What is the reason for Knock in the diesel engine?

Diesel knock is generated due to fully advanced timing and retard conditions. If the timing is retard the fuel will not be burned purely and rapid pressure will be developed and pinking noise will be generated. In a advance condition the fuel is injected in to the combusion chamber before reaching the piston tdc the burning will start suddenly otherhand the piston is being compresses the charge. The combusion should be done at maximum pressure and temperature but in this case the fuel does not burnt at that stage (actually piston wants the load at that time)the pressure is not developing instanteniously rapid pressure developed thats why the diesel knock generates. Another reason for diesel knock if diesel does not have the good cetane number knocking will be generated