The oil engine was the lower cost variant of the compression ignition engine. With compression ignition, Dr. Rudolph Diesel had a great idea but at around the turn of the century, the technology was not perfected. “True” diesels were large, expensive and had complex injection systems. They also required a license to manufacture them under the Diesel patent. The door was open, however, to other methods that skirted around the Diesel patent and delivered some of the benefits of a diesel. They were called oil engines.
Here is the Muncie hot bulb combustion chamber and it shows the way combustion works in a crankcasescavenged oil engine. This is from an old manual to which we added the colors of blue for intake and red for combustion and exhaust. In case you hadn’t figured it out, the chamber to the left is the hot bulb that gets heated for startup.
TRI-STATE GAS ENGINE