Okay i have had a request to tell you lot a bit more about what i work with as it apeals to some of the petrol heads out there.

it is assumed by many the biggest piston engines you are liable to ever get are truck engines well very wrong on this acount i sail on engines that are huge but what i work with are by no means the biggest you get those on containerships the biggest i know of is a sulzer (maker) 12RTA96C which is a 12 cylinder engine of the RTA model with a bore of 960mm and is optimised for Container ship use which produces about 98,000Bhp at 80rpm.

they compression ignition engines where the heat of compression of air heats fuel to the point of buring basically and they operate of a 2 stroke cycle instead of the four stroke cycle most cars operate on.

Four stroke being 2 rotations of the crank for each power stroke or SUCK SQUEEZE BANG BLOW as it is known

2 strokes fit it all into 1 rotation of the crank by getting rid of the exhaust gas and bringing in the fresh air at the same time called scavenging to me

To achieve this a 2 stroke engine must be either supercharged of turbo charged At this point some of you will say rubbish your lawn mower is 2 stroke and not supercharger well i am afraid it is it uses under piston charging where the mixture is compressed below the piston and then realeased into the ombustion chamber throught the inlet ports.

The engines i work on are turbo charger with two turbos which both stand about 6 foot tall including thier mounts.

I also mentioned previously exhaust valves yet another thing not found in your lawnmower/motorbike/outboard/whatever. A 2 stroke that uses ports in the side of the liner to control exhaust and inlet is termed a loop scavenged engine as the charge comes in and does a loop round the combustion chamber (leads to mixing of exhaust and frsh air not good) the two strokes i work with have the normal inlet ports at the bottom of the liner timed by the piston but the exhust port is controlled by a valve in the clyiner head so the exhaust and air are flowing in one direction called uniflow scavenging. It looks just like a normal exhaust valve out of a car but needs two people to lift it and is about five foot tall.

We open this massive valve hydraulically using a pump off the camshaft (rotates at engine speed unlike 4 stroke where it is half engine speed) and then we close it using compressed air springs which is now almost standard in formula 1 engines.

The engines run at slow speeds due to two main factors a piston on its own wieghs about 2.5 tonnes and a conrod is about the same these don't take to kindly to high speeds and propellors are more effiecent when they are big and slow. So the last ship i was on max Rpm was 64 flat out pedal to the metal27,000bhp from a sulzer 7RTA84M

So another thing that you might wander at is how do you start this this thing with about 80tons of rotating parts.
starter motors are a complete non starter so what is done is that we introduce compressed air into the clyinders in sequence.

We have two big bottle with air stored at 30bar which is then pipe into the clyinders in sequence. But it is a compression engine has a compression pressure of 100bar how does it over come this? what is done is air is introduced through most of the stroke so since one crank will be a about 90degrees when another is at top centre we get by it by the increased leverage.

One little thing to think over is we have a peak pressure of 130bar when running in the clyinders which are 840mm in diameter work out the firing load for yourself.

things are also starting to get intresting in marine engines as the sulzer company have just built the flex engine which is based on the RTA but has no camshaft everything is controlled by a computer which opens and closes valves and also controls fuel injection which is pretty damn clever.

so anymore questions will be happily answered and i shall try and dig up some pictures to post or i might be brave and attempt a website to use up me free 50meg with my ISP

Wow!!! . I love machinery. Especially Engines that are a bit different to the norm. I think this qualifies .

Thank you very much for this post. I promise you that there are a lot of people on this bbs who will find it fascinating. (pca, schofiel, n6mod, bonzi, to name just a very few)

I am not familiar with the reference to "RTA". Can you clarify?

At "max Rpm was 64 flat out" that's about one firing cycle per second in a two-stroke engine. That would seem to allow a great deal of time for fresh intake charge to mix with exhaust as it is going out the exhaust valve. Is this indeed a problem? How is it dealt with?

"...start this this thing with about 80 tons of rotating parts." That's how I figured it would be done (compressed air). But 80 tons! Absolutely glorious! Just imagine what would happen if you ever threw a rod in that baby! Probably sink the ship!

How big are the connecting rod and main bearing journals? What type of beaings? Probably plain babbit bearings -- I'll bet they're poured in place if they have to be replaced? What kind of machine could grind a crankshaft with three-foot throws?

Would the engine ever be removed from the ship for repairs, or would they scrap the whole ship if there were a catastrophic engine failure? How would they get it out? I'm guessing the engine would weigh over 200 tons altogether?

So you're running a Diesel (compression ignition) engine, that means minimum 16:1 compression ratio, but probably much higher. Are there giant glow plugs for use in starting the engine from cold (as in a Diesel engine automobile) or does it light off on its own after you get those 80 tons spinning over? How many RPM does it take to get it started?

Please do start a website... I could spend *hours* on this stuff!

tanstaafl.

A friend of mine was into extreme caving (i.e. more often than not crawling into deep places you're not really meant to be crawling into) and did an exploration of a military installation on the Mendips near Bath (UK). Strictly speaking it's still classified, but obviously deserted for decades.

