120 lehman oil usage

nomadwilly wrote:
"2 stroke engines are the most efficient engines on the planet"

What kind of scavenging systems are employed on those monster 2 strokes Rick?

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*THOSE 2-strokes are the most efficient engines on the planet, not 2-strokes in general.

They are valve uniflow. The turbocharger discharges into a large (walk-in on larger engines) manifold that opens into the scavenge space.

A single hydraulically operated exhaust valve at the top of the cylinder opens as the piston nears the bottom of the stroke.* Circumferential slots near the bottom of the cylinder allow air to enter when the piston clears them on the way down after the exhaust valve opens. Fresh air washes the exhaust gases out of the cylinder, the valve closes, the piston moves up and compresses the charge after it passes and closes off the ports.

Benn mentioned the cylinder oil. It is delivered by a separate pump to ports drilled through the liner that feed grooves to distribute a special high base number cylinder oil to lubricate the piston. There just isn't any other way to lube the piston since it is not in common with the crankcase, plus a few other major reasons that would take up too much space here to talk about.

Since not all the cylinder oil burns away, some poor junior engineer has to crawl in the scavenge space to muck out the sludge that collects around the packing gland where the piston rod enters the space.

The line drawing shows the gas flow through the engine. The stuff between the turbo and the scavenge space is a charge air cooler and mist eliminator then the scavenge air manifold itself.

The first picture shows a view inside the "intake manifold" looking toward the far end where there is another access door. The boxy looking bit on the lower left is a set of check valves that allow using an electric blower to supply air when starting. The openings on the right are where air goes into the scavenge space. If I had turned the camera a bit more to the right you would see the cylinder and the slots where Benn talked about inspecting the rings.

The next picture shows the top of the engine with labels.

Next is an exhaust valve being removed for service and inspection. Note the valve itself is hanging open. Air pressure keeps it closed rather than a spring. That air is called "spring air" of course.

Next is the valve after being removed from its house. The angled vanes are there to use energy in the exhaust gas to rotate the valve so it self cleans carbon and crud from seating surfaces. The smiling gentleman is a warranty tech from Denmark who was there to inspect the parts as much of this was a warranty job rather than unplanned maintenance.

Really good stuff Rick. Thanks a lot for sharing w us. Basically it looks like a DD w some rather large mechanical differences. Why the exhaust gas receiver? Does it reduce the force of the pulses? I'll bet the cooler really helps w efficiency. How many cylinders? How is it for noise?

Except it is a crosshead engine like a reciprocating steam engine. The piston and piston rod are solidly connected and the piston rod only moves vertically. There is a crosshead between the connecting rod and the piston rod and that is where the wristpin is located and there are vertical bearings to take the side thrust.

Slow speed 2-stroke engines gain quite a bit of efficiency (>5 percent) through "constant pressure" turbocharging rather than the pulse type on smaller engines. The exhaust receiver converts the velocity of the initial exhaust pulse to pressure and supplys the turbine with a constant flow at a constant pressure.An interesting bit of trivia ... the turbochargers on these engines turn slowly compared to those on a trawler sized engine, around 10,000 rpm rather than 150,000 or so but each turbine blade "feels" a force of around 100 tons trying to pull it off the disk.

The engine in the pictures is an 11 cylinder version. They are noisy but not as miserable as a smaller engine. At low speeds you can hear the rings singing as they move up and down in the cylinder an dyou can hear and feel each combustion event. The turbos will kill you though, they are very large, turn very fast and move a huge volume of air. Even though they are pretty much sound-shielded, just the air flow noise is gruesome. A lot of the noise in the engine room comes from all the auxilliary machinery, pumps, compressors, centrifuges, fans that are needed to support the main engine.

Rick:

Your whole explanation of this topic is extremely well written! Even I can understand it!

Thanks Seahorse, I am glad you liked it.

It's not all that difficult to write about something you know and enjoy.

RickB wrote:
*It's not all that difficult to write about something you know and enjoy.

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Interesting discussion.

So what size / types of ships are these 2 cycle engines used on? *Why would they use these rather than a 4 stroke, what are the advantages? Are they burning diesel or bunker fuel?

