- We've talked about engines before,
and I don't know if I'll ever get tired of it.
The air gets compressed by the piston,
and the spark...
What?
No, stop it!
There's no piston here!
What if I told you we could skip all of that crap?
Not worry about turning downward force into rotational force
and cut the size of the gall dang engine in half?
That's the Wankel rotary engine!
In 1951, Felix Wankel got this idea in his head
that if you put a triangular rotor in a well-designed
circely, oval-ish shape, you could make an engine
that took care of intake, compression, combustion,
and exhaust, just like the traditional piston-drive
Otto Cylce engine.
And because it's a spinning motion, you wouldn't need
to worry about crankshafts and valves and timing belts
and lifters and all that crap that other people
are goofin' around with.
He had some trouble getting it right, though.
So it was in 1961 that Mazda, intrigued by this idea,
helped him out, and here's how it works.
A curved triangle sits in the engine.
It's what'll drive the driveshaft, which is also weird.
Instead of a piston, this magic triangle is called a rotor,
because it spins.
The rotor sits inside of a housing and rotates
around a fixed gear attached to the housing.
This gear makes sure that the rotor follows the right path,
so it's not just floating around in there.
The rotor then spins an eccentric output shaft,
and this is what'll give the car moving.
You can call it a driveshaft if you want,
I'll know what you're talking about.
But just the names of the parts should let you know
that the Wankel rotary engine plays by its own rules.
Now that we know the parts, let's see how they fit together
and make the boom.
We'll start with the intake.
As the triangle-shaped rotor draws away from the wall
of the housing, it's creating a vacuum.
As it passes the intake hole, it continues to pull away
from the wall, drawing the air-fuel mixture
into the chamber it's creating, just like a piston
would draw air in on its intake stroke.
When the peak of the rotor passes the intake port,
well, now that chamber's sealed.
The rotation of the triangle, still sealed against
the housing, begins to compress the air-fuel mixture
as it continues its rotation.
When the air is as compressed as it can be and the rotor
has just a bit more mass on the other side of the chamber,
a spark triggers the combustion.
The combustion chamber is long.
If there's only one plug, the flame would spread too slowly
to be effective at producing power.
Most rotary engines have two sparkplugs.
When the sparkplugs ignite the air-fuel mixture, kapow!
It forces the rotor to move in a direction
that allows the combustion reaction to expand,
continuing the rotor's journey around the housing.
The combustion gasses continue to expand, moving the rotors
and creating power, until the peak of the rotor
passes the exhaust port.
Just like the rotor compressed the air-fuel mixture
against the wall with the sparkplugs, on this side
of the housing, the rotor pushes the exhaust gasses
out of the exhaust port.
And if you look at the other point of the triangle,
the rotor is beginning to draw air into the intake chamber
just as it's finishing with the exhaust down here!
So the cycle continues, over and over and over
and over and over and over, and it continues to go
over and over and over.
But unlike the jerky up-and-down motion of the pistons,
the rotor moves, just like my favorite band,
in one direction.
♪ You don't know you're beautiful ♪
There's so much rubbing going on between the rotor
and the housing that that gave Wankel a lot of problems
as he was designing.
Engineers realized that a hole to let in the engine oil
would reduce wear on the rotor and housing.
Also, to make sure that no chamber of the combustion cycle
loses pressure, apex seals cap the point of the triangle.
These tweaks are what took Wankel's early underwhelming
experiments from curiosity to practicality.
And look at this triangle!
With three sides, as soon as one side begins,
let's say, combustion, another side is completing
exhaust while the third side is drawing in air and gas!
So, unlike a traditional piston-driven engine,
which would need three cylinders to do that,
like the rare but very real in-line three, you only need
one active component, the rotor, to have three stages
of engine combustion occurring simultaniously.
The way Mazda did it on their engines,
like what powered the RX7 and RX8,
was to put two rotors that complimented each-other,
so when one rotor was entering combustion,
the other was about to enter combustion.
You can see how evenly a Wankel rotary engine
can deliver power versus the herky-jerky up and down
of a piston-driven engine.
This evenly-driven rotational force spinning the rotors
drives the output shaft.
The output shaft has round lobes mounted eccentrically,
meaning they're offset from the center line of the shaft.
Each rotor fits over one of these lobes.
The lobes act sort of like the crankshaft
in a piston engine.
As the rotor follows its path around the housing,
it pushes on the lobes.
Since the lobes are mounted eccentric to the output shaft,
the force that the rotor applies to the lobes
creates torque in the shaft and makes it spin.
This makes the eccentric shaft move three turns
for each turn of the rotor, and that's why these engines
can create such high rev.
(engine revving)
And if you check out the horsepower versus torque video,
you'll know horsepower is how quickly
force can be produced.
A high-revving engine doesn't need as much torque
to generate more horsepower,
because it's delivering it so quickly.
And, like Mazda did with the RX7, they can be turboed,
just like any other engine.
And again, because they're revving so high, a turboed Wankel
doesn't have to worry half as much about lag!
Some lag!
So, what are some other benefits of a rotary engine?
First, there's fewer moving parts.
No lifters, no push rods, no camshafts.
All those little things that can go wrong in
a traditional engine simply aren't there in a Wankel,
so they can't break.
In a two-rotor Wankel, you got two rotors and one e-shaft
to worry about, that's it.
And that means these engines can rev higher
and not bust any of those intricate parts.
And also?
You don't need four, five, six cylinders,
you've got an engine delivering consistent power,
making awesome noises!
(engine revving)
And taking up half the room of other engines!
Oh!
And sometimes, when it gets moving really quick,
you get this!
(backfiring)
That is pretty cool!
But that's also a drawback.
Wankels use a lot of gas because they have
a low compression ratio.
When they get moving like that, they make those
sweet-ass flames 'cause they're shooting out exhaust gasses
with unburnt hydrocarbons.
That's not good for fuel economy,
and it's not good for the air!
Also, remember how they're lubed with oil
throughout the housing?
That oil burns when it's hot.
That means more burnt less clean hydrocarbons,
which is tough for emissions.
You remember how they sealed up the different chambers
created by the rotor.
Remember, from before?
Uh, yeah.
You can blow an apex seal, and if that happens...
(screaming)
Those chambers bleed into one another
and you lose most of the benefits that made you fall in love
with your screaming rotary engine in the first place.
Between being different and being good,
Wankel rotaries are pretty rad.
Wankel rotary engines!
If you like the way we show how things work
on Science Garage, then you really need to check out
Brilliant.org.
Brilliant is math and science enrichment learning.
It's engaging, and instead of just getting talked at
about how thing worked, Brilliant is set up
to let you really get in there and apply
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The sequences lead you to thought-provoking,
challenging problems, and that helps you understand
concepts at a deeper level.
Actively solving problems becomes an addictive,
interactive experience, and I gotta tell you,
it's pretty cool.
How do you think the brain trust we just talked about
created the Wankel rotary engine?
They had a deep understanding of physics
and practical application and problem-solving,
just like the courses at Brilliant.org.
A great place to start is with Physics of the Everyday.
This course gets into how things work, things you use
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go to Brilliant.org/sciencegarage and sign up for free!
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Brilliant!
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Like the RX7, you can learn about turbochargers here,
and you can learn about the RX7 in this episode
of Up to Speed!
Don't tell my wife these engines can be a hassle,
'cause I'm trying to get one.