I’ve never actually built a gasifier, but have been interested in the topic lately and done a lot of research. There are two comprehensive resources, about 150 pages each, that give a good history of the topic, as well as the scientific background and many empirical models about how to choose critical dimensions and how to design the gas cleaning systems. Great resources, you could probably build a whole gasification system based on the information in these two links alone. A bit old (1980s), but still relevant. Not much in the way of electronic controls design, but I think there are several members here that can help with that if needed.