[Vwdiesel] Genset RPM and Diesels

[Shirley, Mark R]

The problem with running an automotive diesel engine at 1800rpm for
a genset is that most of the time, you are on the wrong side of the torque
curve.  What you want is to be on the upper side of the torque peak for
generation, so that as you load the motor, your torque increases.  This 
is called torque backup in the industrial engine business.  Running your
VW at 1800rpm, you are most likely on the left side of the torque curve, and
as you load the motor, you lose rpm, and therefore, lose torque, which causes
you to lose more rpm, and more torque and so on and so on....

For instance, if I were to use one of my spare 2.0D Mazda's for a genset, 
which had a torque peak at 2700 rpm, I would either way underrate my genset 
so that I never came close to the torque max at that rpm, or run the engine at
about 2900 rpm so that the rpm sagged and the torque increased as it was loaded.

> -----Original Message-----
> From: Area31 Research Facility [mailto:stephensrw at stn.net]
> Sent: Saturday, May 21, 2005 12:02 PM
> To: James Hansen; vwdiesel at vwfans.com
> Subject: Re: [Vwdiesel] Genset RPM and Diesels
> 
> 
> James,
> 
> I had made a comment that there was no excess heat from the 
> engine at about
> 1250 RPM.  This was with the throttle about twenty or thirty 
> thou advanced
> above idle stop and a light electrical load applied.  The 
> engine maintained
> a water temp 175-180 F.  Little heat was coming from the radiator.  No
> wonder, very little fuel was being processed by the engine!
> 
> At 1800 RPM, and a couple of kW electrical load the 1.5 NA 
> engine has no
> lack of heat issues. When I'm using it as a governor 
> controlled 1800 RPM
> genset the average coolant temp is 195-200 F.  This is 
> probably ideal for
> the engine.  The oil pan is plenty hot.
> 
> I tried to operate my electric welder from the output of this 
> plant last
> niight for the first time and was disappointed that it does 
> not make enough
> power at 1800 RPM for my needs.  I had hoped that this genset 
> would have
> been adequate to run my machine shop. Configured direct drive 
> at 1800 RPM as
> it is, this is unfortunately not the case.  It seems all I 
> have now is a
> nice emergency stand-by plant for the home.
> 
> I guess I need to build another diesel plant, this one with a 
> DC welding
> generator integral to it and run the engine at ~3000 RPM.  
> Time for belt
> drive speed reduction I guess.  I have a Nissan 4 cyl diesel 
> that I could
> use for this next project.  It is 1.8 litres I think.
> 
> Rob
> 
> ----- Original Message -----
> From: "James Hansen" <jhsg at sasktel.net>
> To: <vwdiesel at vwfans.com>
> Sent: Saturday, May 21, 2005 3:36 AM
> Subject: RE: [Vwdiesel] Genset RPM and Diesels
> 
> 
> >
> >
> >
> >
> > I am still a DO NOT USE  TORQUE  -----use RPMs on these 
> diesels.   They
> are
> > designed
> > as high speed diesels -----and as such they do not like 
> high cylinder
> > pressures. ----AND read my lips  ----Gensets are notorious 
> for opening the
> > throttle full
> > power on a load being applied.----------
> > _____________________________-
> >
> > yes.
> > I can't see the vw diesel lasting better at 1800rpm .  
> That's out of it's
> > peak efficiency range.  All you are saving with a vw-D by 
> going low rpm is
> > the friction generated by the bearings, the difference 
> between what it
> would
> > be at 3500 and what it is at 1800.  A fiddling amount really. It was
> > mentioned that at low rpm, the coolant was not very warm.  
> If that's the
> > case, that will kill an engine.  Restrict coolant flow or 
> something to get
> > the engine warmer.
> > Hagar's right about the volks being a high speed engine. 
> Speed and useable
> > torque is a function of displacement and cam profile, one 
> of which the
> volks
> > doesn't have, and the other is the lobes are set up so the torque is
> > optimized around 2500
> > -James
> > --
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