Which flame produces a cooler flame at 3000 degrees Fahrenheit?

• A. Air Acetylene
• B. Oxygen Acetylene
• C. Acetylene
• D. Argon Acetylene

Answer: (A)

The temperature of the flame is governed by the oxidizer used. Acetylene burning with pure oxygen is extremely hot because there’s plenty of oxygen to drive the reaction, producing the highest flame temps. When acetylene burns in air, the air is only about 21% oxygen and contains nitrogen, which acts as a heat sink and diluent, so the flame temperature is noticeably cooler. That mix provides a gentler heat closer to the 3000°F range. Using argon as the shielding or diluting gas with acetylene isn’t aimed at increasing heating; it mainly changes the atmosphere around the flame and generally lowers heat available for heating the joint, and isn’t the typical choice for producing a hotter brazing flame. So the air-acetylene flame is the cooler option compared with the others.