The stroke is a crucial parameter that determines the engine's displacement, which in turn affects the engine's power and torque output. A longer stroke engine typically has a larger displacement and can produce more torque compared to a shorter stroke engine of the same bore (cylinder diameter).
The stroke is also closely related to the engine's compression ratio, which is the ratio of the cylinder's volume at BDC to the cylinder's volume at TDC. A longer stroke engine generally has a higher compression ratio compared to a shorter stroke engine, which can improve the engine's efficiency and fuel economy.
Here's a simplified explanation of what happens during a stroke of an engine:
Intake Stroke:
1. The piston moves down from TDC towards BDC, creating a vacuum in the cylinder.
2. The intake valve opens, allowing a mixture of fuel and air to be drawn into the cylinder from the intake manifold.
3. The piston reaches BDC, and the intake valve closes.
Compression Stroke:
1. The piston moves back up towards TDC, compressing the air-fuel mixture in the cylinder.
2. The compression ratio increases as the piston gets closer to TDC, increasing the pressure and temperature of the mixture.
3. The piston reaches TDC, and both the intake and exhaust valves are closed.
Power Stroke:
1. At TDC, the spark plug ignites the compressed mixture, causing a controlled explosion.
2. The expanding gases generate immense pressure, driving the piston down towards BDC with great force.
3. The piston reaches BDC, generating maximum power.
Exhaust Stroke:
1. As the piston reaches BDC, the exhaust valve opens, allowing the combustion gases to be pushed out of the cylinder.
2. The piston moves up from BDC towards TDC, expelling the exhaust gases through the open exhaust valve.
3. The piston reaches TDC, and the exhaust valve closes, completing one full cycle of the engine.
The stroke length, along with the bore diameter, determines the engine's total displacement, which is measured in cubic centimeters (cc) or liters (L). A larger displacement engine typically produces more power and torque but may also consume more fuel.
It's worth noting that modern engines can have different stroke lengths for different cylinders, leading to variations in engine design and performance characteristics.
