Intake Port Shape Optimization in a Four-Valve High Performance Engine

Abstract

In the intake port shape optimization procedure of a four-valve, high performance engine, two dimensionless numbers play a dominant role. These are the discharge coefficient, and the tumble number. The first is a measure of pressure loss introduced by the port/valve combination, and the second is an index of the rotational motion of the charge about an axis normal to the cylinder centerline. The optimization performed through steady-state flow rigs is generally successful, but for cost and time reasons may not yield the insight needed to understand the flow patterns in the cylinder port. Computational Fluid Dynamics (CFD) applied to this problem can provide relatively fast and accurate results.
This paper presents the intake port shape optimization analysis for a four-valve high performance engine based on the dimensionless numbers mentioned before, using steady state numerical modeling. Geometric modifications were carried out in four critical regions of the combustion chamber, these are:
Volume adjacent to the valve stem.  Portinner radius.  Blend from throat to seat.  Region between of seat insert and underhead contour valve.
The geometry of these regions and the approach angle strongly influence both, the discharge coefficient and tumble number. Simulations were made using the commercial software ANSYS CFX-10.0. An upwind scheme was used to solve the advective term, while the temporal discretization was made using the Backward-Euler scheme. Turbulence was modeled using the two equation k-epsilon model. This work is part of a more ambitious project, which concerns the complement between CFD predictions and experimental research, capable of predicting the in-cylinder flow motion and its effects in the combustion process, in a more realistic way.