What governs diesel engine revs at max. load? Governor or props?

Danfarry said:
Sorry for the inexperienced question. Apart from an exhaust temperature alarm, would the other gauges such as temp and oil pressure react to a situation as described above?
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Apart from the tacho not sure any standard gauges will help if an engine overspeeds.

Its when they start running on their own oil and at, which point the governor becomes superfluous, that things get really interesting !
 
Danfarry said:
Sorry for the inexperienced question. Apart from an exhaust temperature alarm, would the other gauges such as temp and oil pressure react to a situation as described above?
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Quite simply EGT gauge, very common in U.S. Cannot envisage any overload condition would result in engine running on its own lube oil.
 
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Dougal Tolan said:
Turbo oil seal is a good one for that. Been in a car when it happened, best way to stop the engine was hand brake on, select highest gear, drop the clutch and pray for a stall.
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Gawd! engine overload will never precipitate a turbo failure sufficient to start passing sufficient lube oil to run away. Simply all flights of fancy.
 
A note on simple(mechanical) injector pumps/governors.

The high pressure pump is a variable volume device (often achieved by an adjustable bypass system), the volume delivered is a function of the difference between requested revs and actual revs with an upper and lower limit. Due to the nature of mechanical things it will not just increase fuelling until the requested revs are met. In this simple pump the fuelling is of the nature of fuel volume = constant * (requested revs - actual revs) [within max/min limits] So, as engine load increases the difference between requested and actual revs increases (revs decrease with increased load for a set throttle position)
With this set up, since max fuel injected per power stroke is limited then, unless you restrict the air intake it is not possible to over fuel.

Moving on from such a simple beast we then come to road engines where an occasional bit more oomph is desirable (flooring the pedal to overtake). Such a pump will add to the basic fuel delivery function of V=C*(R-A) an additional amount defined by recent increase in throttle, I would write such a function, but it gets all calculusy and is non linear anyway (as in there is no extra reduced fuelling when you take your foot off the pedal)

Now, then add to this fun things like an adjustment defined by air intake pressure (measuring turbo boost pressure) and electronic engine management systems the the simple beast goes out the window, along with many of the previous posts.
 
Dougal Tolan said:
Turbo oil seal is a good one for that. Been in a car when it happened, best way to stop the engine was hand brake on, select highest gear, drop the clutch and pray for a stall.
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Serious danger of thread drift here but diesel engine overspeeding due to failure of turbocharger piston ring oil is highly unlikely as they will never pass sufficient lube oil, this is automotive stuff, let me explain why........

Slobber from turbo bearings particularly from nasty Garrett automotive turbochargers fitted to LDA engines is endemic. However there is never sufficient oil slobber to create engine run away, the villain of the piece is the air to air charge cooler which harvests the slobber. Many numpty tec's never clean the CAC when fitting a replacement turbo, failure mode is real simple, the heat from compressed air causes the reservoir of oil slobber gathered in the air to air CAC to brew eventually vaporising, this is the lethal mixture which causes engines to run on.

In marine engines we have SWAC (Sea Water After Coolers) or JWAC (Jacket Water After Coolers) not air to air charge cooling.
 
Proper Fred Drift.....

We had a Fiat Strada ? in the workshop years ago and in order to carry out a particular job rather than put it on the ramp we jacked up the car at probably a rather alarming angle.
On starting the car it promptly went to max revs and stayed there.
After bit of pointless key turning only way of stopping the horrid thing was with the clutch.Never seen so much smoke in all my life.
Volvo diesels excluded.
 
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Latestarter1 said:
I assume you allude to the fact that many yachts have poor 'bite' when going astern.

Provided the owner is aware that he is over propped and never uses WOT to say punch a tide, but what happens when vessel is skippered by somebody not aware that giving the motor the beans is damaging it?

Yes I have come across the situation when working on a Grand Banks re-power when owner was obsessed with cruising economy and claimed he would never use WOT. We had to re-prop to get manufacturer sign off.

However the absolute no no is on planing vessels.
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Thank you that's very helpful, we'll keep to 80% as we're over propped. Long keel configuration with a high torque low revving Mermaid J444 Dieselmax and heavy displacement for the waterline length means that bags of bite ahead or astern early in the rev curve really helps manoeuvrability but I wasn't aware of the dangers of going WOT with an over propped setup.
 
all this interesting info makes me wondering about the following question:

On a pair of 12cyl MAN 1100HP mechanical engines,
there is any indication of load on the engines,
would it make sense to add a pair of EGT gauges ?
is there data available on what is normal range or too high EGT ?

we have added 2000l more fuel capacity to the boat,
this is a substantial addition of weight,
especially if we would use her in planing mode when completely full with diesel
(not planning to do that on short term)

the specialists advice would be thankfully apreciated !
 
