so today I'm going to explain the
difference between a gasoline engine
cycle and a diesel engine cycle now the
main difference is that with a diesel
engine you have the fuel injected after
the compression cycle and I'm going to
kind of explain how that works here so
this which I've drawn here is the
gasoline or autocycle as it's commonly
referred to um and here's how it works
step one right here you've got this is
the intake stage and so you're going to
be pulling in an air fuel
mixture uh let's go ahead and use green
for that we'll have an air fuel mixture
coming in here and filling this chamber
and this piston inside of the cylinder
here is going to pull down and it's
going to draw in this air fuel mixture
gasoline combined with air the next step
step number
two we're going to have to com press
this so both the intake and exhaust
valves right here are going to be closed
off and it's going to take this air fuel
mixture which is in here and compress
that so it's going to compress it as
much as it can now in gasoline engines
the compression ratio only may be up to
10:1 meaning that the volume when this
piston is down at the bottom compared to
the volume when it's all the way
compressed is 10 times greater
uh so that's that's what a compression
ratio is now it's going to compress that
then you're going to have a spark plug
in a gasoline engine that's going to
ignite uh it's going to just have a
little spark and then that'll explode
the gasoline and that's going to cause
everything to expand well that's going
to be your power stroke that's going to
push the Piston
down and so that in turn is going to
rotate your crankshaft go through your
transmission go to the wheels and then
you've got power you're moving you're
turning your wheels so the last step
then is to get those exhaust fumes out
so those exhaust the exhaust uh valve
here there's usually two of them are
going to open up and then your exhaust
airs can go out and then the cycle
repeats itself now it's a little
different with a diesel engine in my
opinion it's also a little little more
practical so you're still going to
have well you're just going to have an
air this is no longer an air fuel
mixture this is just air coming in and
it's going to take all that air and draw
it down the Piston's going to come down
the same just like it did the only
difference is there's no fuel here now
in the Second Step you're going to have
this piston compress just like it did
with the gasoline engine except it's
going to compress up to the top with no
fuel and then fuel is injected in so
kind of here you can think of this
instead of a spark you're going to have
fuel sprayed
in and this fuel because diesel engines
operate guess I should kind of show you
guys this is no longer a gas cycle we're
talking about diesel
now so because this there's no fuel when
it's compressing you can compress it to
a
higher say 15 to one compression ratio
meaning the volume here is 15 times
smaller than it was when the Piston was
down at the bottom that'll give you much
greater pressure also a much greater
temperature as pressure Rises so does
temperature so when this compresses this
air right here is going to be extremely
hot when you shoot in this diesel fuel
it's automatically going to ignite and
cause the combustion so then that's
going to explode the Piston's going to
come down that'll give you your power
cycle and once again the next step will
be exhausting those
fumes so that's the main difference and
compression uh compression ratio is
directly related to fuel economy the the
curve kind of looks somewhat like this
if uh here's
your uh fuel
economy here on the on the vertical axis
and then here is your compression ratio
it's going to be something like this
where it does taper off and say this may
be a compression ratio of 10 and this
maybe 15 but as you can see you're going
to get better fuel economy at
15 and that is the main reason why
diesels can get better fuel economy I'll
probably do another video later um
further describing why diesels have
better fuel economy but this is this is
the main important fact is that the
compression ratios in diesel engines are
much greater now the added benefit to
having a greater compression ratio um
and also with diesels is that you can
modify a diesel engine since this uh the
air fuel mixture isn't coming in
together it's just air that you're
compressing if you want to get a larger
turbocharger or say a supercharger for
your diesel engine the only thing you
have to worry about is the mechanical
components and they strength whereas in
a gasoline engine you're going to have
to worry about well let's say we get a
compression ratio of 13 and you're using
mid-grade octane fuel then you're going
to have pre-ignition and as this is
compressing the air fuel mixture it's
going to explode before your spark plugs
goes off and then you're going to have
problems so with a diesel engine all you
have to worry about is the mechanical
components and that's the main
difference between a diesel and an auto
cycle