Here is a URL for an article in the Japanese Wikipedia - hopefully you can see photo images:
The “Mokutan”(Wood coal) automobile ( mostly bus) was used in the war and post war era for the lack of gasoline supply. The article described the engine power as much lower than that of gasoline fuel. So, the passenger had to get off and help push the bus going uphill. The gas, mostly CO and a bit of H2, leaked out and caused CO poisoning to some passengers. I thought this “technology” may come back last year, after March 11 earthquake, tsunami, and nuclear melt down disaster, when the gasoline supply logistics was much affected. In Tokyo area, it took two weeks to return to normal.