The objective of this study is to assess the actual impact and complementary function of the air swirling system in the intake manifold on the fuel combustion quality in diesel engines. To achieve this, the research focuses on determining the influence of the air swirling system (Swirl-Flaps) on the quality of the injected fuel combustion by directly measuring the particle emissions (PM) produced during combustion at various engine speed conditions. The use of an opacimeter in combination with the data from the oxygen sensor, which is digitally read from the Electronic Control Unit (ECU) of the injection system, will help minimize the measurement error. To establish the direct correlation between fuel combustion quality and the air swirling system operation, the exhaust gas recirculation (EGR) and the variable geometry turbocharger (VGT) systems were disabled, without activating the failure mode triggered by the engine’s ECU. Combustion gas samples for analysis were collected upstream of the specialized exhaust gas treatment systems: the diesel oxidation catalyst (DOC), the diesel particulate filter (DPF), and the selective catalytic reduction system (SCR).