A Computational Fluid Dynamics Investigation Comparing the Performance of an Alternative Valvetrain Design Against a Traditional Poppet Valvetrain

Abstract

The poppet valve is by far the most widely used in cylinder head design of internal combustion (IC) engines; however, poppet valves themselves create significant flow restrictions during both the intake and exhaust strokes, thus causing a reduction in volumetric efficiency that affects overall engine performance. By removing the restrictive poppet valve from the flow path of air into and out of the cylinder head and allowing air to flow unobstructed, any given IC engine can achieve greater volumetric efficiency and higher specific output. The Vaztec ECOREV rotary valve system utilizes straight-cut flow passages that reduce such restrictions. This rotary valve system is designed to be directly driven by the crankshaft, thereby replacing the camshaft and poppet valve system altogether. This paper will primarily explore the differences in flow characteristics between this rotary valve and a conventional poppet valve cylinder head using both computational fluid dynamics (CFD) and flow bench data. Both configurations will be evaluated on the same single-cylinder four-stroke internal combustion engine. CFD simulations were run at multiple valve opening positions on each cylinder head configuration for both intake and exhaust cycles to validate the CFD process against flow bench test data for both cylinder head designs. The CFD was performed in 3D using hexahedral meshing and steady-state Reynolds-averaged Navier–Stokes (RANS) turbulence models. Comparison between the two engine configurations will include both intake and exhaust airflow rates as well as discharge coefficients and overall flow field evaluation using numerous scalar and vector properties.