As aircraft are bound (still) to a liquid fuel (it has the most energy content per weight) alternative resources need to be converted into liquid fuels. The industry needs to consider which source is the best for biofuel, it needs to be relatively easy to 'harvest' compared to petroleum fuel, with no impact on human food or water supply whatsoever and must be environmentally friendly.
Aircraft engines still cannot run on water but, indirectly, this water can be and is a source of algae. And these algae have a high yield compared to other biomass sources which makes them very interesting to the energy industry. A big advantage of many biofuels over 'normal' fuel types is that they are biodegradable, and if spilled, are harmless to the environment.
At present biodiesel (and its gasoline counterpart) is able to reduce emissions from a diesel or jet engine without any major changes in the engine itself. Just use it and enjoy the benefits. It can be mixed with JET (A1 or A) too and test with a King-Air has shown much cleaner exhaust gases with almost equal performance.
A Delfin L-29 has been flying on biodiesel (made from waste oil) since October 2007. The fuel was produced by BioDiesel Solutions of Sparks, Nevada. This aircraft is type rated to use anything from heating oil, JP-4 and JP-8; and as such is ideal for testing purposes.
Biodiesel has been known to improve engine performance with much enhanced lubricity and reduction of emissions. It is very easy to use, nontoxic, biodegradable and contains almost zero aromatics and sulfur. At the moment the main biodiesel users are mass transit, trucking, marine, military, automotive and other sectors such as mining. Very soon, aviation will be one of them too.
In 1998, a study was sponsored by both the U.S. Department of Energy and the U.S. Department of Agriculture, which determined biodiesel reduces net carbon dioxide by 78 percent when compared to normal petroleum diesel. The carbon cycle of biodiesel is the cause of this. The carbon dioxide released into the atmosphere when biodiesel is burned is recycled by growing plants, which are later processed into fuel. So nothing is added to the atmosphere, except the amount produced by the production process.
The aviation industry is working hard at reducing fuel consumption, mainly by much better engine design, newer cleaner fuels and improved aerodynamics and aircraft design.
Swift Enterprises claims that their biomass replacement aviation gasoline (based on bio-derived mass with acetone as feedstock resulting in an iso-pentane fuel) has the following properties:
Recently (July 2010) the FAA has tested Swift Enterprises biofuel in a Lycoming engine.
Update Mar 2020: Swift now has a UL94 (98 octane, ASTM D7547) unleaded drop-in Avgas replacement for the 100 LL AVgas we use until now (for low compression engines). It has been produced and sold since 2015 in Indiana (US), as of Sep 2021 California is also being provided with this unleaded fuel. Make sure that your aircraft/ engine can handle it by visiting the following link to the website of Swift Fuels. Hopefully the rest of the world will follow soon.
As per Swift: "UL94 is a 94+ Motor-Octane aviation gasoline without Tetraethyllead that meets the ASTM D7547 Unleaded Avgas specification. UL94 is also rated as a super-premium ethanol-free auto-gasoline with a 99 octane (R+M)/2 rating that meets and exceeds the ASTM D4814 autofuel specification. UL94 Unleaded Avgas has an indentical density to 100LL, meaning weight and balance calculations will not change by using UL94."
This means that even Rotax engines can use this new fuel without harming the environment with poisonous lead. And: return to 100 hour oil changes too! Saves a lot of money.
General Aviation Modifications claims a fuel, G100UL, that is based on a 95 octane blend (ASTM D910) with a non lead containing additive to raise the octane to 100, testing should begin early 2010.
Time will tell if these fuels will be a certified drop in replacement for our current AVgas 100 / 100 LL fuels. As we need a 100 octane fuel, if the additives used to reach that level are more expensive than tetraethyl lead then it will not be very economical.
Progress seems slow with this fuel; in 2017 GAMI reported that they had to do a lot of fundamental research and development work with regard to detonation tests.
At this moment a number of international companies are working together to research the use of GTL fuel in aircraft engines. The source for this would be coal, gas or other biomass. The expectation is to start flight tests in a 50/50 mix with JET A/A1 by the end of 2008 and to switch over to a full SYNJET A/A1 by 2010 (SYNJET = Synthetic JET).
Engine manufacturer Rolls-Royce together with Boeing, Air New Zealand (B747-400) and Virgin Atlantic will do tests with biofuel based on algae sources. The USAF has already done a number of successful flight tests on a C-17 Globemaster, B-52 and a Rockwell B-1B aircraft. This biofuel was mixed in a 50/50 ratio with JP-8 fuel. They expect to certify biofuel for general use in 2011.
A number of airline companies are starting tests (early 2008) with bio or GTL synthetic produced JET fuel to assess the performance and gain experience in running engines on these new fuels. Air New Zealand is testing with Jatropha oil as a source for SYNJET. These Jatropha seeds are toxic and using this as fuel (like algae) will not impact food supply.
Air New Zealand (ANZ) reported (end 2008) a successful first test flight of a Boeing 747-400 powered in part by the biofuel Jatropha. The biofuel blend of 50/50 Jatropha and JET A1 fuel was used to successfully power one of the Rolls-Royce RB211 engines on the 747-400. A number of tests were done during the two hour flight from Auckland International Airport all with satisfying results.
Paris, Le Bourget 2009: Boeing and Industry Study Shows Biofuels Perform Effectively as Jet Fuel.
September 2009, ASTM International published a new JET fuel specification for aviation turbine fuels containing synthesized hydrocarbons, D7566.
In November 2009, KLM conducted a test flight (with passengers) in a Boeing 747 were one of the engines ran a mix of Camelina plant oil and normal JET fuel.
February 2010, British Airways and US based Solena announced that they will start manufacturing their own bio-jet fuel made from waste in a factory east of London. Expected fuel volume is more than 16 Mil. US Gallon per year.
From NASA: "In late March and early April 2011, a team at NASA's Dryden Flight Research Center in California tested renewable biofuel made from chicken and beef tallow in one of the four engines of a DC-8 airplane". These where ground run tests in NASA's DC-8 and exhaust gases were cleaner with fewer pollutants.
These new fuels are called bio-derived synthetic paraffinic kerosene (bio-SPK).
It has been quiet lately on biofuels, but French aviation companies are giving it another try with SAF, Sustainable Aviation Fuel. A study and test flight will commence in 2021 in an single aisle airliner, read more in the story from AVweb on Sustainable Fuel StudyWritten by EAI.