What creates momentum in a four-stroke petrol engine?

Momentum in a four-stroke petrol engine is primarily created by the flywheel. The flywheel serves the crucial role of maintaining rotational inertia during the engine's operation. As the engine cycles through its four strokes—intake, compression, power, and exhaust—it generates power in a cyclical manner. However, the power strokes occur intermittently, meaning that there are moments when no power is produced.

The flywheel absorbs the energy generated during the power stroke and releases it during the other strokes, allowing for a smoother and more continuous delivery of power. This helps to stabilize the engine's operation and keeps the crankshaft turning, effectively maintaining momentum throughout the engine cycle. This is essential for smooth vehicle operation, as it ensures that the engine's output remains consistent despite the cyclic nature of combustion.

While other components like the spark plug, exhaust manifold, and fuel injector are critical to engine operation, they do not contribute to momentum in the same way. The spark plug ignites the air-fuel mixture, the fuel injector delivers the fuel, and the exhaust manifold expels exhaust gases, but none of these elements contribute to the flywheel's ability to maintain rotational motion and stability in the engine's performance.