We didn't think the zero-G fire experiments aboard the International Space Station could get any more stunning. We were wrong.
Flame Extinguishment-2 (FLEX-2) is the second iteration of an experiment designed to test how burning droplets of fuel behave in space. But unlike other fire experiments aboard the ISS, FLEX-2 requires the flaming droplets to be suspended, free of other objects (like, say, a candle wick) to better study the rate at which fuel mixtures evaporate and burn, and the conditions required for soot to form. According to NASA, "understanding these processes could lead to the production of a safer spacecraft as well as increased fuel efficiency for engines using liquid fuel on Earth."
Featured below is the full clip of the experiment. Look at how slowly and asymmetrically the flame extinguishes, flitting away at the end like some sort of space-jelly. According to FLEX-2 Co-investigator Vedha Nayagham, changing the mixture of gasses in the space around the burning fuel droplet can dramatically affect this extinguishing process:
We use different diluants [a dilluting agent] in the ambient. For example, on Earth you have oxygen and nitrogen, but we can [change it to] oxygen and carbon dioxide, [or] oxygen and helium. Inert [i.e. non-reactive] diluants... change the behavior of how these things burn. For example, [aboard the ISS, they now] use carbon dioxide as a fire extinguisher [but] is this the most efficient inert that we can use? We try different inerts like helium, carbon dioxide, and also, sometimes, xenon. This tells us what is the most effective fire suppressant in space.
Here's Nayagam, Co-investigator on FLEX-2, with more details on the experiment: