[Gasification] OT - Six Stroke Engine

[doug.williams]

Hi Tom R, and Colleagues

Tom, you raise an interesting observation:

>I know that there are statements that  the flame speed of producer gas
>is low compared to gasoline, and that it requires a slower turning engine.

You will find this confirmed with all the necessary formulas, in the FAO 
Publication Wood Gas as an Engine Fuel.
http://www.fao.org/DOCREP/T0512E/T0512e00.htm
The information in this book was edited by Prof. Bjorn Kjellstrom, the 
person who first drew attention to gasification back in the 70's.  It 
remains the only source of information that I refer every one, as it 
contains the core information that most people need to understand producer 
gas for engines.

>On the other hand, the high hydrogen content of producer gas gives it a
>wide combustion range and fast burning properties.

I would totally agree, but it has to be remembered that on average, producer 
gas has only 40% of it's volume as combustible gas, and only about 50% of 
that, is H2, which has less effect on the behaviour of the gas as the speed 
increases over about 2,500RPM.

> Motorcycles are
>regularly converted to producer gas and they have high RPM.

The fact that high RPM can be achieved, is only relevant in how it transfers 
to power at the end use. Last month, our guys in Australia took their Tasman 
Class out for a drive in their pickup (utility), and found that they had to 
drive along at 50 kms/hr in third gear (of four), with the engine over 3,000 
RPM at times. Engine exhaust temperature was 750C, gas cooling started at 
550C. It drove like a pig, to quote them!  The same engine on their 
generator, runs at 1,500RPM, and the gas cooling starts at 360C. They too 
posed the question of why stick to 2,500RPM as the limiting factor.

Translated into plain practical terms, once the engine speed exceeds the 
flame speed, the engine cannot respond to load change demand, critical for 
most rural power generation, not so, for those who have lesser standards of 
need, and don't like to walk. (:-)

<So I wouldn't worry about it.

I worry about every possible statement since an idiot of my former 
acquaintance, presented the H2 content out of context to less informed 
people.

>The low speed reports may apply to producer gas from coal which have
>very low hydrogen content.

More the reason to ensure that historical information has a line drawn under 
it, and some serious editing done to all new publications to weed out cross 
technology assumptions.

>Do it.

Totally agree, but we must start from an informed base for the application.
Regards,
Doug Williams.