I'm in the process of creating a plausible fire-breathing dragon, halfway there. The dragon has glands that allow it to produce a flammable oil from the fat of the animals it eats. To light the oil I thought about sparks, researched and saw that electric sparks are flammable so I soon thought about electric eels. My dragon could have organs responsible for generating enough voltage to create sparks. However, would an animal be able to produce enough voltage to generate sparks?
The dragon is twice the size of a horse, weighing from 250kg to 300kg. He is also a warm-blooded creature. It has a wingspan of 18.5 m to 19.47 m. (These numbers are the varieties of the species as a whole, it's not that I'm confused about a specific dragon) The composition of the oil can vary depending on the animal the dragon eats as its diet is quite diverse, if it can, it it eats cow, goat, sheep, fish, whale, ostrich, elephant... It only avoids animals that are too small like birds, dogs, cats and rats because it wouldn't be worth the effort for so little calorie and also doesn't eat humans because it knows this would be a very dangerous prey to hunt. If you're going to suggest igniting sparks with friction, then at least it's something from the dragon's own body, not rock found in nature.