Fluid-Dynamic Analysis of the Intake System for a HDDI Diesel Engine by STAR-CD Code and LDA Technique

Abstract

The paper illustrates an experimental and numerical investigation of the flow generated by an intake port model for a heavy duty direct injection (HDDI) Diesel engine. Tests were carried out on a steady state air flow test rig to evaluate the global fluid-dynamic efficiency of the intake system, made by a swirled and a directed port, in terms of mass flow rate, flow coefficients and swirl number. In addition, because the global coefficients are not able to give flow details, the Laser Doppler Anemometry (LDA) technique was applied to obtain the local distribution of the air velocity within a test cylinder. The steady state air flow rig, made by a blower and the intake port model mounted on a plexiglas cylinder with optical accesses, was assembled to supply the, actual intake flow rate of the engine, setting the pressure drop across the intake ports at ΔP=300 and 500 mm of H 2 O. The flow coefficients and the swirl number were computed measuring the flow rate by a turbine flow meter and a paddle wheel to evaluate the air vortex speed into the cylinder test. The LDA technique was used to obtain the tangential and axial components of the flow velocity on two planes and along three diameters within the test cylinder. The computation was carried out by the fluid-dynamic code STAR-CD that solves the ensemble averaged conservation equations for mass, momentum and energy in steady state conditions with the turbulence model k-e. The grid, reproducing the geometry of the intake port and the real fluid system, was made using CAD data and the boundary conditions were the same as the experimental ones. Results of the computed mass flow rate, flow coefficients, and velocity profiles were compared to the experimental ones. The substantial agreement between experiments and computations suggests that an acceptable level of confidence may be assigned to calculations to design the intake port geometry of heavy duty Diesel engines.