Cars

Weird Engines

You’ve probably noticed I’ve been on an automotive kick lately. Don’t worry, I don’t think I’m in any danger of becoming a babbling gear-head. Firstly, I don’t have the patience or mechanical skill to actually put an engine together without blowing myself up and setting the neighborhood on fire. Secondly, where I live, working on cars isn’t a cheap hobby, and the fact that I’m considering going to grad school means all my pennies are spoken for.

I’m interested in engines the same way a little boy would be. They’re big, loud, powerful, complicated, and mechanical. I could probably come up with fancy reasons for being curious about engines, but the fact is, I just like them. But I like them in kind of a shallow way. The more intricate details of engines still confuse me. There’s a reason I call myself Hobo Sullivan: in pretty much all the areas I talk about, I’m like a hobo being dragged into an art gallery. I can say “That painting looks like shit” or “That’s a really pretty painting,” but if you start trying to teach me about composition or Postmodernism, my eyes’ll glaze over and I’ll start asking when I get my bowl of soup.

Which is a really long-winded way of saying that this post isn’t intended for engine experts. If you’re into engines, you probably know every single thing on this list. This is a post for people who are casually interested like me. This is me emerging from the Google Caves with a handful of funny-shaped crystals and saying “Look at this cool stuff I found!” This list has nothing to do with with deciding on the best engine or anything fancy like that. This is a list of the engines I’ve found in my bizarre curiosity that made me say “That’s kinda cool…”

The Boxer-6

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(Image from CarThrottle.com)

The boxer-6 isn’t all that weird, since it’s still in common use. That’s partly because you’ll find it in sports cars like the Porsche 911, and in some of Subaru’s current cars and SUVs. When I first started learning about weird engines, I thought the boxer-6 was just a V6 where the V got all flattened out. Engines like that do exist, but they’re not called boxer-6s. The difference is, in a boxer-6, pairs of pistons opposite each other move in and out simultaneously. Unlike in a lot of V-engines, each piston’s connecting rod has its own bearing on the crankshaft. What does any of this matter? Well, it’s unusual, for one. For two, the peculiarities of engine dynamics (which I don’t pretend to understand) make the boxer-6 a very smooth-running, well-balanced, low-vibration engine. Also, the fact that its cylinders aren’t crammed cheek-to-cheek in a V means that even fairly high-power boxer-6s can be air-cooled (though some are still water-cooled).

But you guys know me by now. You know I always go to extremes if given the chance. I’m not going to be satisfied with a six-cylinder engine, no matter how nice.

The H-16

brm_h16_engine

(From Wikipedia.)

We’ve made quite a leap. While you could go out right now and buy a car with a boxer-6 in it, the only way you could have an H-16 engine is time travel, or by being an insane millionaire and having one built for you.

The engine above is British Racing Motors’ H16 engine. There are plenty of weird, esoteric terms used in automotive circles, but the weird letters that show up in engine names are perfectly sensible (mostly). My car is powered by an I4 engine, which means it’s an inline-four: four cylinders in a straight line. A V6 has six cylinders in two banks of three, with the pistons angled so that their connecting rods form a V-shape, with the crankshaft at the tip of the V. You’d refer to the boxer-6 above as an F6, for flat-6.

What, then, is an H16 engine? Well, it’s horrifying, is what it is:

h-engine

(Again, from Wikipedia.)

An H-16 is two flat-8s stacked on top of each other, each with its own crankshaft. The crankshafts are connected at the end by gears. Like I said, I don’t know engines, but that seems like a bad idea.

For some applications, it’s actually not. H-engines are mechanically pretty well-balanced, for one. For two, they’re a bit more compact than, say, a V-engine with the same number of cylinders, which made them popular for high-power airplanes.

But car enthusiasts will know that the H16 I showed at the top of the section didn’t come from an airplane. It came from British Racing Motors’ ill-fated P83 Formula 1 car, which has a peculiar, and if you ask me, slightly unpleasant sound.

BRM’s H16 was plagued with problems. For one thing, having two sets of cylinder heads on opposite sides meant it needed two radiators and a split fuel system. It also needed dual camshafts (which are the mechanical clockwork-type devices that tell a cylinder’s valves when to open the intake valves and let in fuel, and when to open the exhaust valves to let out burned fuel). It needed dual camshafts for each cylinder head. That’s bad enough in a V-engine, where you have two cylinder heads, but the H16 had four. For another, it was more complicated and fuel-hungry than even its competitor, the mighty V16. Unsurprisingly, the engine wasn’t a success, partly because a lot of them just blew up during races. Apparently, British Racing Motors’ troubles at the time, and their obsession with complicated engines, earned them the nickname “British Racing Misery.”

Still, it’s a weird, interesting engine, and somebody had some serious gonads to say “You know what? A V16 is just too damn simple.”

