Adding a spark plug (and the timing circuitry) is definitely possible. You can often find diesel engine blocks that have been converted to propane or natural g

Adding a spark plug (and the timing circuitry) is definitely possible. You can often find diesel engine blocks that have been converted to propane or natural gas that are essentially this arrangement. You can also run a diesel engine on duel fuel, where the (bio)diesel injection provides the flame front to ignite the woodgas and air mixture. In this case no modification is necessary. Only the bare minimum, equivalent to just idling on diesel is necessary. This is a robust system where the governor for the diesel engine can compensate for lower woodgas fuel content when need be.