[Gasification] water injection of producer gas fired ic engines

[jim mason]

On 7/9/06, Ken Boak <kenboak at stirlingservice.freeserve.co.uk> wrote:
> Gents,
>
> Some interesting comments regarding water injection.  If too much water in
> the biomass causes a shift from CO to CO2 production, then why not introduce
> water vapour directly to the air intake of the engine?
>

this would be an interesting solution for better drying of very wet
fuels in the hopper of the gasifier.  in a manner similar to gasifier
designs with condensing rings and water drain outs to take out the
water, or the similar monorator designs for water extraction, a small
vacuum suction at the top of the gasifier, drawn by the intake of the
ic motor, would continuously pull the water vapor from the top of the
gasifier (assuming it is downdraft).  which would get the water vapor
out of the gasifier, where it is mostly a problem, and into the ic
motor where it seems it might be of some benefit.

i believe this gasifier top water vapor, at low draws, should not be
tar heavy, as the tar heavy gas is coming from the pyrolysis zone
below the drying zone, and most of the that gas is going down.  the
water vapor is what is assumingly rising off the upper parts of the
wood.


> I believe that the expansion of the water vapour in the cylinder will
> increase the downward force on the piston during the expansion stroke, and
> also help remove some heat from the cylinder walls.
>
> In a veg-oil fuelled diesel, I have also heard, though yet to confirm, that
> it is beneficial in reducing the amount of carbon build up in the combustion
> chamber.
>

the water injection fanatics make lots of claims about the general
cleaning effects of its use.  as water is very reactive with hot
carbon, this seems reasonable.

as for the waste heat scavenging with expanding water vapor argument,
it seems oddly to be less important.  but i've yet to see any real
numbers on it.  seems important to me as a guess.


> As a simple experiment, I can introduce some steam directly into the air
> intake of my 6hp veg-oil fuelled Lister, and note any performance change.
>
>
> I have a nominal 3kW load attached, and I can measure any change in rpm or
> voltage produced.
>
> I can also measure the exhaust gas temperature to see if it is lowered when
> the water is introduced.
>

sounds like a great experiment.  you might want to try both steam and
water.  each might do slightly different things.

also, a propane torch at the exhaust pipe outlet, held perpendicular
to the flow, will likley vary in size depending on varying levels of
combustion completion in motor.  as the lister is likely too heavy to
get to the gas chromascope at the smog shop, the "after-burner" test
with a handheld torch might show some related data.


> I have noticed better performance on days of higher humidity, and also when
> the ambient temperature is around 20 C, rather than last week when it was 30
> C.
>

yes, this is long noted in performance applications.  thus one reason
why humidity readings are always given for dyno tests.  along with
temp and elevation.  well also, they are always given at the race
track too.


> If steam introduced via the air intake is beneficial to performance, then
> there is no shortage of water available from the biomass, which in my case
> is woodchips with up to 25% MC before the drying process.
>

the numbers i'm reading suggest that the % of water/steam injection
needs to be rather significant.  10% of fuel volume is minimum.  some
applications are going up to 100% water, (50/'50 water/fuel).  seems
like a good aim for continuous operation is 20%.  either way, not sure
if the water vapor from the biomass is gong to be enough.  the water
spigot may be necessary . . .

lots of water is likely going to be needed to see an effect, as with
the lister you are not going to be able to use the cooling effect of
the water to increase your turbo boost, or lean out your otto mixture.
 these are usually the real places power increases are derived from
water injection, things that are made possible by the water injection,
not directly from the water itself.  you will be without these options
you will be without in the lister test- on liquid fuels that is).
again, with gasifier fuel, the effect will likely be more pronouced,
even with the lister, as completing the CO combustion is the main
issue at hand.


> At 650rpm I am seeing temperatures of 352 C  (666F) at the exhaust manifold.
> The engine is running quite hot, with the coolant close to 98 C at the water
> outlet in the cylinder head.
>
>
> Ken
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