The Napier Deltic

napier_deltic_animation

(From Wikipedia, again.)

You remember that scene in the first Back to the Future where Dr. Brown is talking about inventing the Flux Capacitor? “I slipped, hit my head on the edge of the sink, and when I woke up, I drew this.” I’ve gotta figure a bonk on the head inspired the Napier Deltic. For those who don’t know much about engines, let me explain why the picture above shows one of the weirder engines ever invented.

  1. Opposed pistons. In a common piston engine, the air-fuel mixture burns, and the pressure from the hot gas pushes a piston down, which applies torque to the crankshaft, which drives whatever machine the engine is running. There’s just a cylinder head holding the hot gas in. In an opposed-piston engine, though, there isn’t a cylinder head, but rather, two pistons in a headbutt configuration in every cylinder. The fuel-air mixture enters the space between the two heads and burns there, pushing the two pistons apart, driving two crankshafts.
  2. The delta design. As you can see, the Deltic isn’t even as simple as a regular opposed-piston engine. That picture shows three cylinders, containing six pistons, driving three crankshafts. It’s weird, but it’s got a certain geometric appeal to it. It was also, apparently, a lot more compact and powerful than similar engines of the time, which made it attractive for British torpedo boats and locomotives.
  3. It was a two-stroke. If you don’t know, two-stroke engines are usually what you find powering small power tools like weed-whackers and chainsaws.The engines of most modern cars are four-stroke. The differences are subtle. In a four-stroke engine (which most gasoline engines are), the piston has to go up or down a total of four times to complete a full cycle: It moves down to suck in in air and fuel, moves up to compress the air and fuel before ignition, is pushed down by the burning air and fuel, and finally rises up to push out the exhaust. In a two-stroke engine, the intake and exhaust steps happen at the same time: often, the piston pushes down on a fuel-air mixture in the crankcase, and the pressure pushes the mixture into the engine, which pushes the exhaust out. The major advantage of a two-stroke engine is that it doesn’t need mechanically-operated intake and exhaust valves, since the piston controls intake and exhaust. This saves weight and complexity, which is vital when your engine is powering, say, an airplane, or a boat, or a chainsaw that needs to be light enough to hold up for long periods, without getting tired and dropping it on their foot.

The Deltic was fairly successful, since it packaged eighteen or more cylinders (two pistons each) into a smaller package than was possible with other designs of the same cylinder number. It was a lot lighter than comparable engines, too.

Why aren’t there more Deltic-type engines around? Well, a little research suggests that’s mostly because Napier was bought out after World War 2, and switched to making things like turbine engines and turbochargers, the former of which were rapidly filling a lot of the niches the Deltic once occupied. I suspect the peculiarity of the delta design also played a part, since my first reaction to it was “there’s no way that was a success.” I was wrong about that, but I bet the Deltic scared off more than a few mechanics.

The W12

napier_lion_ii

(Still Wikipedia.)

We’re not done with Napier yet. Above, you see the Napier Lion.

Although it’s not entirely accurate, you wouldn’t be far off if you described a V8 engine as two I4 engines driving the same crankshaft. The Napier Lion is a broad-arrow W12, which is what you’d get if you took a V8 and jammed another I4 down the V (sounds like a weird fetish fantasy…)

You’ve probably heard of W engines before, even if you’re not into cars. A W16 is the powerplant behind the Bugatti Veyron, which is famous for two things: holding the Guinness record for fastest street-legal car, and being a rare example of a supercar that isn’t absolutely horrible to look at. (I mean, it’s still not great, if you ask me. It looks like ergonomic furniture. But look at a Lamborghini Aventador and tell me the Veyron isn’t better-looking, if only because it’s not as…pointy.) But the W16 in the Veyron is a different type: it has two banks with eight cylinders each, and those cylinders are jammed just about as close as you can get them. Each of the banks is essentially a VR8: a V8 with a very narrow V. Since it only has one crankshaft, W isn’t exactly a good letter to use, but as a double-vee, I guess I get it. (I’m tempted to call the Napier Lion a Ш12, but Sh-12 isn’t exactly catchy.)

What the hell are you getting at, I hear you ask.  I get that question a lot. The reason I bring up the Napier Lion is that it demonstrates, better than the Veyron’s W16, that you can take a pretty ordinary set of cylinders (banks of I4s) and turn them into bizarre, high-power variants. It was weird aircraft engines like the Lion that got me interested in weird engines to begin with. Unsurprisingly, someone took a pair of W12 Lions and put them in a car, breaking a land-speed record and becoming the first to break the 350 mph barrier. And trust me, it’s not the last time we’re going to see weird engines dropped in cars.

The Radial

radial_engine_timing-small

(Wikipedia.)

For some reason, I think that looking at that animation while you had a really bad fever (or after eating funny mushrooms) would be really scary. But there’s not that much scary about it. It’s just a radial-5 engine, which proves that, there are more interesting ways to arrange pistons than lines and Vs.

