Propulsion · 5:48am Mar 7th, 2014
It's what moves you.
So I've done a lot of these military blogs but never really talked about how all this hardware gets around. Time to fix that.
With style, of course.
When I say "engine" you probably think of a car. That's a good place to start. Here's a .gif of a typical four-cycle (or four-stroke, if you prefer) gasoline engine. A four-cycle engine can be called an Otto Cycle, after the guy that invented it.
1=intake 2=compression 3=power 4=exhaust
Air and a vapor of fuel are drawn into the cylinder during the intake stroke. The compression stroke compresses the mixture. The sparkplug fires, igniting the fuel and driving the piston down for the power stroke. The exhaust stroke pushes the spent gases out of the cylinder so the cycle can begin again.
Fun Fact: Diesel cycle was named after a guy named Diesel. Yes, they do typically burn diesel fuel, but it's the engine design itself that makes it a Diesel, or an Otto, or something else.
Diesel engines have the same four strokes, but a slightly different process. Gasoline engines typically compress the fuel and air to an average of about eight times atmospheric pressure. Diesels only intake air into the cylinder and they compress it to about eighteen times atmospheric pressure. Under that much compression the air gets super hot. In a diesel, instead of a sparkplug firing, they have fuel injected. When the fuel is injected into the hot air, it spontaneously combusts. Yes, this means diesels require fewer electronics but have to be built stronger to handle the pressure.
Fun fact:
1=intake 2=compression 3=power 4=exhaust
1=suck 2=squeeze 3=bang 4=blow
Another kind of piston engine is the two-stroke.
The intake and compression strokes are combined, and the power and exhaust strokes are combined.
The two-stroke is less fuel efficient but a simpler design. They are generally for small engines like chainsaws or dirt bikes. You'll occasionally also find them in very large diesels, like in ships.
In the above picture of a two-stroke, you’ll notice that the intake fuel and air have to pass around the bottom of the piston. This is why many two-strokes require oil to be added to the fuel, to keep things lubricated.
Most piston engines have more than one cylinder per engine. Sometimes they're in a line, sometimes they're arranged in a V, sometimes they’re flat.
Cutaway showing a V-8.
Sometimes in airplanes they're arranged in a radial.
Another fun engine is the rotary.
You'll generally only see these in certain models of Mazda cars. Their main advantage is fewer parts and higher RPM.
Fun Fact: The rotary engine was invented by a guy named Wankel. Yep, Wankel cycle.
So we’ve covered the basics of reciprocating engines. There are a few things that you can do to increase performance. Superchargers and turbochargers are common on diesels and some higher-performance gasoline engines. Both are pumps that blow more air into the engine. More air means you can burn more fuel and get more power. A supercharger is driven by a belt. A turbocharger is driven by the exhaust gases.
Fun Fact: The Fast and the Furious has lied to you so much. Nitrous will make your car go faster, but it doesn’t explode. It’s not even flammable. It’s merely an oxygen carrying substance. Like previously noted: more air + more fuel = more power.
The one thing that all these engines have in common is the crankshaft. This is the rotating shaft that all the pistons are connected to. It provides the force to drive the vehicle.
If you’re dealing with a ground vehicle, the force probably goes through a transmission and on to the axles. The transmission has gears, which let the wheels turn at different speeds than the engine.
Basic rear wheel drive system. Front wheel drive cars, which are more common, have the engine and transmission packaged together and driving the front tires. Trucks tend to be rear wheel drive. Four wheel drive has more parts.
Some vehicles have the engine drive a generator, which produces electricity to drive electric motors. Automobile manufacturers like to call these hybrids and make a big deal out of them. Meanwhile, trains have been using this technology for decades.
So let’s move on to another common kind of engine: the turbine! (Pronounced the same as “turban.”)
Luuuuuuuulz
A turbine is a name for a windmill, basically. It has blades that get spun by moving air.
The air can come from another source, like wind in a windmill turbine, or steam generated in a power plant steam turbine. Or, the turbine engine can generate it internally:
The turbine section is the part that is being driven, thereby turning the blades in the rest of the engine through the central, rotating shaft. This is just like the crankshaft in the piston engines. And just like piston engines- intake, compression, combustion, exhaust.
