Quote:
Originally Posted by SYN_Bliss
So when you are maintaining 5000 RPMs with 50% throttle and jump the load up significantly to bog the engine down to 4500RPM's (500 revolutions per minute) all while maintaining the same throttle position, you have effectively increased boost because the engine has slowed down it's air intake significantly while the supercharger has only done this marginally.
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Ok, i'm starting to get what you mean!
Found my notes on propulsion class, and i feel extremely embarassed for the fact that
i completely forgot that in an aspirated engine, intake pressure drops with RPM because of the increased friction losses in the intake (higher RPM, higher air speed in the intake, more friction which cause a dissipation of energy and ultimately a decrease in static pressure when the air is brought to rest). Or if you want to think it more simply, more suction, less pressure.
Now, in a supercharged engine you have to take another effect into consideration, which is the fact that the compression ratio (p after sc/ p before sc) the sc is able to deliver is dependant on its RPM, which in turn is directly linked to engine RPM.
So generally the boost the sc is able to deliver increases with RPM, but also the friction losses increases with RPM, so it's all a matter of what is the most important effect. pressure loss in the intake because of friction should be proportional to RPM^2 if i'm not mistaken, hence very important at high RPM. The boost the supercharger is able to deliver as a function of its RPM will depend on the specific type i think, i will try to find some data.
In the end at higher RPM, if you apply more load and the RPM drop, probably the reduction of losses caused by slower air flow, can compensate for the modest reduction of boost by the supercharger; and the pressure slightly rises.
I think however that at slower RPM it should be the other way around (RPM goes up, pressure rises, because the losses are smaller and the predominant effect is the supercharger), can anyone test it in game?