One of the interesting finds was the diesel generator for the installation (which consists of miles of tunnels and caverns). It was missing a head and my friend was able to climb completely into one of the cylinders - that's a big generator! One of the other interesting finds was the fuel tank for the generator, which was still half full of red diesel (red dye is used to indicate that tax hasn't been paid - for military or agricultural use only). There must be hundreds if not thousands of gallons of the stuff in there

Rob

RTA it is just the model number

as to exhaust mixing with air that is no problem as we supply more air to the engine than it needs so some air is caried over to the exhaust manifold since there is no fuel in the ait it is no problem

the engine has a mininum running speed of about 25rpm

The bearings are plain bearing but we use shells just like you do in a car just they are a wee bit bigger

As to getting a dead engine out it would have to be very dead before we evn thought about what is basically done is take the ship into drydock and cut a hole in the side or take the top off and lift it out.

But it is amasing what can be done in place to grind a crank you get a machine that clamps onto it and spins itself round the crank to grind it in place.

As to throwing a rod it would be pretty horrendious but thank fully it don't happen often the bearings tend to wipe out first.

http://www.wartsila.com/asp/empty.asp?P=729&A=closeall&C=11657 see if you can spot the bloke

As to starting a website me thinks me have to learn how first

We open a door and go for walk around in the inlet manifold to check the pistons when we are stopped

http://www.wartsila.com/asp/empty.asp?P=617&A=closeall&C=11637 this is a good page download the RTA-C documnet for some more pictures

Somehow, I think the "when we are stopped" is superfluous :)

Hugo

Well i just know that if i didn't say when stopped someone would ask

I don't know too much about diesels but it's not uncommon to mix the exhaust gas with the incoming intake flow as a trade off of power versus efficiency. If there is some overlap between when the valves open to allow the mixing, sometimes this helps keep the turbochargers spooled by preventing backwards pressure spikes.

Calvin

As I understood, your engine burns something more similar to tar than 'normal' diesel fuel. Do you use lighter fuel for starting the engine? How long does it take to 'catch the fire'?

You wrote in another post that efficiency of this engine is several times better than that of a car engine. How is that accomplished (i.e. which engine characteristic brings that efficiency - higher compression, lower power per displacement ratio, slow rotation, something else)?

I think that how long it takes to catch fire is in the order of a couple of milli seconds but i would have to do some calculation on that but it varies with fuel it is called ignition delay.

Years ago they used to use diesel to start the engine but with moderm materials and method we circulate the fuel to keep it at a high temp as we preheat it before putting it in the engine. the fuel is heated to about 120 centigrade but that is an approx figure as we measure the viscosity and control on that instead of temp. That allows us to get the fuel thin enough to atomise under injection conditions and then burn effiecently

As to the effiecency that is due to many things like waste heat utilisation and long stroke engine and other factors that i am not too sure of and the turbo chargers are incredably effiecent in comparison to automotive type ones

If you can download that PDF file i pointed to it make some intresting reading.

I think that how long it takes to catch fire is in the order of a couple of milli seconds but i would have to do some calculation on that but it varies with fuel it is called ignition delay.

I meant how long do you have to 'crank' it before it starts running and reaches normal RPM. Also, how long does it take to reach normal working temperature?

If you can download that PDF file i pointed to it make some intresting reading.

Just finishing the dowload (ordinary dial-up line... )

the torque generated by the compressed air starting means we only have to lgo about 1 turn before we are going fast enough to put fuel into the engine and start it. This is important as when the ship is manouvering we can't just drop the clutch to go into neutral as we don't have one the propellor is bolted stright onto the end of the engine. This does raise the intresting question of how do we go backwards?

The answer is to most people kind of silly. We stop the engine change the camshaft and then start it backwards and then we have reverse. The process takes about 30 seconds from running ahead to running astern.
instead of changing the whole cam what we do i to retme the cam shaft in the engine. On each section of the cam there is two fuel cams and two exhaust cams mounted ontop of a servo motor which is hydrauically actuated so to go backwards the engine is stopped and then we pump oil into these motors to swing the cams on the cam shaft which turn them and then we have the engine retimed and then we start it again but in the other direction

As to normal working temperature what is done is when we are stopped there is two steam heaters one for the fuel which keeps this hot and we circulate it around the injectors through some clever valves that close when the pressure in the fuel line climbs above 80 bar to allow injection to take place. This heater also runs when we are at sea to heat the fuel but then the circulation is still going but now it is there to cool the injector so the fuel doesn't get to hot leading to poor injection.
The other steam heater is in the cooling water jacket line which heats up the water so that the engine is kept about 70 centigrade when topped climbing to 88 centigrade when running.
Once we are running this heater is switched off and we then pass the jackets through a thing called an evaporator where we get a container and run two sets of tubes through it. one set at the top and one set at the bottom. We then get a sea water pump and pump sea water through a device called an eductor (venturi effect) which produces a suck then using this suck we create a partial vacum in the container. tehn we take the sea water from the eductor and pipe it through the top set of tubes called a condensor. Then the seawater from here is taken and most of it goes over the side back to the sea but some of it is piped into the bottom of the contianer under the lower coils. through these coils we put the cooling water from the engine which heats the seawater to about 70C and it then boils due to being in a vacum and the steam goes up the way and is condensed on the condensor and it then falls onto a tray and we pump out the condensate and we have fresh water and the remaining brine in the container is pulled out by the eductor to ceate the vacum.
This helps to increase plant effiecency as you get fresh water for almost nothing.

