Dragons commonly breathe fire. They can do so over considerable distances, often many times their body length. But this needs to be powered somehow, by a substance that the dragon can generate on its own. Flamethrowers in real life can be powered by either a gas or a liquid.
However, gas based flamethrowers are pretty lame compared to their superior liquid brothers (insert MGS joke here) because they generate what is nothing more than a long flame. This is what flamethrowers look like in the movies, mainly out of safety concerns. Liquid based flamethrowers are a lot more dangerous, firing streams of burning gasoline at targets.
Given that I want my dragon's flamethrower be spelled with an F instead of without, I want to go with a liquid-based flamethrower. However, this means that a dragon will have to generate the stuff somehow. A methane powered one would be relatively simple given that a dragon's digestive system would produce this on its own, but to me creating the equivalent of dragon napalm seems a lot more complex. And needs to be able to combust somehow, preferably not inside of the dragon. They wouldn't want to end like draco vulgaris, after all.
So how would the biology of a creature like a dragon create a flammable liquid? Would it require a special diet, or dedicated organs? Or perhaps something else entirely? I am looking to make it a continuous stream akin to a real-life flamethrower rather than a short spray created by the equivalent of a bombardier beetle.