Abstract: Steady-flow test and combustion analysis of the D19 four-valve and dual-intake-port engines are carried out using the steady-flow test bench and CFD simulation. The results show that with the same valve under the maximum opening there is severe interference of airflow between the two air passages, which limits the increase of the vortex ratio and the flow coefficient; while the different valves designed for the maximum opening of the valve can make full use of the space in the cylinder and make the airflow in the cylinder form mutual staggered flow to avoid serious interference of airflow between the airways so as to increase the flow coefficient and vortex ratio. The increase of the air intake can make most of the fuel and air more fully mixed.The increase of the vortex ratio makes the fuel and gas mixture more uniform and the combustion is more sufficient. As a result, the cylinder heat release is increased, with Soot and CO greatly reduced and NO_x slightly increased

Key words: spiral air-passage, tangential air-passage, different valves, steady flow test, combustion analysis