PARTNER publishes first comprehensive study into comparing life-cycle GHG emissions of aviation alternative fuels on GreenAir Online

Thu 27 May 2010 – The first-ever study into a comparison of the life-cycle greenhouse gas (GHG) emissions of a range of alternative aviation fuels has been published by the Partnership for AiR Transportation Noise and Emissions Reduction (PARTNER), based at the Massachusetts Institute of Technology (MIT). The work uses consistent methodologies to facilitate equitable comparisons, with a range of life-cycle GHG emissions provided for each feedstock. Importantly, it provides an examination of emissions from land use change, a current issue of concern.

The range of drop-in fuels studied cover Fischer-Tropsch (F-T) fuels as well Hydrotreated Renewable Jet (HRJ) fuels such as from jatropha, although camelina, which has already been used on test flights, will be analyzed only in a future study. The report was sponsored by the FAA.

The researchers – Russell Stratton, Hsin Min Wong and James Hileman – point out that life-cycle GHG emissions are but one of many considerations when evaluating the feasibility and sustainability of an alternative fuel option and that few biofuels have zero life-cycle GHG emissions. There are also considerable differences in life-cycle emissions in the various biofuel options, with land use change contributing most to this variability.

Many of the fuel pathways examined have baseline life-cycle GHG emissions that are lower than conventional jet fuel but have the potential to be much higher (see table below). “For this reason,” says the report, “it is essential not to simply assume that biofuels are environmentally beneficial without knowing the specifics of how the fuel is produced.”

The report, which has been driven from a US perspective, says water availability could be a limiting factor for biofuel production in certain US regions and biofuel expansion within the US would require a significant increase in crop and feedstock production. It also warns against introducing non-indigenous species into an unprepared ecosystem.

As aviation is not the only potential user of limited renewable biomass resources, it will have to compete with other sectors. “Furthermore, large land area requirements indicate that it is unlikely that a single region could create sufficient biomass to meet worldwide demand for biofuels,” say the researchers. “Hence, it is probable that large-scale implementation of biofuels would arise as a superposition of regionally appropriate feedstocks. Current actions with regard to biofuel expansion are important in realizing the potential of this industry.”

Some alternative fuels could play a central role in mitigating aviation’s contribution to climate change, says the report, and if appropriate renewable feedstocks were used, both F-T and HRJ fuels could provide aviation with modest (around 10%) to large (around 50%) reductions in emissions. If projections of soil carbon sequestration prove valid, it calculates a salicornia-based biofuel could have a 100% reduction in life-cycle GHG emissions.

The life-cycle assessments have been compared against conventional jet fuel production, with the properties of conventional crude oil based on the average crude oil projected to reach US refineries in 2015. The researchers believe there is a definite trend for crude oil to become heavier and more ‘sour’ (more sulphur) in the future. “Therefore, a business-as-usual scenario would likely see jet fuel production becoming more energy intensive as more hydroprocessing is required to maintain current product quality,” they say. “This means the energy intensity of refining may increase beyond the values used in this study.”

A more complete assessment of land use change emissions that includes indirect effects is being developed as part of ongoing research. According to the researchers, most indirect effects are expected to occur on an international scale and should be analyzed in the context of the global market.

Likewise, the researchers will also expand the project to consider additional fuels such as from camelina, as well as those derived from pyrolysis oils and fermentation. They also plan to quantify their fuel options in terms of production cost, water use impact and production potential.

Although not all feedstocks will have the potential to displace large volumes of petroleum fuel, they say, any feedstock produced can provide valuable experience through benefitting local economies and providing essential lessons in production and processing techniques.

“This experience would be invaluable should a higher-yield crop, such as algae become commercially viable,” concludes the report. “The most significant challenge is not in developing viable alternative fuels that could reduce aviation’s GHG emissions – the technology exists; rather the challenge lies in developing and commercializing the large-scale production of next generation biomass feedstocks that could be grown in a sustainable manner.”

Commenting on the report’s publication, Dr Lourdes Maurice, the FAA’s Chief Scientist for the Environment, said: “This represents a critical step forward in the road to deploying alternative aviation fuels. Through this, and other projects in its portfolio, PARTNER is establishing technical leadership in the field of alternative fuel life-cycle analysis.”