whats the purpose of mixing air with gas when using a bunsen burner
Bunsen burner The amount of air mixed with the gas stream affects the completeness of the combustion reaction. Less air yields an incomplete and thus cooler reaction, while a gas stream well mixed with air provides oxygen in a stoichiometric amount and thus a complete and hotter reaction. The air flow can be controlled by opening or closing the slot openings at the base of the barrel, similar in function to the choke in a carburettor.
Propane torch Oxygen-fed torches use the high pressure of the stored oxygen to push the oxygen into a common tube with the fuel. An air-only torch will burn at around 1,995 °C (3,623 °F), less if heat loss to the surroundings is taken into account. Oxygen-fed torches can be much hotter at up to 2,820 °C (5,110 °F), depending on the fuel-oxygen ratio. These are the theoretical maximum temperatures, in reality they will always be less due to incomplete combustion, heat loss etc.