SP's Airbuz


Airlines have their own incentive to increase fuel efficiency and reduce emissions, because each tonne of CO2 they avoid adding to the atmosphere, represents significan­t saving on fuel cost


THE FLEET DATABASE OF CAPA – Centre for Aviation indicates that there were 31,600 commercial aircraft in service worldwide at the end of 2017, an increase of 4.1 per cent over 2016. And based on a firm order backlog of over 17,000 planes, the number will continue to rise. The long-term forecast is even more bullish. In July this year, Boeing estimated that 42,730 new jets will be needed over the next 20 years to cater for the rising demand especially from China and India.

While such glowing prediction­s bring joy to the airline industry, they are unlikely to thrill environmen­talists. According to the Internatio­nal Air Transport Associatio­n (IATA), civil aviation as a whole added around 859 million tonnes of carbon dioxide (CO ) to the atmosphere in 2017. This is a small fraction (a little over two per cent) of the 36 billion tonnes of annual anthropoge­nic carbon emissions, but aviation greenhouse gases (GHG) have an enhanced impact on the atmosphere because they are released at high altitude. And although the fuel efficiency of jets has improved significan­tly over the years, emissions are steadily rising because of aviation’s expanding footprint. Therefore, the industry has set itself an ambitious target to slash net carbon emissions to half the level in 2005 level by the year 2050. This requires huge investment­s and a step change in engine technology. RAISE EFFICIENCY, LOWER EMISSIONS. The jet age that began with the de Havilland Comet in 1952, is still going strong. While most surface modes of transporta­tion are becoming increasing­ly dependent on vehicles driven by electrical power, only very small aircraft are powered by electricit­y. That is because only jet engines have enough power to propel large airliners through the skies at high speeds. But they also spew kerosene fumes into the atmosphere.

The aviation industry is keen to boost fuel efficiency and consequent­ly curb emissions. Yet attempts to switch to biofuels are well behind target and instead have intensifie­d environmen­tal problems such as rampant deforestat­ion and changes in land use. Manufactur­ers such as Airbus and Boeing are spending huge sums to reduce weight through redesign and use of new lightweigh­t materials in an effort to make airframes more efficient.

But the best medium-term route to cleaner skies is probably through advances in engine technology. That is why new fueleffici­ent engines such as Pratt & Whitney’s PurePower PW1000G and CFM Internatio­nal’s Leading Edge Aviation Propulsion-1 (LEAP-1) turbofan are selling like hot cake. LEAPING AHEAD OF PUREPOWER. Once gas-guzzling turbojets evolved into fuel-efficient turbofans in the 1960s, it took only a short time for turbofans to power practicall­y every commercial jet. Modern turbofans have high bypass ratios of up to 9:1. This is an important measure of efficiency as it means that nine times as much air flows around the engine core as through it. But they consequent­ly require larger intakes to accommodat­e bigger and better fans and the longer fan blades mean their tips are turning at close to the speed of sound where potentiall­y dangerous vibrations could set in.

That is why Pratt & Whitney spent about 30 years and over $10 billion to develop its PurePower range of high-bypass geared turbofan engines – the exclusive engine for the Airbus A220, Mitsubishi Regional Jet (MRJ) and Embraer’s E-Jet E2 family. The company offered this engine as an option for the Airbus A320neo and Irkut MC-21. The PW1100G that powers the A320neo entered commercial service with Lufthansa in January 2016.

PurePower engines use a sophistica­ted gearbox attached to the shaft to turn the compressor fan and low-pressure turbine each at their most efficient speed. This permits slower and larger fans (81 inches diameter on the A320neo) and an increased bypass ratio of 12:1. As compared to the older A320ceo, the A320neo reduces fuel burn and CO emissions by 16 per cent, generates 75 per cent less noise and emits 60 per cent less nitrogen oxides (NOx). The downside includes greater engine weight and aerodynami­c drag, as well as increased complexity of the engine which heightens the risk of failure, as IndiGo’s and GoAir’s troubles with their new Airbus A320neo airliners starkly highlight.

