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

[Art Krenzel]

Mark,

At issue is lubrication.  With adequate lubrication, designed piston ring 
wear rate is acceptable in diesel engines.  When an engine is operated at 
full combustion pressure at lower than designed rpm, blowby increases.  This 
blowby carries with it unburned fuel.  When carbon particles (basically 
unburned fuel) become lodged in narrow channels designed for the rings to 
"float" and expand in, ring lubrication is compromised.  When the rings do 
not have free floating movement, the pressure seal suffers which allows for 
further increases in blowby.  Ultimately (and in much less than the designed 
engine life), the engine blowby increases until there is metal to metal 
unlubricated contact and the rings can scour the piston walls as well as 
overheat the piston to the point of blowing a hole in it.

Properly lubricated pistons have an acceptable wear rate even at high speeds 
and longer distance traveled per unit of time.  It is operating that 
piston/ring system outside of it's designed time/temperature/pressure zone 
that this issue rises.  Changing the oil more often to reduce floating 
carbon particles might extend the engine life again.

There are too many parameters that feed into engine life that it is 
difficult to make a conclusive statement "doing this will reduce engine life 
by 35%" by operating outside of one design point.  That is why I suggested 
that Peter make a concerted effort to monitor blowby to determine what is 
happening to his piston rings.

Mark, to answer your question:  "Taken at the limit, how much wear would one 
expect if the piston
 were static and sealing an equivalent pressure?.

Take a look at the Challenger Space Shuttle accident if you want to see the 
erosive effects of blowby on a static sealing system.

The erosive wear rate of a four piston ring system compared to 12 piston 
ring system would differ by perhaps up to an order of magnitude at slow 
speeds.  In jet engines, they may have up to 5 - 10 labyrinth seals between 
compression stages to reduce blowby.  Designers do not use labyrinth seals 
in a static, long term situation - they use lip seals or some other method 
of full contact seal system.

Art


----- Original Message ----- 
From: "Mark Ludlow" <mark at ludlow.com>
To: "'Discussion of biomass pyrolysis and gasification'" 
<gasification at listserv.repp.org>
Sent: Sunday, July 01, 2007 10:43 AM
Subject: Re: [Gasification] SFC for De-rated Engines Was:small 
scalegasifiers for those that need them


> Bob & List:
>
> Someone pointed out that a linear de-rating of diesels still requires the
> same torque (read: combustion pressure). Higher RPMs imply more frictional
> wear (longer distance traveled per unit of time) which, to me seems more
> relevant. Taken at the limit, how much wear would one expect if the piston
> were static and sealing an equivalent pressure?
>
> Perhaps Art would elucidate us further (?)
>
> Mark