Time is Running Out to Go Green!

Warnings that anthropogenic global warming may result in extreme climate change, are multiplying. According to an August 2018 paper of the Proceedings of the National Academy of Sciences of the United States, human activity could warm the Earth so much that its natural climate systems would themselves trigger further warming. It states that the world is at risk of tipping into a very dangerous state called “Hothouse Earth” where the average global temperature could rise by five degrees Celsius more than it already has. This would render vast regions of the globe uninhabitable and result in rise of sea-level by around 60 metres.

Such scary possibilities may be a couple of hundred years distant, but of more immediate concern is that by the turn of this century, the Earth is on course to warm well above two degrees Celsius – a theoretical “tipping point” where abrupt and irreversible climatic changes are likely. While a dwindling bunch of sceptics will pooh-pooh such predictions and continue to peddle dangerous climate change myths, the vast majority of scientists believe that global warming is real, that human activity causes it and that slashing carbon emissions is now an urgent imperative.

Engines that power aeroplanes, are continuously being improved especially by using new materials that withstand higher temperatures and permit more efficient combustion

GREENING AVIATION

Although aircraft engines emit heat, noise, particulates, as well as carbon dioxide (CO₂) and other Greenhouse Gases (GHG), these do not add very much to the total emissions. Globally, burning jet fuel currently generates just 2.5 per cent of carbon emissions. What intensifies environmental concerns however, is that a significant proportion is released at high altitudes. In addition, jet exhaust products such as nitric oxide and nitrogen dioxide (together called NOx), form ozone that has a significant warming effect at high altitudes. Secondly, most sectors of the global economy are progressively switching to greener sources namely electricity, solar or wind energy. This makes aviation, which currently has no practical alternative to burning fossil fuel, one of the fastest growing sources of GHG emissions. By 2050, aviation could contribute up to 15 per cent of global emissions.

Fortunately, when it comes to increasing fuel efficiency, the airline industry is on the same page as the greens. Fuel is the costliest item of an airline’s expenses, especially so in India where high taxes make fuel account for 35 to 40 per cent of operating costs. And since emissions are directly proportionate to the amount of fuel burned, every tonne of aviation fuel saved, avoids adding between 3.15 and 3.18 tonnes of CO₂ to the atmosphere. Therefore, when an airline selects a new aircraft, its fuel efficiency is a primary consideration.

DESIGN FOR GREEN FLIGHT

Aircraft can be made more fuel-efficient by using lighter materials in their construction and improving their aerodynamics. Accurate weather forecasting and streamlining operating procedures can also help significantly – witness the huge amounts of fuel burned by aircraft circling over Delhi and other congested airports in North India in the winter. But aircraft engines play the most important part in curbing emissions.

One readily available “greenish” engine is the turboprop. A turboprop engine is a gas turbine which turns a propeller. It is most efficient for aircraft on short-haul flights cruising between 480 and 650 kmph at low altitudes. Modern turboprop aircraft fly at nearly the same speed as small regional jets; but cost less to operate and burn just two-thirds of the fuel per passenger. However, as distance increases, turbofan powered jets are more useful and economical because they cruise at about 800 kmph at higher flight levels.

PUSHING THE LIMITS

Like airframes, engines are continuously being improved especially by using new materials that withstand higher temperatures and permit more efficient combustion. Advanced designs for the fan and turbine also generate more thrust with less fuel consumption. However, although technologists claim that CO₂ emissions have reduced by over 80 per cent since the first jet passenger aircraft entered service in 1952, the turbofan design of the 1960s remains largely unchanged.

That is why Pratt & Whitney spent about 30 years and over $10 billion to develop its PurePower range of high-bypass geared turbofan engines. In a geared turbofan, a special reduction gearbox between the fan and the LP shaft allows the latter to run at high speeds thus enabling fewer stages to be used in both the LP turbine and the LP compressor. This increases engine efficiency and reduces weight. On the Airbus A320neo for instance, the slower and larger fan means an increased bypass ratio of 12:1. As compared to the older A320ceo, the A320neo reduces fuel burn and CO₂ emissions by 16 per cent, generates 75 per cent less noise and emits 60 per cent less nitrogen oxides (NOx). However, the gearbox adds complexity to the engine, which means PurePower’s teething troubles persist despite almost three years having elapsed since the PW1100G entered commercial service. Consequently, carriers like IndiGo and GoAir have been hard hit by frequent groundings of their new A320neo jets.

