For years, researchers have been working on methods to combine plant-based fuels with conventional petroleum-based fuels. A key goal is to reduce carbon emissions, though related factors such as cost and sustainability are also driving the studies.
Synthetic fuels made from a range of biofeedstocks are advancing rapidly. ASTM International, a standards group that is shepherding the fuel standard, is expected to approve a document within the next year. Companies as diverse as Boeing, Continental Airlines, Air New Zealand, and Rolls-Royce have all successfully tested a 50:50 version of the synthetic fuel.
Much of the effort centers on synthetic paraffinic kerosene (SPK), a fuel that can be created from a variety of plants. Many feel that it’s nearly ready to move from research into full production. “SPK is very close to becoming a proven fuel,” said Alan Epstein, Pratt & Whitney’s Vice President of Technology & Environment.
One of the key factors that will help drive market success is that this biofuel doesn’t require changes in existing engines. That means the changeover can occur throughout the supply chain without any investment in new equipment.
“Drop-in alternatives allow great carbon relief without modifying engines, the fuel delivery infrastructure, or the aircraft,” said Steve Csonka, ecomagination Technical Leader for GE Aviation.
Once the fuel is approved and production begins, many observers predict that blended fuels will move slowly but steadily to higher percentages of biofuel. There is a strong feeling that the industry will be able to develop the processes needed to continue this trend all the way up to 100% biomaterials.
What those materials will be and how they’ll be processed remains an open question. There are many methods for converting plants to fuel. Many companies are focusing on a single approach rather than spreading their efforts around.
“Embraer has monitored technologies like hydrogenation, fatty acid esters, biomass to liquid, and others, but we are working with one technology based on sugar cane fermentation and biological synthesis,” said Luiz Rimoldi, Technological Development Manager for Embraer. Some initiatives call this sugar cane fermentation technology FRJ, he noted.
Others believe that the selection of plants will have a significant impact on the global production. Some observers note that producing enough feedstock may still be a challenge. It currently takes about an acre of soybeans to produce 100 gallons of jet fuel.
“It will take a lot of acres to provide the 75 billion gallons of jet fuel the world uses,” said Epstein. Much research focuses on algae, which may be able to produce as much as 1000 gallons per acre.
Though researchers are driving a change to bio-SPK, they are also looking at alternatives such as liquid hydrogen and natural gas. However, these fuels may be facing a longer road to full production.
“The conundrum is that it’s not clear there will be any one winner,” Csonka said. “There’s a problem with taking different paths. Another problem is that the infrastructure problems are pretty dramatic.”