Fonte: Business Standard (04/10/2015)
Researchers have discovered a new polymeric jet fuel additive that can reduce the intensity of post-impact explosions that occur during airplane crash.
Before embarking on a transcontinental journey, jet airplanes fill up with tens of thousands of gallons of fuel. In the event of a crash, such large quantities of fuel increase the severity of an explosion upon impact.
Researchers at California Institute of Technology and NASA’s Jet Propulsion Laboratory (JPL) have discovered a polymeric fuel additive that can reduce the intensity of post-impact explosions that occur during accidents.
Preliminary results show that the additive can provide this benefit without adversely affecting fuel performance, researchers said.
Jet engines compress air and combine it with a fine spray of jet fuel. Ignition of the mixture of air and jet fuel by an electric spark triggers a controlled explosion that thrusts the plane forward.
However, the process that distributes the spray of fuel for ignition – known as misting – also causes fuel to rapidly disperse and easily catch fire in the event of an impact.
The additive, created in the laboratory of Julia Kornfield, professor of chemical engineering, is a type of polymer – a long molecule made up of many repeating subunits – capped at each end by units that act like Velcro.
The individual polymers spontaneously link into ultra-long chains called “megasupramolecules.”
Megasupramolecules, Kornfield said, have an unprecedented combination of properties that allows them to control fuel misting, improve the flow of fuel through pipelines, and reduce soot formation.
Megasupramolecules inhibit misting under crash conditions and permit misting during fuel injection in the engine.
Other polymers have shown these benefits, but have deficiencies that limit their usefulness.
The Velcro-like units at the ends of the individual chains simply reconnect when they meet, effectively “healing” the megasupramolecules.
When added to fuel, megasupramolecules dramatically affect the flow behaviour even when the polymer concentration is too low to influence other properties of the liquid.
When an impact occurs, the supramolecules spring into action. The supramolecules spend most of their time coiled up in a compact conformation.
When there is a sudden elongation of the fluid, however, the polymer molecules stretch out and resist further elongation.
This stretching allows them to inhibit the breakup of droplets under impact conditions – thus reducing the size of explosions – as well as to reduce turbulence in pipelines.