What is Power Overlap? Cylinder-Wise Power Overlap.

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. 

Power Overlap-

Power Overlap

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. 

Four-cylinder engine-

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. 

Six-cylinder engine-

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. 

Eight-cylinder engine-  

In an eight-cylinder engine, the power stroke begins every 0 degrees of crankshaft rotation(720/8=90 degrees). This produces a power overlap of 90 degrees(180-90=90 degrees). Similarly, a twelve-cylinder engine would have a power overlap of 120 degrees, and a sixteen-cylinder engine an overlap of 135 degrees. Obviously, the more cylinders in an engine the more the power overlap and the less the resulting vibration produced by the engine.