Scientists are a step closer to using Australia's eucalyptus trees to develop renewable jet and missile fuel.

"If we could plant 20 million hectares of eucalyptus species worldwide, which is currently the same amount that is planted for pulp and paper, we would be able to produce enough jet fuel for 5% of the aviation industry," says Carsten Kulheim, postdoctoral scientist at the Australian National University's (ANU's) Research School of Biology and co-author of a study examining the issue.

Eucalyptus oil contains monoterpenes that can be converted into fuel. Image credit: PixabayAccording to the study, eucalyptus-based fuel would initially be more expensive to manufacture on a mass scale than fossil fuels but Iould produce significantly less net carbon emissions. And, unlike fuels such as ethanol and biodiesel, it has sufficient energy density to be used in aviation.

"Eucalyptus oils contain compounds called monoterpenes that can be converted into a very-high-energy fuel, and this high-energy fuel can actually fly jets and even tactical missiles," says Kulheim.

The study examines how to boost production of monoterpenes to obtain industrial scales of jet fuel from the plants. Such steps involve selecting appropriate species, genetic analysis, advanced molecular breeding, genetic engineering and improvements to harvesting and processing of the oils.

Certain monoterpenes commonly found in eucalyptus oils such as pinene and limonene can already be refined through a catalytic process, resulting in a fuel with energy densities suitable for jet fuel. But the key to eucalyptus' value as a jet fuel source lies in developing the techniques to enhance oil yields, the researchers say.

"We can double, perhaps even triple, the yield that we can get per hectare to make a bigger dent in the aviation fuel industry," says co-researcher David Kainer, a PhD candidate at the ANU Research School of Biology. "We're looking for species that have the right type of oil. In addition to that, since the oil is in the leaves, they need to grow a lot of leaves in a short amount of time."

According to the researchers, eucalyptus plantations globally produce up to 200 kg of oil per hectare annually. But by selecting the best genetic stock, they could produce more than 500 kg of oil per hectare. Moreover, the jet fuel derived from eucalyptus oils would be close to carbon neutral.

"It has minimal ecological impact," Kulheim says. "We can plant these trees on marginal lands that have low rainfall, and we can also plant them in agricultural systems that have salinity problems and help them defeat that problem."