Geoffs
Active member
Hmm lots of interesting things going on here. It seems to have been assumed that if water entered a cylinder it came up from the exhaust outlet via some sort of bow wave surge, either stopping suddenly of going astern fast. Both of which seem unlikely. Perhaps we should remember cooling water is injected into the exhaust, it always surprises me that we don't see more water entering cylinders.
The pressure waveform in an exhaust manifold is quite complex, and will go negative as part of normal cycle. The RMS pressure will be positive, but when an exhaust value opens, gas exits at high velocity. When the valve shuts, the momentum of the gas keeps it moving creating a negative pressure behind it.
With this all going on with 6 cylinders, it is not impossible that a back surge of exhaust water can get into a cylinder, by a combination of operating angle, transient conditions etc. A sound engine/exhaust design should, of course, be able to handle such conditions.
Also, only a very small amount of water is needed to produce a hydraulic resistance. The combustion chamber volume at TDC is quite small, an upward moving piston will only see it’s stroke reduced by a very few mm, the rotational energy in the engine wants to keep the crankshaft rotating, something has to give. It’s the poor old conrod, probably only has to bend a small amount, just enough to get past TDC. Any water is ejected on next exhaust stroke, by which time it’s probably vapour.
There may not have been enough water or time, for water to get past rings and contaminate crankcase oil. The engine will carry on running, with a slightly lower compression ratio in effected cylinder, and the piston moving down a bit further at BDC, damaging the oil cooling jet. The rest is history.
All this still leaves the fact that water had to get past a spinning turbo charger, but Dom has noted turbo damage, so all this could be consistent.
Can’t see, IMHO, how the operator can be held responsible for such events. Got to be a design, or perhaps installation, feature. Can’t remember if the 290 is the design that causes whole engine to tilt on trimming. Seems poor show for VP to wriggle out of warranty claim. If it’s a rare occurrence, a new engine can’t cost much in terms of turnover and basic cost. If a frequent occurrence, design needs looking at.
Well that’s my two pennath.
The pressure waveform in an exhaust manifold is quite complex, and will go negative as part of normal cycle. The RMS pressure will be positive, but when an exhaust value opens, gas exits at high velocity. When the valve shuts, the momentum of the gas keeps it moving creating a negative pressure behind it.
With this all going on with 6 cylinders, it is not impossible that a back surge of exhaust water can get into a cylinder, by a combination of operating angle, transient conditions etc. A sound engine/exhaust design should, of course, be able to handle such conditions.
Also, only a very small amount of water is needed to produce a hydraulic resistance. The combustion chamber volume at TDC is quite small, an upward moving piston will only see it’s stroke reduced by a very few mm, the rotational energy in the engine wants to keep the crankshaft rotating, something has to give. It’s the poor old conrod, probably only has to bend a small amount, just enough to get past TDC. Any water is ejected on next exhaust stroke, by which time it’s probably vapour.
There may not have been enough water or time, for water to get past rings and contaminate crankcase oil. The engine will carry on running, with a slightly lower compression ratio in effected cylinder, and the piston moving down a bit further at BDC, damaging the oil cooling jet. The rest is history.
All this still leaves the fact that water had to get past a spinning turbo charger, but Dom has noted turbo damage, so all this could be consistent.
Can’t see, IMHO, how the operator can be held responsible for such events. Got to be a design, or perhaps installation, feature. Can’t remember if the 290 is the design that causes whole engine to tilt on trimming. Seems poor show for VP to wriggle out of warranty claim. If it’s a rare occurrence, a new engine can’t cost much in terms of turnover and basic cost. If a frequent occurrence, design needs looking at.
Well that’s my two pennath.
)
