Aircraft

Interest in alternative fuels for both commercial and military aviation is enjoying a rebirth on several fronts, with soaring jet fuel costs added to lingering environmental and security concerns about dependence on hydrocarbon-based Jet-A.

But the likelihood of finding a practical, cost-effective alternative appears to be low, if history is any guide.

Except in extreme cases involving national security in Nazi-era Germany and apartheid-era South Africa, all previous attempts to find an alternative to oil for jet engines have failed, undermined by practical issues and ultimately by a drop in fuel prices that - at least temporarily - quenched the economic imperative.

Moreover, key questions about whether alternative energy sources are more economical or even more environmentally friendly have yet to be answered.

Until two years ago, Boeing's managing director for environmental strategy, Bill Glover, was sceptical about the potential for alternative aviation fuels.

"And then we started to see things happen," he explains.

Into a vacuum of technical data comes a variety of new initiatives. The US Air Force is leading the way with a plan to convert a portion of its bomber, tanker and command and control aircraft fleets to a fuel based on a blend of oil and coal, with the latter converted to synthetic gas through the Nazi-invented Fischer-Tropsch process.

Boeing and Virgin Atlantic, meanwhile, will demonstrate biomass fuel on a 747 widebody in 2008.

Making progress

Meanwhile, the US FAA and European policymakers have established the Commercial Aviation Alternative Fuels Initiative, which seeks to answer as many technical questions about renewable energy sources as possible.

So far, the environmental benefits show some promise. The USAF's tests using the Boeing B-52 bombers' ageing Pratt & Whitney TF33 engines show that a fuel blend using a natural gas source can reduce CO2 emissions by 1.6%, with a 1% reduction in fuel burn. The engines also generate 50-90% fewer emissions of particulate matter, according to a study presented by US FAA chief scientist Lourdes Maurice last month in Montreal.

However, producing such synthetic fuel blends presents challenges from a cost and environmental standpoint. A Fischer-Tropsch production plant requires a $3 billion to $5 billion upfront investment. The process of converting coal into a liquid fuel itself generates a great amount of CO2 emissions, which can be mitigated only if a method is invented to trap and store the greenhouse gas underground.

With biomass, as well, "we need to remember the challenges," says Maurice, who presented at the International Civil Aviation Organisation's colloquium on aircraft emissions.

"There are freeze point challenges and safety considerations, and how are we going to grow these fuels?"