Researchers have developed a new additive for jet and diesel fuel that reduces the fuels' tendency to explode when a collision turns them into a mist.
The goal is to reduce fatalities that result from explosive fires during certain types of aircraft or highway accidents and from roadside bombs detonating under or near vehicles in combat zones. Used in diesel fuel, the additive also reduces soot in engine emissions.
"Our hope is that the polymers will save lives," says Julia Kornfield, a chemical engineering professor at the California Institute of Technology in Pasadena, referring to the unique, daisy-chained molecules that make up the additive. Dr. Kornfield oversaw the additive's development.
The additive could represent the end of a nearly 40-year quest to deal with the issue of suppressing explosions from jet fuel, which in modified form also powers the United States military's diesel-fuel vehicles.
A runaway collision between two Boeing 747s at Tenerife Airport in Spain in 1977, in which nearly 600 passengers and crew died, initially prompted the quest. Fuel from the two fully loaded planes turned to mist under the impact and breakup of the planes, then exploded.
Such accidents are rare, but the potential remains. Two airliners nearly collided at Boston's Logan airport in 2005 during take-off along intersecting runways, passing within 20 yards of each other. In June, two airliners at Chicago's Midway Airport began their takeoffs at the same time on intersecting runways, to be stopped short by controllers once the potential for collision became apparent.
A year after the accident at Tenerife, the US and Britain began a hunt for ways to reduce the potential for fuel-mist explosions by developing long chain-line molecules known as polymers. The idea was to use long stretches of polymers to increase the size of fuel-mist droplets, reducing a mist's likelihood of exploding on ignition.
In 1984, researchers with NASA and the Federal Aviation Administration brought a Boeing 720 to a crash landing on a dry lake in California's Mojave Desert to test the effect of these polymers. It was widely seen as a spectacular failure when the craft erupted into a fireball. But a post-crash analysis showed the fireball put itself out in about nine seconds, leaving the plane's paint and plastic windows largely unscathed, explains Dr. Kornfield.
That was a clue that would point researchers in a more-productive direction. The problem: As the polymers moved through pumps, filters, and fuel lines, the stress broke up the molecules, reducing their effectiveness.
The breakthrough came when Kornfield's research team used theoretical modeling to predict the kind of polymer that would suppress fine mists, while not gumming up the works. It had to be long enough to do the job, with bonds strong enough to hold the polymer together through the rigors of moving through a fuel system. And the fuel still needed to form a sufficient mist to work in an engine's combustion chamber.
The result: two versions of a polymer the team has generically dubbed a "megasupramolecule." One of the two, for instance, is held together with the chemical equivalent of Velcro. The polymer breaks up when stressed, as the old ones did. But the Velcro-like bonds allow it to rapidly reassemble once it clears a pump or filter.
Lab tests show that jet fuel treated with the new polymers failed to ignite as a mist. Moreover, when the fuel was run through a pump up to 50 times – testing the polymers' self-repair ability – a small portion of the mist plume ignited, but no sudden burst of flames resulted.
"This looks very promising," says Joel Schmitigal, who is collaborating with the research team. He works at the US Army's Tank Automotive Research Center in Warren, Mich., exploring ways to make safer fuels.
Yet, he adds, the new polymer's biggest contribution may lie in more efficient fuel transportation. The polymers that Kornfield's team has developed reduce a fuel's drag as it moves along a fuel line or pipeline. Other polymers increased drag by fouling pumps and pipes with gunk.
The new polymers have the potential to boost the rate with which pipelines pass fuel along by 40 to 60 percent – "the equivalent of adding a new pipeline," he says.
Kornfield notes that getting approval to use the new additive in diesel fuel could take two years. Approval for use in aircraft could take up to seven years to ensure it meets FAA requirements.
The report on this polymer is set for publication in Friday's issue of the journal Science.