They are the powersource of choice for heavy trucks, boats, generators and equipment. Probably due to gasoline prices and lower emmisions standards. Diesel engines have become a lot more high tech in the past ten years. Most manufacturers are switching over to electronic fuel management. Diesel engines differ from gas engines in a couple of ways.
Diesel fuel is less refined than gas.
This means that diesel will explode if compressed enough. It does not require a spark. Diesels must be fuel injected. They only suck in as much air as they need. To get more power from a diesel usually requires a turbo to push in more air.