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

[Trundlebug]

But are the consequences as serious in a naturally aspirated engine, such as you tend to find in displacement vessels which are often deliberately overpropped? There's no turbo to damage in these engines.

Would they just smoke a bit when at WOT, with elevated piston temps? I guess if the overloading was severe enough and prolonged enough the pistons could melt, but is this likely with a NA engine?

 

[MapisM]

Academic question imho, for two reasons:
1) it isn't true that NA engines are so common in D vessels: they used to be, in very old boats, but mostly because they were old, not because they were D hulls.
2) the reason for overpropping D boats is (AFAIK) strictly because most of them reach their hull speed well before the engine reaches its max rpm/power - in other words, most of them are overpowered (mine included).
In turn, this means that the engine(s) always run well below the rated max rpm/power/load.
If anyone wants or needs to regularly push a D vessel above its hull speed, there's no reason for overpropping, to start with.

 

[Portofino]

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?

Pre turbo in my view is best so the sentry (MAN)-can shut down or reduce before any damage.
post turbo not too far away depending on set up of the risers water starts to enter from the coolers -g box and main .How ever i guess there may be a section post turbo thats dry , but the damage will have all ready been done .Turbo takes a lot of heat out say estimate 200oC

i will be on the boat next week so will play around with speed /EGT-see what it is at the manifold -pre turbo

 

[Latestarter1]

Pre turbo in my view is best so the sentry (MAN)-can shut down or reduce before any damage.
post turbo not too far away depending on set up of the risers water starts to enter from the coolers -g box and main .How ever i guess there may be a section post turbo thats dry , but the damage will have all ready been done .Turbo takes a lot of heat out say estimate 200oC

i will be on the boat next week so will play around with speed /EGT-see what it is at the manifold -pre turbo

I would be surprised and very interested if MAN system shuts down the engine when EGT trigger point is reached. I attended a conference over 20 years ago when due to development of electronic engines we had the ability to initiate engine de-rate or shut down for a whole raft of out of range conditions.

The legal position prevailed that even if the engine sensed a condition which had the potential to become catastrophic taking control away from the operator by initiating engine protection shut down puts a high degree of liability on the engine manufacturer in the event of a serious incident.

I would be very interested if MAN has broken with this convention as they were not a party to the original conference.

EGT turbine out has long been held as industry standard for measurement. As I stated there is always a small opportunity to insert type K thermo couple in dry section after the turbo but before water injection.

Reason for not measuring at manifold is that there can be a significant variance of temperature dependent where in the exhaust manifold sensor is located.

 

[BartW]

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

all very clear!
thank you so much LS for this Usefull and comprehensive information
adding 2x dual gauges is on the todoo list (2 x V engines)
probably not before the coming season, but will report back when we have measurements.

 

[MapisM]

I would be very interested if MAN has broken with this convention as they were not a party to the original conference.

Do you mean that there's a convention based on an agreement between the major builders?
Strikes me as an anti-competitive conduct, more than likely in breach of some competition law...

 

[BartW]

Do you mean that there's a convention based on an agreement between the major builders?
Strikes me as an anti-competitive conduct, more than likely in breach of some competition law...

I read this differently MapisM;
the builders agreed in a convention what is best for the application in this industry with general safety in mind.
but I might be wrong, perhaps I'm too positive about builders intentions

 

[MapisM]

Well, if you re-read LS post, their concern wasn't the serious accident as such, but the potential liabilities implied for the manufacturer.
Not that I find it surprising, mind. Any corporation, in any industry, would think along these lines.
It's just the agreement between the major players for not implementing an innovation because of these reasons, that I suspect isn't 100% kosher...
...though I can only remind bits and pieces of competition law by now, so I might be wrong.

 

[Latestarter1]

Well, if you re-read LS post, their concern wasn't the serious accident as such, but the potential liabilities implied for the manufacturer.
Not that I find it surprising, mind. Any corporation, in any industry, would think along these lines.
It's just the agreement between the major players for not implementing an innovation because of these reasons, that I suspect isn't 100% kosher...
...though I can only remind bits and pieces of competition law by now, so I might be wrong.

I would tend to agree this would never happen in Europe however typical of much that happens in U.S.

