Can you see the problem with this form of gasification?
This form of gasification uses a retort, which is a closed container with a vent and external source of heat. And yes, the gas hob, the retort is sitting upon, is putting as much energy in (if not more) than is being produced in the form of wood gas.
A retort is an interesting way to get into gasification and doesn't require much work to get you started. However, the gas produced will have a lot of tar in it and will be of no use for running engines with. It would be a waste of time and effort scrubbing the gas because of the amount of tar in it.
A MIDGE stove on the other hand consumes most of its own tar. Better still, a downdraught gasifier heats the wood above it so that tars drip down into the combustion area and are converted to wood gas.
We recommend that you build a MIDGE stove first and then move on to a downdraught gasifier. A retort is only suitable for making charcoal and is best fired with a renewable energy source such as a wood fire.