Dad larry and I have been working on a single nozzle gasifier in the center pointed out a lot of people saw it at argos. There is a thread on it called Billy Jakob and larry new lightweight gasifier.
Try the library, there are some awesome papers/books available as per example:
A experianced woodgaser will know if a gasifier is making tar or not just by looking, smelling the gas. Colour of the flame… but for a newbie it can be trickyer. If you do test the gas with a white paper, do that on low gas flow. Gasifiers usualy make tar at idle if they do!