- [Narrator] If you've ever been to a gas station,
you're probably aware
there are two main types of automobile fuel:
gasoline and diesel.
And while they both come from the same source,
petroleum or crude oil,
you're probably also aware they're not interchangeable.
Filling up with the wrong one
can do serious damage to your engine.
But why is that?
What's the difference between a gasoline and diesel engine?
Let's find out.
In the first Engines 101 video,
we broke down the four steps, or strokes,
of a gasoline engine cycle for a typical vehicle.
Well, a diesel engine follows a nearly identical process.
Let's first recap how it works on a gasoline engine:
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 creates the four-stroke process for the next one.
So diesel and gasoline engines
both share this same general process,
but that third step, the combustion stroke,
is where the key difference lies.
While gasoline engines typically introduce their fuel
during the first intake stroke
and then rely on a spark plug ignition system
to set off combustion,
diesel engines simply ignite from the pressure alone.
If you remember your science classes,
you might recall that things get hotter
when they're compressed,
and that's exactly what happens in a diesel engine.
Their compression ratios are much higher
than in a typical gasoline engine,
so when the fuel is introduced into the cylinder,
the air is already compressed and at its hottest point,
so that's all it takes to ignite it, no spark needed.
This high-compression system offers two big benefits:
great fuel efficiency, and tons of torque.
That extra muscle is exactly why diesel is so often found
in heavy duty applications
like long-haul trucks, utility vehicles
and heavy-duty towing.
So with all that engine strength,
why aren't they also popular
for high-performance sports cars?
Part of it comes down to their design
limiting their RPM range and, as a result,
their horsepower potential,
but the bigger reason these engines aren't really found
in sports cars is simply that they're heavy,
and vehicle weight is the last thing you want
when it comes to maximizing speed and agility.
This added weight is due
to the high-compression design mentioned earlier,
these diesel engines need to be built strong enough
to withstand that higher internal pressure.
Now, another interesting difference
is how power output is controlled.
On a gasoline engine,
the accelerator pedal controls the throttle valve,
an opening which dictates how much air
can be pulled into the cylinders.
Whereas on a typical diesel,
that throttle body doesn't exist,
it's just always wide open.
Instead, the accelerator pedal directly controls
how much fuel gets injected.
This works because diesel engines
can operate on a much wider range
of air/fuel ratios than gasoline engines.
Beyond that, there isn't much difference between the two.
Just like gasoline engines,
diesels can also benefit
from forced induction systems like turbochargers.
In fact, turbos are so common in diesels,
you'd be hard pressed to find a vehicle without one.
So that's a brief look at how a diesel engine works,
and how it differs from a gasoline engine.
But this is just one topic
in a wide world of automotive technologies,
so be sure to watch the other videos in this series
to learn more about them.
(pensive music)