Will tomorrow's jet fuel be grown in the sea?

Just over two per cent of the world’s carbon dioxide emissions come from the aviation industry. Intensive efforts are currently being made to reduce that proportion. Research into eco-friendly biofuels is a cornerstone of these efforts.

The most common fuel in commercial jet aircraft is Jet A1. It’s similar to everyday diesel fuel but is adapted to cope with the extra stresses that great variations in air pressures and temperatures entail, so it’s not just carbon dioxide that presents a challenge in the hunt for new fuels. Fuel performance standards are high, and scientists hope to avoid a number of the problems the first generation biofuels suffered from such as excessively high flashpoints and freezing points. Bearing in mind that the early biofuels competed with food crops and forced up food prices around the world it’s easy to see that the next generation of fuels has a number of hurdles to overcome.

Rolls Royce performing test flights with jatropha oil

A number of different fuels based on various energy crops are being developed in parallel in order to increase the chances of finding a fuel that meets the very high standards. In 2008 Air New Zealand and Boeing carried out a test flight together using a 747-400 on which one of the Rolls Royce engines was run on a fuel mixture comprising 50 per cent Jet A1 and 50 per cent biofuel based on jatropha oil from the spurge plant.

In 2009 Continental Airlines carried out a test flight with a Boeing 737 in which one of the engines was run on a 50/50 mixture of biofuel and regular jet fuel. The biofuel concerned was produced from algae. The test proved that performance remained unchanged, and that fuel consumption in the engine using biofuel was actually lower than in the other engine. The energy content in the biofuel was simply higher, which presents opportunities for climate benefits resulting from the lower fuel consumption.

Another example of an energy crop used in tests is camelina, whose oil was used among other things to make fuel when Japan Airlines carried out a test flight in 2009. The U.S.Navy has also shown great interest in fuel based on camelina, and it has tested running different types of helicopters and fixed-wing aircraft on the fuel.

A fourth and final category of energy crop that has been promoted as a potential fuel source are various kinds of halophytes, i.e. plants that can grow in highly saline environments and can therefore be cultivated in areas where traditional crops do not thrive. It is precisely this characteristic – the ability to be cultivated without competing with other food production – that is one of the criteria against which the new biofuels are evaluated.

Half fossil-free air transport by 2040?

So when can we expect to see biofuels forming a significant proportion in fuel mixes in commercial flights? It is of course impossible to foresee, and depends on how well tests proceed, but forecasts point to around 15 per cent of aircraft fuel consisting of biofuel by the year 2020. By 2030 the proportion is expected to be 30 per cent, and in 2040 experts anticipate that half of all fuel used in aviation will be biofuel.

The process of developing efficient, eco-friendly, commercially viable biofuels presents many challenges, but successful test flights and analyses that show potential carbon dioxide emission reductions of 84 per cent over the life cycle mean that these efforts form a crucial part of aviation’s climate adaptation. Furthermore, aviation is at an advantage as it has relatively few nodes that supply a large part of the fleet with fuel. In certain respects the implementation of new standards is therefore easier for the aviation industry compared to surface transport whose supply network is more widespread.

Article first published March 2011