Looking at the size of the valve and pistion, they are huge and for me, having never owned or worked on a 2 cycle engine larger than an outboard, very complicated.

Sorry too many questions

LB

"... what size / types of ships ...?"

Generally the larger ships that operate on long haul voyages where fuel economy is very important.

"Why ...?"

These are slow speed engines, they turn at around 100 rpm. They are directly coupled to the propeller shaft so no reduction or reversing gear is required. They are perfectly matched for the ship speed, propeller size, power requirements, and operating envelope.

They normally burn what is called an "intermediate fuel oil" or IFO. There are a couple of varieties of IFO and they are classed by their viscosity in centistokes. The most common fuels are IFO 180 and IFO 380. These are a blend of "bunker oil" and distillate (diesel fuel) to obtain the required viscosity at a specified temperature.

At "normal" temperature these fuels are very similar to SAE 20 motor oil. They are not as miserable as folklore has it. Both fuels have to be heated before they can be injected since the fuel injector doesn't really know what it is being served, it expects a certain viscosity and doesn't work well if it doesn't get it. At around 125 C or about 260 F, IFO is just like diesel and the injector is happy.

A good illustration of this is that a diesel injection shop will use a "diesel test fluid" instead of diesel fuel for safety reasons. This stuff has the same flow and viscosity as diesel fuel. The same test fluid is used to test your injectors and those on the largest diesel engine made.

Cylinder sizes vary quite a bit. The pictures I posted were taken on an engine with 900 mm pistons or a hair under 36 inches. The stroke on that engine is over 8 feet though, and that is one of the reasons it is so efficient. To get enough fuel into the combustion chamber in the time available requires multiple fuel injectors, some use 2 and others use 3.

RickB

On land based diesels the use of "bunker" fuel has been purportedly stopped due to emissions legislation. At least 25 years ago a generator station I am familiar with suffered this fate. I've read the same is affecting*ships in some harbors such that "bunker" fuels are no longer allowed. BS, facts rumors** ---?

Rick,

I see another way those engines are very efficient. Long stroke engines have less cylinder and combustion chamber area than shorter strokes and these engines you present have extremely long strokes compared to the bore size so minimal heat loss through cylinder walls and combustion chamber is achieved. I suspect that bore stroke relationships of this magnitude probably can't be achieved w the normal piston, crank and rod arrangement. Just say'in.

sunchaser wrote:I've read the same is affecting*ships in some harbors such that "bunker" fuels are no longer allowed. BS, facts rumors** ---?

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Marine fuels fall under a different regulatory regime than terrestrial fuels. The sulfur limits vary all over the board from a maximum of 4.5 percent down to 0.1 percent. The variation is related to in-port, at-sea, in special rules zones or Environmental Control Areas, within 24 miles of California and a few other circumstances. The trend is to ultra low sulfur or exhaust treatment that provides the same reduction in emissions.

When a sea going ship burning a heavy fuel oil comes within 24 miles of the California coast it must changeover to burning low sulfur fuel. In most cases this means changing to diesel fuel. Most ships do this anyway because you can't shut down the engine with heavy oil in the system without risking not being able to start again and maneuvering with heavy oil can be really risky. The problem is that changing over is not without its own risks and loss of power during the changeover is not uncommon.

Several US west coast ports and a few more in Europe have installed shore power facilities so that ships can "cold iron" and shut down their generators to reduce exhaust emissions. This is going to be how it is done in all but the smallest ports before long since fuel costs are rising so fast and emissions are such a big problem.

When I was working on steamships we had to changeover to low sulfur bunkers when we entered California waters. This was a very expensive proposition since we had to keep a separate tank for the stuff and there were not many places to load low sulfure heavy oil ... and this was the heavy heavy oil.

I am not well informed about the power industry but oil burning plants are in the tiny minority these days. The last figure I have for oil foired plants is about 1 percent of total power generation in the US. Coal and natural gas are around 75 percent.

The move to use LNG for ship power is growing in some segments. LNG tankers have used boil off gas for fuel for ages and now LNG powered offshore supply boats are using it for power. There is even talk of building coal fired steamships again since techniques have been developed to clean up the stack gas and coal is relatively common and cheap.

