[Gasification] OT - Six Stroke Engine

[doug.williams]

Hi Ken,


I can offer the following comments:

> What are your thoughts about the optimum rpm range for an engine burning
> producer gas?

When you are locked into an existing engine application, you have no options 
but to deliver the gas in a quality that can match the RPM. Usually this 
means 1,500 or 1,800, but certainly excludes engines at 3,000 RPM.  When it 
is possible to belt drive with pulley speed variation, I try for 1,100-1,200 
at the engine. This comes from the experience gained in a mobile situation, 
where the engine would literally chug away working hard, if you have no need 
for speed !!

> Is it a case of matching the piston speed to the flame speed?

You could say yes, but this needs qualification. The H2 content is the 
factor that affects flame speed, followed by the moisture content, that can 
escape condensation in the cooling phase. In this situation, how the engine 
behaves under load, is a variable that can only be sorted before the engine, 
and so will influence the optimum RPM.

> Would 300rpm to 600rpm  be better for extracting more expansive power from
> the producer gas, than a higher speed engine say running at 1500rpm.

The experience so far certainly shows this to be worth investigating, and in 
recent discussions with really big engine suppliers, they are talking about 
72 RPM as a normal engine speed. Of course these are really big power 
generation engines, and there may be a limit to small engines, and their 
lowest practical RPM.

> Are you suggesting that in a high speed engine, the producer gas charge is
> still  burning at the time the exhaust valve opens.

This was a common problem with many projects reported during the  70's and 
certainly into the 80's, as I was proudly told that it was the practice to 
allow the steam to entrain with the gas, because it enhanced combustion in 
Europe at that time. It was at this point in time, that I stuck the stick in 
the sand and explained why they were suffering valve seat recession, and CO 
emission problems, particularly with dual fuel engines. They were also 
confusing the issue of gasoline and steam, but nobody pointed that out to 
them.

You need to decide which side of the stick you want to aim for, and that 
will determine the success or limiting factor of your endeavours. I should 
also mention that with the advent of greatly improved metal quality of the 
valve seat inserts, the problem can be  hidden unless you are monitoring the 
exhaust emissions.
Hope this clarifies my previous statement.
Doug Williams,
Fluidyne Gasification.