In this woodgas classic, Dr. Tom Reed covers ever aspect of gasification, including a large section on the history from WWII, and the modern (1980s) research on the subject. This single work contains more than enough information to understand gasification, even build a gasifier. Components like cooling and filtration are covered in depth.
Vehicle gasification has a rich history in wartime Europe. Gasification was not optional; they had no choice but to develop workable gasifiers and strict standards. Gengas was written shortly after WWII to document the old gasifier systems before they were forgotten. The peak of development came shortly after the war ended; by the next year, gasifiers were discarded as quickly as the fuel trucks could come. There are advanced ideas in this book which have largely been forgotten or are slowly being rediscovered today.
This paper from the Food and Agriculture Organization details how to operate a gasifier. Several useful insights found in here. Great overview if you want to see what it takes to run a vehicle or generator on wood.
Another excellent overview of gasification, which goes into detail on several systems. This was written "as a reference manual and guide for policymakers, planners, investors and entrepeneurs", but it's also useful to regular folks trying to understand gasification.