In the combustion reaction of acetylene gas and oxygen, oxygen as a oxidizer is needed for high energy release. In line with the stoichiometric prediction, the stoichiometric aerobic ratio for a complete combustion of acetylene (C₂H₂) is 2.5:1 (that is, 2.5 volumes of O₂ per volume of acetylene), while the heat yield of the reaction C₂H₂ + 2.5O₂ → 2CO₂ + H₂O amounts to as high as 54.8MJ/m³. It is 2.95 times higher compared to the calorific value from acetylene combustion in air (only 18.6MJ/m³). For example, by mixing 99.5% pure oxygen and acetylene gas, the industrial welding torch can raise the flame temperature to 3100°C (only 2350°C in air), thereby raising the steel plate cutting speed of 15cm/min (air combustion efficiency below 30%).
The high oxygen concentration directly enhances combustion economy and efficiency. Experimental findings suggest that with oxygen ratio being enhanced from 21% (ambient atmosphere) to 95% (industrial oxygen supply), the combustion rate of acetylene is accelerated from 0.8m/s to 3.2m/s and carbon smoke production reduces by 92%. After a German automotive firm adopted high-oxygen combustion technology, the cost of welding operations reduced from 1.2 euros per meter of weld to 0.45 euros, and annual energy savings totaled over 500,000 euros. But excessive oxygen (e.g., oxygen supply more than 1.3 times acetylene) will lower the oxide flame temperature by 400°C and increase the likelihood of metal oxidation (stainless steel welding oxide layer thickness increased from 5μm to 20μm).
Safety risks are greatly reliant on the proper control of oxygen supply. The acetylene explosion limit in pure oxygen is expanded to 2.5%-93% (volume concentration), and the chance of tempering increases from 0.1% to 4.7% when the flow rate of the gas mixture exceeds 12m/s. In a 2020 shipyard explosion, due to the failure of the oxygen pressure reducing valve, the pressure rose from 1.4MPa to 2.1MPa, and the mixed gas ratio unbalance caused an explosion, and the shock wave destroyed equipment within an 8-meter radius, resulting in a direct loss of $2.4 million. The United States OSHA requires installation of a ±1.5% flow precise ratio control valve, and leveling the pressure of the oxygen supply pipe to 0.3-0.4MPa (0.07-0.13MPa acetylene pipe), which can effectively reduce the occurrence of ignition and explosion accidents by 80%.
Molecular dynamics interprets that oxygen plays a vital role in the chain reaction. Studies have shown that acetylene decomposition to C₂H radical to absorb 837kJ/mol energy, and oxygen molecules (O₂) bond energy is only 498kJ/mol, readily cleaved at high temperatures into active oxygen atoms, accelerate the free radical chain transfer. The calculation of quantum chemistry shows that the activation energy of the reaction of combustion of acetylene reduces from 210kJ/mol to 165kJ/mol through a 10% increase in the oxygen concentration, and the rate of the reaction is enhanced by 2.4 times. For example, for rocket engine testing, NASA increased the pressure of the combustion chamber from 3MPa to 5MPa by changing the ratio of oxygen to acetylene gas to 1:1.1 and improving the efficiency of the thrust by 37%.
Environmental and regulatory considerations also propel the optimization of oxygen involvement. The EU Industrial Gas Emission Directive mandates acetylene combustion with a carbon residue level below 0.1%, whereas high-oxygen combustion can raise carbon conversion from 78% to 99.5% and lower particulate matter emissions (PM2.5 concentration from 150μg/m³ to 8μg/m³). After a steel enterprise adopts the intelligent oxygen control system in 2022, 120,000 tons of the yearly carbon emission quota will be conserved and the revenue of carbon trading will be 4.8 million euros. But it should be noted that when the oxygen purity is less than 99.2%, nitrogen impurities will form nitrogen oxides (NOx formation between 50ppm and 220ppm), which will require additional investment in SCR denitrification equipment (about €1.2 million/unit).
With the combination of thermodynamic equilibrium and engineering control, the oxygen-acetylene gas synergy continues to be the impetus for industrial innovation. The micromixing injector (aperture accuracy ±5μm) developed by the MIT research team enables molecular mixing of oxygen and acetylene in 0.01 seconds, increasing combustion efficiency from 89% to 97% and reducing fuel consumption by 23%. This technology has created an annual market expansion of $120 million in the aerospace precision welding sector.