Here goes, with a different suggestion:
Use several glow plugs welded after your cat, get a model fuel pump, and a mister nozzle (home depot?). I'd pump the model airplane fuel through a check valve and then to a mister nozzle (or carburetor injector pin, a model airplane shop might have that) and then it'll ignite because of the glow plugs. simple 6v system that can be purchased at a model shop for under a hundred bucks. Fuel would be 15 bucks a gallon though, but it burns mostly clear. The cool part is that it wouldn't be visible for a few inches from the pipe and the edges of the flame, which would be blue.
To me, a blue, almost transparent till the tips flame would be pretty spiffy.