For the improvement of engine thermal efficiency

the concept of the Atkinson cycle with high tumble combustion system was proposed

which adopts the combination of high tumble intake port and piston

and coordinates the Atkinson cycle and exhaust gas recirculation(EGR) technology to improve in-cylinder tumble and turbulence level

accelerate combustion speed

and reduce knock tendency. The engine work process model and in-cylinder computational fluid dynamics(CFD) model of a certain engine were set up by the GT-Power and AVL-FIRE software respectively. The simulation results show that a high tumble intake port benefits in-cylinder tumble

which increases from 0.5 of the base engine to 2.6; with high tumble intake ports and pistons

both the initial tumble generated during the intake process and the tumble maintained during the compression process are stronger than the base engine

the average turbulence energy increases by 6.3%

and the average heat release rate increases by 15% compared with the base engine. In order to decrease the knock tendency caused by high compression ratio

the Atkinson cycle

which is realized by late intake valve closing timing

was introduced with EGR based on the foresaid high tumble. The results show that the brake specific fuel consumption(BSFC) in the universal characteristic appears downward trend. The lowest BSFC area becomes larger obviously

and the lowest BSFC decreases by 11.3 g/(kW·h) against the base engine.