RickB

Thanks for the insight. Hawaii remains diesel powered with some wind picking up the slack. I'm surprised they have not gone LNG but capex is pretty high and risk money pretty scarce. An LNG plant could easily be barged in but the population base is too low for capital recovery.

The BC ferry system is serious about converting diesel to natural gas with tanks up high to lessen leak issues. The motivation is $20+ million per year in fuel savings. This assumes of course that methane gas will remain favorably priced to diesel. Washington is considering the same for their ferries.

The fascinating thing about what Rick has been telling us is that it shows how little the average person knows other than their own world. I know a lot about the design, manufacturer, testing, and support of jetliners. It's the world I live in. But I see a bulk carrier or tanker or car carrier heading up Haro Strait for Vancouver and I have no clue whatsoever to what that world is like. There are plenty of assumptions and 25th-hand pieces of questionable information floating around, just as there is about the aerospace industry. So I have always found it fascinating to get a glimpse into one of these other worlds, even a brief one, from people I've met over the years who are locomotive drivers, crew members on RNLI lifeboats in the UK, lock operators on the Panama Canal, ocean-going tug captains, sugar mill managers, and so on. Most of us on this forum have had these kinds of opportunities from time to time. So now, when I see one of these ships enroute to or from Vancouver or the refineries in Anacortes and Cherry Point, I'll have a little bit of understanding about what's going on in their engine rooms. Thanks for the glimpse into the world of big-ship engine rooms, Rick.

PS-- Having lived in Hawaii from 1955 to 1979 with two years off for good behavior in the mid-60s, the power when I lived there was all from oil-fired boilers and steam turbines.* The water sytem got its pressure from a number of magnificent tile-lined plants containing one to three huge stationary steam engines turning immense flywheels that were connected to the pumps with belts.* The boilers were oil-fired.* The sugar mills used the same sort of steam power but their boilers were fired with bagasse, the dried, crushed sugar cane stalks that were left after the juice had been mashed out of them.* When I left the water system had been converted over to big electric motor-driven pumps but the electric power was still from steam turbines.* The island of Oahu had a large refinery out at Barber's Point that provided all the fuel for the island.* I don't know how the other islands got their fuel as there were no refineries on them.* I assume it was barged over from Oahu.

There have been attempts to generate power in Hawaii by using the temperature differential between deep water and the surface, and wind (according to my friends who still work over there) has made some inroads.* But wind is not an efficient way of generating large amounts of power.* I saw figures at Boeing that to use wind to power the island of Manhattan the entire state of Connicticut would have to be covered with wind generators--- border to border, no people no homes, no towns--- and the wind would have to blow 45 mph 24/7/365.* Not too practical.






-- Edited by Marin on Friday 4th of November 2011 02:18:15 PM

It's generally pretty quiet when you see them on the Sound since they are in "maneuvering" mode which is kind of like being below 10,000 feet in an airliner cockpit ... it's not quite a "sterile" control room but there is only one job that needs to be done.

The first* two pictures are what you might see if you could look into the engine control room of a Washington State Ferry.

The next is what you would see in the ECR of a large cruise ship.

The next one is what you would see on a containership. Pardon the mess but they haven't had time to clean it up after some heavy maintenance.

The last one shows what you might see when well out at sea, a pump has failed and is being removed for a rebuild.

The faces have been blurred for the privacy of the people shown.

Rick can I ask a question that I am sure you will know the answer to.

To what depth can these large ships effectivly use their anchors. Off the north of Sydney we see lots of large carriers sitting off shore waiting their turn at the Newcastle port facilities. Given that the continental shelf he is not too far off shore I doubt they can be riding at anchors.


-- Edited by shrimp on Friday 4th of November 2011 08:16:04 PM

It is common for the ships you see (bulkers) to carry 500 to 600 meters or more of chain. I have heard of ships anchoring in 90 meters of water but that is unusual in my experience. When I was on tankers we would anchor quite a lot but most of the time we were in water so shallow that running over our anchor and holing the bottom was a concern.

There is a class notation for tankers that anchor in deep water up to 120 meters and those ships will carry anywhere from 600 meters to over a 1000 meters of chain. The scope in that depth is 3 or 4 vs the 7 or so in water around 30 meters depth.

