Question

Why a mixture of acetlyne(ethyne) and air is not used for welding

Answer 1

as you know acetylene is a time and when Ethane are burnt in air a lot of suit or Carbon dost is released so when a lot of carbon 10 is released then it means that the compound is not work properly so no heat a very less amount of heat is released

but when acetylene is burnt with pure oxygen all the unburnt carbon particles also burn up with the oxygen so a lot of heat is produced which is used for welding purposes

Answer 2

Since, ethyne is an unsaturated hydrocarbon therefore a mixture of ethyne and Air undergo incomplete combustion and the amount of heat produced for welding is not sufficient where is a mixture of ethyne and pure oxygen undergo complete combustion producing large amount of heat and high temperature sufficient for welding(oxy-acetylene flame)