Numerical simulation coupling with experimental study on the non-uniform of each cylinder gas exchange and working processes of a multi-cylinder gasoline engine under transient conditions

• An approach is presented to detect the CTCV of engine under transient conditions.
• The range and influence factors of CTCV of engine performances were revealed.
• The maximum relative deviation of IMEP in each cylinder is larger than ±30%.
• There appears a symmetry relation between CTCV of RGF and excess air coefficient.

Cylinder-to-cylinder variation is unavoidable in multi-cylinder engine and has a severe impact on engine performance. To explore the cylinder-to-cylinder variation of engine under transient conditions, a hybrid method of dynamic signal measurement coupling with gas dynamics and thermodynamics processes simulation is presented to detect the parameters of engine. Then, this method is applied to an automobile engine under road test conditions, and the continuous state and performance parameters of each cylinder were obtained from cycle to cycle. On this basis, the range and influence factors of non-uniform of engine performance parameters were analyzed. The results show that, under transient conditions, the relative deviation of excess air coefficient in each cylinder is within ±5%, which is mainly affected by intake average pressure in low to medium speed operating regions but influenced by exhaust pressure wave and residual gas fraction in high-speed and high-load operating regions. There appears a symmetry relation between the non-uniform of RGF and excess air coefficient. The relative deviation of indicated mean effective pressure in each cylinder depends largely on the gas exchange performance, including excess air coefficient and residual gas fraction, and the maximum is larger than ±30%.