I have just got an email from someone
Can anyone confirm?
Utter nonsense!
Honing marks will disappear in a couple of hundred hours.
Marine Diesel engines run at VERY low RPM.
Peter wrote:
If a large diesel engine under severe conditions can have a cylinder live of 50.000 hours, how come a private plane has to suffer cylinder live of just a few hundred hours?
Stupid question. Trying to compare an industrial engine with an aircraft engine is just a waste of time.
That said, if the oil consumption is in the normal range then it really does not matter how deep the honing cross-hatch is or is not.
When oil consumption gets out of range, then time to hone and re-ring.
Michael wrote:
Stupid question. Trying to compare an industrial engine with an aircraft engine is just a waste of time.
Well, even when all other influences are not considered (temperatures, pressures, mass, materials, types of fuel, vibrations, etc.), if the marine diesel runs at 120 RPM over 50000 hrs, this equates to 360*10^6 revolutions. If you run at (for instance) 2400 RPM, you are getting the same amount of revolutions after 2500 hrs operation…
mh wrote:
Well, even when all other influences are not considered (temperatures, pressures, mass, materials, types of fuel, vibrations, etc.), if the marine diesel runs at 120 RPM over 50000 hrs, this equates to 360*10^6 revolutions. If you run at (for instance) 2400 RPM, you are getting the same amount of revolutions after 2500 hrs operation…
And just what is THAT supposed to prove ?
The numbers of hours are not that important over the actual numbers of cycles for determination of service life, and if the marine engines cylinder is quoted on 50000 hours, this translates roughly in an amount of cycles that can be easily compared to aircraft engines, although the latter have much more constraints due to lower necessary masses, different thermodynamic operation points, different demands by different fuels, different vibration and damping properties of the installation, etc. It is supposed to prove that I am not very impressed by a service life of 50.000 hrs on marine engines, in contrast to even our old aircraft engines, of which at least many non-turbocharged models easily reach the 2500 hrs service life, given some care and regular use.
Marine diesels are everything from a couple of hundred hp to 100k hp. Even though the rpm is low on the largest ones (120 rpm at max), the piston velocity is high due to a huge stroke, 2.5 m. A Lycoming 360 has a stroke of 111 mm.
The piston velocity is omega * stroke = (rpm*2*pi/60)*stroke. For the largest marine diesels at 120 rpm, this is 31 m/s. For a O360 at 2700 rpm it is also 31 m/s. The marine diesel go at 31 m/s for 50,000 h, a Lycoming can hardly do 2500 h.
Anyway comparing a marine diesel to a Lycoming small aircraft engine, is like comparing Mercedes engine to a cheap Chinese lawn mover engine. A marine diesel is an industrial machine, more like the engine in a B-777, which is comparable in both hp and TBO.
Presumably the 30m/s or so is the flame front propagation speed, hence this has to be maintained regardless of the engine dimensions and rpm, otherwise the piston isn’t going to extract the energy from the burning mixture.
For marine engines, whether deisel or coal fueled, steam, reciprocating, mass is not a problem. For aero engines, mass is very important.
They are also water-cooled.
