[Gasification] SFC for De-rated Engines Was: small scalegasifiers for those that need them

[Bruno M.]

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At 02:12 2/07/2007, Harmon wrote:
>Art Krenzel wrote:
> > Bob,
> >
> > It is not a case of RPM only - it is DESIGNED RPM.  The ship engines are
> > designed to operate at 110 RPM.  Their piston ring design and lube system
> > differs widely from an 1800 RPM engines.  They may use 10 or 12 
> rings where
> > the high speed diesel engine may only have 4 or 5 rings.  Piston 
> rings are a
> > form of labyrinth seal.  To hold high pressure over a longer time period
> > requires more labyrinths.  If you change the length of time the 
> ring seal is
> > exposed to high pressure without changing the ring design, engine life
> > suffers.
> > When you operate significantly below the designed RPM (i.e. 40-50%), the
> > designed ring seal engineering becomes inadequate.  Once you start getting
> > ring blowby, the wear rate increases as does oil consumption as you have
>---------
>     One thing about rings that a lot of people don't understand is that
>they are designed to be pushed outward against the cylinder walls by
>pressure coming from behind them, pressure from the crankcase. Which is
>why the ring to piston land clearance is crucial, likewise the lands
>being parallel to one another and the tops and bottoms of the rings. So
>when the lands become worn, they leak.
>     But also this would be affected greatly by low rpm which would not
>keep the crankcase pressure built up enough, thereby not pushing the
>rings out enough, and causing loss of compression.
>--
>Harmon Seaver
>_______________________________________________

Harmon,

I'm afraid you have it all upside down.
You say " ... are designed to be pushed outward against the cylinder walls by
                pressure coming from behind them, pressure from the crankcase."

That is not correct, if you have pressure in your crankcase,
your rings are already worn out and need replacement.
( Or you are running a 2 cycle motorbike. ;-)
Pressure in the crankcase will also quickly lead to oil leaking from 
your main bearingseals.
In some types of motors there is even a bit of vacuum in the 
crankcase. e.g.Lister(-oid)s if I'm not mistaken..

The rings stay against the wall in the first place because they are 
made of spring metal,
and when laying free on a table there outside diameter is larger than the
cylinder inner diameter, you have to compress them a little to get 'm in there.
And, ... the upper ring(s) is helped by the pressure from the 
compressed gas mixture from above
the piston, which can come behind the ring trough the small gap ( the rings are
not a full circle, and their is normally a very small gap 0.04" or 
less), and help
pushing the ring(s) against the cylinder wall.

Oil scraper rings : most types have springs behind them to push them 
against the wall,
(and the oil can run behind these rings).

Then you said:  " likewise the lands being parallel to one another 
and the tops and bottoms of the rings.
                  So when the lands become worn, they leak."

Not really, when the upper land wears out, the upper ring does not 
start leaking,
but might get overheated, and get burned after a wile, and that 
scratches the cylinder,
and than leaking  and skweaking starts.

Grts
Bruno M.
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