Biofuels – made from algae and non-food plants – are emerging as a potentially viable alternative to conventional jet fuels. Although big challenges remain, the reductions in greenhouse gas emissions could be major.
Earlier this year, a Continental jet accelerated down the runway at George Bush Intercontinental Airport in Houston. Nothing out of the ordinary for Capt. Rich Jankowski, who countless times in his 38-year career had eased such two-engine Boeing 737-800s into the sky. Except on this experimental flight, one of the engines Jankowski relied on was burning fuel derived from microscopic algae to push the 45-ton aircraft into the air and keep it aloft — a first in aviation history.
Last year, Virgin Atlantic flew the first commercial jet on biofuels, a 40-minute jaunt between London and Amsterdam in which one engine burned a mix of 80 percent conventional jet fuel and 20 percent biofuel derived from coconuts and babassu nuts. Other test flights have followed, culminating in a 90-minute Japan Airlines flight with one engine burning a blend of biofuel from camelina — a weedy flower native to Europe — and regular jet fuel at the end of January.
As global economies strive to wean themselves off fossil fuels, one of the most daunting challenges is to find a replacement for the liquid fuels that power the world’s aircraft. Biofuels made from algae and non-food plants are now the leading contenders. While homes, cars, and offices can be powered by electricity produced from such renewable sources as solar, wind, and hydropower, there is little likelihood in the near future that battery power will be lifting a jumbo jet into the sky. And the global aviation industry uses an enormous amount of jet fuel — energy-dense kerosene — frequently referred to as Jet A or JP-8: The U.S. commercial airlines alone burn about 50 million gallons of jet fuel every day, at a cost of roughly $150 million.
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That’s a lot of greenhouse gases, released right where they can do the most damage — high in the atmosphere. The warming properties of jet fuel exhaust are intensified at high altitude, where nitrogen oxides from the jet’s turbines react with other molecules in the upper atmosphere to increase levels of ozone, which traps heat, according to the Intergovernmental Panel on Climate Change. The water vapor that forms contrails and other chemically active gases emitted during flight also contributes to climate change. Although the amount of emissions from aircraft compared with other vehicles is relatively small — roughly 3 percent of total worldwide greenhouse gas emissions from fossil fuel burning — the mix of compounds in jet emissions and their release in the upper troposphere intensifies their heat-trapping power.
The environmental appeal of biofuels — especially if they are produced from algae or other non-food sources — is strong. Preliminary results from an Air New Zealand test flight in December show that burning biofuels — in this case jet fuel refined from jatropha oil — can cut greenhouse gas emissions by at least 60 percent compared to conventional fuel. And, as a bonus, about 1.4 metric tons of fuel could be saved on a 12-hour flight using a biofuel blend.
This month, the International Air Transport Association set a goal of achieving "carbon neutral growth" — meaning an increase in air travel would not emit any more CO2 than the present fleet and flight schedule — by 2020. The keys will be increasing fuel efficiency by 1.5 percent per year and using biofuel blends, according to IATA.
The overwhelming challenge is how to produce enough biofuel to supply even a fraction of the more than 60 billion gallons of jet fuel burned every year by the world’s aircraft. Relying heavily on biofuels made from food crops — such as soybeans, sugar cane, or canola — would not only affect food supplies and increase food prices, but would produce significant greenhouse gases during the planting and harvesting of these crops, as well as from forest clearing for more agricultural land. Non-food plant sources, such as jatropha and camelina, are promising, but difficult to produce in large quantities and can end up displacing food crops or lead to deforestation if the price of fuel rises high enough. Finally, making large amounts of jet fuel from algae represents a major hurdle, from perfecting the algae’s growth to extracting the oil cost-effectively.