Focus was all about taking operator control away from the equipment operator, for example one stated set of circumstances was a truck engine performing protection shut down on a dangerous bend vs the driver being aware that he had say absence of lube pressure but being aware that stretch of road was dangerous to stop makes every effort to bring the vehicle to a safe location however destroys the engine in the process.

Likewise vessel maneuvering in confined space, engine protection shuts motor down and vessel collides with a pontoon causing serious damage or injuries.

Suspect all the legal eagles went back to their respective companies and implemented ban of such features being set up as default in factory calibrations only allowing setting as customer specified option.

If one goes into CAT ET or Cummins Insite when logged into a marine calibration it should be easy to see if 'Engine protection shutdown' can be enabled or disabled. If this feature is greyed out then manufacturer has take the decision for you.

 

[Portofino]

I will see if I have a manual at home to night-if not deff on the boat @ W/E

There are various variants of each block -2876 le 401 is a "leisure" application approx. over 2x HP of the many -lower commercial variants ,so for me in a fast planning boat ,I welcome some nannies -Same block in road trucks and rail cars -6cylinder on its side under the carriage .

"Likewise vessel maneuvering in confined space, engine protection shuts motor down and vessel collides with a pontoon causing serious damage or injuries."
quote LS1 above

remember stage 1 alarm only -operator can chose what to do

next level stage 2-alarm + reduce rpm -so here operator can still carry on controlling the boat -or if necessary with EGT shut it down _turn it off .
On a planning boat it will drop off @1000 rpm and de-load =lower EGT -before blow up

then only then stage 3 (parameters wildly out ) -auto shut down -I think -but will re-read manual v soon
perhaps in the commercial side this stage 3 may be disabled + in EGT crisis + blown engine +stop anyway .

YUP early upstream EGT brass or some other cheap sensor in the early days would have issues melting and going into the turbo + knackered
I understand MAN upstream are stainless steel -they have perfected it now -so no issues of the sensor evaporating -these days -I think

 

[Portofino]

Here,s an extract from operators hand book regarding MMDS on how to reset it .
--Last 4 lines at the bottom
(looks like stage 2 rpm drop is to 800 not 1000 )



Commissioning and operation
25
Alarms
If an engine alarm from the central unit MMDS or an alarm configured by the user is issued, the built-in
buzzer is activated and the LED “Alarm” flashes. At the same time, the monitor switches automatically to
the alarm screen. The new alarm is entered in the first line as a flashing message.
The alarms that would be issued if the engine is stopped but the engine ignition is on (e.g. lack of oil pressure)
are suppressed (disabled) until the green LED “Engine run” lights up. This occurs approx. 8 seconds
after ignition engine speed has been reached.
When the acoustic acknowledgement (Horn Quit key) has been pressed, the integrated buzzer switches
off. With the visual acknowledgement (Visual Quit key), the flashing text and the LED “Alarm” switches to
continuous display. When the fault has been remedied, the alarm text disappears from the monitor. The
LED “Alarm” goes out unless another alarm has been issued.
In the case of alarms that have led to automatic stopping or reduction of the engine speed by the
central unit MMDS, the “RESET” key must also be pressed. This function is only enabled in the
case of a stop alarm at engine standstill and in the case of a slow down alarm below an engine
speed of 800 rpm.

 

[MapisM]

Wow. Is there also a panic button, meant to fly in an engineer by chopper from Germany right away...?

 

[Portofino]

1750 - RPM

Load 78%

Speed 27knots @ 1750 rpm
Normal Eco cruise arround 1750 - rpm .

2000 RPM - EGT now just over 600 oC

Load 88% @ 2000 rpm

Speed

EGT - Drops off @1000 rpm .

Boat feels well balanced and correctly propped /engined /gearbox ratioed -- for the weight /drag .
18 T dry , + 3T fluids + stores + people -so 22-24 tons fully loaded .
Never really go above 2000 rpm no real need (WOT is 2200 for the MAN 2876 a700 Hp = 38 knots )
Boat cruises arround 70 some % "load" ,I,am happy with that but as mentioned be interesting to see Bart,s EGT at 2000rpm ?.
It's better to have bigger engines operating in there comfort zone ,than smaller not enough oomph being thrashed to a inch of there life .There in lies a dilema for builders