In order to improve the indicated thermal efficiency of a large-bore natural gas engine with stoichiometric operation

a concept of organizing an in-cylinder air motion with weaker swirl

stronger tumble and higher turbulence intensity was proposed. According to this concept

different shapes of intake ports and combustion chambers were designed. Then

the effects of the shape of the intake port and combustion chamber on the in-cylinder flow and combustion were studied using three-dimensional numerical simulation. Results showed that in comparison with the original engine

when changing the original helical intake port to a straight intake port and adopting the original reentrant combustion chamber and a new vertical-cave

open-cave

and hemispherical-cave combustion chamber in turn

the in cylinder swirl flow was significantly weakened

and the tumble flow was obviously enhanced. Especially

the maximum tumble flow ratio during the compression stroke could reach 0.76

0.83

1.03 and 1.71

respectively

and the in-cylinder average turbulent kinetic energy at the ignition timing was increased by 35.27%

36.26%

50.33%

and 135.99%

respectively

further accelerating the combustion rate and increasing the indicated thermal efficiency. Therefore

the match of the hemispherical-cave combustion chamber with the straight intake port was more beneficial to the formation of a stronger in-cylinder tumble flow and the improvement of turbulence intensity at the ignition timing. Finally

the indicated thermal efficiency was increased from 39.51% of the original engine to 42.14%.