Historically stating, combustion noise from the passenger car diesel engines has been a major drawback for customer acceptance. The present modern automotive diesel engines operate quietly due to advancements in diesel injector technology and noise abatement strategies applied to the engine compartment of the vehicle itself. In the literature, recent experimental and analytical research work with a single cylinder direct-injection diesel engine has shown that the injection dwell time between the main injection pulse and the one preceding to it, is primarily responsible for the noise reduction The objective of the current analytical research work is to bring out the fundamental physics behind the experimentally observed noise reduction phenomena. The computational study was conducted at a key part-load operation of a direct-injection diesel engine (engine speed of 2000RPM and 5Bar BMEP) with five injection pulses. Computational results showed that as the dwell time between the third injection pulse and the fourth (main) injection pulse is reduced, the combustion noise decreased and if the dwell is decreased beyond an optimum value, combustion noise actually started to increase. The heat of vaporization needed for the evaporation of fuel spray in the main (fourth) injection pulse, locally cools the environment and this cooling effect has a profound influence on the ignition delay of fuel injected in the first three (smaller) injection pulses. This cooling affects the rate of pressure rise and heat release in the cylinder, which in turn affects the combustion noise.