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

[Mark Ludlow]

Harmon,

I may be confused, but it was my impression that crankcases are normally
vented, except in the case of two-cycle engines which use the downward
stroke of the piston to force a fresh charge into the combustion chamber.

Mark

-----Original Message-----
From: gasification-bounces at listserv.repp.org
[mailto:gasification-bounces at listserv.repp.org] On Behalf Of Harmon Seaver
Sent: Sunday, July 01, 2007 5:12 PM
To: Discussion of biomass pyrolysis and gasification
Subject: Re: [Gasification] SFC for De-rated Engines Was: small
scalegasifiers for those that need them

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

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