Knock limitation

Fig 1: Knock Limitation Graph

Courtesy of SAAB-SCANIA OF AMERICA, INC.

Knock control first retards the ignition timing for each cylinder. If the mean value for the ignition retardation for all the cylinder exceeds a certain value, fuel enrichment will take place.

If the mean value for ignition retardation increases further, the maximum permissible air mass/combustion will be reduced.

This reduction takes place continuously as the ignition retardation increases.

The value constitutes the maximum air mass/combustion value permitted by knock control.