- [Narrator] Just about everyone knows
that a typical automobile gets its power
from an engine under the hood,
but how many people can say they actually know
how that engine works?
While a modern internal combustion engine
is obviously an extremely complex piece of machinery,
the basic principle behind it is pretty simple.
Let's take a closer look.
At a high level, a gasoline engine
can be thought of somewhat like an air pump,
except that the exhaust coming out is more of a side effect,
this pump's real purpose is to rotate an internal shaft,
which in turn rotates the vehicle's wheels.
It does this by connecting that shaft,
called a crankshaft, to pistons that move due
to a mixture of air and gasoline combusting
inside their cylinders, which creates a sort
of chain reaction that keeps the engine turning.
Before getting deeper into this process,
let's first touch on the two main parts of an engine.
On the bottom, a lower "block" is home to the pistons,
cylinders and crankshaft,
the latter of which sends the engine's power out
to the transmission and wheels.
And above, the "head" contains the top of the cylinders
and manages their airflow and combustion
through valvetrain, fuel injection, and ignition systems.
So let's explain that part a little more.
You may have heard the term "four-stroke"
to describe a vehicle engine.
This refers to its four stages of operation:
First, the piston moves down,
creating a vacuum in the cylinder chamber that pulls air in
through precisely controlled intake valves.
Next, the valves close and the piston raises back up,
compressing all that air,
along with some gasoline that was mixed in
from the fuel injection system.
Now the fun part, the ignition system creates a spark
at the end of the spark plug,
creating a controlled explosion
of compressed air and fuel that sends the piston back down.
Then finally, the piston moves back up,
pushing that spent air/fuel mixture
through the exhaust valves and out to the,
you guessed it, exhaust pipes.
And since we're dealing with multiple cylinders
with pistons all working from the same crankshaft,
each one essentially creates the four-stroke process
for the next one.
Pretty ingenious, right?
Now speaking of multiple cylinders,
let's talk about the various engine configurations.
Four-cylinder engines are probably the most common design
these days, but who doesn't love a V6?
Or even a V8?
These terms simply refer to the number of cylinders
in the engine, and their layout.
Nearly all four-cylinders engines
have their cylinders arranged in a row,
called "inline" or "straight",
but it's also pretty typical
to see engines group their cylinders
into two banks connected at an angle, a vee.
Doing it this way effectively cuts the engine length
in half, enabling it to fit more easily under the hood.
So a V6?
Three cylinders on either side,
creating a vee shape.
And what if that vee shape was opened up all the way?
A 180-degree angle?
Well then you'd have what's called a boxer,
or flat, engine design.
Alright, so what about those other numbers you always see?
2.0? 3.5?
Well, that refers to the engine's displacement,
often simply thought of as its size.
That number is literally the volume, in liters,
that the pistons displace with every engine cycle.
So essentially, if you were to fill up the cylinders
of a two-liter engine with liquid,
it would take, well, two liters.
And if it's a four-cylinder engine,
each one displaces half a liter.
So what's the end result of all this?
Power.
The measurable output of an engine is called its torque,
basically, the strength with which it turns its crankshaft.
Torque is measured in pound-feet,
which, as the name implies, is the force created
by one pound of weight, at a distance of one foot.
Imagine a one-pound weight sitting at the end
of a one-foot wrench,
that nut is being turned with one pound-foot of torque.
So now, going back to the displacement concept,
bigger cylinders pull in more air and fuel,
typically resulting in more muscle,
they turn the crankshaft with more force,
which is perfect for large vehicles,
towing, or even just spirited driving.
So now you're probably thinking, isn't that horsepower?
Well, yes and no.
In fact, horsepower doesn't technically exist.
Okay, yes, that requires a bit of explanation.
Horsepower is obviously a real thing,
but it's actually a calculation,
not a physical measurement like torque is.
It's basically torque over time.
So this means the faster that engine turns,
its revolutions per minute, or RPM,
the more work it can do, and the more horsepower it has.
Put in extremely simplified terms,
torque times RPM equals horsepower.
But that doesn't mean making big horsepower
is as simple as spinning the engine faster,
since that takes more and more energy
as the engine speed increases.
And as that torque decreases,
the horsepower calculation eventually can't keep up either.
This is also why transmissions
are so critical in keeping everything
in the appropriate "sweet spot",
but that's a topic for another video.
So that's the general idea
behind internal combustion engines.
But this was just a high-level look at the basics,
Engines 101, if you will.
There's obviously a whole lot more to say about engine tech,
so be sure to check out the other videos
in this series to learn more.