Small
two-stroke engines, such as in
motorcycles and
lawnmowers, have
total loss lubrication. Such engines use
crankcase compression to feed the
fuel/air mixture through the crankcase. This precludes the use of both wet sump and dry sump systems, as excess oil here would contaminate the mixture, leading to excess oil being burned in the engine and so excessive
hydrocarbon emissions. These small engines run on specifically prepared fuel, a mixture of gasoline and
two-stroke oil in a ratio recommended by the manufacturer. In some engines this mixture may also be independently pre-injected into the engine cylinders and bearings by a pump.
Four-stroke engines and large (non-petrol) two-stroke engines used in locomotives and
ships may have either wet or dry sumps. Large two-stroke engines do not use crankcase compression; instead they use a
mechanical blower or a
turbocharger to aspirate air. == Types of wet sump ==