Caracterización experimental y numérica del flujo en motores de combustiónInfluencia de las tolerancias de fabricación

Abstract

The air flow that crosses the intake port of a low-capacity engine is studied both theoretically and experimentally in the steady regime. For high enough Reynolds numbers, the experimental values of the discharge coefficient and swirl number do not significantly depend on that parameter. While the discharge coefficient increases with the valve lift, the swirl number becomes almost constant for sufficiently large values of that geometrical parameter. The formation of the turbulent vortex in the cylinder is described by measuring the 2D velocity distribution over several cylinder cross-sections with the PIV method. This vortex tilts downstream to become parallel to the cylinder axis, and occupies most of the cylinder cross-section at the entrance of the torque meter. This indicates that the swirl number measured in our experiments is essentially determined by the angular momentum transported downstream by the vortex. The vortex center position does not significantly depend on the valve lift at the entrance of the torque meter. On the theoretical side, the RANS equations were integrated with the RSM-w turbulent model. The numerical results reproduce satisfactorily the experimental data, especially the swirl number values. The influence of four geometrical parameters on the swirl number is determined from numerical simulations. The variations of those parameters within their range of tolerance lead to swirl number variations greater than 5%, the limit established by the manufacturer. The numerical results indicate the manufacturing tolerances must be significantly reduced to verify the imposed requirements on the swirl number value.