I really like radial engines. There’s something pleasing about that five-fold symmetry. It’s like a starfish made of explosions. It also offers some serious advantages if you’re looking for an engine to stick in a propeller-driven airplane: compact and powerful, but with pistons still far enough apart that you can air-cool them, which eliminates the radiator, which is a notoriously brittle piece of hardware. And you don’t want brittle stuff on, say, a fighter plane.

For symmetry and smoothness, nearly all four-stroke radial engines have odd numbers of cylinders. A two-cylinder radial is just a two-cylinder boxer. I’ve seen videos of three-cylinder radials, but I like pentagons better than triangles, so I won’t bother with those. Plus, talking about five-cylinder radials gives me an excuse to show you a video of a Toyota being powered by an airplane engine. And this whole section has pretty much been an elaborate segue to talk about two bad-ass vehicles. The first is the Plymouth Air Radial Truck:

016-1939-plymouth-radial-airplane-truck-gary-corns

(From Motor Trend.)

Because, sometimes, you wake up in the morning and think “You don’t see enough nine-cylinder hot rods out there.” That is a 300 horsepower Jacobs 9-cylinder radial airplane motor from the 50s. There are plenty of things about hot rods that I don’t like (they’re always alarmingly low to the ground, for one, which bothers me for some reason), I will never deny that hot rodders are insanely creative in all the right ways. My proof? Look at that picture again.

Naturally, the radial engine lost a lot of its popularity when turboprop and turbojet engines became reliable and affordable for airplanes. It didn’t help that, eventually, engines like the I4 and F4 became refined enough and powerful enough to do the same job as a radial without needing the specialized radial construction.

But there was a period when the radial was king of the air. Within that period was a really wild period when planes needed more power than an ordinary radial could give them. Trouble is, if you want to make a radial engine with more than 11 cylinders, you have to make it really wide so that those cylinders can stick out to be air-cooled. And if you do that, then you’ve just stuck what amounts to a dinner plate on the front of your airplane, which is no good for aerodynamics. Engine manufacturers solved this with multi-bank radial engines.

The Wasp Major

biggest_rotary_cutaway

(Bet you can’t guess the source.)

That is a cutaway of the Pratt and Whitney Wasp Major, which is a beast of a machine. It has 28 cylinders (four banks of seven cylinders) and a built-in supercharger. It has a displacement of 71 liters (compare that to the Bugatti Veyron or Dodge Viper, two high-power cars, both of which displace all of 8 liters.) It produced up to 3,500 horsepower in its original form, and over 4,000 once they added turbochargers. It also sounds pretty fucking awesome. If I was a millionaire and wanted to build a hot rod, I think this is the engine I’d put in it. Either this, or our next weird engine…

The Zvezda M503

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(From Flickr, this time.)

I live in North Carolina. We’re one of the home states of NASCAR, which might be the ultimate in redneck racing. I went to a monster truck show last weekend, at which one of the events was lawnmower racing. That’s kinda what we do down here. We like big trucks, noisy cars, and bizarre racing. Tractor pulling is popular down here, too.

If you don’t know, tractor-pulling is an odd sport where you hook a tractor to a weighted sled and try to pull it a specified distance (usually 300 feet or 100 meters). On top of the sled is as sliding weight which is geared to the wheels so that it moves forward in proportion to the distance pulled, making it harder the farther you pull. Unsurprisingly, that takes a lot of power. I’ve seen pictures of tractors with as many as five or six supercharged V8s, tractors with 18-cylinder radial engines, tractors with two diesel V12s, and tractors with helicopter turboshaft engines.

I always assumed tractor pulling was exclusive to American rednecks. Clearly, I was ignorant, because a lot of the really good tractor-pulling videos are from Germany, the Netherlands, and Australia, where it’s apparently a really popular sport. And my favorite tractor by far is the German “Dragon Fire.” I don’t care if you don’t like big engines or tractor pulls. I insist you watch this video of Dragon Fire in action.

As much as I like big engines and weird engines, I’ll freely admit that tractor pulling seems a bit excessive. I mean, no wonder it’s so expensive to get into engines: how can I hunt down a good V8 when there are bastards out there sticking five of them on one tractor? And, while I’m at it, stop hogging all the damn superchargers!

Dragon Fire, though, has a more elegant solution. Well, kind of. It depends how you define “elegant,” I guess. Dragon Fire isn’t powered by a bunch of V8s. It’s powered by a single 42-cylinder radial engine: the Zvezda M503, built for use in Soviet missile boats. The 503 has 42 cylinders (6 rows of 7). It weighs five times (almost five and a half times) as much as my car. It displaces 143 liters (which is about the volume of a bathtub, according to Wolfram Alpha). In its stock form, it produced nearly 4,000 horsepower. And it’s a diesel, too.

