Methane Dragons

Question

The Leech Dragon, so named for its round, leech-like mouth, is by far one of the creepiest and most vicious dragons. Part of the reason for its infamy is its ability to exhale toxic and very flammable clouds of methane gas. These relatively small dragons, (about 5-6 feet long and very thin), congregate together and can rapidly turn enclosed or poorly ventilated areas into lethal gas chambers. In addition, these dragons can create sparks by rubbing their teeth or scales together, which ignites their methane breath attack and creates a large and very fast moving fireball.

So here is my question. Where does the dragon get the methane and how does it release it? Alternatively is there some other gas that would work better/be easier to obtain?

Answer 1

Your dragons are vegetarians and have a lot of different stomachs - just like cattle

To cite from the Wikipedia article on cattle (emphasis mine):

Gut flora in cattle include methanogens that produce methane as a byproduct of enteric fermentation, which cattle belch out. The same volume of atmospheric methane has a higher global warming potential than atmospheric carbon dioxide. Methane belching from cattle can be reduced with genetic selection, immunization, rumen defaunation, diet modification and grazing management, among others.

You need the same gut flora as in cattle and then you select those individual dragons that produce a lot of methane to produce offspring. Evolution might for example favour them because their gut flora is better suited to their environment - or maybe dragons found methane sexy because it's harder to hide from your prey if it can smell you for miles.

In the end you have a very high amount of methane that gets produced. Especially if you think about the size of a dragon. Dragons are huge - there is a lot of room for stuff to produce methane. Methane is also lighter than air, which can be used as a pseudo-scientific way to help explaining why they are able to fly (the square cube law would still get in the way, but we are talking about dragons and as everyone knows dragons don't care about physics - physics is too scared of them).

Answer 2

/Alternatively is there some other gas that would work better/be easier to obtain?/

The problem with methane is that it is a gas at all biologically relevant temperatures and pressures. That means it occupies a large volume and is hard to store. Also it is difficult to project a cloud of gas - the large volume and low mass means that air resistance slows it down a lot. The dragons would be largely within their own gas cloud and would have to deal with the "whoever smelt it dealt it" principle.

A better gas would be something which could be a liquid at biological temperatures and pressures - it could be stored compactly in the animal and projected as a dense flaming liquid that rapidly turns into a gas heat. Consider butane - it is a gas at STP but a liquid at 2.6 atmospheres which can be achieved in a disposable lighter. Pentane has one more carbon than butane and boils to a gas at 36C, so could be kept at atmospheric pressure in a cool animal.

Vertebrates do not make alkanes. Better yet would be a volatile flammable liquid which actually is produced in animals. I propose acetone.. It is a liquid with a low vapor pressure. A Bronx cheer breath weapon of acetone droplets would turn into a sweet cloud of flame. Enthalpy of combustion is double that of methane (though lower than propane). Acetone is in animals, produced by ketogenic fat metabolism - even humans normally make small quantities of acetone. Plus it has that great smell of nail polish remover.