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

[Harmon Seaver]

Mark Ludlow wrote:
> 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


   That's irrelevant, there's still plenty pressure built up. Take a
look at any piston, you'll see the slots behind the rings for the
pressure to push against them.


> 
> -----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