How is the length of the stroke in an engine determined?

The length of the stroke in a reciprocating engine is directly related to the crank throw, which is the distance from the center of the crankshaft to the center of the crank pin. The stroke length is essentially the total distance the piston travels from the top dead center to the bottom dead center in the cylinder, which corresponds to the complete rotation of the crankshaft connected to the piston through the connecting rod.

When the crankshaft completes a half-rotation, the piston moves from one extreme of its stroke to the other. Therefore, the stroke length is twice the crank throw because the crank throw only measures the distance from the center of the crank to its furthest point, covering only half of the motion cycle of the piston.

This relationship between the crank throw and the stroke length is fundamental in engine design, as it affects both the displacement and the operating characteristics of the engine. The other options do not accurately describe the relationship governing stroke length, focusing instead on factors that do not correspond directly to how stroke length is determined in the context of engine mechanics.