During the ignition cycle, at what point should the spark occur ideally for efficient combustion?

The ideal timing for the spark to occur during the ignition cycle is before the top dead center (TDC) of the piston’s stroke. This pre-ignition timing allows for optimum combustion efficiency. By igniting the air-fuel mixture slightly before TDC, the combustion process can occur as the piston is nearing the top of its stroke. This timing ensures that the pressure buildup results in a more effective force that pushes the piston down during the power stroke.

Firing the spark before TDC facilitates a more complete burning of the air-fuel mixture, leading to improved power output and fuel efficiency. Additionally, this timing helps to ensure that the combustion process has fully developed its pressure when the piston reaches TDC, maximizing the energy transfer. Setting the spark at TDC or after would result in less effective combustion, and the power stroke would not harness the full potential energy of the combusted gases.