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

Mixture of ethyne and air is not used for welding because when ethyne is burnt in air ,incomplete burning takes place and produces sooty flame due to limited supply of oxygen present in the air, whereas when mixture of oxygen and ethyne is burnt, it gives high temperature because of complete combustion and gives clean flame. Hence, this is the reason, oxygen is used instead of air to burn ethyne and is used for welding.