Turbines engines power many modern warships and almost all military helicopters. The M1 Abrams tank even has a turbine engine. You get power out of a turbine through the shaft. Turbines tend to spin at very high speeds, so big gears are used to slow them down. This creates a bigger mechanical advantage, thereby seeming like more power – just like you gearing down on your bike.
An example of four engines (green boxes) driving two propeller shafts through gears.
The biggest use of turbines, however, is aviation. With airplanes, you can put a propeller on the shaft of a turbine engine to turn it into a turboprop. Or, you can just skip the propeller and make a whole lot of air go out the turbine’s exhaust - a jet engine.
Some jets have afterburners, which shoot fuel into the hot exhaust, and the resulting combustion gives the engine an extra boost. It’s not very fuel efficient, though.
Most jet engines these days are turbofans, that flow a lot of air around the main body of the engine. That is why commercial jets have such large-looking engines. Fighter jets have them too, but not to the same extent.
Turbofan
Let’s take a step back and talk about external combustion turbines. For example, boilers in older ships are burning fuel to boil water for steam to drive the turbines, which then turn the propellers and electrical generators.
The condenser cools the steam back into water. The water is pumped back into the boiler to be reheated into steam. And thus the steam cycle goes.
Nuclear propulsion is just like the basic steam cycle, except you’re using a nuclear reactor to generate heat instead of a boiler.
Advanced jet engines:
(a) The jet engine we covered earlier.
(b) The ramjet. At supersonic speeds, its nosecone slows down the incoming air so it can be combusted.
(c) The scramjet. The air goes through it supersonic all the way.
Because of their design, ramjets and scramjets can only be used at supersonic speeds. The famous SR-71 Blackbird used engines that used regular jets to go supersonic and ramjets to take over from there. Ramjets work best as speeds up to Mach 6. Scramjets can go faster than that.
NASA’s X-43, using a scramjet to go Mach 9.65, making it the fastest air-breathing vehicle in the world.
So what’s faster than that? Rockets.
Burn, baby, burn.
A rocket is technically defined as a motor that creates propulsion by using pressure to push against something. The water bottles you may have launched in science class count. More impressive are rockets the burn fuel, like the lovely Saturn V.
Rockets come in solid and liquid fuel varieties. Solid fuel rockets, once ignited, can’t be shut off. Liquid fuel rockets can be accelerated or decelerated just like anything else with a throttle.
Fun Fact: We actually are very good at building rocket nozzles for maximum thrust efficiency. The problem is materials: we can’t build more powerful rockets until we come up with something with a higher melting temperature.
And that brings us to fuel. You’re probably familiar with gasoline. When refining crude oil into the stuff you buy at the pump, a lot of other products are also created.
If you’re into chemistry, the C numbers are the carbon chains. Vapors like propane (C3) come off the top. Heavier stuff is down below.
Fun Fact: Kerosene, jet fuel, and diesel are all pretty similar. I wouldn’t recommend putting kerosene or jet fuel into your diesel engine because they are lighter fuels and don’t lubricate as much, but it shouldn’t immediately hurt anything.
So as we draw this blog to a close, you probably noticed a few recurring themes:
Cycles and hot gasses are important. Engines are basically all about the flow of heat.
There, I reduced every Thermodynamics class ever into two sentences.
So think about all of this the next time you get in the car.
I've always found it funny that no matter how advanced a Nuclear powered vessel was... It essentially ran on an old steam powered design!
Good stuff, yo. The jet turbines are really cool, as I never knew how exactly they worked.
You're half right about nuclear reactors. However, we still have boilers, of a sort. They are called steam generators. The primary water (that comes in direct contact with the reactor core) heats up the secondary water (water separate from the primary water) in the steam generator. That water boils, and continues down that turbine cycle you showed.
Think of it as a two stage system, instead of a single stage. Here's a good example of how a nuclear reactor is set up, generically speaking.
world-nuclear.org/uploadedImages/org/info/Nuclear_Fuel_Cycle/Power_Reactors/PWR.gif
Hope that helps!
