As a two-stroke Diesel engine is incapable of this natural aspiration, some method of charging the cylinders with scavenging air must be integrated into the engine design. This is usually achieved with a positive displacement blower driven by the crankshaft. The blower does not act as a supercharger in this application, as it is sized to produce a volume of air flow that is in direct proportion to engine's requirement for combustion, at a given power and speed. By the Society of Automotive Engineer's definition, a mechanically scavenged two-stroke diesel engine is considered to be naturally aspirated.