Cool flames in space to lead better engines on Earth

A new space experiment can change the way humans travel. In a series of trials on board the International Space Station (ISS), researchers have discovered a type of cool-burning flames that could lead to cleaner, more efficient engines for cars.

"This technology is not currently available in cars but it could potentially lead to engines that burn fuel at cooler temperatures, emitting fewer pollutants such as soot and nitric oxide and nitrogen dioxide while still being efficient," said Forman Williams, professor of mechanical and aerospace engineering at University of California, San Diego.

A better understanding of the cool flames' chemistry could help improve internal combustion engines in cars, for example by developing homogenous-charge compression ignition.

During the experiments, researchers ignited large droplets of heptane fuel.

At first, it looked like the flames had extinguished themselves, just as they would have on Earth.

"But sensors showed that the heptane was still burning, although the resulting cool flames were invisible to the naked eye," Williams said.

The cool flames occurred in a wide range of environments, including in air similar to the Earth's atmosphere and atmospheres diluted with nitrogen, carbon dioxide and helium.

Researchers believe that the cool flames are the result of elementary chemical reactions that do not have the time to develop around burning fuel droplets on the Earth, where they can only exist for a very short period of time.

The challenge for future applications is to get the right mix of fuels to generate this cool flame combustion here on the Earth.

To investigate this question, NASA is planning a new series of experiments tentatively called "Cool Flame Investigation".

Researchers emphasized that the research is only possible on the ISS, where scientists have access to a microgravity environment that provides a sufficient amount of test time for cool flames to occur.

The discovery was reported in the journal Microgravity Science and Technology.