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

[Peter Singfield]

Hi Ken;

At 09:53 AM 8/2/2006 +0100, Ken Boak wrote:
>Peter,
>
>Thanks for your explanation regarding running the diesel at half rated
>speed. I had not made the conection that reducing the speed, allows the air
>fuel ration to be reduced accordingly thus maintaining efficiency.
>
>I think some further experimentation is needed, and I now have the means to
>run the engine at a range of speeds,and make electrical power measurements
>using the PM dc motor as a dynamometer.
>

Yes -- you do indeed. But -- to be fair -- you will have to compare fuel
consumption in both "modes".

That is producing -- say -- 1 kw with regular generators and fixed RPM set
up -- then producing 1 kw using the DC dynamo at peak performance per
stroke -- at what RPM that should be (probably 375 or abouts)

Otherwise -- as you mention -- the fuel consumption rate will not be much
different.

Still -- it would also be interesting to know if --

The engine is rated for 268 gm per kwh at 850 RPM full load 8 HP

What will it do at 375 RPM at full load (which probably will be around 3 HP??)

Right now most of us Lister operators go by the sound and the amount of
black smoke in exhaust to gauge how far up the maximum power curve we be.

So deep Phuff --phuff - and light puff of black smoke -- to me -- indicates
I am at the peak performance point in that curve.

I believe all diesels will follow this same set of thermodynamic rules --
but the Lister makes a very nice test bed device for checking it out.


>These I will plot against fuel consumption, so I can get specific fuel
>consumption figures for  various rpm figures - and not just the rated speed
>(650rpm) as the manual quotes.
>

Yes -- exactly!!

>I am still slightly sceptical of your figures, as the best fuel efficiency I
>saw was at rated speed,  where 1 liter of vegetable oil (c.v. 9.4kWh/liter)
>produced 2.125kWh of electricity,  giving an overall conversion efficiency
>of 22.6%.  All I can suggest is that more fuel consumption experiments with
>measuring cylinders and fixed electrical loads are necessary  to qualify
>your findings.
>

Those figures I supplied are from the literature available for Lister and
lister clones. Not from real time experiments on my part.

The only thing I can vouch for is the cutting fuel use by half or more by
derating as illustrated.

>At part load, but rated rpm, I have found that the exhaust gas temperature
>is very low. I guess this is because the air to fuel ratio is higher than
>needed, and the excess air has the effect of cooling the exhaust gases.

Sounds reasonable -- 

I use a small cooling tank to gauge engine waste heat production -- rather
than exhaust observations.

I do notice that I boil much more water running an 800 watt load at 750 RPM
that running it at 375 RPM. (I have my engine set up for 750 RPM not 850
RPM in "normal" mode -- actually)

>Under these circumstances the engine will fail to reach a sensible working
>temperature.    By reducing the speed, and maintaining a more optimum air
>fuel ratio, does the engine run at a reasonable temperature?
>

Explained that above -- yes -- it does -- when you examine the results by
measuring heat to coolant rather than heat in exhaust flow.

Remember -- in the full RPM model much more air is being physically pushed
through the engine for that same power developed -- in my example --
exactly twice as much. So theoretically it should be at least half the
temperature.

It probably is much less than half - -as the lean mixture mean -- according
to theory -- means less flame speed -- ergo -- less combustion in the
precombustion chamber -- more in the down -- the power stroke -- thus more
heat energy not going into expanding to do work -- but flying out the exhaust.

So even though your exhaust gas temps are in fact lower -- more "heat"
energy is fly out there.


>When I first installed the dc starter/generator, I was cranking it over at
>36V.  The pm motor makes a great dc generator and produces a dc voltage
>proportional to the shaft speed.
>

Your using a large PM magnet gear head big diesel (as truck motor)starter
adapted for direct drive??

>When the engine fired fired, the pm motor started to generate and force a
>lot of current back into the starter battery, and the resulting charging
>load was such that the engine rpm stayed low, about 180 rpm -effectively
>fixed by the terminal voltage of the battery, which slowly crept up towards
>42V.
>
>By adding additional batteries into my series string, I could get the engine
>to run at several discrete speeds from about 180rpm at 36V,  up to 650rpm at
>130V.  I can measure the charging current and the battery terminal voltage,
>and thus get the electrical power.
>

Great!! As I have been planning to acquire such a DC starter and do those
same experiments.

>I agree that reducing our electricity consumption to a minimum, and using a
>woodgas fuelled gen set to provide that power is a worthy direction.
>
>I am running a fridge/freezer, a PC,  a circulation pump for the solar water
>heater, some lighting, a cooling fan and my radio on about 300W.  My highest
>wattage appliance is my kettle at 2500W, but this is only used for a few
>minutes per day.
>

300W is excellent!! My use is high because of numerous electrical fans in
operation all about the house.

The freezer uses 120 watts.

We also have to do some development work on "heating" -- 

Your right about using waste heat from the engine for house heating. But we
also need flame heat -- for cooking -- boiling water. 

For here in Belize that solution will probably be in making up one of AD
Karve's fast biomass digestors -- I have to get started on that -- using
cane juice for fuel. Then it is cooking with gas.

In the tropics we have no need of low temp waste engine heat -- however --
there are three items where it can be applied on the Lister tank cooling
system.

1: A slow cooker for riece -- beans -- stews -- soups -- a steam cooker

2: For simple distillation of crude oil

3: For simple distillation of mashes to produce alcohol.

Fortunately one gets used to bathing in water at ambient temperatures here
-- so no need to heat water for washing body -- clothes -- dishes -- etc.

Now -- a bit on the proposed small charcoal gasifier set up.

I tend to imagine the ideal set up would be the Lister engine running at a
fixed RPM using a DC set up like you have charging batteries. This would be
run at mostly a fixed load to charge battery pack once per day -- probably
taking 6 hours.

The rest of the time would be running from batteries.

This could be further augmented by hooking up solar or wind.

But in the very end -- the simplest -- most reliable set up -- and most
economic -- would be to just make AC power directly into the home "grid" --
with maybe a small battery and inverter set up to run through the night.

I have some very economical 1000 and 2000 watt inverters on the way.

Batteries are always going to be a problem -- at some point we need
consider recycling our own batteries at local shops set up for just that.

I imagine this could be best done by refining expired car batteries back to
pure lead -- then casting thick plates of pure lead -- and using those to
build the old style Plante lead acid batteries.

Though these can not put our power in high surges -- as required to run an
electric starter to start an engine -- they can produce a steady power flow
well. And one just needs design those to meet the that power flow.

Say -- 48 bolts -- 1000 watts -- 21 amps -- which is ideal; Plante style
territory.

Plante batteries are also the most efficient of the lead acid designs -- in
power in over power realized out.

and -- they live the longest -- to 20 years.

After which one simply refines the lead -- recasts the plates -- and new
battery again.

Think large tall boxes -- very heavy. Here in Belize I will have to
experiment with waxed wooden boxes.

If one is really going to do this right -- a large amount of the sulfuric
acid can also be continuously recycled.

And last -- the small charcoal gasifier for the engine can also be used to
supply some cooking gas!!

Peter Belize


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>Ken
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