- [Instructor] Hi guys, and girls, welcome to another Savree Nuggets video, the second in the series. In our last video, we
took a look at this ship. This ship is a 210,000 ton container ship. It's about 400 meters
long, about 60 meters wide. And as you might imagine,
it takes quite a lot of effort to push this
thing through the water. So we're gonna need
some pretty big engines in order to get the propellers to turn. This ship has two propellers
on the left there, and one over on the right-hand side. So let's pull up another
model and have a look at where the engines are
that drive these propellers. So here's our container ship again. Let's just zoom in, and see
we've got some containers down in the hold, come a
little bit to the right here. We can see we've got our engine. This is actually a six cylinder engine. One, two, three, four, five six. And those Christmas tree shaped items on the top of the engine, they are actually exhaust gas valves. We'll have a look at those in a moment. You can see the engines
line up quite nicely with the funnels, that's 'cause we want
to get the exhaust gas out of the ship as quickly as
possible or out of the engine. And then we've got a propeller shaft and the propeller shaft comes along here and it
connects to our propeller. And I'm gonna start the engine and our propeller begins to rotate. And that's how we push the
ship through the water. We've actually got two of these engines. And I think now we can go and take a look at this
engine in more detail. And here we are, once again, we've got our six cylinder
inline diesel engine. This is a large two-stroke
Marine diesel engine. And you can see, it's got
quite a unique design. There's some parts here
that you don't typically see on a normal two stroke engine. Two stroke engines are
only ever used really for very small applications,
lawn mowers, leaf blowers, motorcycles, and things like that. And for very large applications
like for pushing 200,000 ton ships through the water. Despite the name, this
type of engine does not usually burn diesel fuel oil or diesel. What it actually burns
as fuel is Heavy Fuel Oil and heavy fuel oil is quite nasty stuff. It's quite sticky. You heat it up in the tanks
to about 40, 50 degrees Celsius prior to pumping
it to the engine where it's again heated up to a
hundred degrees Celsius, and then it will be
injected into the engine. I Can actually show you an
injector on the top here. This item here is a fuel injector and we use that fuel injector, And one on the opposite side. Usually there's actually three. We've got two here and we'll pass the fuel down this pipe into the injector and we inject the fuel
into the combustion space. How much fuel are we burning? Well, it depends upon how
fast you want the ship to go. I looked up some of the facts and figures associated with the engines of the container ship that we
were looking at a moment ago. And to give you a rough idea of how much fuel these
engines might be burning, You're looking at between
150, 250 tons of fuel a day. Although this type of engine
is a six cylinder engine, the largest engine in the world, which is also used for a single screw or single propeller E-Class
container ship has 14 cylinders. The engine itself weighs over 2,300 tons. So you can start to see now
while we might consume 250 tons of fuel a day. the crankshaft alone weighs 300 tons. That's 660,000 pounds. A single piston weighs
five and a half tons. That's 12,000 pounds. Here's an image of me, You get an idea of the scale
of just how big this engine is. A lot of people like to
talk about brake horsepower When they're talking about engines, personally I like to use
kilowatts, but either way this 14 cylinder engine produces
84,000 kilowatts of power. That's 84 megawatts. in terms of brake horsepower, that's about 115,000 brake horsepower. To put that in perspective, if you're looking at a standard bus or a coach that carries about 50 people, the engine in that coach will only have about 450 brake horsepower. The engine itself is only
ever gonna operate at speeds up to about a hundred RPM,
which sounds quite slow. But if you consider that
the stroke of the engine, that is the distance from top dead center to bottom dead center that each piston has to travel is 2.5 meters, that's 8.2 feet. Then a hundred RPM is quite a lot. In terms of speed, you
might reach speeds of up to about 23 knots and knots
is a nautical mile. If you want to figure out
what a knot is in miles you times it by about 1.15. So if we are traveling 23 knots then we would reach a speed
of about 26 miles per hour. That's about 43 kilometers an hour, if you like to work in metric units I appreciate that sounds
pretty slow, 26 miles per hour, but it's still over 600 miles per day or about a
thousand kilometers a day because ships travel day and night. And if you leave a port like San Francisco and
you want to go to Japan there's not many reasons to stop off or slow down on your way there. So let's now take a look at our large two-stroke
Marine diesel engine. We'll start off by looking
at some of the outside parts. We've got an exhaust gas manifold. That's this silver item,
the exhaust gases pass out of the top of the cylinder. They actually come up through this channel and then into this hole and the exhaust gases
would go through the hole. And then into the manifold. Exhaust gases are fed to a turbocharger because this is a turbo charged engine. Turbocharging the engine
increases efficiency because when the engine
is running, it tends to run constantly for potentially
a long period of time. If we take our example of traveling from San Francisco to Japan, then we may be at sea for 10 to 14 days. It really depends upon the
speed that you're traveling at. If we pass the exhaust gases to the turbocharger,
though, down through here we can compress the incoming air. Air actually gets sucked
