Hi Craig
On (16 Aug 97) Craig Healy wrote to Alec Cameron...
You wrote a biggie, excuse me for chewing on the easier bits..
-> I baulk at the cogeneration bit. The interesting rig you describe is
-> liable to
-> be unprofitable to you, a good citizen helping the utility Co.
 CH> But I would also need to calculate the value of the heating fuel I
 CH> would save.  It's not just for electricity, but residence heating in
 CH> the cold season.  Not even sure I would use it outside that time of
 CH> year.
Ahah. The sweet sound of reason. Cancel the engine option and move hot air or
hot water from your furnace in the usual proven way!!
My house was built in 1750, and does not lend itself to the
 CH> mega-insulation that efficient homes have.
That is a big issue. Dress yourself to suit and make few mods to the house.
-> Many engine labs USE a "calibrated" generator as the method to
-> determine shaft HP. Others use a dynamometer.
 CH> Yes, but is it done at a specific, accepted temperature/humidity and
 CH> barometric pressure?  And do they have a "standard" fuel?
I was addressing the issue of measuring shaft HP into the calibrated
generator. The variables you mention have a mighty effect on the drive 
ngine,
but have little effect on the accuracy of measurement. There is a wee effcet
and yes, it is used for making small corrections to the generator
characterisics.
-> Do you think you have the necessary skill and other resources to make
-> alteration to cam [?profiles]
 CH> Cam profiles?  Yes.  I don't grind the cam myself, but I sure know of
 CH> at least a dozen very qualified shops who can handle this.
I was taught that the cam curvature is not a simple arc of a circle, it may 
e
very complex and the difficulty in making the best front and back curves is
much more complicated than the mere grinding of those to the required shape.
The design is not a job for a shop, but for an engine designer.
  And I know
 CH> how to check the camshaft installation timing for maximum compression.
Ideally you should do that at service rpm not while cranking. Is that 
ossible
with your resources?
-> and ig timing? Wouldn't the auto advanc
-> dodgy problem since at constant rpm the centrifugal feature would be
-> inoperable.
 CH> My intent is to use a Vertex magneto with fixed advance.
Sounds wasteful of energy, unless you plan to run at constant power. At
changing power doesn't the manifold pressure vary, hence the need for vacuum
advance in efficient gas engines
-> If you fiddle with say three different cam changes and
-> three alternative ign settings then there are 3x2 ie six set ups
-> that might be tested in order to pick an OK one. Cancel your
-> vacation away!!
 CH> With the input of the camshaft maker, I doubt I'd need to make even
 CH> one cam change.  These guys are pros.
Betcha the big time pros [Rolls Royce, Allison, BMW] put a huge expenditure
into fiddling camshaft geometry and dynamics. The reason, being for provable
energy efficiency. And betcha quite a few sound looking designs and
prototypes are junked by those really truly Pros!
As far as timing, what's wrong
 CH> with putting a load on the engine, and adjusting timing for maximum
 CH> RPM?  Same with fuel mixture.  Adjust for maximum RPM at a fixed load,
 CH> then either increase load or drop RPM and repeat.  If that couldn't
 CH> be dialed in within a matter of hours, I'd be *really* surprised!
 CH> Very simple process, actually...  The load becomes the dynamometer.
You are treating the load like a constant. As soon as you change the rpm the
load changes considerably. If you use a large fan load for example, then 20%
speed change means 73% power change. The method you describe is pretty rough.
it is shooting at a moving target. Agricultural rather than scientific.
                     
-> CH> not proposing that .  I was thinking about a standard
-> synchronous CH> AC generator,
 CH> I'm not sure I understand your objection.  As long as the generator is
 CH> large enough so it doesn't burn out, and small enough to be realistic,
 CH> there shouldn't be a problem.  If the engine tries to run it at 59 Hz,
 CH> then it will supply no power to the grid.  As the engine tries to
 CH> increase RPM over the 60 Hz grid, it will supply power in relation
 CH> to the amount of "push" up against the 60 Hz grid.  Heck, a large
 CH> electric motor would work.
Have you changed the subject? A large electric motor would work yes BUT you
said a synchronous AC generator. Elec motors are very rarely synchromous, 
ost
are induction type and yes these are readily available.
Your reasoning re operation at 59Hz, 60 Hz is sound. But there are serious
risks, notably that the supply voltage is pulled down even though you succeed
in delivering energy into the grid. SO do not consider a bigger induction
motor than needed. Aim to run it at close to the ratingplate amperes.
If you used [say] a 5HP machine and ran it for long periods each day, the
Utility would tolerate you. But if you use a 20HP for just the odd hour or so
they might hate you. Their substation on load- tapchangers might become 
nduly
exercised and you would soon be discovered. Your neighbours would possibly
have lamp flicker and shrunken TV pictures.  Cheers....ALEC
... If you don't go to other people's funerals, they won't go to yours.
--- PPoint 1.92
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