Another way to increase effiecency is the hot exhaust gas is used to make the steam needed to heat the fuel.

As to time to get from stopped to full speed it is about 2 hours as we don't want to over stress anything with too rapid an increase in temperature.

Ah, that's why you need tugboats in the harbour. I guess those ferries and cruise ships I see maneuvring by themselves in Adriatic ports have some kind of hydraulic or electric transmission to main propellers (and bow thrusters, vectored ducted propulsors and what not).

Yeah oil tankers have bugger all manouvering ability but cruise ships normally have electrically driven bow thrusters and stern thrusters but the more modern ships have azi-pods where the propeller is mounted along with its electric motor under the ship in a pod which spins round and lets the thrust from the propellor be directed in any direction. And in normal service they provide the thrust.

http://www.wartsila.com/asp/empty.asp?P=617&A=closeall&C=11637 this is a good page download the RTA-C document for some more pictures

I don't understand... I can't find the RTA-C document you refer to. What am I doing incorrectly?

tanstaafl.

Okay i can't get the link to work either but if you go to the wartsila home page then click on marine and then look at thier product portflio you will be taken to a screen with loads of downloadable stuff where you will find the document on the RTA-C engines.

OK so just how loud are these things?

No where near as loud as you would think but the turbo chargers are pretty loud but that said i am always wearing ear defenders. You can hear each clyinder firing

What is the fuel delivery system like?

Clearly the fuel is injected into the cylinder just before top-dead-center, when compression temperatures are high enough to ignite it. What does the injector look like? how big is it? How much fuel does it deliver on each firing stroke? What is the specific fuel consumption of the engine as a whole -- that is, how many pounds of fuel are consumed per horsepower hour (or whatever units are used)? A rule of thumb I've gone by in the past for gasoline engines is about 1/2 pound of fuel per horsepower hour. Is that in the ballpark for these Wartsila engines?

I tried to print out that 60 page .pdf file, but it keeps choking on page 8. I'll have to work with it some more...

tanstaafl.

Thanks a bunch for the info, awesome stuff!

I love big crazy machinery like that.

I only wish that site had some decent pics...

If you download some of the PDFs if you can find them there is pictures of engine outside of the ships where you can see the true size of them.

But i do want to know if anyone has gone and looked at a lawnmower or something and thought wow i have a superchargered lawn mower.

if i have time i might try and learn how to write a small website and put it somewhere. The idea of climbing around inside an engine fraks some people out.

Okay a fuel injector is about 40 to 50 pound in wieght and about two foot long has an opening pressure of about 380 bar and an operating pressure of about 1000bar at peak injection pressure. It has some of the most accurate machineing on the ship. (did you know that a VHS video head is one of the most accurately machined compnents in mass production). Some engines have two some have three dependant on age and design etc. Apart from a strange jap design with three exhaust valves and a central injector and older loop scavenged engines that had a central injector.

the injetion pump is a real complex piece of work but very clever in its design. i shall try and remeber to post a picture of one but this is how it works.

A normal injection pump for a small diesel (500bhp and up) is a jerk pump where you have a plunger going up and down in a barrel with a hole (spill port) on the side of the barrel and a helix is cut into the side of the plunger and by turning the plunger you can control when the hole is uncovered to spill presure and control injection.

On the sulzer/wartsila it is totally different you still have the plunger but it is plain and you still have the barrel but it too is plain. On top of the cam follower there is a yoke onto which two arms are connected which go up and down with the cam and plunger.
These arms pivot on two excentrics one per arm the left one is pivioted in the middle the right one at the end. On top of each of these arms the is mounted a rod which goes into the fuel pump and lifts a valve off its seat when it goes up.
The left one is sat on the end of the arm and control the suction valve.
the right one is sat in the middle of the arm and controls the spill valve

As the follower climbs the cam the suction valve will drop down onto its seat and seal the pumping chamber and injection will begin when the pressure climbs above the opening pressure of the valve. Then the follower will continue to climb the cam which at the same time raises the spill valve control rod which will then come into contact with the spill valve and lift it from its seat and injection will finish

it might help if you give above a quick sketch or wait till i post a drawing.

the clever bit is the control the two exccentrics gives us the one on the spill side is used to control the end and therefore the amount of fuel injected the suction one is used to control the start of injection and therefore we can alter the timing of the injection whie the engine is running.

A similar idea is being used to control the exhaust valve to give variable compresion which has advantages. As you will of seen with saab and their new variable compression head which i really like.

There is alot more to injection than i have descibed above as there is strange things like wave reflections etc to deal with as well as things like fluid compression etc.

As to amount of fuel used it is about 76tonnes a day at full power but that does include a generator running 24hrs a day. Which works out about 0.26 pound of fuel per horse power hour i think.