[Gasification] Engine knock

[Fredrik Ek]

The Thechnical researh centre of Finland VTT made tests with diesel 
ignition of woodgas in Valmet tractors in the 80s. VTT used a compression 
ratio of 1:17 in these tractors but recommended 1:16 if I remember things 
correctly.

At least two Finnish woodgas car enthusiasts have converted diesel engines 
to spark ignition. The highest used compression ratio used here is 1:15 as 
knocking has been a problem with higher ratio. 1:15 is on the border of 
what reliably works, although arrangements for adjusting ignition timing 
manually are used. The composition of the woodgas is according to practical 
Finnish experience important for when knocking starts to be a problem. Good 
hydrogen rich gas more easily causes knocking than poor gas.

A compression ratio of 1:25 sounds very high. Can someone come up with more 
information about this?

Fredrik Ek

Tsiteerin Harmon Seaver <hseaver at gmail.com>:

> Fredrik Ek wrote:
> 
> (snip)
>  
> > 
> > If you use diesel injection for igniting the mixture, you can use a 
> > compression ratio of 1:17. With spark plugs you have to lower the 
> > compression ratio to about 1:13 in order to avoid knocking.
> > 
> 
>     That's not what many others have reported. There should be no need
> to reduce the CR below 1:17 when converting to spark ignition -- the
> octane of the producer gas stays the same regardless. And some people on
> this list reported running 1:25 okay. You could always adjust the timing
> a bit to compensate if it was a problem, with either injection or spark.
> 
> -- 
> Harmon Seaver
> 
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