Mark Lorch: In George RR Martin's fantasy land of Westeros from Game of Thrones and House of the Dragon, the spectacle of fire-breathing dragons captivates audiences with a mix of myth and fantasy. At least for me, it's also a scientific curiosity.
The images of dragons unleashing torrents of flame in the up-to-date House of the Dragon series got me thinking: if dragons existed, what actual biological mechanisms and chemical reactions could they exploit?
But first, a chemistry recap. To ignite and sustain the flame, we need three ingredients; fuel, an oxidizing agent – usually oxygen from the air – and a heat source to initiate and sustain combustion.
Let's start with fuel. Methane could be a candidate. Animals produce it during digestion. Images on the Westeros screen show that dragons are eager to eat sheep. However, our methane-fueled dragons would need to have a diet and digestive system more similar to a cow's to produce enough gas to burn a city.
Storing enough methane is also a problem. A typical methane cylinder can withstand a pressure of 150 atmospheres, while even a distended intestine can only tolerate just over one atmosphere. Therefore, there is no biological basis for non-marine animals to store gases at high pressure.
Liquid would be a better option. Ethanol may be the solution. Perhaps our dragons have a vat of fermenting yeast in their guts, or they may have a metabolic system similar to the Devil's Hole puppies that live in scorching springs in Nevada, USA. In low oxygen conditions, these fish switch to a form of respiration that produces ethanol.
However, storage is again an issue. Ethanol passes through biological membranes quickly, so keeping it at high concentrations and ready for exploit on the signal of “dracarys” (which means “dragon fire” in the fictional High Valyrian language) would require otherworldly biology.
So if we stick to explanations with at least one foot in real-world biology, then my preferred option is something more oil-based. Anyone who has accidentally set a pan on fire knows that it can be the source of roaring flames. In the case of the Fulmar gull, this has a biological basis.
They produce energy-rich stomach oil, which they regurgitate to feed their chicks. The oil also has a repellent function. When threatened, the fulmar vomits sticky, smelly oil on predators. Fortunately, seagulls have not yet developed a way to set fire to vomit.
Fanning the flames
Now that we have a fuel source, let's turn our attention to the oxidizing agent. As with most fires, it will most likely be oxygen. However, it takes more than just the oxygen in the surrounding air to create a jet of burning pressurized oil scorching enough to melt the Iron Throne. And it would have to be mixed well with the fuel. The better the oxygen supply, the hotter the flame.
The dragon could draw on the chemicals used by the bombardier beetle. This insect has evolved tanks adapted to store hydrogen peroxide (a substance you can exploit to lighten your hair). When threatened, the beetle pushes hydrogen peroxide into a vestibule containing enzymes that quickly break down the hydrogen peroxide into water and oxygen.
It is an exothermic reaction that transfers energy to the surroundings and in this case raises the temperature of the mixture almost to the boiling point. The reaction is so aggressive that it is sometimes used to power rockets.
The augment in pressure caused by the rapid production of oxygen and boiling water pushes the noxious mixture from the vent in the beetle's abdomen towards the prey or threat.
If used by a dragon, this reaction has some fascinating features. This would create the high pressure needed to drive the oily fuel jet, the exothermic reaction would heat the oils, making them more ready for combustion, and most importantly, it would produce oxygen to fuel the combustion reaction.
The only thing the dragon will need is some biological equivalent of a gasoline engine carburetor that will mix oil with oxygen and create an explosive mixture. As a bonus, the exploding mixture would likely create a fine, aerosol-like mist of oil droplets that would ignite all the better.
spark
Finally, you need a spark to ignite the mixture. To this end, I will suggest that dragons have evolved an electric organ similar to that found in many fish, especially electric eels.
They can generate miniature pulses of up to 600 volts, easily enough to create a spark in a miniature air gap. If these sparks discharged in the channels at the back of the dragon's mouth, they could ignite a high-pressure jet of oil and oxygen.
While we'll never see a dragon unleashing jets of flame outside the realm of fiction, it's intriguing to wonder about the science behind fantasy. So the next time you witness a Targaryen commanding “dracarys”, think about the biology behind this magical hell.
Mark Lorch, Professor of Science Communication and Chemistry at the University of Hull
This article has been republished from Conversation under Creative Commons license. Read original article.
Image Source: Pixabay.com
