Effects of tumble combined with EGR (exhaust gas recirculation) on the combustion and emissions in a spark ignition engine at part loads

•Both EGR and enhanced tumble offer benefits in fuel economy for spark ignition engines at part loads.•The combination of enhanced tumble with EGR is capable of realizing a low level of CoVIMEP.•Increasing the tumble ratio is beneficial to accelerate the flame propagation in EGR dilution environment.

The effects of tumble combined with EGR (exhaust gas recirculation) on the combustion and emissions were experimentally investigated in a spark ignition engine in this study. A low pressure loop EGR system and a variable tumble valve in intake ports were employed, by which wide range of EGR ratio and tumble ratio could be achieved. All the tests were performed at part loads, and the equivalence ratio was kept constant at 1.0. The results show that the combination of EGR and enhanced tumble motion produces a significant improvement in fuel economy (13.1–19.5%) and a reduction in the coefficient of variations of indicated mean effective pressure (CoVIMEP) due to the significantly shortened combustion duration. By optimizing the combustion process with EGR and enhanced tumble, NOx (nitrogen oxides) emissions drastically decrease, while HC (hydrocarbons) emissions slightly rise. For CO (carbon monoxide) emissions, the enhanced tumble takes a positive effect.