"Airlines are faced with the challenges of progressively improving environmental performance and lessening impacts to global ecosystems while continuing to reduce operating costs. Bio-derived jet fuel is a key element in the industry strategy to address these challenges."
A biofuel is a fuel that is derived from renewable plant or animal sources and used in an engine.
The energy of a biofuel is derived from biological carbon fixation, which is the conversion of carbon dioxide to organic compounds by living organisms. The most common mechanism for carbon fixation is photosynthesis in plants.
For use in an engine, the energy stored by carbon fixation must be extacted from the biomass (biological material from living, or recently living organisms) by various processes to produce biofuel. As examples:
- Bioethanol - an alcohol produced by the fermentation of the carbohydrates found in crops such as corn. Non-food sources, such as grasses, are being developed for ethanol production
- Biodiesel - made from vegetable oils and animal fats using a chemical process known as transesterification
- Methane - a biogas produced by anaerobic digestion, the breakdown of biodegradable material by micro-organsims, from animal manure, diverted landfill waste or from plant material.
Biofuels, if produced in sustainable ways, can contribute less to climate change than their fossil fuel conterparts. This is because, unlike fossil fuels, biofuels have the potential to remove carbon dioxide from the atmosphere during the biomass growth portion of their production and utilisation cycle.
Aviation Carbon Emissions
The aviation industry has targeted the achievement of carbon neutral growth by the year 2020. By 2050, the industry is further committed to reducing its carbon footprint by 50%, using 2005 levels as the benchmark. The development and widespread use of aviation grade biofuels is a key strategy in this initiative.
Significant and sustained research and development of biofuels suitable for aviation use is relatively new. Driven by the need to find an alternative to finite fossil fuel reserves and the requirement to improve environmental performance, lessen the aviation carbon footprint and reduce operating costs, industry, operators and regulators are turning their attention to biofuel solutions. The current primary focus is on a sustainable "drop-in" biofuel suitable for use in turbine engines.
A "drop-in" fuel is one that can be blended with fossil based fuel and used without requiring any changes to engines, airframes or fuel distribution systems. It must also have an energy density that matches or exceeds that of petroleum derived jet fuel and be usable at the temperature extremes of the operational envelope.
To be considered sustainable, the biofuel should come from renewable sources that do not displace food crops or compete with food crops for land use or water. Ideally, they will also have a carbon neutral lifecycle (growth/production/use) and it is also desirable that growth and production of the biomass stocks create a locally positive socioeconomic impact. Some of the oil bearing plants meeting these critera include:
- Camelina - An oil seed crop used as a rotational crop in modern agricultural practices
- Jatropha - A drought resistant, nonedible plant that can grow on marginal land
- Algae - Simple, photosynthetic organisms that can be grown in wastewater or seawater
The aviation biofuels produced from these and other plants are referred to as synthetic paraffinic kerosene (SPK) or as hydroprocessed fatty acid esters and free fatty acids (HEFA) fuels. The international specification for the chemical composition of HEFA fuel is more strict than for conventional jet fuel, greatly reducing the likelihood of potential contamination caused by the biofuel. In 2011, the international aviation and fuel communities approved the blending of petroleum and bio-based fuels for use in commercial aviation.
Aviation Biofuel Milestones
Prior to in-flight use, HEFA fuels were exhaustively tested under both laboratory and ground engine run conditions. Blends containing conventional jet fuel and up to 50% biofuel were compared against unblended petroleum based fuel with no significant performance variances observed. Inflight testing milestones include:
- February 2008 - Virgin Atlantic 747-400 flight with one engine burning a 20% biodiesel blend
- December 2008 - Air New Zealand 747-400 flight with a 50/50 blend of Jatropha based biofuel and convential fuel
- January 2009 - Continental Airlines operates the first flight with an algae derived biofuel
- January 2009 - Japan Airlines 747-300 flight with a 50/50 blend of jet fuel and Camelina/Jatropha/Algae based HEFA fuel
- June 2011 - Boeing Company 747-800 freighter transAtlantic flight with all engines burning a 15% HEFA fuel blend
- August 2011 - Aeromexico 777-200 transAtlantic flight with revenue passengers using a 30% Jatropha based blend
Since 2011, the use of blended biofuel in commercial operations has become increasingly more common although price and availability have, thus far, limited its widespread utilization.
- ^ Leading the Way to a Biofueled Future, Boeing AERO Magazine QTR_1 2013