acetylene (C₂H₂) combustion must be founded on the chemical reaction between acetylene gas and oxygen, which is a REDOX reaction essentially. From thermodynamic calculations, the theoretical combustion ratio between acetylene and oxygen is 1:2.5 (molar ratio), and the reaction is 2C₂H₂ + 5O₂ → 4CO₂ + 2H₂O + 1,300kJ/g energy release. In case of insufficient oxygen (O₂/C₂H₂<2.5), the burning will produce toxic carbon monoxide (CO), and experiments show that by reducing the oxygen-to ratio to 1:1, the CO concentration is 12% (far more than 240 times the allowed OSHA level of 50ppm), and the flame temperature drops from 3,400 ° C (complete combustion) to 2,200 ° C (35% loss of efficiency).
Presence of oxygen accelerates the chain reaction. The activation energy for acetylene combustion is 120kJ/mol, and oxygen molecules (O₂) increase the rate of reaction to 1.5×10⁶ L/(mol·s) by introducing free radicals such as ·O and ·OH (only 2×10³ L/(mol·s) in nitrogen). NIST tests confirmed that the burn speed in the oxygen acetylene mixture is as high as 14.3m/s (pure acetylene – air only 1.1m/s) and burning intensity rises by 13 times, which is very important for piercing industrial cutting (steel sheet thickness ≤300mm).
Safe operation requires precise ratio control of oxygen. The acetylene explosive range in oxygen is 2.5%-93% (2.5%-81% in air), so the volume ratio of oxygen and acetylene needs to be strictly controlled between 1:1 and 1:1.2 when welding. BAM Institute tests in Germany show that when the oxygen supply exceeds the safety threshold (oxygen pressure 0.15MPa cf. acetylene 0.12MPa), the flow rate of mixed gas from 7L/min to 15L/min, and the probability of backfiring from 0.1% to 4.7%, there is a possibility of explosion (peak pressure 20MPa).
Industrial accidents demonstrate the importance of oxygen control. In a shipyard accident in the United States in 2020, the operator mistakenly adjusted the oxygen ratio to 1:3 (excess acetylene), resulting in low flame temperature (2,500 ° C) and high CO content, poisoning three people. Welding guns with ISO 5172 standards (e.g., Harris 53-5) reduce oxygen pressure from 15MPa to 0.3-0.4MPa and acetylene from 1.5MPa to 0.1-0.15MPa through a two-stage pressure reducing valve, with a steady gas flow rate of 5-7L/min. Reduce the accident rate to 0.02 cases per million hours.
Equipment design for better oxygen action. The oxy-acetylene torch with an inject-suction structure (nozzle diameter 1.2mm) uses the negative pressure (-5kPa) generated by the high-velocity flow (30m/s) of oxygen to suck in acetylene, and the mixing evenness is 98% (manual premix only 85%). Swiss Berner Group’s intelligent torch combined oxygen flow sensor (accuracy ±1.5%FS), real-time adjustment ratio, neutral zone of the flame (oxidation and reduction balance) length stabilized at 3-5mm (deviation ≤0.2mm), cutting face roughness Ra≤12.5μm (better than 25μm manual control).
The availability of oxygen is affected by environmental conditions. At 3,000 m above sea level, the oxygen content drops to 14% (21% at sea level) and the oxygen flow rate has to be increased by 30% (from 7L/min to 9.1L/min) to obtain the same burning efficiency. Statistics of the 2023 Qinghai-Tibet Railway welding project show that oxy-acetylene cutting operations with unregulated flow have their efficiency reduced by 42%, while equipment with pressure compensation valves (e.g., Victor J28A-580) keeps the cutting speed at 25cm/min (flat level) and the engineering time is reduced by 18%.
In summary, the synergistic interaction between oxygen and acetylene gas is not only the chemical basis of energy release, but also the most important control parameter of industrial efficiency and safety. Deviation from the ideal proportion of oxygen will lead to energy loss, gas and explosive hazards, and only with scientific matching and precision equipment can there be effective and controlled burning applications.