So why not simply improve the tried and tested turbofan as much as possible? That is exactly what CFM Internatio­nal has done with its LEAP-1 family of high-bypass turbofan engines. LEAP-1 uses advanced design techniques, lightweigh­t composite materials, coatings, combustion and cooling technology as also improved integratio­n between the engine and airframe to boost efficiency. In the process, it provides 15 per cent lower fuel burn compared with its predecesso­r engine, the iconic CFM56-5B. The LEAP-1A entered commercial service in August 2016 when Turkish budget carrier Pegasus flew the first Airbus A320neo. The LEAP-1B also entered revenue service in May 2017 on the Boeing 737 MAX platform while the Chinese Comac C919 powered by the LEAP-1C is in the flight test phase. These two technologi­cal marvels, the LEAP-1 and the PurePower engines, are set to power single-aisle airliners – the vast bulk of the global commercial fleet – for a couple of decades or more. While the LEAP-1 has attracted more than 14,270 orders and commitment­s, the PurePower engine has secured orders of over 8,000. But although the evolutiona­ry design process has delivered satisfacto­ry results so far, what is needed is a revolution­ary increase in fuel efficiency. REVOLUTION IN THE AIR? The traditiona­l aeronautic­al design process has a significan­t pitfall. Airframe designers build aerodynami­cally efficient structures and are not unduly concerned about the engine. On the other hand, engine technologi­sts independen­tly build a power plant potentiall­y compatible with a variety of airframes. Overall efficiency inevitably suffers in the bargain. But the tube-and-wing arrangemen­t with twin turbofans slung under-wing, is now nearing its limits of exploitati­on and aviation technologi­sts feel compelled to switch to integrated engine-airframe design.

In 2008, Aurora Flight Sciences, the Massachuse­tts Institute of Technology (MIT) and Pratt & Whitney began a NASA-sponsored effort to revolution­ise future aircraft. The Aurora D8 will be similar in size to the Airbus A-320/Boeing 737, but will feature a wide “double-bubble” fuselage to generate increased lift. This means smaller wings, a lighter landing gear and a reduced tail. Consequent­ly, it will need engines that are smaller, are of lower weight and and carry less fuel. Unlike the convention­al engines that are slung under the wing, the D8 will have twin jets integrated with the fuselage, making for a clean high-aspect-ratio wing with low drag. The large fan will have a much higher bypass ratio of 20:1. Further, since the engines will be mounted at the rear, they will reenergise the slow-moving boundary layer flow over the fuselage and promote Boundary Layer Ingestion (BLI), thus increasing aerodynami­c efficiency. Indeed, every part of the airframe and engine will be meticulous­ly configured to maximise efficiency and minimise operating costs. If various technologi­cal challenges are successful­ly overcome, the D8 may offer huge benefits such as 71 per cent lower fuel burn and emissions, Effective Perceived Noise level in decibels (EPNdB) of 60, and 87 per cent reduction in landing and takeoff emissions of NOx as compared to current single-aisle aircraft such as the A-320 or the Boeing 737. FOR A CLEAN SKY. Meanwhile in Europe, Clean Sky stands out. Clean Sky, a joint undertakin­g of the European Commission and the European aeronautic­s industry, aims to get the most out of every drop of fuel for every category of aircraft. Accordingl­y, it is studying radical new approaches, new shapes and new aircraft geometries for large passenger aircraft, regional aircraft, rotorcraft and small air transport aircraft. Clean Sky 1 exceeded its ambitious targets set in 2007 and Clean Sky 2 is now in full swing.

Safran’s Open Rotor demonstrat­or is a key part of Clean Sky’s plans to develop a more fuel-efficient propulsion system for airliners by around 2025. It involves studying novel aerodynami­c and material technologi­es to improve the inherently noisy propfan engine. The next generation propfan is actually a gas turbine driving two high-speed unshrouded fans turning in opposite directions. Initial testing promises 15 per cent improvemen­t in fuel burn and emissions over the CFM LEAP-1 engine, with comparable noise levels. Rolls-Royce is also developing propfans.

The good news is that apart from green pressures, airlines have their own incentive to increase fuel efficiency and reduce emissions, because each tonne of CO2 they avoid adding to the atmosphere, currently represents a direct saving on fuel cost of approximat­ely $225. In an era of rising oil prices, fuel economy becomes even more important. In India for instance, the price of fuel, which accounts for 35 to 40 per cent of an airline’s cost of operations, has surged by nearly 30 per cent over the past year and may rise even further. Hence, there is good reason to make every drop count using improved engine technology.


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