Numerical Simulation Of Marine Diesel Engines Gas Flow

Flow plays a very important role in internal combustion engine working process. Well-organized flow can improve combustion, increase thermal efficiency and reduce emission. As a cost effective and time saving method, numerical simulation can provide the detailed effect of geometric parameters and is widely employed in ICE flow study. To understand the cause of swirl ratio fluctuation among different cylinder heads of Weichai 170 series marine diesel, numerical simulation is carried out to study steady-state intake and 3D transient in-cylinder flow. Steady-state intake simulation reveals the cause of swirl ratio fluctuation, and transient in-cylinder flow simulation shows the effect of combustion chamber on fuel atomization and mixture formation.To compare the results of simulation and steady-state flow experimental testing, the same boundary conditions and evaluation methods are applied. Comparison shows that flow coefficient and swirl ratio from numerical simulation are consistent with those from testing, and the accuracy of simulation is acceptable. According to the proportional relation between swirl ratio and valve lift, the machined eccentric chamfer on valve seat of tangential port has a profound impact on swirl generation, especially in condition of small valve lift.The numerical simulation of tangential port without valve seat chamfer and inclined tangential port indicates that swirl ratio fluctuation among different cylinder heads is caused by inadequate manufacturing accuracy. As a result, manufacturing accuracy should be improved to ensure required engine performance.Dynamic simulation is carried out to study the transient intake and in-cylinder flow generated during intake and compression strokes using CFD code Fire. Well convergent results show formation and development of swirl, squish, tumble and turbulence. In-cylinder flow generated during intake stroke is disorganized at the beginning, and then it develops into a large number of...