What does the stroke refer to in a reciprocating engine?

In a reciprocating engine, the stroke refers specifically to the distance the piston travels between top dead center (TDC) and bottom dead center (BDC). This movement is crucial because it determines the volume of the cylinder and, consequently, the engine's displacement. When the piston moves down from TDC to BDC, it creates a vacuum that allows the air-fuel mixture to enter the cylinder during the intake phase. Conversely, when the piston moves back up, it compresses the mixture, which is essential for effective combustion.

Understanding stroke is vital for grasping the overall design and performance of an engine, as it impacts factors such as torque and power output. The dimensions of stroke, along with the bore (the diameter of the cylinder), contribute significantly to an engine's configuration, influencing its efficiency and capability.

Other choices, such as the speed of piston movement or the volume of the fuel tank, describe different aspects of engine operation but do not accurately define what stroke means in the context of a reciprocating engine. Similarly, the duration of the power cycle pertains to the timing of the engine's operations rather than the physical movement of the piston.