Diesels can be started with a compression release (forcing exhaust values to stay open ) lever. Manually spin the flywheel, then close the compression release. In theory, this engine can operate with just fuel, oil and air for 1000's of trouble free hours.

But, diesel fuel in small aircraft does not work well because the fuel takes much more oxygen than can be compressed safely.

The ratio of oxygen does not change, however, diesels have a higher compression ratio than normal gasoline or av gas engines. The weight that is involved with higher compression is prohibitive in most cases.