diesel engine, type of internal-combustion engine invented by
the German engineer Rudolf Diesel and patented by him in 1892.
Although his engine was designed to use coal dust as fuel, the
diesel engine now burns fuel oil. The diesel engine does not
require a large water supply or a long warming-up period and is
highly efficient in converting heat energy into work. Diesels
are widely used in both stationary and mobile installations
where the power required is between that furnished by the
gasoline engine and that of the steam turbine and where the
relatively high initial cost can be written off over a long
period. For example, diesels having capacities of 100 to 5,000
hp are employed on industrial and municipal electric generators
and on continuously operating pumps (e.g., on oil pipelines).
Moreover, they occupy relatively little space compared with
steam units, since no boiler is needed—a factor of importance
aboard ships. The diesel engine differs from the gasoline engine
in that the ignition of fuel is cau