I've been following the trend-setting ways of Richard Branson's Virgin Group of companies for many years, so I'm not surprised to see them on the cutting edge of alternative fuels for commercial jet aircraft. Running a normal 747 on a blend of 80% jet kerosene and 20% biofuel is a daring move, especially coming just a few weeks after the remarkable Heathrow crash-landing of a British Airways B-777, in which fuel contamination now seems to be the leading focus of the accident investigation. As this article in the San Francisco Chronicle makes clear, it's going to take years of testing before large passenger aircraft are certified to fly on something other than petroleum distillate, but the rewards for finding suitable substitutes have energized both private and military aviation to pursue this goal.
Each generation of new passenger jets seems to be more fuel-efficient than the one before it, with Boeing's new 787 Dreamliner representing the current state of the art, coming in at just a hair under 100 passenger-miles per gallon, compared to an industry average of around 60 mpg. Nevertheless, the cost, emissions and long-term availability of jet fuel derived from crude oil look like major limitations on the future growth of commercial aviation. Fuel accounts for more than a quarter of the US commercial airlines' cost structure and exceeds labor as a component of unit costs per available seat-mile. That's why United has started charging extra for checked bags. This gives airlines a big incentive to find cheaper, more sustainable energy sources for the long-term, an incentive shared by the Pentagon, as it seeks to reduce the cost of its operations and logistics.
None of this changes the fact that aircraft engines and their fuel systems must work in very challenging environments, with widely-varying temperature and humidity. You can make a turbine engine pretty tolerant of fuel quality when it's sitting on the ground generating electricity at a power plant, and I wouldn't be surprised if biofuels became a popular fuel for gas turbines, when natural gas gets back to BTU parity with crude oil. However, put that same engine at 40,000 feet and -40 degrees F., and suddenly fuel quality matters very much indeed. That's why oil refiners are choosy about the crude oils from which they produce jet fuel, and then go to extraordinary lengths to segregate it from any possible source of contamination from the other products in the distribution system.
The pursuit of alternative forms of jet fuel raises two key questions, relevant to both military and commercial use. First, can the fuel be manufactured to meet the necessary specifications for jet fuel with absolute consistency? Most manufacturers of high-speed diesel engines will not certify a fuel containing more than 20% biodiesel, so Virgin's choice of a 20% biofuel blend for this even more sensitive application looks aggressive. The US military's choice of alternative fuels produced using the Fischer-Tropsch synthesis (FT) and starting with very simple molecules (from natural gas or gasification) looks much safer in this regard. In fact, this route should provide even greater control over the specific properties of the resulting jet fuel blend than if it all came from the distillation and conventional processing of crude oil.
The bigger question is whether any of these substitutes can be produced at a lower cost than oil-based avjet. Although unsubsidized oilseed-based biodiesel typically costs more than untaxed petroleum diesel, fuels produced using FT synthesis could be significantly cheaper. At a typical 60% conversion efficiency, synthetic jet fuel from natural gas would cost about $1.60/gallon, based on gas at $8/MMBTU. That's a lot less than the $2.56/gallon average price that airlines are reportedly paying for Jet-A today, and synthetic jet fuel from coal-to-liquids or biomass gasification might cost even less, at least before the cost of the extra carbon emissions from coal is considered.
For a long time, aviation appeared to be the only transportation segment without a viable energy substitute for petroleum products. The high price of oil, new technology--or at least new applications of an old technology--and the rapid development of the biofuels industry looks set to alter that conclusion in this decade. The prospect of creating synthetic kerosene from scratch from a wide variety of materials at a lower net cost than oil should provide all the incentive necessary for airlines and aircraft and engine manufacturers to plow through the lengthy testing and certification process for these fuels, without cutting any corners on safety. I'll be watching the results of Virgin's test flight with great interest.