Jon Elson writes:

I have used MAPP, and now get "Propylene" the generic substitute
from the local gas supplier.

Lower case "propylene", is not MAPP, a trademark for a blend of
methylacetylene and propadiene. They are not necessarily substitutes,
depending on the application.

Oxygen is much more a temperature factor than the fuel. Since air is only
1/5 oxygen, you're diluting any flame 4 to 1 with cold inert gas.