$A$ mixture of oxygen and ethyne is burnt for welding. Can you tell why a mixture of ethyne and air is not used?

(N/A) The chemical reaction for the combustion of ethyne is: $2HC \equiv CH + 5O_2 \to 4CO_2 + 2H_2O + \text{Heat}$.
When ethyne is burnt in air,it produces a sooty flame due to incomplete combustion caused by the limited supply of oxygen in the air.
However,when ethyne is burnt with pure oxygen,it undergoes complete combustion,producing a clean,high-temperature flame reaching approximately $3000 \, ^\circ C$.
This oxy-acetylene flame provides the necessary heat for welding metals.
It is not possible to attain such a high temperature using only air,which is why a mixture of ethyne and air is not used for welding.