hello everyone and welcome in this video
we are talking about two shaft turbos so
what in the world is a two shaft turbo
well it simply uses two different types
of compressors uh within one turbo
packaging and so it's going to be using
an axial compressor as well as a radial
compressor so what are axial and radial
compressors well an axial compressor
simply means that the airflow remains in
the axis of rotation of the compressor
uh that's just a fancy way of saying
that it goes straight the air goes
straight through much like a jet engine
a radio compressor that actually changes
the direction of the airflow so it then
curves out this is what you see in
turbochargers and centrifugal
superchargers used in automotive
applications so a two shaft turbo is
going to be combining these now before
we get into two chef turbos i want to
talk about an axial radial turbo i found
a sae article talking about these
turbochargers from 1990 and it said the
goal of it was to increase the pressure
ratio in a compact form and so what does
that mean increase the pressure ratio
well the pressure ratio is the ratio of
the pressure coming out of the
compressor divided by the pressure
that's going in and that's going to be
some number that's greater than one so
for example if atmospheric pressure is
one bar and the pressure ratio of the
turbocharger is two to one then you
would have two bar coming out of the
turbocharger
getting back to the goal of this axial
radial turbocharger there was a quote
that i particularly enjoyed in the
journal article about it they said of
course no matter what horsepower is
being developed someone somewhere can
think of an application for 10 or 20
percent more power now i don't know how
many of you uh spend your time reading
sae journal articles generally they're a
lot like my videos in that they're very
dry and void of any uh resemblance of
humor so what i enjoyed about this was
that they actually kind of threw a
little uh somewhat ounce of a joke in
there where they said you know people
just like horsepower uh people want more
of it that's what we all crave and so
that was the goal of this project and
cool that they included that little note
in the article so how does this turbo
work well this one started off very
simple so you've got your exhaust
portion of the turbocharger here you've
got your intake portion of the
turbocharger here there's a common shaft
of course which that compressor shares
with the turbine there and so as this is
spooled up it turns both of these
compressors here they're on a common
shaft and so you have an axial
compressor which is going to pressurize
air somewhat before getting to that
radial compressor which then compresses
it further now it was weird to me that
these seem to be on the same axis we'll
get into that later on with this
honeywell design here but basically they
were saying that with this axial
compressor they could compress the air
with a pressure ratio of up to 1.25 to 1
before the axial before the radial
compressor right here
and as a result they were seeing 20 to
30 percent improvements in the pressure
ratio overall with the same mass flow
through the exhaust so certainly an
improvement they were able to increase
boost levels with you know the same
amount of exhaust flow
so that means this overall had a greater
power density so it actually extends the
turbocharger in length they were saying
by about two to three inches 60 to 80
millimeters uh but the width of it stays
exactly the same so from a packaging
standpoint it's not much of a sacrifice
and yet it gives you a significant
increase in boost and so that was the
benefit of doing this now as i mentioned
looking in this article i didn't see
anything that was saying that these
rotated separately it seemed they were
all paired on the exact same shaft and i
thought that was a bit strange which led
me to looking into other solutions and
there was a patent in 2006 by honeywell
honeywell which of course designs
garrett turbochargers
very popular turbocharger company so
they had this patent which was
explaining a two shaft turbo the main
focus of this video
so how does this two shaft turbo work
well you have two separate shifts wow
what do you know i like the name
explains and so you've got one shift
which has that axial compressor on both
sides so it's driven by the exhaust and
then rotates it here on the intake side
just like this one except it's on its
own individual shaft and then you have
the radial compressor on its own shaft
after that
initial axial compressor so you've got
those two stages there of compressing it
and then you can complicate things
further by adding in variable vanes so
they've got variable vanes
on all sides so for the intake and the
exhaust between the two compressors and
then they also have variable vanes this
right here is a lot like a variable
geometry turbocharger i'll include a
link in the video description talking
about how this portion of it works in
this video we're going to talk about
these but i do have a separate video
covering
why you might want veins right there
that's the whole thing behind variable
geometry turbos so what's going on with
these variable guide vanes right here
well the idea is is that you can change
how the flow enters into this axial this
radial
compressor right here from the axial
compressor so this is trying to push in
air to this guy right here and you can
change how that airflow enters using
those veins so at low flow the idea is
you can create a swirl with the air and
help out what this is going to be doing
with that air because it's going to try
to rotate it but you're basically
helping that out initially using these
veins and this axial compressor before
it enters into it so the idea there is
that you can improve the low flow area
of this turbocharger so the low rpm
regions where you're not getting quite
as much exhaust flow
then on the high flow end you can
straighten out these vanes right here
and just allow for the maximum amount of
airflow through it and so overall
honeywell claims that this design right
here will give you improved packaging
and a lower cost versus using sequential
turbos so is it better than using
sequential turbochargers uh well from a
cost and packaging perspective according
to this patent according to honeywell
yes i don't see it used in today's
production vehicles at least that i am
aware of uh there probably are some
examples that i just don't know about
but you do tend to see uh twin turbo
setups and sequential turbo setups uh
more often at least that seems like a
common thing within the industry i don't
hear about this as much but perhaps it's
out there and i'm just clueless and
don't know about it
so the whole benefit of this over you
know just using a single radial style
compressor with a turbocharger is that
you're increasing its flow range so on
the low end you have these veins and you
can help create swirl uh to aid this
second style compressor uh in creating
boost and then on the top end you're
using uh this axial compressor here to
increase the pressure before it enters
the radial compressor and so as a result
because you've got boost already right
here that means you've got a higher air
density and it allows this to take
things another step further so you've
already got some boost and then you put
it in this stage compressor and that
takes you further so you increase on
both ends of you know with just the
purple alone you're going to be in this
range and then by adding this secondary
style compressor you can increase the
range at which you have good flow so the
useful boost that the engine can create
uh is is a wider range of rpm
so a great useful thing to do and have a
pretty neat design again i don't know
about current cars or or engines that
are using this but it's pretty
fascinating to think about so thank you
all for watching and if you have any
questions or comments of course feel
free to leave those below and i will
include some relevant links to other
style turbo chargers if you're
interested in checking that out