DOE issues report on reducing commercial aviation GHG emissions

The U.S. DOE’s National Academies of Sciences, Engineering and Medicine recently released a report dedicated to reducing carbon dioxide emissions from commercial aviation, with the focus on large single- and twin-aisle planes that transport more than 100 people. The report found that these aircrafts account for more than 90 percent of greenhouse gas (GHG) emissions from all commercial aircraft.

The report, entitled “Commercial Aircraft Propulsion and Energy Systems Research: Reducing Global Carbon Emissions (2016),” found that approximately 2 to 2.5 percent of global CO2 emissions comes from aviation each year. This percentage is lower than many other transportation and industry emissions, however, the need for such research was acknowledged as commercial air travel continues to increase and it takes a new technology a long time to spread into and through the aviation fleet.

In order to produce the report, the National Academies of Sciences, Engineering and Medicine organized a committee to develop an approach for decreasing CO2 emissions in commercial aircraft. The committee identified 12 high-priority projects and divided them into four topics focused on propulsion and energy system technologies. The four topics include: 1) advances in aircraft-propulsion integration, 2) improvements in gas turbine engines, 3) development of turboelectric propulsion systems, and 4) advances in sustainable alternative jet fuels.

The committee recommended that researchers focus on these topic areas to implement emission-reducing projects within the next 10 to 30 years.

According to the report, improvements in gas turbine engines research are needed to increase gas turbine engine efficiency by as much as 30 percent compared to current engines and therefore reduce CO2 emissions. Developments in turboelectric propulsion systems research are achievable for single-aisle aircraft in the 10 to 30-year time frame, and these planes will have the capacity to reduce fuel burn by approximately 20 percent compared to current commercial planes. Sustainable alternative jet fuels (SAJF) can substantially decrease life-cycle CO2 emissions. The report uses the term sustainable alternative jet fuels or SAJF to characterize a family of drop-in fuels that are intended to lower the net life-cycle carbon emissions of commercial aviation.

The committee relayed in the report that it is essential to develop drop-in fuels since they can have an immediate impact on lowering global aviation GHG emissions due to their compatibility with existing aircraft and infrastructure. Another point the committee made is that SAJF could also reduce other harmful emissions, such as sulfur oxides and particulate matter, compared to conventional jet fuel.  Further, the committee felt that SAJF could also be pursued in parallel with the three other approaches to achieve GHG emission reductions.

Of the 12 projects identified in the report, for SAJF, one project would undertake research to enable detailed and comprehensive modeling and analysis of SAJF development efforts for both individual projects and nationwide efforts to support the needs of policymakers and industry practitioners. The report stated that the variability in the many different sustainability frameworks relevant to SAJF complicates the process of developing these technologies.

One example provided in the report is the U.S. renewable fuel standard (RFS) program and the Roundtable on Sustainable Biomaterials requiring advanced fuels to achieve at least a 50 percent reduction in life-cycle CO2 emissions. “This 50 percent minimum reduction disincentives the potential of some synthetic fuel production pathways that could produce lesser but still substantial life-cycle reductions in carbon emissions,” the report stated.

Another SAJF project outlined in the report is focused on developing sustainable, low-cost feedstocks and associated systems that have the potential to enable the large-scale production of economically viable SAJF. Waste streams of potential interest include municipal solid waste, human waste and sanitary waste treatment, animal waste, animal processing waste and gaseous waste.

A third project would develop technologies and processes for cost-effective feedstock conversion, fuel production and scale up from pilot and demonstration facilities to enable full-scale production of SAJF.

The last SAJF-focused project is aimed at improving fuel-testing, evaluation and qualification efforts to lower testing costs, increase throughput and enhance understanding of fuel properties.

To date, more than 20 airlines have flown more than 1,600 demonstration and proving flights using SAJF produced in limited production runs from pilot facilities and facilities temporarily configured for SAJF production, according to the report. The U.S. Navy, Defense Logistics Agency and others have expressed interest in supporting and purchasing biofuel blends. AltAir Biofuels facility in Paramount, California, is the first commercial production facility for SAJF, which was commissioned last year. This facility serves United Airlines and World Fuel Services.

There are currently five qualified fuel production pathways, and the report noted that an additional three pathways could be approved before the end of 2017. ASTM D7566 (Standard Specification for Aviation Turbine Fuel Containing Synthesized Hydrocarbons) will be expanded to provide specifications that encompass all of the feedstocks and conversion processes approved for use in each new pathway that is accepted.

Companies that have received funding from the Defense Production Act include Fulcrum Bioenergy, Red Rock Biofuels and Emerald Biofuels. These three are targeting starting production in the 2017-18-time frame and two have agreements with major airlines. These facilities estimated 50- to 100-million-gallon production volumes per year could constitute 0.3 percent of total U.S. demand for jet fuel. With U.S. commercial aviation consuming 20 billion gallons of jet fuel in 2020, 308 million gallons of conventional jet fuel would need to be replaced by SAJF with a 65 percent reduction in life-cycle carbon emission to lower the total net carbon emissions of U.S. commercial aviation by 1 percent, the report gathered.

There are challenges—systemic, policy, technical and economic—to reducing CO2 emissions in commercial aircraft, but according to this report, research needs to continue on all four approaches to address CO2 emissions caused by the global growth of the aviation industry.

The full report can be downloaded here.