1903736 Imagine my suprise when I was preparing a presentation for physics class and I came across that little tidbit of info.
Basicly, one can say that nuclear power plants are steam engines on steroids.
Very good! What about Opposed Piston Engines, like old diesel subs used, along with a few types of locomotive and the Junkers Jumo 205 aircraft engine.
Opposed Piston engine with 2 crankshafts
Napier Deltic opposed piston engine
Suck
Squeeze
Bang
Blow
This is how I remember the stages of propulsion.
I would like to ask that at some point you go into more detail about steam power, if only to show that steampunk leaves out a lot of detail.
Got all excited for a moment because I drive a Mazda. But I looked up it and mine wasn't the right kind to have a rotary engine.
what about the boats that use the large spinning towers to propel themselves, their name escapes me. Ah, they are called Rotor or Flettner ships.
1903756 This is true - for a pressurized water reactor like you showed in your picture. The water is under pressure so it can't boil and needs a secondary loop to generate steam to power the turbine.
A boiling water reactor generates its own steam and can be one loop. Yes, this does put some radiation in the turbine, but the overall system is considered to be safer because it has fewer parts and runs at lower pressure.
1904174 I did mention that there were all kinds of shapes of piston engines.
As a personal note, I've never really liked the idea of opposed engines. I guess it's nice not needing heads, but two crankshafts seems like more complication than it was worth.
Another lovely informative blog! I know lost of this stuff, but it was a great refresher. Pip pip, Cheerio!
1904206 Well, it still needs something to power the rotors. I suppose the rotors could be classified as an alternate propulsion train. I didn't include that in the blog because rotor ships are about as common as those that use magnetohydrodynamics.
So thats how piston engines work!
Thank you!
1904230 I think that they provide more torque and power in a smaller space.
Aren't Magnetohydrodynamics supposed to be very efficient and fast?
Where is fuel oil in the distillation process?
1904221
You're absolutely right, but I think that's going beyond the scope of propulsion. As far as I know, boiling water reactors are only used on land, as part of a power plant. Maybe I'm wrong as far as other countries go, but U.S. naval nuclear power only uses pressurized water reactors. And we've been using it safely for over 60 years now!
Personally, I prefer PWR over BWR any day. The thought of water boiling in the reactor core scares me more than the high operating pressures of a PWR. But then again, I'm used to said high pressures.
Do Electric motors fall under this category, or are they something else?
Or you just didn't?
1904281 Magnetohydrodynamics are the "caterpillar" from The Hunt For Red October. Basically, they use electromagnetic charges to move water. Think of them like railguns, except instead of shooting a bullet they shoot water. There's only been one real prototype ever built (Yamato 1) and it managed to move a small boat at eight knots.
Fuel oil is a broad term that typically refers to diesel and heavier.
1904396 I guess I could have gone a little more in depth, although electric motors are typically used in conjunction with something else that provides them electricity or charges their batteries.
1904309 Yeah, I suppose propulsion does typically use PWR. And when you put it that way, the core possibly being exposed by water boiling away, PWR does make a lot of sense.
Can you blame me? The nuclear safety elective I took in college was a few years ago.
1905183
lol, no, I can't blame you. I didn't even know you took a nuclear safety class! I couldn't say if BWRs are safer, but I know naval nuclear propulsion like the back of my hand.
Did that nuclear safety class ever show the SL-1 videos?
1905216 Never saw the vidoes, but after reading about it I'm not sure I'd want to...pinned to the ceiling...
1905216 So, you're a Nuke? A few years ago, my cousin's (Who is a nuke) shipmate (also a nuke) was giving his family a tour of the sub he was stationed aboard, the standard "this is the periscope, here's where we eat" type of stuff. When he got to the reactor compartment (I forgot the proper name for it), he was explaining the stuff and how it works, when he suddenly stared at a gauge/monitor for a few seconds, screamed "OH MY GOD! ITS GONE CRITICAL!!" and ran out. Everyone waited a second, looked at the gauge, and followed him, screaming their heads off! The captain wasn't happy when he found out!
Also, I've seen the SL-1 stuff on Engineering Disasters. That was just an accident waiting to happen.
