Quote:
Originally Posted by Nisgeis
Diesels have a direct relation between the amount of diesel injected and the power produced, right up until the smoke goes completely black and starts ejecting unburnt fuel. That comes at a cost of fuel efficiency of course and if you run your engine at too high an RPM it can be damaged with joints parting / bearings overheating or melting etcetera.
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Since I doubt they could have messed with superchargers or turbocharges (I don't know if U-Boats had them), the only other way is to advance the combustion - normally the ideal combustion midpoint (per Vibe) is 15-20° after the
Top Dead Center => for older Diesel engines with pre-combustion chamber. If you delay the combustion, and move the mid point (T) further back - you get what
Nisgeis said. By moving it forward, or advancing it, pressure and temperature will rise in the cylinder, and with that the engine power as well.
By manipulating the combustion midpoint (T) you can either achieve max power, max economy or min. achievable emissions (engine and fuel dependant). I am guessing that they have set it for max economical efficiency (furthest range with min. fuel).
What kind of engines were U-boats using? I assume 2 stroke Diesels, judging by Diesel locomotives. If so, they had to be lubricated as well by adding oil to the fuel before it is injected into the cylinders.
So I am rather incline to believe that they could have squeezed out a few extra RPM by either manipulating with the fuel or oil intake system...
But that is my theoretical guess.