WATCH IN HD This Reid oil field engine was being demonstrated at the Arizona Early Day Gas Engine & Tractor Association Show in Apache Junction, Arizona on Saturday March 14th, 2015. This engine was very loud, so I may have misheard or just misunderstood what was said to me by one of the guys operating it. He explained that the cylinder on the outside of the flywheel is a "charging cylinder", and he said that these engines ran on gases or fumes from the oil wells, but those gases need to be compressed in order to burn more effectively, and that was the purpose of the charging cylinder. For this demo, it was burning propane.