Experimental study on the effect of in-cylinder inclined swirl characteristics on cyclic variation of combustion pressure in a four-valve SI engine at low engine speed and load

A variable inclined swirl system (VISS) was developed to generate in-cylider inclined swirl air motion in a four-valve SI engine, the in-cylinder inclined swirl characteristics generated by VISS were studied in steady flow rig, and the effect of inclined swirl characteristics on cyclic variation of combustion pressure were analyzed with combustion analyzer in engine test-bed. The steady flow results show that by adjusting the VISS the inclined swirl ratio can be varied between 0 and 1.53, and the inclined swirl angle can be changed between 0° and 80.2°. The combustion results show that the indicated thermal efficiency increases at initial stage and then decreases gradually with increasing inclined swirl ratio and angle at low engine speed and load, the inclined swirl ratio and angle corresponding to peak indicated thermal efficiency decrease gradually with increasing engine speed. when the inclined swirl ratio is between 0.35 and 0.6, the coefficient of cyclic variation of mean indicated pressure increases significantly with increasing inclined swirl ratio and angle, and also increases with increasing engine speed. While the coefficient of cyclic variation of mean indicated pressure increases modestly with increasing inclined swirl ratio and angle at low engine speed and load when the inclined swirl ratio is between 0.6 and 1.53. Both coefficients of cyclic variation of mean indicated pressure and the maximum combustion pressure reach the minimum values on condition that the inclined swirl ratio and angle are 0.35 and 45° respectively. The results also show that poor stability of combustion pressure leads to lower indicated thermal efficiency.