Two Stroke Diesel Engines
Unlike their 4-stroke counterparts, which may be naturally aspirated, or turbocharged, 2- stroke diesels must have a method to force air into the cylinder(s) to run, period. Most do this via a roots style supercharger, which does not really provide any 'boost,' or a combination supercharger/turbocharger.
Probably the most famous and well known engine brand that used 2-stroke diesels with superchargers and also super/turbo combos, is none other than Detroit Diesel. You do not see very many two stroke diesels on the road anymore, and even engines in stationary power situations are beginning to disappear. The reason is emissions. Like 2-stroke gasoline engines, 2-stroke diesels also pollute much worse than their 4 stroke counterparts. However, nearly all 2-stroke diesels have oil reserviours just like 4 stroke engines.
On the intake stroke, the supercharger is spinning, and forcing air into the cylinder, as the cylinder reaches the bottom of it's bore, the intake valve closes, and then the piston comes up to the top, where fuel is then injected, and the piston is forced down. That is the 2-strokes. The neat thing about these engines, and also why they pollute so much, is the supercharger also functions as an exhaust scavenging device, in that it pushes the exhaust out as well as brings in fresh air, during the last few moments before the piston comes up for another compression stroke.
Most train locomotives, most notably the GP38-2 use 2-stroke engines. Most large container ships also use 2-stroke engines running at very slow speeds, sometimes full throttle is 100 rpm!
Another charecteristic of these engines are their sound. If you've ever heard a Detroit coming down the road, you KNOW it. at 600 rpm, the engine sounds like it's turning 1200. and at 3,000 rpm, it sounds like it's turning at 6,000 rpm.