in through these filters here in the turbocharger, and then we pass that
compressed there into a cooler. This would be a air cooler. And then the air cooler discharges the air into our air manifold. What we call our charge air manifold. That would be this space inside here. How much air do we need? A lot. Not just depending upon how
fast the engine is going, but generally just quite a lot. I used to have to walk
around the engine room and I'd walk around measuring
the pressure differential across the filters here that
were on the turbo charger. And normally there's not
so much space to walk past the turbocharger here,
because there might be a railing or something that makes
you walk quite close to the turbocharger filter. What actually happens is you
walk past and as you walk past you get sucked onto the
side of this filter. And if you wanted to you could give it a little hug almost most and you'd really feel it trying
to suck you into the engine. When you walk past with a clipboard, it tries to suck the
paper off the clipboard. I used to actually have quite a cool trick that I used to do when
I did my engine rounds or the rounds as they're called, I used to take the piece
of paper I was working with and then I'd just stick it onto the filter while I went round the other side of the turbo charger to check
the differential pressure across the turbocharger filter. And you could just go back
over here and pick up the paper off the side of the filter,
which had remained stuck because of all the air
being drawn into the engine. The reason you measure the
differential across the filter is because at some point
the filter gets dirty and you need to change the filter. As the filter gets dirty over time, you end up with a larger
differential pressure across the filter. That is to say a larger
differential pressure measured on the outside of the filter
compared to the inside. And that's what tells
you when it's time to change the filter. The filter itself is just filter cloth. And usually you can just wrap it Let's keep going though, 'cause we're getting a bit
sidetracked by details here. We pass air down to our air cooler and then we need to cool the air. We're gonna use water to cool
the air or cooling water. And the reason we cool the air is because we want the air
density to increase. We don't want to cool the air too much because then we get drops
of moisture in the air. So typically we'll cool it down
to about 40 degrees Celsius, and not much further. In terms of pressure, we may have about 1.5 bar,
which is about 20 PSI. Once we've compressed the air
to increase the air density and cooled it again to
increase the air density, then this oxygen rich air is fed into the charged air manifold. We call it charged air because it's passed
through the turbo charger and this charged air will then be fed into our combustion space
or our combustion cylinder. So it'll come from this direction here and it will actually travel up and straight in to
the combustion space. So we're inside the combustion
space or the cylinder, and we've got this long
piece of cylindrical steel, which is inside our
combustion space as well. That is a piston rod. Below the piston rod, we
have a connecting rod. This differs from most combustion engines, especially small or medium-sized engines because they don't
actually have a piston rod and a connecting rod. They have a connecting rod. Another name for a
connecting rod is a con rod. In between the piston rod and the connecting rod is a crosshead. That's this sweet
wrapper shaped item here. Come across here, we can see the guides. The guides fit into these items
on the side of the engine. You can see the right
angle where they slide along the guides and that's
to hold the crosshead in position and keep it
moving along a linear path. Due to the size of the engine
and the relatively small bore, the bore of the piston, the bore is just the
diameter of the piston, but due to the small bore and very long stroke length of the engine we need to have this crosshead. If we didn't have the crosshead, the very large pressure that builds up when we get our combustion, let me just move this
piston out of the way. Let me get our combustion
in the space here. There's a huge amount of pressure and that's gonna force
the piston downwards. We want the piston acting
in a linear direction. That's why this piston rod is installed within the engine in a straight line. It's parallel with the cylinder. In smaller engines, this isn't the case, but with larger engines we have to do this because the bore is so small
compared to the stroke length. And because we don't want
these loads being applied onto the crank shaft at an angle. You can see that occurring
here with the con rod, but the con rod is much shorter now because it connects only to the crosshead. If we didn't have this
arrangement, then what we'd end up with is a very long
connecting rod that would have to stretch from the top of the piston. So say the piston head here, all the way down to where it connects
with the crank shaft. So this place here. That's quite a large distance, maybe about four meters, I would say. And that's simply too long. So the piston rod
connects to the crosshead and the connecting rod connects
to the crossroad as well. The connecting rod then
connects to the crankshaft and the crankshaft will
connect to a propeller shaft. After that the propeller shaft
connects to the propeller, but only after it's been
passed through several bearings and what they call a sterntube seal. The sterntube seal is what stops water entering the vessel through the space between the propeller
shaft and the ship's hull. You can see we've got little ladders here. These are the rungs of a
