U.K. engine builder Paxman Diesels has developed a new supercharged engine in a bid for submarine orders. Derived from Paxman's Valenta engine line, the new model relies on a mechanical supercharger rather than a turbocharger. The company hopes that this engine will operate satisfactorily when a submarine is running with only the snorkel above the surface, when there can be a severe restriction on incoming air and outgoing exhaust gases.
Paxman took full advantage of existing centrifugal compressor technology by using the supercharger rotor and involute from the Napier NA250 turbocharger. The result, according to the company, is an engine with an output similar to the turbocharged engine less the power required to drive the supercharger, but with much greater tolerance of changing inlet depression and exhaust back pressures.
To maintain commonality with the standard Valenta engine, the supercharger drive has been added to the free end of the engine. The drive increases the crankshaft's 1,350 rpm to 24,000 in two stages. Primary speed increase is by epicyclic gears that drive into a fluid coupling before the secondary spur gear stage.
The first engine is undergoing comprehensive testing and has been run at outputs up to 1,518 kW at 1,350 rpm. A second unit is undergoing acceptance tests under submarine conditions at a Ministry of Defence facility.