When should ignition ideally occur in relation to the piston’s position?

Ignition timing is critical for the efficient operation of an internal combustion engine. Ideally, ignition should occur a specific number of degrees before the piston reaches top dead center (TDC) during the compression stroke. This timing allows the air-fuel mixture to ignite and start expanding before the piston actually reaches TDC, ensuring a smooth and forceful power stroke.

By igniting the mixture a few degrees before TDC, the combustion process begins to generate pressure that pushes the piston downward. If ignition were to occur at TDC, the peak pressure would not yet be utilized effectively, leading to less power being produced. Conversely, if ignition occurs too far before TDC, it could lead to pre-ignition or knocking, which can cause engine damage.

This timing is carefully calibrated in accordance with the engine's design and operating conditions, including engine speed and load. Therefore, firing the spark plug at a specific angle before TDC is fundamental to optimizing performance and efficiency in the engine.