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I was seeing in this post an answer about an organic way for a carnivorous dragon to produce fire. It is said that the dragon produces a synthesized oil from the diet that, in conjunction with the dragon's body temperature, instantly ignites on contact with air. But how long would it take the dragon's metabolism to produce this oil and why would it take that long? Responder said 5-10 minutes, but I still have my doubts.

If necessary, here is some information about my dragon:

  • It's big, bigger than a horse, you can even ride it;
  • Carnivore;
  • It is used as a war mount;
  • There is a small subspecies that can be used as an assistant to blacksmiths, cooks, among others who need fire to work.

If you want to suggest changes to my dragon for a more believable answer, feel free.

enter image description here

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  • $\begingroup$ Producing the oil takes a long time. Like any other fat or oil animals produce. It requires a lot of calories to make. Heating it to spontaneous ignition temperature is what takes 5-10 min. $\endgroup$
    – Willk
    Sep 29, 2021 at 14:08
  • $\begingroup$ But oil production couldn't take less time, could it? After all, the dragon is made to produce and expel hypergolic oil while any other animal in our world is not, including us. $\endgroup$ Sep 29, 2021 at 14:36
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    $\begingroup$ The dragon produces and stores the oil in advance. Just as we (not including me as I have 0% body fat) produce and store fats in advance of need. Or whales - they produce and store oil. Then they (and we, except me) tote it around to be used on need. $\endgroup$
    – Willk
    Sep 29, 2021 at 15:25
  • $\begingroup$ Complementing @Willk's comment is my answer to your previous question: the sperm whale, which stores copious amounts of the oil naturally in its head. This is actually valuable to you as it represents a limitation: the dragon only has so many shots before it must rest and rebuild its stores. A dragon that could incinerate at will without consequence is godlike and unrealistic. $\endgroup$
    – JBH
    Sep 29, 2021 at 19:24
  • $\begingroup$ Oil is already present in food, it would just need to be separated. And finely dispersed upon breathing out, and ignited. Unfortunately, making the oil instantly pyrophoric as suggested would probably not be so easy... but would it be necessary either? ... well, if you breathe it out together with pure oxygen or a strong oxidizer .... $\endgroup$ Sep 29, 2021 at 20:44

3 Answers 3

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Fat

Oils are a form of fat that is liquid at room temperature. To give a very, very rough estimate, we can check how long it takes before fat is created in a human body. According to a 2012 study, it takes about 4 hours before carbohydrates are stored as fat in a human body.

Now to the non-scientific part. You can massage the following numbers a lot.

Fat is created as a storage medium. It is one of the later processes that starts in digestion. Your dragon can start much earlier with the creation, shaving off maybe an hour or so. It is still something to be done last, as spewing oil isn't required for immediate survival and basically an incredibly wasteful way of offence. Imagine being able to spew your own fat. It took quite a bit to create it, store it and even more effort to get it down again. Suddenly you just throw away 200g of fat in an attack?

The dragon is likely more optimised for the production as well as having more available for such production due to size. I would say 30 minutes to half an hour after eating that a sufficient oil production can be finished for a few bursts of attack.

Do note that you can optimise the process a lot. If you can create a forceful, directional mist of oil, you can increase the available oxigen to a great degree. This increases the chance of ignition as well as a cleaner, hotter burn. You'll also need a lot less oil per attack to be damaging or at the very least be exceptionally frightening.

Doing this can also improve your chances of igniting the oil. Instead of relying on unsaturated oil to spontaneously combust, you only need a small starter after which the flash point is reached, igniting the rest of the oil vapour. The starter can be as simple as a small electric charge as you find on many gas stoves, or maybe some parts of the dragon rub or bang together for a reliable spark. Do note that the spark in this case needs to be a bit bigger with many kinds of oils. Having a stable oil until ignition also means a lot more safety inside the dragon.

If you want to further increase plausibility of a quick generation of oil, you can have specific diets. Sunflower and olive oils have a lot of energy in them. They are more difficult to light than petroleum for example, but burn longer and bigger. This is great if you can ignite it, as it'll be more dangerous for a longer period of time. As many people don't fully understand digestion and the times, we can nearly say that eating olives can go in minutes to the storage chambers.

