I made an oil burner to heat my furnace (for melting aluminium).
Its a small pipe (1/4"), inside a large pipe (scaffolding tube).
Feed oil down the small tube.
Feed air (from a bouncy castle blower, or whatever) down the large pipe.
The trick is to get it lit -
I used a ceramic chimney pot/flue liner about 12 inches long.
drill a hole through the side for the oil feed.
Fill with charcoal. Drop of Isopropyl alcohol (or meths, or BBQ lighter fluid).
Get the charcoal lit, then turn on the blower.
When the charcoal is nicely going, turn on the oil.
Sounds like a jet engine, and melts anything above it.