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joshuamunson t1_j2bp5me wrote

Essentially, impurities, the material being burned, and uneven combustion. A clean hydrogen flame is almost invisible. When burning a propane flame it is blue and purple when it has good even combustion and ionizes the gasses in the flame and it turns blue. Orange flames are more uneven combustion as well as different fuel being burned.

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brownlawn OP t1_j2bqdrs wrote

So for gas fireplaces is it not burning natural gas provided by the gas company via a line from the street?

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joshuamunson t1_j2bqwv4 wrote

It is. Hotter more complete gas fires are blue. "colder" less complete gas fires are orange.

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brownlawn OP t1_j2br0c0 wrote

What do you mean by complete ?

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zekromNLR t1_j2bsa66 wrote

In a wood fire (and also similarly in a candle flame, or the flame of a simple lighter, or a bunsen burner with the air valve closed, number 1), because the air has to flow into the flame from the outside, there is not enough oxygen in the flame to burn all of the fuel.

Because the fuel in all of these cases is a carbon-based material, one of the products of this incomplete combustion is just... leftover solid carbon, which forms into tiny particles of soot. And because these tiny particles are in a hot flame, they are also hot, and so glow a bright yellow.

On the other hand, in a gas burner for heating, or a bunsen burner with the air valve open, the gas is mixed with air before it enters the flame. That way, there is enough oxygen available to quickly react all of the carbon and hydrogen in the fuel to carbon dioxide and water (this is what is meant by "complete combustion), so there is no soot that can glow, and you get both a hotter flame, and also more heat per each unit of fuel.

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joshuamunson t1_j2br7d1 wrote

There is a perfect ratio of fuel to air that is perfect. For example, 2 parts fuel to one part air. If you stray from that perfect mixture, you'll have different flame properties

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Aldayne t1_j2czz25 wrote

A blue flame means the fuel (gas) is combusting fully - complete. Incomplete means not all the gas is being consumed in the reaction with the excess being released into the atmosphere.

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