Oil is mixed into the fuel and lubricates the engine as it passes through the crank case. It's called "pre-mixing" the oil.
or
The oil can be injected into the engine downstream of the carburettor. This is called "oil injection".
Most 2 strokes of the last few decades have been oil injected as opposed to pre-mixed.
Both systems work the same, pre-mix is generally thought to be more reliable as the injection components can fail and cause engine failure due to no lubrication.
Actually, the lubrication systems utilized are a separate issue from engine firing frequency.
Low specific power output 4T engines running at low stress levels can get by with rudimentary 'splash' lube,
such as was common in the early years of automotive use..
Yet large 2T CI engines such as the 'Detroit Diesel' - are uni-flow externally scavenged,
& use a typical plain-bearing crankshaft, pressure fed from a sump, akin to most current 4Ts.
On the other hand, a very high specific output 2T racing mill which utilizes rolling element bearings,
can operate with its lubricant premixed with its fuel, at a ratio which balances power gain via sealing,
VS potential combustion issues from fuel 'contamination'..
Current production DFI 2T's such as used in marine & snowcraft typically have a low ( ~100/1) ratio
of high-spec lubricant, pump-injected at metered rates to specific points within the engine, to offer
best function, for lowest feasible hydrocarbon burning /emissions concern.
Note that in current F1 racing, it has recently been asserted that lubricant is being burnt at a much higher
ratio (~5 ltr oil - to 100 ltr fuel), as a defacto performance fuel additive, but then, in F1, emissions are not an issue..
"Well, we knocked the bastard off!"
Ed Hilary on being 1st to top Mt Everest,
(& 1st to do a surface traverse across Antarctica,
in good Kiwi style - riding a Massey Ferguson farm
tractor - with a few extemporised mod's to hack the task).