Latestarter1 said:
Bart,

With your MAN's I would run all day at 520 Degrees C but give her tight wire and once EGT touches 650 C I would back off.........
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thank you Latestarter,
so you considder adding a EGT gauge is welworth doing ?
the small cost of this, and the work involved is no excuse not to do it.

any advice on where to install the probe ?
I assume somewhere inside the Exhaust manifold,
iirc the manifold has a water cooled jacket (I'm not sure if that is the correct expression)
 
BartW said:
thank you Latestarter,
so you considder adding a EGT gauge is welworth doing ?
the small cost of this, and the work involved is no excuse not to do it.

any advice on where to install the probe ?
I assume somewhere inside the Exhaust manifold,
iirc the manifold has a water cooled jacket (I'm not sure if that is the correct expression)
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Bart, temperatures quoted were EGT (Turbine Out) I.E. the gas temperature after the turbo has taken a slug of heat energy out of the gas.

You need to find a dry section no more than a pipe diameter and a half downstream of turbocharger outlet.

Drill and tap the exhaust, most probes other than VDO are 1/8th NPT. This guy does good stuff http://www.designatedengineer.com/ Website looks a bit Micky Mouse however he supplies nice quality gauges and ships to Europe with no probs.

Good luck
 
For those still interested in EGT -found this "tinternet ing "

We've already mentioned that excessive EGT can cause engine damage or turbocharger damage, but let's get more specific. Which parts will fail first is a matter of the design and materials used in the various parts of the turbo-diesel, but usually it starts with the turbocharger. Under sustained excessive EGT, the square corners at the outer ends of the vanes, where the material is thinnest on the turbine wheel, can become incandescent and then melt, resulting in a rounding off of the square corners. If you or your mechanic finds this indication before anything more serious happens, consider yourself very lucky, because shortly after the tips melt, the turbine wheel goes out of balance and wipes out the turbocharger bearings, which may or may not result in shaft failure and destruction of the turbine and compressor wheels. Excessive EGT can also erode or crack the turbine housing. In extreme cases, high EGT can drive the turbocharger into an overspeed condition that exceeds the designed operating speed due to the additional heat energy. When this happens, either the turbine wheel or the compressor wheel may burst. If the turbo doesn't go first, excessive EGT, if sustained, will damage the pistons. Such damage can include piston deformation, melting, burning, holes, cracking, etc. This damage is cumulative, so if you slightly burn a piston top, the engine may continue to run without problems, but the next time you run excessive EGT more damage may be done, and so on, until failure occurs. Piston failure can be catastrophic -- that means very expensive. At a minimum, an engine overhaul will be required, and that too is expensive. Excessive EGT can also cause exhaust manifold and cylinder head cracking. Exhaust valves can fail from high EGT as well. Among the first engine parts to suffer damage will be those made of aluminum since aluminum has a lower softening and melting temperature than steel or cast iron. Diesel pistons are aluminum, and a growing number of diesels also use aluminum cylinder heads.

So the big question is, what constitutes excessive EGT? If everything is working properly, 1250º to 1300º F. is a safe turbine inlet temperature, even for sustained running, mile after mile. Above 1300º F. things can start to get edgy. Remember, excessive EGT damage is cumulative. Over 1400º F., you're usually gambling against a stacked deck and it's only a matter of time until you lose. The higher the EGT, the shorter that time will be.

Above is EGT before the turbo -from memory I think I,ve seen 800oC on the MMDS - getting a sprint on :)no alarms

Salient point is " cumulative " ie engines may be damaged from previous unknown overloading -hence importance of EGT + sentry
Hope this helps
 
Sailorsam101 said:
My two AD41-Ps running A7 props reach 200 rpm above the max that VP say they should do at WOT

Any ideas?
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If your tachometer,s are accurate ? -they may not be ?

Sounds under propped ( assuming we know what correct pitch ever was in the 1st place )
Leave it that's good , just keep it 10% or so below VP WOT figure .
Remember they are old girls now .
It's overloading -t,other way ,over propped ,overweight ,and /or excess fouling -that's leads to a dangerous rise in EGT and the consequences of post # 37
 
Portofino said:
So the big question is, what constitutes excessive EGT? If everything is working properly, 1250º to 1300º F. is a safe turbine inlet temperature, even for sustained running, mile after mile. Above 1300º F. things can start to get edgy.
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Mmm... Those numbers are, respectively, 677° to 704° C, and 760° C for the "edgy" limit.
I'd rather trust LS suggestion of not exceeding 650°, than any other generic web post.
Or was the comment you quoted related to pre-turbine values, as opposed to post-turbine that LS was considering, maybe?
 
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