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Cars 101, episode 2: 2-stroke, 4-stroke, 6-stroke, rotary...

YF19pilot

YF19pilot

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Welcome to the second session of Cars 101! If you missed last week's be sure to read up, because today's lesson is related:

http://forum.finalgear.com/viewtopic.php?t=9421



So, now that you know how engines work, it's on to today's topic:

2-stroke, 4-stroke, 6-stroke, rotary, and other ways to go fast


Today's lesson is about different ways for engines to work. I'll be providing some sketches that will hopefully give you an idea of how things work.

You didn't give us a diagram last week! What does a 4-stroke engine look like?

Well, here it is:

4stroke.jpg


I drew the cylinder mid way through the intake downstroke, the dashed lines mark roughly where Top Dead Center and Bottom Dead Center are located. So, now that we know what the basic car engine looks like:

Okay, I've heard of a two-stroke before. How's that work?

First, here's a sketch of a common two-stroke engine:

2stroke.jpg


A two stroke engine does what a four stroke does, only once up and once down to complete a cycle. Two stroke engines generally don't have valves or lubercation systems, thus meaning less moving parts and more power effeciency. I did draw in a small flap on the intake -- this valve flap is to prevent back flow during the engine cycle.

Two stroke engines are commonly found in small applications like lawn mowers and rc cars. Their advantage comes from being able to produce more power from the same amount of space as a four-stroke, and being able to operate in any orientation (handy for chainsaws).

The disadvantage, is that due to the lack of lubercation, you have to mix a special light-weight oil with the fuel. The oil tends to be costly, and two strokes tend to be less reliable than four-stroke engines. Also, because two strokes burn oil, they are more pollutant, and sometimes leaks gasoline because of the lack of exhaust valves.


So what is this 6-stroke you're talking about?

The six stroke engine is an invention by an Austrailian farmer. It replaces the valve system of a 4-stroke with a 2-stroke engine. Here's a quick diagram to give you an idea:

6stroke.jpg


This set up is said to deliver more tourqe and also more power effecency from the traditional 4-stroke. The inventor claims the engine can be revved to 20,000 rpm, theoretically.


Okay, my friend has a Mazda RX-8 and says it has a "rotary" engine. How is that different from a 4-stroke engine?

It's entire construction is different. First, some pictures:

rotary-engine-intro.jpg

rotary-engine-housing.jpg

rotary-engine-rotor.jpg

(sorry, didn't have a proper diagram)

The rotary engine is an alternative engine that has actually seen mass production. Credit is given to Felix Wankel, of whom it is often named after (Wankel engine or Wankel rotary).

The triangular shaped rotar spins counter-clockwise, performing the same steps as a 4-stroke engine, as it rotates. The rotary engine offers a light-weight alternative that has fewer moving parts.

However, the rotary engine makes a distinct sound (that some find unpleasent) and tends to be finicky when performing tuning upgrades (like a turbo charger). Also apex seals are known to go bad. Apex seals are used to seperate each stage -- because at any given time, the rotary cylinder is undergoing three stages at the same time.


So what other kinds of engines are there?

There are other types of engines which even myself am still unfamiliar with. For example, there's the ReveTech engine, round engine, and ring motor (a variation of the round engine).

You can visit the ReveTech website at: http://www.revetech.com
The round engine website is located at: http://www.roundengine.com
Currently the ring motor website is down.

You can read more about the 6-stroke here: http://www.jack-brabham-engines.com/
Also, more explanation about the rotary engine can be found on the forum here: http://forum.finalgear.com/viewtopic.php?t=8265&highlight=
which includes a link to the following article (which has moved to this link): http://www.myrotarycar.com/portal/forum/forum_posts.asp?tid=16
Also, picture source for rotary engine: http://travel.howstuffworks.com/rotary-engine.htm


Also, if anyone has some animated gifs, they will be appreciated.

Next week's topic: Carburators and Fuel Injectors
 
Great write-up, thanks for your effort! :thumbsup:

Even I learned something new...6 stroke?? Never heard of that one before...
 