Different flames

This can immediately make differences between your dragons. Changing oils for different effects of oil. Some are good starters, while others for long burn times.

Summary

Oils are fats that are liquid at room temperature. With plants and probably animals able to make oils, we can glean some insight about how long it takes. I expect 30 minutes to an hour after a sufficient (very large!) meal can restore the reserves as quickest. Do keep in mind that digestion is in all cases a difficult and time consuming process.

I wouldn't count on a spontaneous combustion oil. In nature we can find not too energy consuming ignition sources for a reliable oil fire. With spewing oil we're pushing out a ton of valuable resources anyway, so using a bit more energy to ignite it should be fine. We can go for more stable mixtures of oil that can be very dangerous regardless. With the most well fed dragons you can have the most energetic oils, burning hot and long, or insanely hot and short.

With different oils you can also explain different dragons easily. Changing a diet can also change the oil of the dragon to some degree.

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  • $\begingroup$ Any of the usual oils have a flash point too high to reliable ignite with a simple spark, especially in cold weather, even when misted (they're combustible not flammable). Better have something more volatile in the mix, maybe some acetone (which diabetic ketoacidosis produce in significant amount) $\endgroup$ Oct 1, 2021 at 8:24
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The main challenge in the mechanism you propose seems to be that the dragon needs to keep the substance away from oxygen to prevent it igniting, since it has already the temperature and the combustible available.

If the dragon has a metabolism based on oxygen, this means it has to keep a part of its body with no available oxygen, which can be done but, going against a concentration gradient, requires energy and time.

Considering that the synthesis of the substance will happen in a part of the body where necessarily oxygen is present, this implies that it has to be transported to the storage and at the same time any oxygen has to be removed.

Minutes seem like a reasonable timescale for this process to occur.

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    $\begingroup$ "to keep the substance away from oxygen" not necessarily. Hypergolic propelant. Make the digestion of the dragon based on nitric (rather than hydrochloric) acid, being a carnivore, nitrates are already more available than in other diets. Ignition is by regurgitation and spitting of a small amount of nitric acid followed by the jet of fuel that reacts hypergolic with the acid and normal with the oxygen in the air. $\endgroup$ Sep 29, 2021 at 8:19
  • $\begingroup$ Important to note that in the organism, there wouldn't be available oxygen in sufficient quantities to induce combustion - for example, pure methane will not combust if the available oxygen in the mix is at 12% or below. Check out Limiting Oxygen Concentration $\endgroup$ Sep 29, 2021 at 9:49
  • $\begingroup$ @AdrianColomitchi This could work if the beast had a special bladder to hold the hydrazine. It would then need a special liver to specially filter out ammonia out of the blood and a special organ to produce hydrogen peroxide to then mix the two to fill the bladder with hydrazine. $\endgroup$
    – Sonvar
    Sep 29, 2021 at 13:39
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    $\begingroup$ @Sonvar s/special liver/usual kidney/ Then see Bombardier beetle $\endgroup$ Sep 29, 2021 at 16:45
  • $\begingroup$ @AdrianColomitchi ok, I was kind of lazy and didnt search much on how H2O2 is made biologically. I did know it is commonly made in nature, just wasnt sure of the biological mechanism. Thank you for the info $\endgroup$
    – Sonvar
    Sep 29, 2021 at 17:17
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That hyperflammable oil isn't the fuel for the fire, it's just the ignition mechanism.

The dragon only produces tiny amounts of this oil, and only in a small gland at the roof of the mouth. Even if the gland catches fire, the small amount of oil may mitigate the damage.

The actual fuel for the fire is a gas or other oil which, while still flammable, doesn't spontaneously ignite. The dragon's body produces large amounts of this fuel with little fear of accidentally exploding. Viable candidates are most biological oils, or hydrogen gas, both of which should be relatively easy to synthesize. (It may even use some combination of both.)

When the dragon breathes fire, it exhales a lot of the fuel, along with a tiny amount of the ignition oil. The ignition oil lights on fire, and ignites the fuel. The dragon avoids burning it's mouth by expelling the fuel substance at high velocity, so that it doesn't have time to burn the mouth.

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