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strange flames on the international

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space station

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presented by science at nasa

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fire it is often said is mankind's

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oldest chemistry experiment

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for thousands of years people have been

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mixing the oxygen-rich air of earth with

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an almost endless variety of fuels to

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produce hot luminous flame

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there's an arc of learning about

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combustion that stretches from the

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earliest campfires of primitive humans

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to the most advanced automobiles racing

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down the super highways of the 21st

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century

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engineers study burning to produce

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better internal combustion engines

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chemists peer into flames looking for

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exotic reactions

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chefs experiment with fire to cook

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better food

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you would think there's not much more to

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learn

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dr foreman a williams a professor of

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physics at the university of california

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san diego would disagree

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when it comes to fire he says we're just

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getting started

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flames are hard to understand because

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they're complicated

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in an ordinary candle flame thousands of

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chemical reactions take place

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hydrocarbon molecules from the wick are

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vaporized and cracked apart by heat

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they combine with oxygen to produce

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light heat carbon dioxide and water

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some of the hydrocarbon fragments form

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ring-shaped molecules called polysilic

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aromatic hydrocarbons and eventually

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soot

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simply drift away as smoke

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the familiar teardrop shape of the flame

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is an effect caused by gravity

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hot air rises and draws fresh cool air

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behind it

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this is called buoyancy and is what

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makes the flame shoot up and flicker

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but what happens when you light a candle

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say on the international space station

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in microgravity flames burn differently

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they form little spheres says williams

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space station flame balls turn out to be

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wonderful mini labs for combustion

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research

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unlike flames on earth which expand

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greedily when they need more fuel

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flame balls let the oxygen come to them

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oxygen and fuel combine in a narrow zone

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at the surface of the sphere

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not hither and yawn throughout the flame

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it's a much simpler system

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recently williams and colleagues were

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doing a space station experiment called

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flex to learn how to put out fires in

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microgravity when they came across

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something odd

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small droplets of heptane were burning

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inside the flex combustion chamber

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as planned the flames went out

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but unexpectedly the droplets of fuel

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continued burning

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that's right burning without flames says

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williams at first we didn't believe it

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ourselves

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in fact williams believes the flames are

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there just too faint to see

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these are cool flames he explains

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ordinary visible fire burns at a high

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temperature between 2200 and 3100

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degrees fahrenheit

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heptane flame balls on the space station

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started out in this hot fire regime

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but as the flame balls cooled and began

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to go out a different kind of burning

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took over

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cool flames burn at the relatively low

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temperature of 400 to 1000 degrees

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fahrenheit says williams

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and their chemistry is completely

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different

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normal flames produce soot carbon

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dioxide and water

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cool flames produce carbon monoxide and

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formaldehyde

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similar cool flames have been produced

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on earth but they flicker out almost

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immediately

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on the space station however cool flames

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can burn for nearly a minute

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there are practical implications of

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these results notes williams

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for instance they could lead to cleaner

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auto ignitions

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one of the ideas that auto companies

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have worked on for years is hcci

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short for homogeneous charge compression

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ignition

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in the automobile cylinder instead of a

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spark there would be a gentler less

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polluting combustion process throughout

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the chamber

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the chemistry of hcci involves cool

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flame chemistry says williams the extra

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control we get from steady-state burning

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on the space station will give us more

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accurate chemistry values for this type

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of research

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just getting started indeed

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for more information about strange