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

[Mark Ludlow]

Wayne,

The issue of discussion was originally the notion of running a diesel at
half-speed at but at identical torque as at higher speed (linear de-rating,
or 1/2 the horsepower output). At idle, the engines can have a very lean
mixture, (there's a very low torque requirement), which requires much lower
combustion pressures. In practice, the multi-ranged gearboxes of semis are
designed so that the engines are always operating at their optimum RPM
(except during idling).


Mark

-----Original Message-----
From: gasification-bounces at listserv.repp.org
[mailto:gasification-bounces at listserv.repp.org] On Behalf Of WJ Seidl
Sent: Sunday, July 01, 2007 5:34 PM
To: Discussion of biomass pyrolysis and gasification
Subject: Re: [Gasification] SFC for De-rated Engines Was: small
scalegasifiers for those that need them

In all of this discussion, I must wonder at how the engines on large 
trucks last for 
hundreds of thousands of miles.  Their engines are operating from idle 
to whatever the maximum
rpm is, varying constantly. Daily.  For years.

Can an engine be "designed" to run at a variable rpm? And maintain its 
compression?
Apparently it is already being done.
Best,
Wayne Seidl

Harmon Seaver 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.
>
>
>   

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