Abstract: A diesel engine comprises a plurality of cylinders (2), an inlet duct (4), an exhaust duct (6), a turbocharger (8, 10) and a supercharger (14), the turbocharger being of variable output type and including a turbine (8) in the exhaust duct (6) and a supercharger (14) being of variable output type and situated in the inlet duct (4) between the compressor wheel (10) and the cylinders and being electrically driven or mechanically driven by the engine. The engine also includes a first sensor (25) arranged to produce a signal indicative of the speed of the engine, a second sensor (27) arranged to produce a signal indicative of the load to which the engine is subjected and a third sensor (26) arranged to produce a signal indicative of the pressure in the inlet duct (4) downstream of the supercharger (14). The sensors (25, 27, 26) are connected to a controller (29) which is also connected to the turbocharger and the supercharger and is arranged to vary their output independently.