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

[Ken Boak]

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