The answer (or at least, one new possibility) appears to have been found in a biofuel that is already in widespread use. New Boeing research suggests that “green diesel” – a renewable fuel that is used in trucks and other ground transportation – is chemically similar to today’s aviation biofuel and can be used to power aircraft.
Green diesel is made from oils and fats such as recycled animal fat, used cooking oil and inedible corn oil, and Boeing says that if it is approved, the fuel could be blended directly with traditional jet fuel. As it is already in use, green diesel production capacity already exists in the US, Europe and Singapore, and the aircraft manufacturer calculates that the fuel could fulfil as much as one per cent – about 600 million gallons – of global commercial jet fuel demand.
It also comes at the competitive cost of $3 a gallon at wholesale, albeit that figure includes US government incentives. Additionally, Boeing estimates that green diesel would emit at least 50 per cent less carbon dioxide than fossil fuel over its lifecycle.
Green diesel – also called renewable diesel – still needs to be approved for use in aviation, but Dr. James Kinder, a technical fellow in Boeing’s commercial propulsion systems division, said this step would represent a “major breakthrough in the availability of competitively priced, sustainable aviation fuel”. He commented: “We are collaborating with our industry partners and the aviation community to move this innovative solution forward and reduce the industry's reliance on fossil fuel.”
To this end, Boeing will now work with the Federal Aviation Administration, engine manufacturers, green diesel producers and others in compiling a detailed research report that will be submitted to the relevant parties in the fuel approvals process.
Green diesel can be used in any diesel engine and is chemically different to the fuel known as biodiesel. On its own, it seems there won’t be enough of it to be considered the “definitive” alternative fuel, but the potential to fulfil a significant proportion of jet fuel demand could just help in accelerating the overall development of a range of biofuels, decreasing dependence on fossil fuels still further.
Jason Holland, Editor, Aircraft Technology Engineering & Maintenance