Flame

A flame of a burning area, or otherwise exothermic reacting gases and vapors is known, emitted in the light.

Process

The radiation released during a reaction is caused by the light emission of molecular bands and the atomic line spectrum of those involved in the combustion molecules and atoms as well as by solid particles and aerosols. Solid particles such as carbon black or ash emit a radiation spectrum which corresponds to a black body at the flame temperature. Insofar as solid particles contained in the flame, the thermal radiation is predominant.

In most commercial applications, the visible reaction of a fuel with the oxidizing oxygen is meant by the term "flame". The reaction zone comprises the pre-heating zone, the reaction zone and the equilibrium zone. The flame is formed out of the reaction zone. This usually leads to an intense glow that the reaction region sharply demarcates ( flame front ) and different colors can take. A significant proportion of the flame coloration is caused by different components in the reaction zone:

• Yellow to orange: by ( glowing ) soot particles (of the order a few 10 nm). Your emission spectrum approximates a black body
• Blue: by excited CO2, CH radicals
• Turquoise: by C2 molecules.

Terms

In contrast, the reaction products of the combustion of hydrocarbons (CO2 and H2O) only (not visible ) radiate infrared spectral range. In the flame are introduced impurities are present, there will be intense flames coloring whose color depends on the content. Here mainly transmits the radiation energetically low-lying resonance transitions ( first excited state) to the flame lights. A particularly simple color change to yellow can be achieved by the sodium content in table salt. Used this possibility with fireworks that react in all the colors of the color wheel.

Characterization

There are several ways to characterize a flame. This includes the type of flow (laminar or turbulent), the ratio of fuel and oxidizer, and whether they are available already mixed before combustion or non- mixed.

So is " premixed flames " have a homogeneous mixture of fuel and oxidizer ago, before the combustion process takes place (eg Bunsen burner or Otto engine ). In "non- premixed flames " meet fuel and oxidant only in the reaction zone to each other and react to each other there. The combustion process takes place here at the interface at which the gases mix (eg, candle, fire, aircraft turbine).

Moreover, one can describe a flame over their fuel -oxidizer ratio. Are flames with a fuel surplus as "fat " Flame referred while flames with Oxidatorüberschuss " lean " flames. A more precise indication of which mixture is obtained, via the equivalence ratio ( chemical name ) or the air ratio ( technical term ).

Furthermore, a distinction between laminar and turbulent flames.

• As a reducing flame ( bright flame ) a flame with a low oxygen content is known. In the flame to thereby form mainly carbon black, which is responsible for the intense lighting of the flame.
• Oxidation flames contain oxygen in excess. Because of the low soot content they glow only weakly.

A jet of flame occurs as soon as an oxidation -performance, pressurized gas mixture can suddenly combine with oxygen. The activation energy of this reaction to be achieved by an external ignition source, especially when the ignition temperature of the reaction mixture is exceeded.

Trivia

• The previous hottest flame is obtained at a reaction of Dicyanoethin and ozone at 40 bar pressure and achieves a flame temperature of about 6000 ° C. The theoretical combustion of hydrocarbons with air temperatures will be around 2,000 K. Such possible under ideal conditions, temperatures are not achieved in everyday flames by far. Very hot flames come out even with the launchers for space satellites.

• The derived meaning "flame" is used since the 18th century metaphor for a girl, you fall in love and for which it is so inflamed. Compare also the lyrics No fire, no coal can burn so hot / / As secretly still love that nobody knows nothing. ( Folk song, 18th Century )

• On July 12, 1918 exploded as a result of spontaneous ignition of cordite ammunition chamber of the Japanese battleship Kawachi. A 200 -meter-high jet of flame arose; the ship sank in just four minutes. 621 of 1059 people on board died.