Interesting topic. A few years ago I was operating a field with steadily increasing CO2. I was concerned that as the BTU content of the fuel gas decreased it would be progressively harder to pull full load. I found out that this was a non-issue because the air/fuel ratio could be adjusted to provide full power down to very low BTU ratings (the example I got from Waukesha was their machines could run a full hp on land fill gas that was over 50% CO2 and other inerts). It was just a matter of getting the right jets an/or changing out the carb for a "digester carb". My field only got to 25%, but we were able to load the machines to the hp as derated for elevation (but no deration for fuel quality).
David
David