System to control combustion noise of a diesel engine

The system has a pressure gradient detecting unit (32) to find pressure gradients in a cylinder during principal and control injection phases. A control quantity detecting unit (34) detects quantity of fuel injected in the cylinder to optimize criteria of the cylinder operation based on a ratio between the gradients relative to the phases for optimizing operating noise of a diesel engine. The control quantity detecting unit (34) detects the quantity of fuel injected in the cylinder during the control injection for a preset quantity of fuel injected during principal injection.