[Stoves] Diesel as an excellent fuel for rural households

[Ken Boak]

Hi Andrew - yes back in UK.

Steam conversions are never easy involving high temperatures and pressure
in order to maintain efficiency.

Converting a ubiquitous diesel to spark ignition is much simpler - it can
be done with low cost parts taken from an Indian scooter magneto &
electronic ignition.  This could be done in any mechanical workshop that
has a lathe, drill and basic metalworking equipment.

The mixer valve and throttle body can be made from plumbing fittings -
again very suitable for a low tech conversion.  The engine can be started
on diesel, whilst waiting for the gasifier to heat up and reach the point
where it can produce "engine grade" gas. Then the diesel can be shut off
and the engine runs entirely on woodgas using spark ignition.  This gives
the flexibility of diesel for startup, and the economy of woodgas for long
periods of constant power output - such as power generation or water
pumping.

About 1.5kg of woody biomass is needed to produce 1kWe of power.   Larger
gasifiers with thermal recuperation or 2 stage pyrolysis -gasification will
better this figure  - almost approaching 1kg per kWe.

Efficiency is maintained because the diesel engine can work at its intended
high compression ratio - woodgas will not pre-detonate at even 17:1 CR.  So
my experiments showed a 2.75kW generator output from a 6hp Lister.

Wood/biomass gasification can use up all those crop residues that livestock
will not eat.  Biochar residues from wood gasification can be returned to
the soil as a soil improver.  Gasification will pyrolyse and gasify
cellulose - so even dried animal dung may have potential as a fuel stock.


The best efficiency I read for a steam plant was for a bash-valve uniflow
engine made from a converted Lister HR3.  It came in at 21% - but this was
exceptional. It was steamed by a flash boiler on a solar array furnace.

Here's what I found out in 2008   see -
http://www.rossen.ch/solar/wcengine.html

The White Cliffs Solar steam project (late 1970s) converted a Lister HR3
engine to uniflow flash steam.  This achieved an amazing 21% efficiency on
steam so they had to have something right. It did however use 600psi steam
at 500C generated by a solar furnace.

http://www.rossen.ch/solar/wcengine.html

They used the existing pistons running in the cylinders as the cross head
slides, and then built the 3 uniflow cylinders on top of this using
2-stroke diesel cylinder barrels salvaged from a  GM 3 diesel.  They fitted
ball valves in the fabricated heads of the new steam cylinders activating
the steam inlets. Steam exhaust was via the ports and plenum from the GM 3
engine.

Keeping the steam condensate out of the crankcase lube oil was always a
problem, so most high speed steam engines   have a physical break between
the crankcase and the steam cylinders, with the piston rod passing through
a stuffing box.

A 4 stroke diesel engine does not make a very easy conversion to steam. The
valve gear is all wrong and you would at least need a new cam system
running at crankshaft rpm.  I'm not saying its impossible but it would
certainly not be easy.

I have considered Stirlings (bot free piston and reciprocating) - but
unless you go to high tech metallurgy, H2 or He filled and fancy sealing
technology the efficiency is only around 5%.



Ken




On 19 April 2015 at 12:23, <ajheggie at gmail.com> wrote:

> [Default] On Sat, 18 Apr 2015 15:09:43 +0100,Ken Boak
> <ken.boak at gmail.com> wrote:
>
> >
> >1.5kg biomass produces 1kWhe of electricity using gasification and spark
> >ignition route.
> >
> >That gives biomass to electricity a 20% conversion efficiency - plus a
> load
> >of useful waste heat
>
>
> Hi ken, are you back in Blighty?
>
> What's the comparison with a flash tube boiler running a reciprocating
> steam engine?
>
> I do like the idea of a stirling free piston generator but Efficiency
> is not great, it's the possibility of longevity that's attractive.
>
> AJH
>
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