What are liquid sodium reactors classified as?
1905157 That's the movie. In the book, the caterpillar drive is a pumpjet.
1905258 Yeah, I've read all Clancy's work that he authored himself.
"OH MY GOD! ITS GONE CRITICAL!!"
But wait, since when do they allow civilians in the reactor compartment?
1905263 I know, right? Hollywood fails at nuclear power.
1905263 Like I said, I forgot where he was.
1905255
The vids don't actually show the guy pinned to the ceiling. I sorta wish I could see pics, but I'm pretty morbid in that way. The SL-1 videos don't show any dead bodies, just the aftermath and recovery. The videos ARE on youtube, though I highly recommend checking them out. IN fact, I'll link the video right here!
[youtube=qOt7xDKxmCM]
1905258
LOL, that's awesome. I get the CO's response though. No need to cause an unnecessary panic. I know one time, before I showed up to my ship, they were doing a tiger cruise (which is a week where family and friends of the crew sail with them towards their homeport. It's a really fun time for them). The doors to the engineering spaces are right next to the mess decks. One day, a guy comes running out of the door with anti-contamination clothing on, screaming for everyone to run for their lives. It was hilarious! And the guy got away with it too, because an aircraft carrier is a big ship, and too many people are on board to single out one person, even if the only person that could do something like that is in reactor department.
That's one thing I hate, is that movies are ruined for me because people will say "the reactor is going critical" like it's a bad thing! IT'S SUPPOSED TO GO CRITICAL!!!
Also, with SL-1, part of that was because the Army wasn't as concerned with safety as Rickover was, and there was no backup provided for those fellows. I could lead an entire post about SL-1. ACTUALLY, we could talk about SL-1, because it was designed to be a mobile reactor, suited for cold-war conditions! Sorta like a mobile home, except with more bang for your buck.
liquid sodium reactors... probably molten salt reactors, because MSR is easy to remember, and salt has to be pretty hot to get into the liquid phase without burning it. When you get to reactors that use compounds other than water to cool the core, their designations get weird.
1905295
— Susan M. Stacy, Proving the Principle
Source:
http://en.wikipedia.org/wiki/SL-1
Just shows that these guys knew the design was unsafe. Come on, a portable reactor? That is just asking for trouble!
Also, Rickover was awesome. I read that he drank a glass of coolant in front of congress to show how safe it was! Plus, who knows how many guys he saved by fixing the Mk 14 during WWII!
What ship were you on?
1905320
That's the Army for ya. Rickover would never approve of such stupidity. In fact, it is on record that he said he would get rid of ALL nuclear progress if it meant the atomic bomb wasn't developed. He was the father of the nuclear navy, and he said that!
If it's a rumor about Rickover, chances are it's true. In this case, I can confirm that he did do that. There are stories where he would walk into the main control room, touch the operator's panel, walked out, and had the CO kick the operator out of the navy for letting him do that. BTW, coolant is perfectly safe. Just tastes funny.
USS Ronald Reagan. Left my ship, and the Navy, about 4 months after the Fukushima disaster.
1905349 I'm impressed that he lasted as long as he did. He had powerful friends. Isn't Reagan going to be decommissioned soon, or are they waiting for the next Enterprise?
1905351
He had some friends. But the Navy didn't like Rickover at all, and they were looking for reasons to get rid of him every chance they got. President Reagan was the one who finally force retired him, and Rickover didn't even get the courtesy of being informed! He found out by watching the news!!
The Reagan has only been commissioned for 11 years! It still has another 40+ years before they would even talk about decommissioning. And the new Enterprise, CVN-80, will be coming to us by the end of the decade~
1905384 Ok.
Yeah, the Navy didn't like him because he didn't play by the rules, his or anyone else's! He couldn't be used like every other admiral. He was a good man, and one hell of a sailor.
1905420
He wasn't a sailor! He was a nuclear engineer! All nukes are nuclear operators first, and sailors second. At least, that was what Rickover wanted. Nowadays, they are sailors first, but that isn't as fun as nuclear operator. Rickover wanted nuclear operators that knew how to run a nuclear power plant without even having to glance at a book. He hated things like saluting and Navy traditions.
