I see that this fuel/oxidant combination is most commonly used, but it's never stated why.
1 Answer
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Because it gives a very high temperature: 2200-2400 $^\circ$C. This is due to its high heat of combustion, around 1300 kJ/ mol.
If still higher temperatures are required, as for Al, Si, Ti, etc., a combination of acetylene and $\ce{N2O}$ is used, which reaches 2600-2800 $^\circ$C.