Intake port structure directly affects the flow characteristics and combustion process of diesel engine, and then affects the comprehensive performance of diesel engine. To the intake ports of a four-valve direct injection diesel engine, the flow characteristics are analyzed on the four combined intake ports : (1) helical (left) and tangential (right), (2) tangential (left) and helical (right); (3) helical (left) and helical (right); and (4) tangential (left) and tangential (right).And the influence of air flow in four combined intake ports to incylinder gas flow is also analyzed. Results show that the helical and tangential combination intake ports flow velocity increases with the valve lift increases, and small turbulence arises at the valve guide lug, and the intake flow velocity of the minimum cross-section of the junction of the guiding section and the helical section is the maximum. The air flow in-cylinder moves from top cylinder head bottom to the cylinder bottom, the air flow is enlarged gradually by the small-scale irregular swirl, which eventually converges to a single swirl. The turbulence kinetic energy is very big when the air is just entering the cylinder, the flow space expands rapidly, and the dissipation of turbulent kinetic energy is very significant with the gas moves to the bottom of the cylinder.
In order to analyze intake port flow characteristics of a four-valve direct injection (DI) diesel engine, steadystate flow bench experiments and numerical simulations method were coupled to investigate the following four combined intake ports: (1) helical port (left) and tangential port (right); (2) tangential port (left) and helical port (right); (3) helical port (left) port and helical (right); and (4) tangential port (left) and tangential (right) port. Results show that the simulation of port flow coefficients matches experimental findings very well, and the port coefficients of the above four combinations do not vary much, but their swirl ratios are very different. Specifically, when the valve lift is the maximum, the swirl ratio of the combination of "helical and tangential" is the greatest among the four combinations, and the swirl ratio of "tangential and tangential" is the minimum. And the3D fluid simulation method and steady-state experiment are important means to investigate the flow characteristics of the combined intake ports.
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