I was looking at some documentation on the engine builders site and came across this: ". The cylinder liner wear rates are in the region of 0.02=960.03 mm/
1000 hours maximum."
in the document:
formatting link
That equates to about 1 thou in 42 days - I don't now much about internal combustion engines but that seems quite high. Is it because of the large bore of the cylinders that the rings can cope with a relatively large amount of cylinder and ring wear ?
That equates to about 1 thou in 42 days - I don't now much about internal combustion engines but that seems quite high. Is it because of the large bore of the cylinders that the rings can cope with a relatively large amount of cylinder and ring wear ?
Regards Tim
You've got to take it in proportion to bore size though. For example -
1 thou on a 3" bore is equivalent to 0.0003% wear
1 thou on a 3' bore is equivalent to 0.000025% wear
If you take 85mm as being the average bore of a car engine and 3 thou as a reasonable bore wear limit before reconditioning then you get 33 thou wear limit or 33,000 hours running for the 965mm bore of the Sulzer. That equates to 3.7 years continuous running and container ships need to spend some time loading and unloading so probably over 4 years actual service. Well within their target of rebuilds every 2 to 3 years.
Compared to a car engine that's a very low rate of wear. Even a well looked after car engine is unlikely to see more than 5000 hours service. The Sulzer will undoubtedly have much better oil and air filtration systems than car engines do though. Most car engine wear is caused by what gets past the air filter or doesn't get removed from the oil. Truck engines with 500,000 mile service lives also use much better filtration systems than cars.
"4 years actual service. Well within their target of rebuilds every 2 to 3 years."
OK - the figures make sense then - I thought that such a massive engine would only be rebuilt every 10 years or so - but that was a totally subjective figure. Guess I thought when you spend so much money you don't have to worry about it for a long time !!! But seen in light of the profits they must make its probably doesn't work out too badly.
You have to remember that you are linear, squares and cubes.
10 times a "reference" engine size =3D..
10 times the bore and stroke
100 times the area
1000 times the volume
so the ratio of volume (cumbustion charge) is cubed, the area on the piston is squared but all that torque (which works against the barrel, therefore barrel / ring / piston wear as quoted, is linear... to some extent this is countered by lower rpm, but lower rpm is somewhat countered by longer stroke so mean piston speed isn't that low.
that 5.6 million pound feet is all working against the barrel / ring / piston every power stroke so the wear figure given is actually more than merely good.
0.02mm per 1000 hours is 50k hours per mm wear which is 5.7 years, and
1mm wear isn't going to stop that engine running, go work out the coefficients of expansion of a piston that size from ambient (cold start) to operating temp.
0.02 mm per 1000 hours really is, as the saying goes, something to write home about.
Ten to twelve years is approaching the design service life of very large commercial ships (maybe 15 at a push). They are build with multiple redundant systems. Each system has a few years life. As systems fail, backups are switched on - the original and subsequent failed systems are left by-passed and switched off. No major component or system that would cost mega-money and/or take the ship of the water is planned for by it's original owner.
These types of engines are capable of being run with entire cylinders not working, pistons missing, parts out for replacement etc, in a way impossible for smaller engines. Also, there will be no reduction gearbox to the propeller. Direct drive at propellor revs. Going in reverse means stopping the engine and starting in the opposite direction. No parts to wear out :)
When the ship is no longer viable to a first-world company, it is then sold to a flag of convenience country and operated for the next X years with very little, if no servicing done.
After 30/40 odd years use, on rejection as a rust-bucket by its tenth,
3rd World operator, the ship is in prime condition to be bought and operated by a Greek shipping magnate.....................
Sometimes ships that touch our shores are served a writ. Basically they must be serviced to a suitable standard before they move another inch. The usual result is the captain, crew and vessel are abandoned by the owners. It happens... and more than you think............. John
Having built this splendid piece of engineering - how do they transport it to the vessel. The background to the pictures does not seem to indicate that they are building it in situ. Dismantle it and take it piece by piece perhaps?
Why don't they just wrap a big bungie cord round the output shaft, then when the cord tightens enough to stop the engine it would restart automatically in the other direction ?
It's also my understanding that these engines have an oil pump driven by an electric motor, which is in turn driven by their auxiliary generator. So they can switch on the oil supply before they start the engine, and greatly reduce the wear which occurs at starting.
They do that with diesel engines? I know that ships steam engines were reversed like that, but I never heard of a diesel engine being (deliberately) run in reverse.
Same as you do it with an O gauge locomotive, stop the engine, move the valve and injector cams to the right position, re-lock them onto the shaft, then hit the air start. If you're clever, you move the cams and don't bother stopping the engine...
It varies with engine type, but usually the valve gear is changed for reverse running, as is the fuel cam, which is also on the camshaft.
Although very big diesels are two-stroke engines, they have valves and camshafts just like four-stroke engines.
Get hold of a copy of "San Demetrio - London", an old Ealing film (true story) about a petrol tanker that is set on fire and abandoned in WWII and then re-boarded by some of the crew. There is a short sequence where the camshaft is lifted and moved axially and then lowered so the reverse running cams are the ones in use.
Some of the engine shots apparently were of the studio's own Ruston & Hornsby generating engines.
Peter
-- Peter & Rita Forbes Email: snipped-for-privacy@easynet.co.uk
It is true that all the big direct reversing engines are two strole. Modern designs are camless, all injection etc is electronically controlled actuators. The biggest designs have cylinder bore up to about 1 metre and stroke of about 3 metres +. They can be built in various numbers of cylinders to suit power requirement. The country with the largest orderbook is South Korea followed by Japan with China rapidly catching up. The designs are predominantly MAN Denmark, Wartsila (ex Sulzer) Switzerland and Mitsubishi Japan. Phil
PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.