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Related:

What are the scientific issues with this method of dragons breathing fire?

Could dragons theoretically breathe alcohol based fire?

Can a dragon's fire breath be liquid based?

Recreating dragon fire

I, like many others, am trying to find a way to science-ify dragonfire. I have settled on liquid hypergolic chemical reactions for the methodology, as hydrogen, methane or ethyl just don't have enough 'oomph' to them, and most of those kinds of solutions require the dragon to eat masses of plant matter. But the problem with most extant hypergolic reactions mentioned in the other questions is that they invariably require something so weird and niche (dragons eating coal, dragons eating phosphene-containing rocks, dragons eating limestone, etc) that the geographical range of dragons would be extremely narrow. Considering just how much meat a predator the size of a dragon would need, it's infeasible to have them all huddled together in one cave so they can drink phthalic acid from some natural oil well.

Bombardier beetles, for comparison, have an enormous territorial/climate range and manage to produce the two chemicals necessary for a reaction via normal organic processes from their diet of other bugs. If they produced giant gouts of flame, I'd stop right at hydrogen peroxide and hydroquinone.

So! My question. Are there any combinations of chemicals that form a flaming hypergolic reaction that:

  1. Can be found or synthesized inside an animal body in a wide range of biomes/climates without major alteration of the terrain.

AND

  1. Can be procured via a non-obligate (ideally, obligate) carnivorous diet?
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Unsaturated fats can spontaneously burst into flame.

This is why you need to be careful about leaving oily rags crammed in a bucket. Some oils and fats spontaneously oxidize. That propensity to oxidize is dependent on iodine value which measures how many unsaturated double bonds are in the oil. Higher iodine value = more iodine can get soaked up by those double bonds. The double bonds also soak up oxygen.

Linseed oil is an example of a high iodine value oil. It is one of the oils which can cause fabrics to burst into flame on their own, especially if there is a metal catalyst. Fish oils are unsaturated oils of animal origin and are "notorious for their self-heating properties"

Your dragon makes unsaturated high iodine value oil in its body and stores it in an internal reservoir. It must get it ready to use it as a breath weapon. When fire breathing is needed, it heats the oil by bringing to bear metal catalysts (cobalt, iron, manganese; all available as biomolecules) and oxidants (oxygen or biologically generated peroxide). Perhaps there is a durable organ made of cartilage which it can push into the oil reservoir, increasing the surface area for reaction and bringing in reactants.

This oil heats up as it oxidizes inside the dragon. When it is very hot it will burst into flame on its own if given access to oxygen. When the dragon spews fire this is what happens - a spray of hot oil meets oxygen in the air and energetically burns. As opposed to a hot gas, hot oil would be a good breath weapon. The very liquid unsaturated oil might contain within it larger biomolecules and waxes which do not auto-oxidize but will ignite with the main mass once it is out in the air. These greasy waxes have even more fuel value, and are also sticky if the breath is used offensively.


This has some ramifications.
1: One is that fire breath for a dragon has a limited number of shots after which it must regenerate its oil reserve.

2: Two is that once a dragon heats up its internal oil, if it does not get rid of it as a breath weapon it must somehow get rid of the excess heat. It might need to drink a lot of water or eat snow or swim.

3: Oil has a lot of caloric value and is energetically expensive to make. Use of this breath weapon for predation means that whatever you kill has to be at least worth the caloric cost of the oil you used to kill it. Use of this breath weapon to ward off predators would mean you need advance notice that you are intended prey which predators do not like to give.

Use of the breath weapon as a flashy and expensive display of fitness makes a lot of sense. A dragon able to waste calories as fire is a healthy strong dragon and a good potential mate. Fire is visible and flashy and there is no faking it. A dragon lek would have many dragons at height in the dark, blowing giant clouds of fire.

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  • $\begingroup$ Great answer! What kind of timeframe would we be looking at between the beginning of the process and it being 'ready'? Minutes? Hours? $\endgroup$ – Carduus Jul 17 at 12:35
  • $\begingroup$ @Carduus - I am going to say 5-10 minutes. You want it when you want it, but you want things under control also and so it has to introduce oxygen in a controlled manner. $\endgroup$ – Willk Jul 17 at 14:54
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It’s certainly possible for hypergolic components to evolve as in the case of the Bombardier beetle. Many other hypergolic combinations are known and there a probably a multitude waiting to be discovered for example diethylenetriamine and hydrogen peroxide https://www.sciencedirect.com/science/article/abs/pii/S0094576517300267

Hydrogen peroxide is already produced by the Bombardier beetle. Diethylenetriamine is not generated in nature as far as I know, however it is a simple organic compound and given sufficient evolutionary pressure it might well evolve. Nature has found ways to push reactions “uphill” as in photosynthesis and ATP.

Many powerful oxidizing agent and powerful reducing agent combinations are hypergolic especially where a catalyst or high temperatures are involved. I have no doubt that if forced nature could well generate such hypergolic combinations as the scope of organic chemistry coupled to evolution are vast beyond measure.

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