Green Resolve

Though the aviation sector accounts for less than two per cent of human-induced CO2 emissions, it is continuously working on becoming more and more environment-friendly

Issue: 3 / 2014By R. ChandrakanthPhoto(s): By Safran, Airbus, Virgin Atlantic

The aviation sector’s contribution to climate change represents two per cent of human-induced carbon dioxide CO2 emissions. It is said that all flights put together produce 628 million of carbon dioxide annually which is 12 per cent of all kinds of emissions from all modes of transport. Combustion in transport throws up carbon dioxide and other greenhouse gases into the Earth’s atmosphere, contributing to the acceleration of global warming and also ocean acidification. Carbon dioxide is the principal greenhouse gas emitted from powered aircraft. Other emissions may include nitric oxide and nitrogen dioxide (NOx), water vapour and particulates (soot and sulphate particles), sulphur oxides, carbon monoxide, hydrocarbons, tetraethyl lead from pistonengine aircraft and radicals such as hydroxyl, depending on the type of aircraft in use.

A 2007 report from the Environmental Change Institute, Oxford University, posits a range closer to 7-9 per cent cumulative effect. Even though there have been significant improvements in fuel efficiency through better technology and operational management, these improvements are being continually eclipsed by the increase in air traffic volume.

Preliminary figures released by the International Civil Aviation Organisation (ICAO) confirmed that 3.1 billion passengers made use of the global air transport network for their business and tourism needs in 2013. The annual passenger total is up approximately five per cent compared to 2012 and is expected to reach over 6.4 billion by 2030, based on current projections. The number of aircraft departures reached 33 million globally during 2013, establishing a new record and surpassing the 2012 figure by over one million flights. ICAO also confirmed that scheduled passenger traffic grew at a rate of 5.2 per cent in 2013 , slightly above the UN body’s July 2013 projections. Besides, we have significant growth of non-scheduled flights and private aircraft in the skies, adding to the environmental concern.

The aviation sector has come a long way from the first flight in terms of efficiency, fuel burn, noise, etc. Modern-day jets are significantly more fuel-efficient (and thus emit less CO2 in particular) than 30 years ago. Today’s aircraft are designed for more than 15 per cent improvement in fuel burn than comparable aircraft of a decade ago and will deliver 40 per cent lower emissions than aircraft previously designed. Airframers are relentlessly working on reducing the impact further and are committed to achieving reductions in both CO2 and NOx emissions with each new generation of design of aircraft and engine. Thus, the accelerated introduction of more modern aircraft represents an opportunity to reduce emissions per passenger kilometre flown.

Another improvement is the way airliners are manoeuvred on the ground. Honeywell and Safran, a French aerospace company, are jointly working on electric green taxiing system (EGTS) for airplanes, a move that will save money, fuel and carbon emissions. The EGTS will use an airplane’s Auxiliary Power Unit to power motors in the main wheels without using primary engines while on the ground. Today, airplanes use their main engines and taxiing eats up four per cent of total fuel consumption, that equates to five million tonnes of fuel used just to taxi.

Other opportunities arise from the optimisation of airline timetables, route networks and flight frequencies to increase load factors together with the optimisation of airspace. However, these are each one-time gains and as these opportunities are successively fulfilled, diminishing returns can be expected from the remaining opportunities. Another possible reduction of the climate-change impact is the limitation of cruise altitude of aircraft. This would lead to a significant reduction in high-altitude contrails for a marginal trade-off of increased flight time and an estimated four per cent increase in CO2 emissions. Drawbacks of this solution include very limited airspace capacity to do this, especially in Europe and North America and increased fuel burn because jet aircraft are less efficient at lower cruise altitudes.

While they are not suitable for long-haul or transoceanic flights, turboprop aircraft used for commuter flights bring two significant benefits: they often burn considerably less fuel per passenger mile and they typically fly at lower altitudes, well inside the tropopause, where there are no concerns about ozone or contrail production.

Bio and Other Fuels

Some companies such as GE Aviation and Virgin Fuels are researching biofuel technology for use in jet aircraft. Some aircraft engines, like the Wilksch WAM 120can (being a 2-stroke diesel engine) run on vegetable oil. Also, a number of Lycoming engines run well on ethanol.

