Dear Tom, and Greg, Thankyou for clarifying that it is the ~50% nitrogen content in producer gas that gives it a high octane number, and the simple rule of thumb that links the octane number and the maximum compression ratio.
Having read IISc literature about running converted diesel engines on wood gas at 17:1 CR, this inspired me to continue with the conversion project of the Lister type engine at All Power Labs, so that it could be run at it's stock compression ratio of 17:1 on wood gas. The conversion involved keeping the original diesel injector and fitting a spark plug through a side port, which gave direct access to the spherical combustion chamber. The rationale behind this conversion, was to allow the diesel engine to be started and run as a diesel, providing immediate thermal, pneumatic and mechanical energy, which could be used to start up the downdraft gasifier. When the gasifier was producing good, engine grade gas, the diesel fuel could be shut off, the woodgas introduced to the air intake through a mixing valve and the engine would continue to run in spark ignition mode on woodgas. This approach seems to make absolute economic sense, where the engine would only be started and run for 5 minutes or so on diesel (or biodiesel, WVO) and for the remainder of the daily duty would be run on wood gas. The small team working on the Lister conversion project at the April weekend workshop, found that the 6hp engine and alternator was still capable of generating 2.5 kWe electrical power in wood gas mode at 600 rpm - hardly any power derating from what it could achieve at 600 rpm in diesel mode. The Lister type engine is a simple durable engine, still produced, sold and in common usage around the developing world. It's basic construction lends itself to this simple spark ignition conversion so that it can benefit from the much reduced running costs offered by woodgas operation. regards Ken Boak
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