I should mention that the M503 powering Dragon Fire is running on methanol, not diesel fuel. And it, apparently, produces closer to 8,000 horsepower, which is absolutely ridiculous, and which makes me happy.

The Swashplate

swash20plate20motor3

(From the website of Douglas Self, who’s compiled a whole bunch of awesomely weird engines.)

I wouldn’t want to be the guy who proposed that design. I’m sure some stuffy executive looked at that, took out his monocle, took his cigar out of his mouth and said “Stop bringing me nonsense and bring me a real engine!” But the swashplate engine is real, and it’s pretty damn cool. It operates just about the same as any other piston engine, but instead of turning a crankshaft, the swashplate engine pushes on an eccentrically-mounted disk. Not only does this squeeze four (or more) pistons into a compact package, but it also eliminates the heavy crankshaft and provides a natural gear reduction. Apparently, it has been used on a few cars, and was considered for use in airplanes, its main use is as the powerplant in torpedoes, where its small frontal area and corresponding tiny drag is vital.

For some reason, I really like the swashplate engine. It’s about as far as you can take a traditional fixed-cylinder design. It’s just delightfully weird, and it’s weird that it actually works. (Make it any weirder, and you’ll get awesome stuff like the Duke engine, which didn’t make the list because its cylinders aren’t fixed, and that was one of the arbitrary qualifications I came up with.)

I also like that the swashplate engine has been built in Lego form, by the awesome YouTuber DrDudeNL.

The Chrysler A57 Multibank

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(Found via Jalopnik.)

When the United States entered World War 2 in 1941, apparently, Chrysler was tasked with producing a high-power engine for the M4 Sherman tank as quickly as possible. They delivered a 30-cylinder engine. 30 cylinders isn’t as many as 42, so the A57 shouldn’t be as impressive as the Zvezda M503. But it is, for my money. Because Chrysler did a clever thing to meet the deadline. To allow them to use existing engineering, they didn’t exactly build a 30-cylinder radial. They built a 30-cylinder engine made of five Chrysler I6 engines, attached to the main output shaft by gears. Here’s what that looked like:

chrysler-a57-multibank-gears

(From Old Machine Press.)

Using five existing I6s saved Chrysler design time, and they already had the machinery set up to make I6s, so they didn’t have to retool any factories, presumably. The A57 really is just five straight-6 engines stuck together. That’s the kind of Mad Max/McGyver creativity I like. Sure, the engine only produced 450 horsepower, but it was surprisingly compact, and I love this kind of simple innovation.

Honorable Mentions

I wanted to include the Junkers Jumo 205, but I’m running long as it is, and I already talked about opposed-piston two-stroke engines when talking about the Napier Deltic. I wanted to include the Duke Engine, but it’s got rotating cylinders, which disqualified it. For the same reason, I didn’t talk about the weird rotary radials developed early in piston-engined flight. I didn’t include the Wankel rotary engine, because it has no pistons. I didn’t mention awesomely weird concepts like the nutating engine or the gerotor combustion engine for the same reason. Plus, there’s only so much time in the day, and I’ve taken up enough of yours. But if you’ve got any weird engines you think I should’ve included, leave them in the comments. I might stick then in an addendum later on.

 

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The Biology of Dragonfire

In a recent post, I decided that plasma-temperature dragonfire might be feasible, from a physics standpoint. There’s one catch: my solution required antimatter (and quite a bit of it). Antimatter does occur naturally in the human body, though. An average human being contains about 140 milligrams of potassium, which we need to run important stuff like nerves and heart muscle. The most common isotope of potassium is the stable potassium-39, with a few percent potassium-41 (also stable), and a trace of potassium-40, which is radioactive. (It’s the reason you always hear people talking about radioactive bananas. It also means that oranges, potatoes, and soybeans are radioactive. And cream of tartar is the most radioactive thing in your kitchen, unless you’ve got a smoke detector in there.)

Potassium-40 almost always decays by emitting a beta particle (transforming itself into calcium-40) or by cannibalizing one of its own electrons (producing argon-40). But about one time in 100,000, one of its protons will transform into a neutron, releasing a positron (the antimatter counterpart to the electron) and an electron neutrino. The positron probably won’t make it more than a few atoms before it attracts a stray electron and annihilates, producing a gamma ray. But that doesn’t matter, for our purposes. What matters is that there are natural sources of antimatter.

Unfortunately, potassium-40 is about the worst antimatter source there is. For one thing, its half-life is over a billion years, meaning it doesn’t produce much radiation. And, like I said, of that radiation, only 0.001% is in the form of usable positrons.

