Tom

Propane gets hot enough but it doesn't deliver nearly as much energy
as acetylene does.

Brazing is soldering but at higher temperatures.

Can you get by with a soldered joint ?

Try cleaning the area with a strong caustic such as Easy Off oven
cleaner to remove oils and greases.

You need to get all three parts (the two parts to be joined and the
braze alloy) hot enough at the same time.

Theoretically you can use propane because it gets hot enough. However
it delivers the energy so slowly that you lose a great deal.
(Theoretically you can move the same load in a pick up truck that you
can in a semi. You just make more trips.) You could get fire bricks
and try to make a little oven type set up to trap some heat.

Mostly I'll go with the other guys and recommend an oxy acetylene
torch. There are an awful lot of these around. If you were to ask
enough folks I'm sure someone would know of one.

Tom