency? Modern turbofan engines create thrust by expelling fast-moving hot gases from their core. But they also use their fans to push slower air around the outside of the engine, so it mingles with the faster hot gases at the rear, increasing thrust. Typically, engines have a bypass ratio of 8:1; eight pounds of the air hitting the engine bypass the core for every pound that enters. The higher the bypass ratio, the greater the engine’s thrust and efficiency. Pratt’s geared engine has a ratio of 12:1. A jet engine’s fan works more efficiently at slower speeds than does the core’s turbine and the gearbox allows the two to spin independently, each at its optimum speed. Accordingly, PurePower engines have larger fans and smaller, lighter turbines.

LEAP’s Revolutionary Technology

Throughout its history, CFM has had a policy of continuous investment in the CFM56 product line, introducing new technology into the mature fleet to help customers improve fuel efficiency, reduce its impact on the environment and reduce overall lifecycle costs. As recently as 2011, CFM introduced the CFM56-5B PIP for the Airbus A-320 family and the CFM56-7BE for the Boeing Next-Generation 737.

For the future, CFM is bringing all of this experience to the advanced new LEAP engine family, incorporating revolutionary technologies never before seen in the single-aisle aircraft segment. These engines will provide up to 15 per cent better engine fuel efficiency which, at current fuel prices, translates to as much as $1.6 million in fuel cost savings alone for customers per airplane, per year. LEAP technology will also achieve double-digit improvements in CO₂ emissions and noise levels, all while providing the industry’s best reliability and lowest maintenance costs.

The foundation of the LEAP engine is heavily rooted in the industry’s most advanced aerodynamics, environmental, lighter, more durable materials and leading-edge environmental technologies, making it a major breakthrough in engine technology. For more than 20 years, Snecma has been developing composite fan blade technology. More recently, the company has focused on the revolutionary three-dimensional, woven resin transfer molding (3-DW RTM) technology that dramatically reduces engine weight while providing a more durable blade. Development of Ceramic Matrix Composite (CMC) technology has been underway at GE for more than 30 years. This ultra-light-weight material can support the higher temperatures found in the high-pressure turbine that provide thermal efficiency. This higher temperature capability is paired with state-of-the-art cooling and coating technology to keeps the temperature profile of the metal the same as the current CFM56 engines to keep maintenance cost comparable to today’s product line. Titanium-aluminide, a light-weight alloy that has been under development for the past 25 years, will also be incorporated into the engine.

Advance and Ultrafan from Rolls-Royce

Rolls-Royce is also working on two new engines the Advance and Ultrafan. The Advance could be ready to enter service by 2020, it said, bringing efficiency improvements of up to six per cent on its Trent WXB engine, which will be powering planes later this year. Advance which offers some 20 per cent better fuel burn than the first Trent engines and the second UltraFan, a geared design that could be ready for 2025. There would be at least 25 per cent improvement in fuel burn and emissions.

At its headquarters in Derby, Rolls-Royce unveiled the light-weight Advance’s carbon-titanium fan blades, suspended from the roof of one of the huge kerosene-smelling hangars scattered around the vast site. The blades will be attached to a core smaller than the Trent model’s before the engine is put through its paces over the coming years.

Rolls-Royce is investing heavily in research to maintain its leadership position in advanced engine technologies such as:

• High efficiency compressors and turbines with fifth-generation 3D aerodynamics.
• Advanced lean burn low emission combustors.
• Advanced light-weight heat resistant materials such as ceramic matrix composites or CMCs which allow the engine to operate at temperatures equivalent to half the temperature of the surface of the sun, while maintaining component lives.

Aircraft engines are built to very different criteria to those in automobiles. As you cannot pull over to the side of the sky in the event of breakdown, reliability has been the first and foremost priority and all engine manufacturers ensure that even when they are addressing issues of fuel burn.