[Gasification] Engine knock

[doug.williams]

Hi Jim,

You need clarification:

> nearly every diesel I know of is over 16:1.  especially if they are
> non turbo, they are usually going to be 18:1 or more.

This is the lean burn principle incorporated into modern diesel engines, to 
squeeze more power out of lighter engines, or to increase the output from 
smaller engines, which if were naturally aspirated would be operating at 
16-17:1.  The other factor to consider, is that these smaller high 
compression (22:1) engines all get their extra power at higher RPM 
generating power (3,000 RPM), and this piston speed exceeds the flame speed 
of producer gas.

> but i of course could be very wrong.  I've yet to dual fuel
> a diesel, but everyone here seems to not have problems.

I am not aware of any other commercial expertise on this list that is duel 
fuelling diesel engines, and if they are, then they will all be operating at 
compression ratios of under 17:1.


> listers, which are relatively low compression, are over 16:1.  i think
> they are 18:1, and indirect injection/precombustion usually.

Listers are not likely to be 18:1, as all the Listers we worked with were 
16:1. I am not aware of any Listers with pre-combustion chambers, but some 
of their older engines may have such features. I have a number of their 
engine manuals, and will see if I can find reference to them.

> so can you give us some of your experience with woodgas detonation in
> diesels in dual fuel mode?  especially in indirect
> injection/precombustion chamber engines.

No, because we could not gasify engines over 16-17:1 compression ratio, 
because of the detonation problems, unless the gas/air mixture was so weak, 
it was a waste of time doing it.  If you have not followed previous 
discussions of our work on this forum Jim, Fluidyne worked very closely with 
Listers here in New Zealand, for power generation in the Pacific Islands, 
and were the only company to receive their approval to maintain engine 
warranties.

 > all the diesel engines i
> have lined up to wood gas dual fuel are of this type.  my heart might
> break if i learn they are no go.

Better a broken heart than  going bankrupt.

> i'm confused by this doug.  as you know, thermodynamic efficiency has
> a direct relationship to compression ratio.  we gain efficiency the
> higher we can compress before combustion.  this was the main "a ha"
> that led away from early atmospheric pressure internal combustion
> engines.  mechanical friction becomes a smaller fraction of total
> cycle energy the higher compression goes.  and more importantly, the
> delta T we can mine goes higher the higher pressure under which the
> original combustion happens.

You miss the difference Jim.  Diesel is injected into the cylinder pressure, 
not compressed like producer gas to it's spontaneous ignition temperature , 
which coincides with about 16:1. purpose built gas engines are all around 
the 12.5:1 ratio, so I expect the engine designers have checked out all your 
theories.   I did not set these rules, they are straight out limitations set 
by the gas chemistry, and the forces applied to them. You may wish to 
disregard what I say, but nothing can change my comments, which are based on 
many thousands of engine hours observing producer gas fuelled engines.

> if we had a fuel that could run at 100:1, and a motor that would stay
> together, that would be a very high efficiency motor.

There is a big gap to apply theoretical calculations to the manufacture of 
producer gas, and,it's application in engines. The advise I give to every 
one, is to first learn to make gas correctly, then use a standard spark 
ignition engine to create your motive power. Learn the limitations before 
you try to design gasification systems to overcome the limitations, and if 
this sounds to easy, then take note of how much money has been wasted 
chasing rainbows! Gas is easy to make for a demo, but try relying on you 
system every day for the rest of your life, as some people will need to do 
very soon.

Doug Williams,
Fluidyne Gasification.