On hindsight, CFM International prudently stuck to improving the tried-and-tested turbofan. For its LEAP-1 engine that powers the Boeing 737 MAX, CFM used advanced design techniques, lightweight composite materials, improved combustion and cooling technology. The company emphasised integration between the engine and airframe to boost efficiency. The LEAP-1 provides 15 per cent lower fuel burn than its predecessor, the CFM56-5B.

While LEAP-1 and PurePower are set to be engines of choice of most single-aisle jets for three decades or more, many aviation designers believe that the conventional tube-and-wing airframe powered by turbofans, is near its maximum limit of exploitation and it is time to change tack.

The Aurora D8, a NASA-sponsored effort to revolutionise future aircraft, will be similar in size to the Airbus A320/Boeing B737; but will feature a wide “double-bubble” fuselage to generate increased lift. With every part of its airframe and engine meticulously configured to maximise efficiency and minimise operating costs, the D8 may reduce fuel burn and emissions by as much as 71 per cent over current aircraft. Passenger aircraft based on the D8 demonstrator, could enter service in the 2030s.

IS IT ENOUGH?

The airline industry aims to cut its CO₂ emissions to half by 2050 from 2005 levels. While this is commendable, much of it will come through the purchase of carbon offsets rather than actually reducing emissions. Environmentalists criticise carbon offsets as avoiding immediate changes of behaviour in favour of less verifiable ways of reducing emissions that are prone to manipulation, misuse or abuse. Besides, the International Air Transport Association (IATA) in its 20-Year Air Passenger Forecast predicts that about 7.8 billion air passengers will travel in 2036, almost double the 4.1 billion travellers of 2017. No amount of improvement in fossil fuel burning engines can compensate for this huge increase. That is why there is the need to pursue electricity powered aircraft with greater zeal.

In some countries, rail and road transport are well on the way to going electric. Norway is taking the lead despite being the largest oil and gas producer in Western Europe. Norway’s market share of electric cars is already more than any other nation in the world and it is committed to all new vehicle registrations being zero emission by 2025. Norway has also decided that all the country’s short-haul airliners – those used for flights lasting up to 1.5 hours – will be entirely electric powered by 2040. This decree would cover all domestic flights and those to neighbouring Scandinavian capitals. Avinor, a state-owned company that operates most civil airports in Norway, will soon float a tender for a commercial route to be flown with a 19-seat electric plane starting 2025.

ELECTRIFYING THE SKY

The operating cost of electricity powered aircraft is much lower than others of similar capacity due to cheap electricity and simpler motors. But using batteries for flight is challenging because they must deliver huge amounts of power while being small, light and safe. However, thanks to mobile phones, laptops and cars, battery technology is attracting considerable investments globally and consequently, is making rapid progress. If electricity powered aircraft do succeed commercially, the airline industry should be eager to go electric. Such aircraft would probably attract support from governments and environmental groups alike due to their huge reduction in emissions and noise.

Time is running out for every sector, including commercial aviation, to do whatever it takes to reduce emissions

While it is possible to build and operate small electric planes, it becomes more difficult as size increases. Airbus in fact has given up attempts to develop fully electric planes and instead, is working with Rolls-Royce and Siemens to develop a hybrid-electric plane, where the turbine powering the generator will run on jet fuel and provide power for the electric motor. According to Airbus, “The E-Fan X hybrid-electric technology demonstrator is anticipated to fly in 2020 following a comprehensive ground test campaign, provisionally on a BAe 146 flying test bed, with one of the aircraft’s four gas turbine engines replaced by a two megawatt electric motor. Provision will be made to replace a second gas turbine with an electric motor once system maturity has been proven.”

In the US, Zunum Aero, a start-up based in Washington and backed by Boeing, HorizonX and JetBlue Technology Ventures, has been working since 2013 on a family of hybrid-electric regional aircraft with up to 50 seats. It plans to bring a small hybrid plane to the market as early as 2022.

Time is running out for every sector, including commercial aviation, to do whatever it takes to reduce emissions. Some decades down the line, if the dire predictions of global warming induced climate change start coming true, the airline industry will surely feel the heat. It may then be faced with the stark choice of either switching to non-polluting energy sources or shutting shop. Electric aircraft might well be the best option to remain in business.