Dropping one of those* anchors was a real treat to watch, the foredeck disappeared in a cloud of rust dust and the whole ship shook and rattled as the chain rumbled out of the locker and hawse.


-- Edited by RickB on Friday 4th of November 2011 09:27:53 PM

Rick--- Since this thread has derailed a bit anyway...... As you probably know a regular holding spot for tankers in this area is in the mouth of Padilla Bay between Bellingham Bay and Anacortes. There are almost always a couple of tankers waiting here plus one or two notch fuel barges. The water is proabably about 90 feet deep. I'm curious if ships experience the same things we do but on a much larger scale. If it's windy or there are strong currents, can they bury their anchors to the point where they have to use the ship to break it out? Or is the scale of the anchor to the bottom such that the anchors don't have to dig in all that much to hold?

Hi Marin,

It's gonna really be derailed now that anchors are in the mix! We never knew (or as far as I know, particularly cared) if the anchor was buried or not. We knew when it held and that is what matters.

The anchors are sized for the ship as is the chain (see the link). The objective is to make sure that the shank lies flat on the bottom so that the flukes dig in. That is assured by enough scope and heavy enough chain. If the weather is forecast to be bad, another shackle or two is let out and the engine is put on standby. If it gets really bad the engine is used to hold in place or we leave the anchorage.

Unless I misunderstand your question, the ship is always used to "break out" since the weight of the chain is so high the ship moves up to the anchor by the reaction of the windlass and if there is a lot of chain out the engine is used to move up toward the anchor and minimize the strain. The windlass is sized to lift the chain and anchor, not the ship, and they have been known to explode under unusually severe loads.

When the chain is "up and down" it means the ship is directly over the anchor and any further lift will "weigh" it off the bottom and the ship can begin to maneuver.


http://www.eagle.org/eagleExternalPortalWEB/ShowProperty/BEA%20Repository/Rules&Guides/Current/2_SVR_2011/part3

Rick-- Thanks for the explanation and the link. What I was getting at is there have been times in our boat when our anchor was set well enough that to continue to haul on the rode with the windlass once the boat had been hauled up to be over the anchor seemed like it could tax the windlass more than we wanted to. So we use a line we have for this purpose with a chain hook on one end to secure the tight (all chain) rode to a heavily backed deck cleat. Then we slack off the windlass a bit, and the use the boat's normal motion in the water or give it a shot of reverse if there isn't enough motion to break the anchor out. Once the anchor is out, we remove the chain hook line and retrieve the anchor with the windlass.

So I was wondering if large ships ever do this--- secure the chain somehow to take the load off the windlass and then use the ship itself to break the anchor out if it looks like it's set too hard for the windlass alone to break it out. Or do they just haul away with the windlass until the anchor comes free or the windlass fails?

Just like the fisherman's reel winch I'm sure the shipboard anchor winch is fully capable of breaking out the anchor and since the anchors they employ are not burying type anchors "breaking out" probably is'nt an issue either. But when you get older Marin you could get a hydraulic reel winch and not need to worry about your*yachtie winch being damaged pulling up the anchor. That's the main reason the fishermen use what they use is to make it quick and easy. They do'nt even set the anchor most of the time. They lower their ground tackle down and they raise it up in the morning. Many to most anchor every night and say to me "we can't be bothered w all that stuff you pleasure boat guys do". But the thing I'd like to know most about big ship anchoring is what size anchor do they use and how does it compare w our yachtie anchors. How many lbs of anchor to how many tons of vessel? I suspect their anchors are very small in this regard. And since they employ very low performance anchors like the Navy thpes their anchoring security must be very low. But I do'nt know since big ships are'nt my world I'm just say'in and guessing.

Marin wrote:
Or do they just haul away with the windlass until the anchor comes free or the windlass fails?

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*Once the chain is up and down the shank is vertical and the flukes have rotated about 45 degrees so I guess you could say the anchor has broken out ... even if the water is really deep the windlass lifts it up with no more load than it is designed to take.

What risks windlass parts is a runaway anchor in deep water or shock loads if using the anchor as a brake.