percentage of extra fuel for cooling

how much extra fuel is required to cool the charge? and when is it needed?

The amount of additional fuel you use will depend on the amount of load on the engine. For example on a N/A engine we may target 0.88-0.92 lambda under WOT. With a turbocharged engine we may target 0.78-0.82 lambda. Generally in the cruise areas we would target lambda 1.00 for good economy and minimal emissions. As we increase the throttle opening and hence load, we would taper the target lambda richer until we reach the WOT target.

Check out these webinars for more detail:

https://www.hpacademy.com/previous-webinars/065-planning-your-afr-targets-naturally-aspirated-engines/

https://www.hpacademy.com/previous-webinars/066-planning-your-afr-targets-forced-induction-engines/