The paper aims to establish the real influence and the complementary role of the exhaust gas recirculation system on the quality of hydrocarbon combustion in diesel engines. For this purpose, the practical determination of the influence of the EGR system on the combustion quality of the injected fuel was proposed, by directly measuring the emissions of particles resulting from the combustion, in different speed regimes of the diesel engine. In order to establish the direct relationship between the quality of fuel combustion and the operation of the EGR system, the air swirl system in the intake manifold was canceled (without the activation of the breakdown mode triggered by the electronic engine control unit). The combustion gas samples for analysis were taken upstream of the specialized combustion gas treatment systems.