ladder, and here's another one. These get very slippery. You can climb into the crank case and use these runs to have a look around inside the crank case. What's actually going to happen is you enter through
the crankcase doors. I'm just gonna go through this one here and then you can climb
around and inspect the area. Maybe you've got a disconnect. Let's just imagine for a moment we've got to disconnect the
piston rod from the crosshead. So we'd need to get into this space here and
then you'll stand around, hook up some hydraulic bolt tensioners, and then you have to try and undo the nuts using
this hydraulic equipment. And then you can separate the
piston rod from the crosshead. Notice on the other side, go over here. This item is not a crank case door. Let's just go out of the engine. You can do a little spin. So what is it? If it's not a crankcase
door, why do we even have it? You can see there's quite a few of them. Well, the reason we have them is because they're what are called
crank case explosion doors. I know. It doesn't
sound very good does it? Another name for them, which sounds slightly
less terrifying is crank case pressure relief valves. PRVs for short. Why do we have them? Well inside this engine, there's going to be lubrication oil. A lot of it, tons of it, usually sitting at the bottom of the engine
here, but also covering all of the internal surfaces of the engine. Especially within the crank case. If this oil gets heated up, maybe there's a hotspot
between the bearings. Let's just say for a
moment where our con rod connects to the crankshaft, there'll be a bearing that we can't see. About here and here. And if this bearing gets hot, it heats up the lubrication oil and you end up with lubrication oil vapor. This vapor then begins to accumulate. Let's just imagine in the top
corner of the crank case here and this cloud of oil
vapor will get bigger and bigger and eventually
it might actually reach back on to the hotspot that
originally created it. If this happens, we might
end up with combustion. If that happens, we might
end up with an explosion. And if that happens,
then all of these valves on the side of the engine
here are designed to pop open and relieve the pressure in
aa safe a way as possible. The alternative to relieving the pressure in this manner is that the
doors get blown off the engine. And the crank case maybe explodes. The other disadvantage when this occurs and it used to happen in the past, before they started using
these pressure relief valves or pressure relief doors, is that after the initial explosion, air is then free to enter into the crank case and you end up with another explosion and
it's bigger than the first. This scenario has killed
engineers in the past which is obviously not good because the last thing
you want to happen when you're walking around in the engine room maybe you're doing your
rounds at four o'clock in the morning is to walk past here and then have the engine explode. So to try and stop this occurring you'll constantly sample the
air within the crank case. And if the oil vapor
level becomes too high, if there's a bit too much oil in the air or suspended in the air, then you'll get an alarm and
you can slow the engine down or even shut the engine down. If for any reason that doesn't occur and you do have an explosion at least you have these
pressure relief valves or these pressure relief devices
on the side of the engine and they can relieve some of
the pressure in a safe manner. When you go into the crank
case, it's actually quite funny because you put on these white paper suits and that stops you carrying
any dirt and grit et cetera into the engine. And then you go inside. And the first time I went inside nobody bothered to tell me
that everything's covered in lubrication oil and
just how slippery it is. So you reach in to the crankcase. Let's just say, where
you're going in here, you grab hold of the ladder there, you put your foot on the ladder rung that's a bit further down. And then you put your weight on your foot and then your foot slips and you end up just
hanging on for dear life, with your one hand on the
rung of the ladder up here. It's incredibly slippy inside
because everything is coated in very slippy lubrication oil. Despite this, it's always
good to go inside the engine. It's always quite a unique opportunity because how often do you
ever get the chance to walk around inside an engine? So we've talked about
some of the main parts. Maybe we should have a look at what happens when we start the engine. We don't start the engine with a starter motor
or anything like that. You can turn the engine over very slowly using
what's called a turning gear and it will move a lot slower than this. Typically, it's going
to take over a minute for the engine to do one complete rotation using the turning gear, but you can see now that
the engine is running. If you want to increase
the speed a little bit maybe we can add some more fuel. And then we can pause the engine again. I mentioned that we can
use the turning gear to turn the engine very slowly. The reason we do this is because when we start the
engine, we use compressed air. We're going to feed compressed
air into the combustion space in order to drive the piston downwards towards the crankshaft. So let's imagine for a moment we feed
compressed air into the engine. The piston is pushed down and we need to give the piston momentum, all of the pistons in order
that they can draw the air in and then race back up,
and that's what gives us our initial compression ignition cycle. Once we have injected fuel
into the combustion space, the engine then no longer
requires compressed air. It can keep going using
the momentum that it gets as we inject fuel and get combustion. But in order to get that initial momentum, in order to get the compression and the high temperature and pressure rise that we need in order to get combustion, we use compressed air. It's called a compressed air
