Dubai Air Show

In search for alternative fuels, the focus turns to synthetics

 - November 8, 2007, 2:12 AM

Synthetic fuel seems to be the new Holy Grail of air transport. The prospect of oil reserve depletion, the need to curb CO2 emissions and energy security concerns are all encouraging the industry to find a viable alternative to the current jet-A1 kerosene that can be used in current engines.

One recent initiative in the pursuit of synthetic fuel has been that of Rolls-Royce. The UK-based engine manufacturer is teaming with Air New Zealand and Boeing to test a blend of biofuel and kerosene. The in-flight evaluation is scheduled to get under way in the second half of next year. One of the four RB211-524 engines on an ANZ 747-400 will use the still-unspecified mix.

In fact, one of the organizations most active in synfuel development has been the U.S. Air Force. Its scientists are turning their attention to certifying the large Boeing C-17 military transport to use an alternative fuel mix that was approved for the B-52 bomber in August. The mix is a 50/50 blend of conventional petroleum-based fuel and a fuel derived from natural gas via the Fischer-Tropsch (F-T) process. The USAF hopes to have its entire fleet, including fighters, qualified by 2010.

The F-T process can produce kerosene from natural gas, coal, oil industry refuse or biomass. The main feature of the process is that it is a serious option to help achieve energy independence for those countries with little oil but an abundance of another hydrocarbon, such as coal in the U.S. One additional benefit is lower emissions, especially soot.

However, the process’ relatively low thermal efficiency translates into huge CO2 emissions and a high price for the fuel itself–at least twice that of the hydrocarbon matter from which it is derived. The USAF claims it will buy synthetic fuel only from those companies with CO2 capture programs. (For example, Tulsa, Oklahoma-based Syntroleum supplied the F-T fuel for B-52 tests.)

FAA Asks for Air Force Help
Now the U.S. Federal Aviation Administration wants to leverage the USAF’s experience with synthetic fuel. Under the commercial aviation alternative fuels initiative, the FAA is studying solutions to replace today’s jet-A1. It is focusing on fuels with smaller CO2 footprints and results of two studies to this end are due to be released imminently.

The FAA has requested the USAF’s input into its own studies and it will also explore biofuels. The first FAA study relates to feasibility, costs, barriers and technical issues. The second focuses on environmental benefits.

“Airlines have huge incentives to switch to an alternative fuel but this needs to be
a drop-in–they cannot afford changes on in-service engines,” former FAA Administrator Marion Blakey insisted in a June 2007 announcement.

Last spring saw the launch of multiple new synfuel initiatives. CFM International– the aero engine alliance between General Electric and Snecma–announced it had successfully tested a CFM56-7B engine using an ester-type biofuel. The trial took place at Snecma’s Villaroche facility near Paris.

The biofuel used for this test was 30 percent vegetable oil methyl ester blended with 70 percent conventional jet-A1. The aim was to check the operation of a jet engine using a fuel made from biomass–without making any technical changes to the engine. With this type of biofuel, the target is a net reduction of 20 percent in CO2 emissions compared to current fuels, CFM said.

The company is also evaluating second-generation fuels derived from biomass. They offer better environmental performance, the company said, and they use waste rather than purpose-grown vegetable. The latter hide several well-recognized drawbacks, including food price hikes and monoculture vulnerability to diseases. However, a major challenge with vegetable waste (wood chips, straw and so forth) is collecting it.

Virgin’s Biofuel Demo
In April, Virgin Atlantic Airways revealed that it is planning a joint biofuel demonstration on one of its Boeing 747-400s next year in cooperation with sister company Virgin Fuels, Boeing and GE. Virgin Fuels has invested in several biofuel startup companies in the U.S., namely, Cilion, Ethanol Grain Processors, Indiana Bio-Energy and Gevo. The latter focuses on butanol, which produces more power than ethanol (a more common biofuel).

In Ottawa, NRC Aerospace is studying the case for building a dedicated facility for alternate fuel research and development. The Canadian aerospace research institute, which announced the evaluation at June’s Paris Air Show, said it would be an extension to its gas turbine laboratory.

In the future facility, researchers could work on fuels such as ethanol, biodiesels, synthetic gasoline and hydrogen-enriched fuels.

It would include two new full-scale combustion test cells and a research-scale hydrogen combustion test facility. NRC would install tanks to hold nitrogen, hydrogen and carbon monoxide, and would use burners to treat exhaust gases and make them cleaner when released into the environment.

Companies would benefit from a technology demonstration environment, NRC said. 

Aviation Fuel Has Stringent Specs

If alternative fuels are to be used in the aviation industry, several major technology challenges must be overcome. For instance, the correct energy density and thermal stability must be ensured to avoid coking at high temperatures. Also, the fuel must be suitable for use at very low temperatures without freezing, as well as at high temperatures. Finally, the constituent parts of the fuel must have sufficient lubrication qualities to work with aero engines.