Luckily, modern medicine gives us another option. Nuclear medicine, specifically (which, by the way, is just about the coolest name for a profession). As you may have noticed by the fact that you don’t vomit profusely every time you go outside, human beings are opaque. We can shoot radiation or sound waves through them to see what their insides look like, but that usually only gives us still pictures, and it doesn’t tell us, for instance, which organs are consuming a lot of blood, and therefore might contain tumors. For that, we use positron-emission tomography (PET) scanners. In PET, an ordinary molecule (like glucose) is treated so that it contains a positron-emitting atom (most often fluorine-18, in the case of glucose). The positron annihilates with an electron, and very fancy cameras pick up the two resulting gamma rays. By measuring the angles of these gamma rays and their timing, the machine can decide if they’re just stray gamma rays or if they, in fact, emerged from the annihilation of a positron. Science is cool, innit?

One of the other nucleides used in PET scanning is carbon-11. Carbon-11 is just about perfect, as far as biological sources of antimatter go. It’s carbon, which the body is used to dealing with. It decays almost exclusively by positron emission. It decays into boron, which isn’t a problem for the body. And its half-life is only 20 minutes, which means it’ll produce antimatter quickly.

There’s one major catch, though. Whereas potassium-40 occurs in nature, carbon-11 is artificial, produced by bombarding boron atoms with 5-MeV protons from a particle accelerator. I may, however, have found a way around this. To explain, here’s a picture of a dragon:

Whole Dragon

No, those aren’t labels for weird cuts of meat. They’re to explain the pictures that follow.

Living things contain a lot of free protons. They’re the major driver of the awesome mechanical protein ATP synthase, which looks like this:

(The Protein DataBank is awesome!)

Sorry. I just really like the way PDB renders its proteins.

Either way, we know organisms can produce concentrations of protons. But in order to accelerate a proton, you need a powerful electric field. The first particle accelerators were built around van de Graaff generators, which can reach millions of volts. Somehow, I doubt a living creature can generate a megavolt.

Actually, you might be surprised. The electric eel (and the other electric fish I’m annoyed my teachers never told me about) produces is prey-stunning shock using cells called electroctyes. These are disk-shaped cells that act a little bit like capacitors. They charge up individually by accumulating concentrations of positive ions, and then they discharge simultaneously. The ions only move a little bit, but there are a lot of ions moving at the same time, which produces a fairly powerful electric current that generates a field that stuns prey. The fact that organisms can produce potential differences large enough to do this makes me hopeful that maybe, just maybe, a dragon could do the same on a nanometer scale, producing small regions of megavolt or gigavolt potential that could accelerate protons to the energies needed to turn boron-bearing molecules into carbon-11-bearing molecules. Here’s how that might work:

Bio-linac

There’s going to have to be a specialized system for containing the carbon-11 molecules, transporting them rapidly, and shielding the rest of the body from the positrons that inevitably get loose during transport, but if nature can invent things like electric eels and bacteria with built-in magnetic nano-compasses, I don’t think that’s too big a stretch.

The production of carbon-11 is going to have to happen as-needed, because it’s too radioactive to just keep around. I imagine it’d be part of the dragon’s fight-or-flight reflex. Here’s how I imagine the carbon-11 molecules will be stored:

Storage Zone

Note the immediate proximity to a transport duct: when you’ve got a living creature full of radioactive carbon, you want to be able to get that carbon out as soon as you can. Also note the radiation shielding around the nucleus. That would, I imagine, consist of iron nanoparticles. There might also be iron nanoparticles throughout the cytoplasm, to prevent the gamma rays from lost positrons from doing too much tissue damage.

Those positrons are going to have to be stored in bulk once they’re produced, though. This problem is the hardest to solve, and frankly, I feel like my own solution is pretty handwave-y. Nonetheless, here’s what I came up with: a biological Penning trap:

Usage Zone

These cells are going to require a lot of brand-new biological machinery: some sort of bio-electromagnet, for one (in order to produce the magnetic component of the Penning trap). For another, cells that can sustain a high electric field indefinitely (for the electric component). Cells that can present positron-producing carbon-11 atoms while simultaneously maintaining a leak-proof capsule and a high vacuum in which to store the positrons. And cells that can concentrate high-mass atoms like lead, because there’s no way to keep all the positrons contained. That’s probably wishful thinking, but hey, nature invented the bombardier beetle and the cordyceps zombie-ant fungus, so maybe it’s not too out there.

The process of actually producing the dragonfire is very simple, by comparison. The dragon vomits water rich in iron or calcium salts (or maybe just vomits blood). The little storage capsules open at the same time, making gaps in their fields that let the positrons stream out. The positrons annihilate with electrons in the fluid (hopefully not too close to the dragon’s own cells; this is another stretch in credibility). The gamma rays produced by the annihilation are scattered and absorbed by the water and the heavy elements in it, and by the time they exit the mouth, they’re on their way to plasma temperatures.

