[Gasification] Prime movers -- The Slow Go diesel concept

[Art Krenzel]

Peter,

The power available from a combustion engine follows the formula:   PLAN
P = cylinder pressure    L = length of stroke   A = area of piston   N = 
number of strokes per minute.

If you want to reduce the power output of an engine to one half by reducing 
the rpm, the L and A stay the same.  This means the combustion pressure must 
be the same at half the rpm.
If the combustion pressure is the same, the time for the threat of blowby 
doubles by reducing the rpm to half.

Your memory must be combining two stroke diesel engines with four stroke 
diesel engines.  Cummins engines (the newer engines built since 1995 or so) 
builds four stroke engines and they do NOT like to run much above 1900 RPM 
any more however does have lugging power down to about 1250 rpm but then the 
power falls off dramatically.

A Detroit two stroke engine, as an example, does not have good slow speed 
lugging power and MUST run at high rpm all the time to deliver its 
horsepower.  If you lug a Detroit engine, you are staring an engine overhaul 
in the face at a small fraction of the normal engine life.  The oil 
consumption in a two stroke diesel engine skyrockets when you lug it at low 
rpm for long periods.

Using the engine as a Jake Brake is another matter.  Alot of engines were 
"lunched" by over-revving down mountain passes.  I am glad you survived all 
your death defying trips!  :-)  Those are sort of a rite of passage for all 
surviving truck drivers.

I am pleased to see that we have another experience in common, Peter.  For 
me, it adds more "meat" to your already interesting postings.

Art Krenzel

----- Original Message ----- 
From: "Peter Singfield" <snkm at btl.net>
To: <GASIFICATION at listserv.repp.org>
Sent: Wednesday, August 02, 2006 9:12 AM
Subject: Re: [Gasification] Prime movers -- The Slow Go diesel concept


>
> Hi Art:
>
> I did hours and hours truck driving pulp and logs and lumber -- and always
> watching that tack needle and when to shift.
>
> Never knew why though -- thanks for that info!!
>
> I always thought it was cause if you lugged hard at below lower RPM 
> ratings
> you would shorten the life of the crankshaft.
>
> This when pulling load -- when just idling around -- it made no difference
> -- like bob-tail in a yard --
>
> Then came those low RPM cummins truck diesels -- could go down to 1200 RPM
> pulling hard with out shifting -- and the drivers needed shift a lot less.
>
> Before -- if I remember -- it was between 1800 and 2150 -- and always --  
> so
> a four four or 13 speed splitter -- of 10 speed spicer with five in the 
> low
> extra.
>
> Old -- old -- memories.
>
> Art -- these old Listers are much lower operating pressures -- being as
> just 16 to one compression ratios.
>
> I have noted no blow back at all to date above normal. 800 watts at 375 is
> still but half of a full pull -- to ---
>
> In serious testing -- I can load it up to 1700 watts -- but lot's of black
> smoke results -- just about the end of the power that can be produced --
> for 375 RPM on this setup.
>
> In your truck example -- you could run low rpm is not pulling hard --  
> think
> on it.
>
> Why did we do that back "when"
>
> Well -- the engine ran cooler thus -- and used less fuel -- 
>
> Further -- the real killer was over revving.
>
> So if your cruising real light -- say 30 mph on a flat -- it paid to run
> lower RPM -- instead of holding it at 2150 -- say.
>
> You can tell by the sound -- and if black smoke is coming out of the
> exhaust -- right??
>
> The other scenario is pulling up a long -- 1 miles or more grade -- steep
> -- with a forty ton load -- and pedal to the metal all the way -- as the
> old 250 cummins stains to keep thing going front ways -- then it is 
> 1800 --
> 2150 -- 1800 -- 2150 -- till you finally are crawling at -- say -- 5 
> mph --
> at 2000 to 2150 -- and not daring to shift up until you get over the 
> crest.
>
> Always watching that tach.
>
> And even worse was coming down a long grade like that with bad curves and
> not being able to go faster -- than say 35 mph -- and hoping your brakes 
> do
> not over heat so much as to catch fire to your tires -- cause you know 
> your
> going to blow that motor if you use that to slow it down!!
>
> Going up the hills full loaded I could handle -- it was coming down a long
> steep grade in the mountains with an "overload" to a T intersection at the
> very bottom that made me so nervous!!
>
> In those case you stopped the truck -- or almost so -- at the top -- and
> used brakes and compression of engine to work your way down -- going 2150
> -- 1600 -- 2150 -- 1600 --
>
> Saving the brakes -- saving the brakes -- then -- when you have reached
> past 20 mph or so -- apply brakes -- watch for the smoke -- apply 
> brakes --
> slow down -- slow it down --
>
> Oh -- those were the days!!
>
> But I never blew a motor -- many others did -- and all the time!!
>