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

[Mike Redler]

Art,

That's a good point. The only thing that makes me wonder is the rate of 
combustion. I'm sure the engine could be slowed down to the point that 
all of the combustion occurs in a relatively small volume near the top 
of the stroke, causing high stresses and low torque at the crank. If 
you're "lugging" an engine with direct injection, your injection 
pressures and oil temperatures might play a roll as well.

What if other fuels (like producer gas) burn more slowly and allow the 
pressure from the expanding gases to be better distributed to the piston 
during the power stroke at slower speeds?

I would imagine that having a cetane value less than that of diesel 
might be an indicator but, I'm not 100% sure.

...my $.02

Mike


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
>>