Nineteenth century electrolytic cellfor producing oxyhydrogen.
Oxyhydrogen is a mixture of hydrogen (H2) and oxygen (O2) gases. This gaseous mixture is used for torches for the processing of refractorymaterials 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 required to avoid an oxidizing flame.
This mixture may also be referred to as knallgas (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".
Brown's gas and HHO are fringe science terms for a 2:1 mixture of oxyhydrogen; its proponents claim that it's endowed with 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.
When ignited, the gas mixture converts to water vapor and releases energy, which sustains the reaction: 241.8 kJ of energy (LHV) for every mole of H2 burned. The amount of heat energy released is independent of the mode of combustion, but the temperature of the flame varies. The maximum temperature of about 2800 °C is achieved with an exact stoichiometric mixture, about 700 degrees hotter than a hydrogen flame in air. When either of the gases are mixed in excess of this ratio, or when mixed with an inert gas like nitrogen, the heat must spread throughout a greater quantity of matter and the temperature will be lower.
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