According to the Intergovernmental Panel on Climate Change (IPCC) in the year 2000, theaviation sector was responsible for 13% of global greenhouse gas emissions within the transportation sector (or 1.7% of anthropogenic greenhouse gas emissions from the global economy as a whole). As incomes continue to rise around the world, air travel is also expected to increase. Some estimate that global aviation traffic will continue to rise by roughly 5% a year.
In an effort to get ahead of the curve in September of this year, the US Federal Aviation Administration (FAA) partnered with some of the nation’s leading universities to develop a new Air Transportation Center of Excellence, charged with the goal of developing 1 billion gallons of jet fuel from renewable sources by 2018. This comes on the heels of the 2011 EU Advanced Biofuels Flight Path Initiative, which calls for the development of 2 million tons (or roughly 635 million gallons) of aviation biofuels by 2020. With annual jet fuel consumption in the US alone estimated at nearly 18 billion gallons, the goal of 1 billion gallons a year is merely a drop in the bucket. However, both the US and EU targets offer a step in the right direction.
A jet fuel from non-petroleum sources must overcome a series of hurdles before it can displace all or part of conventional jet fuel as a “drop-in” fuel. In order to be competitive with petroleum-based fuels, alternative jet fuels must meet the same safety and performance standards and also use the same transportation, storage, and delivery infrastructure as conventional fuels. There are two bodies that govern international jet fuel standards: ASTM International (Jet A Fuel) and the UK Ministry of Defence (Jet A-1 Fuel). These standards cover a variety of characteristics essential to jet fuel performance, such as safety (freeze and flash points), performance (heating value vs density), wear on fuel systems, and electrical conductivity. While any alternative jet fuel must meet these same rigorous standards, it is not necessary that it meets these standards entirely on its own. An alternative jet fuel may be blended with conventional jet fuel to compensate for the necessary properties that it lacks, just as ethanol is mixed with unleaded gasoline to power cars in the United States and elsewhere.
The only non-petroleum based jet fuel in widespread use today has been in use in South Africa for over two decades. This fuel uses a method called the Fischer-Tropsch (FT) process to turn coal into jet fuel, which is then blended with conventional jet fuel to be used in aircrafts. While the FT method may lead to a reduction in some pollution causing particulates in the air (see page 5 of this report by Chevron), it is still fully reliant on fossil fuels, and, as such, is not a renewable form of energy.
Alternatively, the HEFA (hydroprocessed esters and fatty acids) process for turning plant and animal fats into jet fuel was certified in 2011. According to this fact sheet published by the International Air Transport Association (IATA), 16 airlines have successfully and safely flown more than 1500 commercial passenger flights using a blend of conventional jet fuel and renewable biojet fuels developed through the HEFA process. The source material for these biojet fuels included plant matter, algae and even recycled cooking oil. While 1500 flights provide a meaningful test sample, it represents only a small fraction of air travel since 2011. However, the IATA believes that up to 6% of jet fuel could come from renewable sources by the end of this decade.
The technology to deliver biojet fuels has been developed, tested and certified. However, other hurdles still remain. To achieve widespread deployment, a reliable source material must be identified that can be produced in sufficient quantities and in such a way that does not compete with agriculture or other priorities for land and water usage. Also, absent an explicit price on carbon that would drive up the price of fossil fuels, supply chain, production and transportation efficiencies must be developed that lower the costs of biojet fuels to a level that is competitive with conventional fuel.
Both the the FAA’s Center of Excellence and the EU’s Flightpath Initiative are very much in their infancy. It remains to be seen whether public support for this project will be enough to lead to an appreciable reduction in greenhouse gas emissions from the aviation sector.