A transient simulation of different intake port configurations was carried out using AVL FIRE software

and their influences on the combustion process of a natural gas engine were investigated. The results show that the variation of turbulent kinetic energy has weak relationship with swirl ratio

and it is mainly affected by tumbling motion in Z direction. High average turbulent kinetic energy in cylinder does not signify fast combustion rate

and the combustion rate mainly depends on the turbulent kinetic energy distribution around the spark plug. With the optimized junction angle between the intake port and valve seat of the intake port scheme Ⅲ

the in-cylinder air motions of tumble and swirl are enhanced significantly

in addition the turbulent kinetic energy distribution is improved remarkably

resulting in the promotion of chemical reaction rate and flame propagation velocity. Furthermore the combustion characteristics are improved dramatically. Finally the bench tests were carried out with two different intake ports. The results show that the modified intake port scheme Ⅲ can improve the efficiency

reliability and high speed performance of a natural gas engine.