[Gasification] Tar on inlet valves

[doug.williams]

Hi Ian, and Toby,

Sorry to see you getting mixed signals on this issue, but not every one has 
the same experience with producer gas, due to the differing systems they 
develop.

In the first instance, it is possible to make a gas that has no condensable 
tars, and to do this you need to build a gasifier that has a tar cracking 
throat, and a high temperature oxidation zone. The parameters are tight in 
these designs if you want to fuel an engine. It begins with the actual fuel 
to be used,either hardwood or softwood, which then determines the fuel size, 
and how it might be prepared. You do have to do the work to get the results, 
but first learn as much as you can before you start, as you do not have to 
invent any thing, because that is where diversion from true gas making 
evolves, and tar making begins. Study this free book, it's more than enough 
to get you going.http://www.fao.org/DOCREP/T0512E/T0512e00.htm

You then have to build a gas cooler/condenser, filter system, to remove the 
dust and water before you can use it in an engine. It is in these components 
if present, that tar becomes a problem. You might filter the heavy tar, but 
the pyrolysis oils will condense out when they hit the vacume of the engines 
inlet manifold. Heating it will not remove the tar, and if you add air and 
burn it, you just make CO2, and that will kill the ignition combustion. The 
valve stems are very hot, and stay clear in the guides while moving. After 
cooling, the tar baked onto the stem during the cooling phase, jambs the 
guides, and the valve sticks. Usually it will bend the valve push rods,  and 
possibly punch a hole in the piston crown.

Engine oil for producer gas is only a problem when you lack information, or 
understanding of the controlling factors. Not many even understand normal 
engine oil lubrication, so you will hear lot's of myths on this subject. 
The best oil to select is one you would normally use in a heavy diesel 
engine, bearing in mind that climatic conditions apply to the correct 
viscocity.

To control contamination, you should seek out a oil by-pass filter that has 
a toilet roll type element, but not pleated paper. These filters take out 
the moisture as it appears, and retain the fine soot and particulates that 
can act as a catalyst causing oil oxidation. The moisture is the main issue, 
as this is the final ingreadient needed to form the acid, and that eats the 
engine.
You can monitor oil condition using a simple " Filter Paper Test", even 
without a filter, so you need never really endanger your engine using dirty 
producer gas. You can read about all this on the Fluidyne Archive 
www.fluidynenz.250x.com so you are not about to try something that is not 
well and trully proven in commercial use. You might also consider building 
the DIY gasifier that in it's smaller form, is very good to learn the "art" 
of gas making. Others on this Forum can offer assistance if you ask, as 
quite a few have been built in the last five years.

Hope this assists you to improve your understanding of gasification.
Doug Williams,
Fluidyne Gasification.