I will have to go back 45 years to my initial training ...... the four stroke cycle, Suck, Squeeze, Bang, Blow. The cylinder fires every second revolution, so has and induction stroke, piston going down, inlet valve closes, piston rises, injection of fuel at top of stroke, piston goes down with the firing pressure and so on.
Now to use a two stroke motorcycle engine for an example, that uses the lower crankcase area as a primary compression area to compress the intake before transferring it to the upper cylinder for further compression and firing. With a large diesel such as a Foden or GM Detroit, this is impractical so the supercharger or blower is there solely to compress the intake air, when this is blown in through the lower cylinder ports it does push the waste gases out, but without this blower the engine will never run. Another misconception is people think they run faster, but as the two stroke fires twice as often, this is where they are mislead. To increase power, it can have a turbo charger fitted to the exhaust manifold.
Hope that is clear?
regards Richard