This is not, of course, the kind of thing nature tends to do. Evolution is a lazy process. It doesn’t find the best solution overall (because if you wanna talk about dominant strategies, having a built-in particle accelerator is up there with built-in lasers). It just finds the solution that’s better enough than the competitor’s solution to give the critter in question an advantage. So, although nature has jumped the hurdles to create bacteria that can survive radiation thousands of times the dose that kills a human on the spot, and weird things like bombardier beetles, insect-mind-controlling hairworms, and parasites that make snails’ eyestalks look like caterpillars so birds will eat them and spread the parasites, the leap to antimatter storage is probably asking a bit too much, unless we’re talking about some extremely specific evolutionary pressures.

Which is not to say that nature couldn’t produce something almost as awesome as plasma-temperature dragonfire. Let’s return once again to the bombardier beetle. The bombardier beetle has glands that produce a soup of hydrogen peroxide and quinones. Hydrogen peroxide likes to decompose into water and oxygen, which releases a fair bit of heat (which is why it was used as a monopropellant in early spacecraft thrusters). But at the beetle’s body temperature, the decomposition is too slow to matter. When threatened, however, the beetle pumps the dangerous soup into a chamber lined with peroxide-decomposing catalysts, which makes the reaction happen explosively, spraying the predator with a foul mix of steam, hot water, and irritating quinone derivatives. Here’s what that looks like:

So if nature can evolve something like that, is it too much of a stretch to imagine a dragon producing hydrogen-peroxide-laden fluid, mixing it with hydrogen gas, and vomiting it through a special orifice along with some catalyst that ignites the mixture into a superheated steam blowtorch like the end of a rocket nozzle? Well, look at that beetle! Maybe it’s not as far-fetched as it seems…

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The Physics of Dragonfire

Last year, I wrote a post about the physics of the plasma-temperature dragonfire from Dwarf Fortress. Today, because my frontal lobes are screwed on backwards, I wanna work out whether or not biology could produce a plume of 20,000-Kelvin plasma without stretching credibility too far. I have a hunch that the answer will be disappointing, but my hunches are usually wrong. Must be those faulty frontal lobes.

The first thing we need to work out is how much power we’re going to need to heat all that air. Let’s say dragonfire comes out of the dragon’s mouth at 50 meters per second (111 mph, about as fast as a sneeze or a weak tornado). As a rough approximation, let’s assume that a dragon’s mouth has a cross-sectional area of about 0.0600 square meters (about the area of a piece of ordinary printer paper). This is one of those nice situations where we can just multiply our two numbers together and get what we’re looking for: a flow rate of 3.120 cubic meters per second.

So here’s what we know so far: we’ve got a dragon breathing 3.120 cubic meters of air every second. That air has to be heated from 300 Kelvin (roughly room temperature) to 20,000 Kelvin. The specific heat capacity of air is close to 1,020 Joules per kilogram Kelvin over a pretty wide range of temperatures, so we’ll assume that holds even when the air turns to plasma. That means that every second, our dragon has to put out 79.96 million Joules, or 22.2 kilowatt-hours. But we’re not talking about hours here. We’re talking per second. That’s 79.96 megawatts, which is almost twice the power produced by the GE CF6-5 jet engines that power many airliners. That’s a lot of power.

But, much to my surprise, there are some fuels that can deliver that kind of power. Compressed hydrogen burning in pure oxygen could do it. Except I’m basing that assumption entirely on the power required. There’s a lot more physics involved than that. The highest temperature that a combustion reaction can reach, assuming no heat loss, is called the adiabatic flame temperature, and although this is an impressive 3,500 Kelvin for a well-mixed oxy-hydrogen flame, that’s nowhere near the 20,000 Kelvin we need. The only fuels with higher energy densities than hydrogen are things like plutonium and antimatter, and for once, I’m going to be restrained and try not to resort to antimatter if I don’t have to. Let’s see if there’s another way to do it.

In my previous post on dragonfire, I described Dwar Fortress’s dragon’s-breath as a medieval welding arc. So to hell with it–why not use an actual welding arc to heat the air? Well, it turns out that something like this already exists. It’s called an arcjet. Like VASIMR, it’s one of those electric-thruster technologies that has yet to get its day in the spotlight. But arcjets have found another purpose in life: allowing space agencies to test their reentry heat shields on the ground. Here’s a strangely satisfying video of one such arcjet heater being tested on an ordinary metal bolt:

That certainly looks like how my brain tells me dragonfire should look, but from a little research, it seems that the Johnson Space Center’s arcjet only puts out something like 2 megawatts, thirty-five times less than the 79 we need. According to these people, the arc in an arcjet thruster can reach the 20,000 Kelvin we need, but it seems pretty likely that the actual plume temperature is going to be a lot lower.

And besides, our dragon’s powerplant has to be (relatively) biology-friendly, since it has to be inside a living creature. The voltages and currents needed to run an arcjet would probably make our dragon drop dead or explode or both.