There is a Barbara Walters interview with Rickover somewhere on Youtube. I suggest finding it, because it is awesome to hear how he did things, and get a glimpse into his mind. He's really one of the few people I wish I could have met.
I love this series of blogs. I've learned a lot that, and I've used one or two to teach my younger brother about military vehicles.
I only have one thing that I want to mention from this blog:
I may be wrong, but I'm thinking that there is a difference between a vapor and atomized fuel.
A vapor is a gas.
While atomized fuel is still technically a liquid.
I'm not 100% sure of this. I'm not a chemist or into the chemical side of automotive work. I'm on the physical side, so got any problems with like, replacing an alternator or something, I'm your man.
Keep up with the awesome blogs!
1905446 Same here. I also wish that I could have met Doolittle, Ernest E Evans, Captain of the USS Johnston (DD-557), Ted Briggs, Captain Smith, Jim Lovell, Neil Armstrong, and Buzz Aldrin. I was able to cross Brig. Gen. Paul Tibbets Jr.
1905263 I meant to ask where bunker fuel, like the stuff coming out of Arizona, is in the distillation process.
Also, some of the crude that came out of Indonesia was so "sweet", you could burn it as a bunker fuel right out of the ground!
1905638 I met Jim Lovell once. Well, by "met" I mean that I was standing next to the guy he was talking to. Close enough, right?
Wolf used to cater, and (twice!) worked events that Neil Armstrong attended.
1905566 Hmm, you might be right on the terminology. I would say that turning the gasoline into a gaseous state would be more accurate, because if it was still liquid you couldn't compress it in the cylinder.
1905638 Bunker fuel is pretty far down. Some of it is thick enough that you basically need to heat it so that it will flow well enough to go through the pipes.
1905739 Closer than I'll ever get! I met Tibbits personally when he was at EAA a few years back, just three years before he passed away. He was telling the story of dropping the Bomb, and how he trained for it. The way he told it, you could hear the roar of the four Wright R-3350-23 and turbosupercharged radials of Enola Gay as she took off and headed towards Hiroshima.
1905750 I knew about having to heat the oil. Try having to fire up a completely cold steamer in the winter like a friend of the family had to. The oil was frozen solid! He ended up tossing a few buckets of diesel in the firebox on top of a wood fire built by the previous shift to heat the water enough to get the steam up so it would flow into the atomizer and sustain itself.
This is the most informative blog post that I've ever seen on this site. EVER.
I came here for all the fanfics, (oh god, all the fanfics), but left with a slightly better knowledge of various propulsion systems.
Hell, this almost reads like a brief summary paper for an English class. Nice work.
Also, if you want to turn the fun up to 11:
http://en.wikipedia.org/wiki/Nuclear_pulse_propulsion
Not kidding, they actually seriously looked into doing this!
That was really informative... Also, want to do an info blog to help me out?
Radios.
Frequency spectrum, AM/FM, high to super high frequency, Transmission... all that good stuff...
We had to compress most of what we learned in class into a 3hour lecture, and unfortunately, it's basically the most important class I have for my career.
I have literally no idea how radio waves do their thing to transmit intelligence...
1907057 That's a good idea.
TNaB, you make the prettiest blogs, you know that?
We all appreciate them very much, and enjoy them as much as anything going.
1905741 Yeah, it's true that as a liquid, stuff can't be compressed. But when you atomize it, the fuel particles are so small that they bond (?) with the air, creating the mixture that is ignited. So It is still a liquid, because if the mixture is brought into the cylinder, but not burned, after it settled, you'd find a puddle, all bit it a very small one, in cylinder.
I don't know, maybe we're both right in a way. Just thought I'd bring it up.
1905741 Yeah, it's true that as a liquid, stuff can't be compressed. But when you atomize it, the fuel particles are so small that they bond (?) with the air, creating the mixture that is ignited. So It is still a liquid, because if the mixture is brought into the cylinder, but not burned, after it settled, you'd find a puddle, all bit it a very small one, in cylinder.
I don't know, maybe we're both right in a way. Just thought I'd bring it up.