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

Wed Aug 2 11:12:24 CDT 2006

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!!

Listen to your motor -- watch for the black smoke. Watch the tach

Guess we are getting way off the gas topic ---

Back to the topic -- in the present example I am not going for maximum
theoretical cylinder efficiencies -- that is full loading -- just shaving
greatly the distance between full load and partial loading. Figure I am
picking up efficiencies and increasing engine life span.

Peter

At 08:38 AM 8/2/2006 -0700, Art Krenzel wrote:
>Ken and Peter,
>
>As an old Trucker who ran diesel engines for a few lifetimes, I am wondering 
>if you are considering the reduction in ring life due to operating the 
>engine under load at the reduced RPM.  As a trucker, the quickest way to get 
>your hands slapped was to "lug" as diesel engine at low rpm under load.  The 
>high combustion chamber pressure would begin to blow by the rings and you 
>would be staring an engine overhaul in the face after only a fraction of the 
>normal life of the engine.  At the proper operating rpm, the time available 
>for the high combustion pressure gasses to "blow-by" the rings was 
>sufficiently short that the rings could retain the pressure without 
>significant blowby.  At the lower rpm, blow-by can occur sort of like the 
>Discovery Space Shuttle Booster Rocket failure (with the same final result).
>
>Check the flow of gases out of your crankcase and see how they vary with rpm 
>over time.
>
>Art Krenzel
>
>
>----- Original Message ----- 
>From: "Ken Boak" <kenboak at stirlingservice.freeserve.co.uk>
>To: "Peter Singfield" <snkm at btl.net>; <GASIFICATION at LISTSERV.REPP.ORG>
>Sent: Wednesday, August 02, 2006 1:53 AM
>Subject: Re: [Gasification] Prime movers -- The Slow Go diesel concept
>
>
>> 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.
>>
>> 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.
>>
>> I am still slightly sceptical of your figures, as the best fuel efficiency 
>> I
>> saw was at rated speed,  where 1 litre of vegetable oil (c.v. 
>> 9.4kWh/litre)
>> 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.
>>
>> At part load, but rated rpm, I have found that the exhaust gas temperature
>> is very low. I guess thist is because the air to fuel ratio is higher than
>> needed, and the excess air has the effect of cooling the exhaust gases.
>> 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?
>>
>> 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.
>>
>> 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.
>>
>> 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.
>>
>>
>>
>>
>>
>>
>> Ken
>>
>>
>>
>>
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>
>
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