Power overlap in a cylinder means the two or many cylinders are reciprocating for one power stroke. More cylinder number means a smoother operation. In this article, I will discuss the power overlap in automobile engines.
It has already been started that multiple-cylinder engines are smoother in operation than single-cylinder engines. The more cylinder in an engine, the more continuous will be the flow of power and smoother will be its operation.
|Power flow in a four-cylinder engine
In a four-cylinder engine, each piston in turn pushes the crankshaft through 180 degrees of rotation during its Power Stroke. Each power stroke begins every 80 degrees exactly as the previous one ends. There is no overlap between the power strokes in a four-cylinder engine, as shown in the figure.
|Power flow in a six-cylinder engine.
In a single-cylinder engine, each power stroke begins every 120 degrees of crankshaft rotation and is continuous for 180 degrees(half a rotation). This produces a 60 degrees overlap between power strokes that follow each other in the firing order of the engine, as shown in fig. As one piston completes the last 60 degrees of its power strokes, the next piston is operating on the first 60 degrees of its power stroke.