starting circuit or start air. So what's happening when
the engine is running? The piston moves down
to bottom dead center. The piston rod is sliding this item here. This is called a stuffing box. And it's what we use to
separate the crank case from the area above it,
which contains the cylinder and the air inlet ports, et cetera. The piston head has piston rings. It's these black items here,
and they seal the space between the piston head and the cylinder. So air is passing into the
cylinder through these ports. The piston then begins to travel up from bottom dead center,
up towards top dead center. And as it does so the pressure and temperature is increasing. We get enough of a temperature increase in order to ignite fuel that is fed into the cylinder through the injectors. Here is one of our injectors. They'll normally be two
or three. Typically three. The piston gets to the
top of the cylinder. We get our controlled explosion and then the piston begins
to move back down again. And as it does so it's gonna
push the crosshead down along its guiding rails. And then the crosshead connects it to the crank shaft via the con
rod and the process repeats. What's interesting here is
that we've got the air coming in at the bottom of the cylinder. And then we've got the exhaust
gas passing out of the top of the cylinder in what they
call a Uniflow arrangement. There were three main
scavenging modes that you're likely to encounter. Scavenging is the process
of taking fresh air into a cylinder and removing exhaust gases from a cylinder, that's called scavenging. And the exhaust gases that are produced after combustion have to pass
by this exhaust gas valve. So let's zoom out. The exhaust gas valve is now open. It's open because we're
letting air in to the cylinder and we're gonna flush
out the exhaust gases. Remember the air is coming in at pressure. And that pressure difference
is what's going to allow the air to come in and push all of the exhaust gases out to
flush them out as a cylinder, they'll pass by the exhaust gas valve. And then once the air inlet
ports are covered up again, just gonna happen in a moment. The exhaust gas valve will close because we want to
compress all of that air in order to get the temperature rise we need for combustion. Diesel engines are
compression ignition engines. There's no spark plug here. It's not a spark ignition engine. So the exhaust gas valve,
it should already be seated if I'm being honest, but
it's a little bit late there. Now it's seated. The piston is gonna move back up. We compress all the air, we get combustion and then we get our controlled explosion. The power stroke starts and the piston moves back down again. And then when we uncover
the air inlet ports the exhaust gas valve opens. Let's back that up again
so we can see that. So here we are. There you go. As the air ports are uncovered, the air inlet ports,
exhaust gas valve is opened and we flush out the exhaust
gases from the cylinder. What's also interesting about this Uniflow scavenging
arrangement is what happens to the exhaust gas valve when it opens. Keep your eye on this part of the exhaust gas valve
where my mouse is now. So exhaust gas valve opens and rotates. Now, why would we rotate
the exhaust gas valve? The reason that the exhaust
gas valve rotates is because we want even wear
on the exhaust gas valve and on the seating area where
the exhaust gas valve seats. In order to get even
wear, we put these veins onto the valve spindle or the valve stem and as the exhaust gases pass
up and out of the cylinder they're going to pass over these veins and those veins cause the
exhaust gas valve to rotate Just like that. And then the exhaust gases pass out and they go to our
turbo charger again. Specifically at turbocharger turbine. This particular exhaust
gas valve is operated by a hydraulic system. We can feed hydraulic oil into the space at the top here to push
the exhaust gas valve down. We can feed hydraulic oil
into the lower space here to push the valve back
onto its seat again. So hydraulic oil on the top causes the valve to open, hydraulic oil on the bottom causes the valve to reseat and close. And if we press play, we should be able to
see this circular disc that separates the top and the bottom hydraulic oil
chambers move up and down. Hydraulic oil is fed to the
top of our exhaust gas valve via this pipe here. And also the one a little bit lower down. Fuel is fed to our fuel
injectors by this pipe here. Fact, if we go in the middle, we can actually see an injector on the right and an injector on the left. That's high pressure fuel that's being fed into the combustion space and there'll be a fuel pump,
usually located somewhere around here or perhaps a bit higher up. And that's what feeds the
fuel to the fuel lines and then the fuel injectors. It depends upon the engine design though, because more modern engines use common rail fuel injection systems. We can talk about those
maybe in a different video. I think that pretty much sums
up our short introduction to this large marine two
stroke diesel engine. I hope you enjoyed the video. If you did, then please do like or share this video on social media. If you want to access any
of the 3D models shown in this video, then just
head over to savree.com. And if you want to learn
even more about engineering then check out savree.com
because we've got over 25 hours of video
tutorials, just like this one. Our courses cover everything
from pumps to diesel engines to valves, to transformers,
and many other topics. If you liked the video please leave a comment
in the comments area. I really do appreciate it. It's pretty much what gives me the energy and motivation to make more
and more of these videos. And I hope to see you
on another video soon. Thank you very much for your time.
