Ideally, where should peak cylinder pressure occur during the power stroke?

The peak cylinder pressure during the power stroke of an engine ideally occurs 10 to 20 degrees After Top Dead Center (ATDC). This timing allows for optimal power generation as the combustion process reaches its maximum efficiency.

When the fuel-air mixture ignites, the resulting pressure and temperature increase rapidly, causing the piston to begin its downward stroke. Having the peak pressure occur slightly after TDC (instead of at TDC) allows the piston to take advantage of the force from the expanding gases effectively. If peak pressure were to coincide exactly with TDC, there is a risk that the engine would not harness the full force of combustion, potentially leading to increased stress on engine components and potential knock, which can be detrimental long term.

Positioning peak cylinder pressure at 10 to 20 degrees ATDC ensures that the piston is already in motion downward when the pressure is at its highest, optimizing the torque and power produced, and maximizing engine performance. This relationship indicates proper combustion timing, which is crucial for efficiency and is also a key consideration in engine design and tuning.