I'm in the process of creating a plausible fire-breathing dragon, halfway through. As I don't want my dragon to have to eat stones to spit fire or light sparks because that could limit the dragon to certain regions, but as it will be used as a mount, this is impractical, I have made it have glands that allow it to produce a flammable oil from the fat of the animals it eats. Initially I thought of the dragon heating the oil so much that it would self-ignite when it was expelled, but the temperature needed for an oil to self-ignite varies, but is usually around 200º C. I thought the dragon could raise the oil's temperature through blood circulation around the oil bags that could accelerate until the oil is hot enough to self-ignite. However, according to L.Dutch, the blood temperature does not increase above the animal's body temperature, so it would not be possible to do that. He suggested using a mixture similar to the bomber beetle but in a stronger version as the mixture only goes up to 100º C. But I don't know of any more potent substance that an animal can produce biologically. So, to light the oil I thought of sparks, researched and saw that electric sparks are flammable and then I thought of electric eels. My dragon may have organs responsible for generating enough voltage to create sparks. However, would an animal be able to produce enough voltage to generate sparks, and if so, what would be the complications for the animal itself?
Dragon information: When with the neck raised (like a quetzalcoatlus), the species can reach a maximum of 4 m in height, with a weight ranging from 250kg to 300kg. The wingspan varies from 16m to 19.50. These numbers are because, although the species is no taller than a quetzalcoatlus, it is larger because the neck is thicker which is where the flammable oil will be produced and stored, the tail is larger to help sustain stationary flight while firing (although it hinders flying straight as birds and bats do because the tail would sink and the nose would rear up), it has horns as it makes it more menacing and also helps to attract mates and it also has teeth (unlike quetzalcoatlus). It's a warm-blooded creature. It is carnivorous.