Oil in the combustion chamber. Could be a sign of worn out piston rings.
Burning oil
Could be a diesel? If not then replace your oxygen sensor on your exhaust. A bad oxygen sensor causes the exhaust smoke to be dark in color.
if it is white smoke engine need to rebuilt.
White smoke means head gasket, cracked head or equivelant.
If you are talking about "smoke" that fills the interior it can be one of two things. One, a leaking heater core. Two...if your engine smokes from oil dripping on the exhaust, etc you could have a crack in the housing for the A/C and it's pulling in the smoke and gasses from the engine compartment.
Piston rings or Rich oil .
Head gasket
It can be a number of things, but the most common problem is worn valve guides.
Black smoke means you're burning fuel, blue smoke, you're burning oil, white smoke, you're burning coolant.
grey exhaust smoke is caused by your engine burning oil during the combustion process. this could be caused by a piston ring that doesnt properly seal, or another leak in your engine.
bad head gaskets, or a crack in the block or head.
If you mean the smoke it's usually related to the quality of petrol