Aviation Industry Explores Alternative Fuels

Seeking alternatives to kerosene with greater environmental benefits and minimal impact on land used for foodstuffs.

(April 16, 2008) -- The Society of British Aerospace Companies (SBAC) has published the fourth in its series of eleven briefing papers looking at the technological progress being made by the aviation industry to reduce its impact on the environment. This paper covers research seeking practical alternatives to the current aviation fuel, kerosene.

Recent test flights using alternative fuels have been carried out by consortia made up of Airbus with Shell and Rolls Royce and Virgin Atlantic, General Electric and Boeing. Another group comprising Air New Zealand, Rolls-Royce and Boeing are aiming for a test flight in the near future.

Ian Godden, SBAC Chief Executive, said: "The aviation industry is committed to reducing its impact on the environment. As well as designing quieter and cleaner engines we are also looking at new fuels that deliver an environmental benefit.

"Recent test flights by Airbus and Virgin Atlantic have begun the testing process for alternative aviation fuels. There is, of course, a long way to go but the search for alternative fuels is another avenue that the aviation industry is exploring as it seeks to combat the challenges of climate change.

"The industry's Sustainable Aviation initiative aims to cut CO2 emissions by fifty per cent of 2000 levels by 2020. We have already cut fuel burn that leads to CO2 emissions by seventy per cent over the last fifty years. Alternative fuels research is a further line of enquiry for us as we seek to meet these tough, self-imposed targets."

Road transport fuel systems have one key requirement: to provide an uninterrupted fuel supply to the engine for a small range of conditions (ground temperatures, pressures etc.). As a result, meeting the requirements for alternative fuels for cars is relatively straightforward. For air transport the challenge is much greater. Aviation fuel systems must be able to operate over a much wider range of conditions (from hot day take-off to the cold temperatures and pressures at altitude) and power settings whilst satisfying multiple requirements.

To date, the only fuel that has been shown to fulfil all of these criteria, at a reasonable cost is kerosene. Therefore, kerosene has been utilised almost exclusively by the aviation industry throughout the world for many years. Aircraft engines, fuel supply and storage systems have been specially designed for this fuel type. Any new fuel should be able to operate without changes to existing aircraft or the current fuel supply and storage systems. Airlines would not be able to purchase whole new fleets of aircraft to deal with new fuels - they would need to be 'drop-in' replacements for existing aviation fuel.

Further challenges facing the industry seeking alternative aviation fuels include:
- A fuel must have a high energy content - to minimise CO2 emissions, fuel burn and operating costs;
- It must have a low freezing point so that it does not freeze at altitude;
- It must be stable in storage so that it does not degrade over time; and
- It must be compatible with aircraft materials.

In addition to fulfilling all of these requirements it must offer an environmental benefit. Over the whole life cycle of the fuel it must produce less greenhouse gas emissions than kerosene. It should also have minimal environmental impact in terms of its land and resource use.

Proposed alternative fuels include:
- Synthetic kerosene made from coal, gas or biomass.
- Biodiesel from crops such as rape, sunflowers, or plants such as palm or algae.
- Hydrogenated plant or vegetable oils.

However, each of these alternatives faces practical challenges - some offer little environmental benefit while others have many technical and logistical challenges to overcome. Academia and industry are working closely together to address them.

Source : SBAC