Oxy-hydrogen
Oxyhydrogen is a mixture of hydrogen (H2) and oxygen (O2) gases. This gaseous mixture is used for torches to process refractory materials and was the first gaseous mixture used for welding. Theoretically, a ratio of 2:1 hydrogen:oxygen is enough to achieve maximum efficiency; in practice a ratio 4:1 or 5:1 is needed to avoid an oxidizing flame.
This mixture may also be referred to as Knallgas (Scandinavian and German : "bang-gas"), although some authors define knallgas to be a generic term for the mixture of fuel with the precise amount of oxygen required for complete combustion, thus 2:1 oxyhydrogen would be called "hydrogen-knallgas".
The term Brown's gas refers to oxyhydrogen with a 2:1 molar ratio of H2 and O2 gases, the same proportion as in water. It was named after Yull Brown (Ilia Valkov, Bulgarian: Илия Георгиев Вълков), who suggested it to be produced by the electrolysis of water to be used as a fuel for the internal combustion engine. Later "Brown's gas" and HHO has become fringe science terms for a 2:1 mixture of oxyhydrogen obtained under certain special conditions; its proponents claim that it has special properties.
Oxyhydrogen will combust when brought to its autoignition temperature. For the stoichiometric mixture, 2:1 hydrogen:oxygen, at normal atmospheric pressure, autoignition occurs at about 570 °C (1065 °F). The minimum energy required to ignite such a mixture with a spark is about 20 microjoules. At standard temperature and pressure, oxyhydrogen can burn when it is between about 4% and 95% hydrogen by volume.
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