[Vwdiesel] Genset RPM and Diesels

Mon May 23 13:08:44 EDT 2005

What Shirley, Mark R has just said makes a lot of good sense.  If my present
1500 RPM (50 Hz) alternator being turned at 1800 RPM (to make 60 Hz) wasn't
likely to self destruct from RPM related grenade forces I'd sure not mind
spinning the 1.5 up at 2500-3000 and see what kind of fuel economy numbers
I'd get at the same loads that I have done extensive testing at in the lower
RPM regieme.  It DOES make sense that the engine should get better fuel
economy where it has 'resonance' but such testing is not possible with my
present state of affairs.

Right now I can get 9 kW of useable electricity at 60 Hz from this plant and
near max power when all is hunkered down hot and working hard but not overly
I have seen my fuel economy max at about 0.35 litres per kWh. That's pretty
good!  At light loading this economy drops to about 0.5 litres per kWh,
still very acceptable.  What I'm afraid of is that by operating considerable
higher RPM, more bursts of the injectors each second, the low power
efficiency will drop and the actual net fuel consumption per hour will
increase even though the total power availabe will also be higher and at
high load the litres per kWh number will perhaps be better. If I am going to
load it to 12 kW all the time then increasing the speed makes every bit of
sense, but what fuel usage sacrifice do I then pay on 2 kW loading for hours
on end?

My purpose of experimenting in the ultra low RPM regieme is to see how
little the hourly fuel consumption could go, despite a drop in efficiency.
If one uses the plant merely to charge a large battery bank that feeds the
load through an electronic inverter then frequency and voltage are not
critical.  That is how I plan to run a smaller diesel as a secondary/prime
source working in tandem with a large wind turbine here eventually.

The idea of torque backup on the plant I may build to power a welding
generator directly makes really good sense!  Thank you Shirley, Mark R

Rob

----- Original Message -----
From: "Shirley, Mark R" <MarkRShirley at eaton.com>
To: "Area31 Research Facility" <stephensrw at stn.net>; "James Hansen"
<jhsg at sasktel.net>; <vwdiesel at vwfans.com>
Sent: Monday, May 23, 2005 10:05 AM
Subject: RE: [Vwdiesel] Genset RPM and Diesels

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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> >
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