So, as much as I hate to do it (I’m kidding; I love to do this) I’ve gotta turn to antimatter.

Antimatter is the ultimate in fuel efficiency. Because almost all of the universe is made of matter (and nobody really knows why), if you release antimatter into the world, it’ll very quickly find its matching non-anti-particle and annihilate, producing gamma rays, neutrinos, and weird particles like kaons. The simplest case is when an electron meets a positron (its antiparticle). The result is (almost) always two gamma rays with an energy of 511 keV, meaning a wavelength of 2.4 picometers, which is right on the border between really high-energy X-rays and really low-energy gamma rays.

This presents yet another problem: hard x-rays and soft gamma rays are penetrating radiation. They pass through air about as well as bullets pass through water (which isn’t an amazing distance, I’ll admit, but I’m still not about to sit in a pool and let someone shoot at me). At 511 keV and ordinary atmospheric density, the mass attenuation coefficient (which tells you what fraction of the radiation in question gets absorbed after traveling a certain distance) is in the neighborhood of 0.013 per meter, which means a beam of 511 keV photons will get 1.3% weaker for every meter it travels.

Working out just what fraction of these photons need to be absorbed is a bit beyond me. If the radiation has to be 1,000 times weaker, it’ll have to pass through 1.6 meters of air. That sounds to me like it’d be enough to burn our dragon’s tongue right off. And indeed, if we run the equation a different way, we see that, after traveling through 30 centimeters (about a foot) of air, the gamma rays will still have 25% of their original strength. I’m trying very hard not to imagine what burning dragon teeth would smell like.

But there’s no reason our dragon has to be making its death-dealing plasma out of air. Water is the most common molecule in biology, so why not use that instead? A 511 keV photon can still travel over 10 centimeters in water, but that’s a heck of a lot better than the 150 centimeters we were looking at before.

Of course, we can add a dash of metal atoms to the mix to absorb more of the x-rays and protect our poor dragon from its own flame. The heaviest metal found in organisms in large quantities is iron, usually in the form of hemoglobin. So let’s just throw some hemoglobin in that water, handwave away how the dragon is producing so many positrons, and call this experiment a success.

Well, it’s not a total success, since what I just described is essentially a dragon vomiting a jet of blood and then turning that into scalding-hot plasma. No wonder everybody’s scared of dragons…

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Dragonfire

So, I’ve been playing a lot of Dwarf Fortress lately (which goes a long way to explain the lack of new posts). If you don’t know, Dwarf Fortress is a bizarre and ridiculously detailed fantasy game where you send a squad of dwarves into the wilderness to dig for gems and ore and try to stay alive as long as possible. That’s harder than you might think, since all dwarves are born alcoholics who must have booze to function properly, they’re surrounded by horrible creatures that want them dead, the environment is harsh, and they’re…well, they’re a little dim.

I love Dwarf Fortress. I love it because the creators have put such an insane level of love and detail into it. For example, how many other fantasy games do you know where they actually use the specific heat of copper when calculating whether or not your armor is melting?

But one detail in particular caught my eye: Dwarf Fortress’s temperature system. Temperatures in Dwarf Fortress are, to quote the Wiki, “stored as sixteen-bit unsigned integers,” which means temperatures between 0 and 65,535. The cool thing is that Dwarf Fortress doesn’t use some wimpy unspecified temperature scale. There is a direct correspondence between Dwarf Fortress temperatures (measured in degrees Urist. Don’t ask.) and real temperatures. To convert from Dwarf Fortress temperatures to Kelvins, for instance, just do a little simple math: [Temperature in Kelvins] = ([Temperature in degrees Urist] – 9508.33) * (5/9) . As it turns out, the Urist scale is just the Fahrenheit scale shifted downward by 9968 degrees (which, incidentally, means you can go several thousand degrees below aboslute zero, but that’s an issue for another time).

Better yet, Dwarf Fortress has DRAGONS! I love dragons, far more than any twenty-six-year-old adult male probably should. I turn into a hyperactive eight-year-old boy when I think about dragons. And Dwarf Fortress combines two of my great loves: dragons, and being unnecessarily specific about things. Here’s a typical encounter between a human swordsman in bronze armor (the @ symbol; the graphics take some getting used to) and an angry dragon (the D symbol).

Dragon Fight 1

Round 1. FIGHT!

Dragon Fight 2

The dragon breathes fire. The human’s chainmail pants are now filled with poo.

Dragon Fight 3

The human is engulfed in dragonfire and begins burning almost immediately.

