100 Deg Celsius (212 Deg Fahrenheit) biomass starts vaporizing out trapped water trapped inside of it.
200 Deg Celsius (393 Deg Fahrenheit) biomass starts to break down.
250 to 350 Celsius (482 to 662 Deg Fahrenheit) is the core area where pyrolysis starts to happen (producing fuel) biomass reducing.
350 Celsius (662 Deg Fahrenheit) pyrolysis is self sustaining. (Produces enough oxygen from the wood to be self sustaining)
Tar cracking happens around 900 Deg Celsius (1652 Deg Fahrenheit) and above but you really want to keep the
temperatures in the range of 1100 Celsius (2012 Deg Fahrenheit) or even a bit above as a comfort zone.
Anything below 900 Deg Celsius (1652 Deg Fahrenheit) will not crack the tars correctly and it can cause serious issues with
an engine without some good filtering. Another negative is that un-cracked tar is potential fuel that is wasted and a tar laden
gas is less robust than a gas where the tar has been cracked. When cracked, the tar becomes part of the usable fuel source.
A big problem with a simpler gasifier design like the open top stratified downdraft gasifier (FEMA) is that the temperatures
do not get hot enough to crack the tars. The FEMA style gasifiers will only run in the range of 600-800 Deg Celsius (1112-1472
Deg Fahrenheit) which is well below the temperatures needed to handle cracking the tar into a useful fuel along with a cleaner gas.
Another issue is cleaning the system along with the disposal of tar. The best way to have a clean gas along with a clean system is
to either cut way down or eliminate the production of tars period. The Imbert is a bit more involved to build but the trade-off is worth it.
Even with the temperatures in the correct range your air velocity must not be too fast because the gas needs enough time passing
through the ember bed to allow the tars to be cracked. In other words, if the air flow is too fast you will have tar issues. This is why it's
important that the gasifier build is basically tuned to match or to fit the engines needs that it will be feeding and this also applies to
the fuel (wood chunks etc) too. Everything comes into play and this is why you hear people with first hand experience discuss the
importance of their restriction zone, reduction zone along with their nozzles and the reaction zone diameter and depth etc.
In the end it really comes down to the end user and that they have a good understanding of the mechanics of their gasifier along
with the basic theory of operation including using the correct fuels they will be trying to convert over into syngas. You don't have to
be an engineer or a scientist but you do have to have a "feel" for your setup and this is why you can see someone build a gasifier
out of rusty junk that runs clean and to perfection and then have someone build a gasifier with the "best" of materials money can
buy and even have it correctly designed for their engine size and still have a poor gas with a disastrous outcome to their engine.
In a perfect world your gasifier will crack 100% of the tars 100% of the time but the reality is things can change or happen during a
run that could make the tar vapor levels vary to undesirable levels such as fuel inconsistencies or even operator error. This is where
a good filter system comes into play... It's your "piece of mind" insurance. "You never solve a tar problem. You can only manage it."
That quote came from Jim Mason, Co-Founder and CEO of ALL Power Labs from one of their youtube tutorial videos.
Basic explanation of temperatures and how it effects the biomass (wood fuel)
Basic explanation of tar issues and management.
Rocket stove videos and links
Useful misc electronic projects