I admire your effort to tackle on such a tedious task!
I'm sure it will help many people on this forum to learn more about the automobile.
 
Thanks for the update, have heared of the six stroke but that was it. You might like to add a quick reminder to the diagrams above explaining that they're applicable to petrol powered engines only as the Diesel doesn't have a spark plug but is ignited by high pressure and the resulting temperature (well, only know that for the four stroke for sure to be true :unsure: )
 
I always called the six stroke engine the Miller Cycle. :dunno:
 
the miller cycle is sth completely different, and works with a supercharger. during compression, the intake valve is kept open, so the mixture is compressed against the pressure of the supercharger instead of the closed valves, resulting in low compression ration, yet a high expansion ratio.
in human words: lot's of power when piston goes down, very little power loss when he goes up

the six stroke engine isn't used anywhere yet. they're still researching it

and i'm sorry, but 2 stroke deserves a better explanation ;)

they idd kinda do what 4 strokes do, but are a lot simpeler in design, but a lot harder to make much power.
like the name says, they only have 2 strokes, so when the cylinder is going up, he sucks in mixture underneatht the cylinder, and at the same time, compressing the mixture he inhaled before. same on the downstroke, one mixture is expanding and being pushed into the exhaust, while the mixture from below the piston is pushed up, to above the cylinder. this means that the cylinder is a pure piece of art. it has canals, and holes all over, and the shape of these for a great deal determine your performance. that's why you can gain loads of power just by drilling them bigger or to other shape with a dremel.

but that's not all. most of you will have seen that a 2 stroke engine most of the time has a HUUUGE exhaust system. that's called an expansion exhaust. since a 2 stroke features port instead of valves, there's an overlap in open and close time of intakeports and exhaustport, so a part of the mixture is dumped in the exhaust, is wasted. they solved this with the big exhausts, they contain a lot of soundvibes (which make the 2 stroke sound so cool), and those vibs suck mixture out of the cylinder, into the exhaust, the sound reflects on the other side of the expansian chamber, bounds back on the other side, and pushes the mixture back into the cylinder, having about the same effect as a turbocharger, increasing the boost and injecting twice the amounth of mixture normally available

and on scooters, after you made the power, you use a vario to get it to the rear wheel, which is the coolest transmission in the world, small changes here can create a completely different engine
 
^^ see, this is what Cars 101 is all about. The education and discussion on how cars work. Thanks, bone.
 
another extention: you said the 2 stroke engines are mostly used in very small applications, true, but in very large applications as well. like the 30 000 000cc ferry engines, are all 2 stroke diesel engines.

the first diesel engine was a 2 stroke engine by the way, and ran on arachid oil, caus diesel wasn't discovered yet.



and there are plenty of sorts of rotary engines, the wankel is the best known, but look here for a whole list of types of rotary engines (why did citroen make a site for this???)

PS: go on writing stuff, i'll add ;)
 
Great effort guys! Thank you! :)
 
Here is the rotary engine doing it's thing :D
http://img23.imageshack.**/img23/6299/wankel20uz.gif
 
I?m Learning. Keep going.

^So the blue ones are fuel, the yellow is explosion and grey ones ae exhaust?

Questions:

So the 4-strokes explodades every second time it goes up?
 
^ Yup (to both questions)
 
^ Once the piston reaches the top, the spark plug ignites and pushes everything down. This is why it all has to be synchronized or you will destroy the engine. If spark plugs fire at random orders and push the wrong piston down due to the explosion, you will break the camshaft most likely.
 
Does the rotary engine consist from only one of these or are there many behind eachother?
 
I know the Mazda is a 2-rotor engine but I don't know how that is set up.

Care to explain, resident experts?
 
Here's a better picture of a two-stroke engine, from the same site that mgkdk found that rotary engine picture.
twostroke.gif


The Mazda engine is just two rotary units placed side-by-side, joined together at the center shaft, if I'm not mistaken.
 
As BlaRo says, the Rotary engine used in Mazda's road going cars are two rotars connected to a crankshaft. Their racing RX-8 uses a 3 rotor.
 
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