Dragon Fight Aftermath

To nobody’s surprise, the dragon wins. I’d also like to note that this dragon is a real jerk: while his poor prey was burning to death, it swooped in and knocked the human’s teeth out…

Dragon fights in Dwarf Fortress end very quickly. That’s because, as the wiki tells us, dragonfire has a temperature of 50,000 degrees Urist. Which translates to a horrifying 22,495.372 Kelvins (22,222.222 ºC, 40,032 ºF). That’s higher than the boiling point of lead. It’s higher than the boiling point of iron. It’s higher than the boiling point of tungsten, for crying out loud. In fact, it’s sixteen thousand degrees hotter than tungsten’s boiling point. Dwarf Fortress dragons don’t breathe fire like those wimpy Hollywood dragons. They breathe jets of freakin’ plasma. Plasma hotter than the surface of the sun. Plasma almost as hot as a lightning bolt.

With this in mind, we can take a scientific (and somewhat gruesome) look at what happened to our unfortunate human swordsman just now.

From the images above, let’s say the dragon’s plasma jet reached a maximum length of 10 meters before the dragon stopped spitting. Just before it struck our adventurer, it was spread out in a rough cone 10 meters long and 5 meters wide at the base. It was broiling away at a temperature of 22,500 Kelvin. When you’re working with absurd temperatures like this, the radiated heat and light do as much or more damage than the plasma itself. This kind of thing (unfortunately) also happens in more mundane circumstances: when high-voltage, high-current equipment shorts out, it can produce an arc flash, an electric discharge that produces a dangerous explosion, a deadly flash, a flare of plasma, and a shower of molten metal.

Arc flashes are horrifying. They’re a serious source of danger to electrical engineers. They’re also not terribly funny. But they give us an idea of the effects of dragonfire.

At a temperature of 22,500 Kelvin, the front surface of the fireball would radiate about 0.285 terawatts of energy. The formula for a blackbody spectrum tells us that the fireball will be brightest at a wavelength of 128.79 nanometers, which is in the far ultraviolet. That’s more energetic than the ultraviolet light from germicidal lamps, which is already more than enough to cause burns and damage the eyes. So our unlucky swordsman would be looking at instant UV flash-burns.

Lucky for him, he probably won’t have long to worry about those burns. The fireball is radiating at 1.453e10 watts per square meter. If we assume the swordsman knew he was about to fight a dragon and therefore put on some sort of bizarre medieval bronze spacesuit and polished it to a mirror finish. He’s still dead meat: copper, one of the main components of bronze (the other is most often tin) is a terrible reflector at the wavelengths in question here, bottoming out at around 30%. That means our foolish knight is still going to be absorbing 70% of the radiant heat, which will (given a long enough exposure) raise its temperature to around 20,500 Kelvin, more than hot enough to flash-vaporize the outer layers.

But if we’re nice and pretend the knight was smart enough to have his bronze armor coated with something decently reflective at all wavelengths (like ye olde dwarven electropolished electroplated aluminum), he would only absorb about 5% of the incident radiation. Well, bad news, sir knight: your armor’s still heating up to 7,600 Kelvin, which is much hotter than the surface of the sun.

Of course, producing a plume of 22,000-degree plasma takes a lot of energy (I’ll resist the urge to nitpick the biology of that), and even if we put that aside, according to the game’s own internal logic, dragonfire doesn’t hang around very long. Each in-game tick (in adventure mode or arena mode) lasts one second, and our bronze swordsman was only exposed to these ridiculous temperatures and irradiances for around 10 ticks, or 10 seconds. If we consider the fact that the plume of dragonfire is going to lose a lot of energy to radiation and thermal expansion, our knight probably wouldn’t evaporate right away. But he will probably wish to his randomly-generated deity that he did.

Metals are good conductors of heat, and copper is one of the most conductive metals, heat-wise. Therefore, although our knight only got exposed to that horrifying draconic welding arc for a few seconds, his armor’s going to soak up a lethal amount of heat from that exposure. Arc flashes, lightning, and nuclear explosions can cause second- and third-degree burns from just a few seconds’ exposure, so our night is going to be blind and scorched, and then he’s going to poach like an egg inside his armor.

Don’t worry, though–he probably won’t feel it. Unless he has superhuman willpower (and is therefore able to hold his breath while the rest of his body is bursting into flames), he’s going to take a panicked gasp, and that’ll put an end to his battle very, very quickly.

The inhalation of superheated gas kills very rapidly. The inhalation of gas at thousands of degrees (meaning: the dragon’s plume and every cubic centimeter of air in contact with it) kills instantly. So our knight would probably lose consciousness either instantly, or within 15 seconds, which is how long it takes you to pass out when your heart and/or lungs quit working. And what would be left? A knight cooked Pittsburgh rare, wrapped in a blanket of broken bronze welding slag.

So, if you think you’ve outgrown being scared of dragons, imagine this: a scaly reptilian horror older than a sequoia, fixing you with its piercing gaze and then spewing a jet of gas as hot and bright as a welding arc. That’s good–I didn’t need to sleep tonight, anyway…

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