In addition, there are also several tests done combining regular petro-fuels with a biofuel. For example, as part of this test, Virgin Atlantic Airways flew a Boeing 747 from London Heathrow Airport to Amsterdam Schiphol Airport on February 24, 2008, with one engine burning a combination of coconut oil and babassu oil. The majority of the world’s aircraft are not large jetliners but smaller piston aircraft and with modifications many are capable of using ethanol as a fuel.

In December 2008, an Air New Zealand jet completed the world’s first commercial aviation test flight partially using jatrophabased fuel. In January 2009, Continental Airlines used a sustainable biofuel to power a commercial aircraft for the first time in North America. This marked the first sustainable biofuel demonstration flight by a commercial carrier using a twin-engine aircraft, a Boeing 737-800, powered by CFM International CFM56-7B engines.

One alternative to avgas that is under development is Swift Fuel which was approved as a test fuel by ASTM International in December 2009, allowing the company to continue their research and to pursue certification testing. Mary Rusek, President and coowner of Swift Enterprises, has said that “100SF will be comparably priced, environmentally friendlier and more fuel-efficient than other general aviation fuels on the market”.

As of June 2011, revised international aviation fuel standards officially allow commercial airlines to blend conventional jet fuel with up to 50 per cent biofuels. The renewable fuels “can be blended with conventional commercial and military jet fuel through requirements in the newly issued edition of ASTM D7566, Specification for Aviation Turbine Fuel Containing Synthesised Hydrocarbons”.

In December 2011, the US Federal Aviation Administration (FAA) awarded $7.7 million to eight companies to advance the development of drop-in commercial aviation bio-fuels, with a special focus on alcohol to jet fuel. As part of its Commercial Aviation Alternative Fuel Initiative and Continuous Lower Emissions, Energy and Noise programmes, the FAA plans to assist in the development of a sustainable fuel from alcohols, sugars, biomass, and organic matter such as pyrolysis oils that can be “dropped in” to aircraft without changing current infrastructure. The grant will also be used to research how the fuels affect engine durability and quality control standards.

Emissions Trading

As part of that process, the ICAO has endorsed the adoption of an open emissions trading system to meet CO2 emissions reduction objectives. Guidelines for the adoption and implementation of a global scheme were developed and presented to the ICAO Assembly in 2007, although the prospects of a comprehensive inter-governmental agreement on the adoption of such a scheme are uncertain.

A report published by researchers at the Centre for Aviation, Transport and Environment at Manchester Metropolitan University found that the only way to have a significant impact on emissions was to put a price on carbon and to use a market-based measure (MBM), such as the EU Emissions Trading Scheme.

Worldwide, it is estimated that the equivalent of 1,300 new international airports will be required by 2050 with a doubling in the commercial aircraft fleet. ICAO projections show that the commercial aircraft fleet is expected to increase to about 47,500 by 2036, of which more than 44,000 (94 per cent) aircraft will be new generation technology.

The challenge facing aviation is to meet the predicted growth in demand for air travel increasing 4-5 per cent per annum over the next 20 years, but to do so in a way that ensures that the environment is protected. The aviation industry in Europe has long recognised this challenge and in 2001 the Advisory Council for Aeronautical Research in Europe (ACARE) established the following targets for 2020:

  • Reduce fuel consumption and CO2 emissions by 50 per cent per passenger kilometre.
  • Reduce NOx emissions by 80 per cent
  • Reduce perceived noise by 50 per cent
  • Make substantial progress in reducing the environmental impact of the manufacture, maintenance and disposal of aircraft and related products

ACARE has identified the main contributors to achieving the above targets. The predicted contributions to the 50 per cent CO2 emissions reduction target are:

  • Efficient aircraft: 20-25 per cent
  • Efficient engines: 15-20 per cent
  • Improved air traffic management: 5-10 per cent

With 2020 now not far off in terms of civil aircraft development cycles (typically 10-15 years), ACARE has been evaluating the progress towards the 2020 targets and conducted a consultation process to identify priorities for a new vision for 2050. The effort is to ensure that aviation is as environment-friendly as possible.