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Encontrei, em vários sites em espanhol o termo "acetylene feather" traduzido como pluma de acetileno. Não há nenhuma referência deste termo em sites em protuguês. Creio que o termo pluma seja uma referência à cor branca da chama.

- s.m. Hidrocarboneto gasoso de tríplice ligação C2H2, que se obtém tratando o carboneto de cálcio com água: o acetileno queima com chama branca; ...
www.kinghost.com.br/saber/acetileno.html - 12k

- O acetileno queima com uma luz branca muito pura e brilhante, ... Se você adicionar oxigênio puro à chama, o desempenho do acetileno aumenta em mais de ...
ciencia.hsw.uol.com.br/macarico-de-mao2.htm - 47k


- NO ACETYLENE FEATHER INNER CONE BLUE ... Les cuento que me decidí por pluma de exceso de acetileno. Encontré varias páginas donde explican esto. ...
forum.wordreference.com/showthread.php?t=96568 - 52k

- Vea acetylene feather, pluma de acetileno. Polaridad, Polarity. Vea direct current electrode negative y direct current electrode positive, corriente directa ...
metalurgia-metalurgia.blogspot.com/2007_08_01_archive.html - 660k

- ´m posting the last sentence and the title ACETYLENE FEATHER, as it is on the document. ... Les cuento que me decidí por pluma de exceso de acetileno. ...
forum.wordreference.com/showthread.php?t=96568 - 52k


- An excess of acetylene creates a carbonizing flame. This flame is characterized by three flame zones; the hot inner cone, a white-hot "acetylene feather", and the blue-colored outer cone. This is the type of flame observed when oxygen is first added to the burning acetylene. The feather is adjusted and made ever smaller by adding increasing amounts of oxygen to the flame....en.wikipedia.org/wiki/Oxy-fuel_welding_and_cutting - 89k

- As the oxygen supply increases the acetylene feather cone decreases. This continues until the acetylene feather almost disappears inside the small white ...
books.google.com.br/books?isbn=0748702334...

Hi Sandra
I would go with "pluma de acetileno" or "cone de acetileno".
This is what I know from chemical reactions:
An acetylene/oxygen flame can be carburizing, when there is excess acetylene and you see an acetylene feather two to three times the length of the inner cone; or neutral, when there are equal amounts of oxygen and acetylene and it shows a clear edged inner cone; or oxidizing, when there is excess oxygen and you see no feather cone.

You only see that inner plume when there is too much acetylene in the mixture seeing that oxygen is invisible. Thus, when we say "pluma de acetileno" or "cone de acetileno" we are referring to that feathered inner cone caused by excess of acetylene in the mix.