Boeing is working with the US Federal Aviation Administration (FAA) and other stakeholders to gain approval for the direct blending of renewable “green” diesel into aviation fuel, thereby further reducing the aviation industry's carbon emissions.
Renewable diesel made using oils and fats is chemically similar to today’s aviation biofuels, according to Boeing analysis. If approved, the fuel would be blended directly with traditional jet fuel. A blend percentage would be established through the testing and review/approvals process, according to Jessica Kowal in Boeing’s Environmental Communications. The company’s internal goal is to see this approved this year.
If approved, the green diesel fuel could be used for jets as well as in diesel engines, at price parity with fossil jet fuel—a huge advantage. Renewable diesel could quickly and significantly provide a large supply of sustainable aviation biofuel for airlines, cargo companies with air-ground operations, and the military.
Green diesel approval would be a major breakthrough in the availability of competitively priced, sustainable aviation fuel. 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.—Dr. James Kinder, a Technical Fellow in Boeing Commercial Airplanes Propulsion Systems Division
Significant green diesel production capacity already exists in the US, Europe and Singapore that could supply as much as 1%—about 600 million gallons—of global commercial jet fuel demand. The wholesale cost—about $3 a gallon with US government incentives—is competitive with petroleum jet fuel.
Boeing, the F.A.A., engine manufacturers, green diesel producers and others are now compiling a detailed research report that will be submitted to key stakeholders in the fuel approvals process. These efforts follow Boeing’s leadership in working with the aviation community in 2011 to include a blend of up to 50% aviation biofuel in international jet fuel specifications. Biofuel approved for aviation must meet or exceed stringent jet fuel performance requirements.
The concept of a single fuel servicing multiple transportation platforms has some similarities to the JP-8 strategy followed by the military—a kerosene-based fuel used for jet aviation now used as a replacement for diesel fuel in tactical ground vehicles, electrical generators and other applications.
In that case, studies have found that using JP-8 in diesel engines offers significant benefits, such as less fouling of the fuel injection system and potentially lower soot emissions. However, JP-8 also has a lower volumetric calorific value than diesel, which translates to higher fuel consumption and shorter range.
As another issue, the cetane number (CN) of JP-8 is highly variable, potentially leading to misfire and a compromise in the ability of an engine to start reliably. Further, the high volatility and low cetane number of JP-8 translates to more vigorous combustion, resulting in knocking and potential damage to the piston.
Researchers from the University of Michigan, with colleagues from US Army TARDEC and Daimler, are among those investigating the impact of JP-8 on ground vehicle combustion, performance and emissions.
However, Boeing is not proposing a “universal fuel” approach, Kowal noted. Rather, the company has an “all of the above” strategy for alternative fuels. The goal is not to predict winners but to identify fuel pathways or feedstocks that can be grown, harvested and processed sustainably and at a price point that’s competitive with fossil fuel.