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

[Art Krenzel]

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 
noted.  Cooled unburned fuel forms carbon (the sticky black stuff)  in the 
lubrication slots in the piston ring system and finally blocks the movement 
of lubricating oil to allow ring movement.  Without the ability of the ring 
to "float", you might as well have ringless pistons.  As blowby increases, 
localized overheating of the piston increases causing the piston to "grow" 
until there is more unlubricated metal to metal contact and the piston locks 
up.

Art Krenzel






----- Original Message ----- 
From: "Bob Stuart" <bobstuart at sasktel.net>
To: "Discussion of biomass pyrolysis and gasification" 
<gasification at listserv.repp.org>
Sent: Sunday, July 01, 2007 10:36 AM
Subject: Re: [Gasification] SFC for De-rated Engines Was: small 
scalegasifiers for those that need them


>> <snip>  Prolonging the time duration the
>> rings have to contain high combustion pressures by slowing the
>> engine to a
>> lower rpm than recommended is a diesel engine killer.  This is
>> especially
>> true of the 20+:1 compression ratio engines in modern vehicles.
>>
>> Art
>
> That is an interesting point.  At lower RPM, there is more loss to
> blow-by, although I don't see how it would increase the wear rate per
> hour.  The big diesel engines in ocean freighters are only turning
> 110 RPM, and getting 50% efficiency on cheap oil.
>
> Best,
> Bob Stuart
>
>
>
>
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