CHECK OUT WHY DO WE MIX OIL WITH FUEL IN 2 STROKE ENGINES BUT NOT IN 4 STROKE ENGINE !!

In a 4 stroke engine, we have a dedicated system for lubrication. We have lubricating ports which supply the lubricating oil from the sump so that all the parts are thoroughly cooled. 

But most of the two stroke engines can't use such dedicated lubrication systems because in two stroke engines the inlet and outlet (exhaust) bores are on the sidewalls of the cylinder.

So if a splash type or pump based lubrication systems as used in four stroke engines would be used in two stroke engines then the lubricating oil may enter these bores and block them. 

Moreover, unlike four stroke engines in which there is an oil sump inside the crank-case, the crank-case in two stroke engines is used for pumping and circulating air-fuel mixture to the combustion chamber (thus making it unusable for storing lubricating oil ). So, instead of using a dedicated lubrication system as in four stroke engines, most of the two stroke engines use a lubricant oil mixed with fuel so that the wear of piston and cylinder liner can be minimised. So while fueling, we mix gasoline with an oil to be distributed throughout the engine for lubrication. The two-stroke oil is ultimately burned along with the fuel. But this can contribute to more smoke and distinctive odor.